comprehensive catchment management plan - … · 3 catchment analysis ... management plan for the...

Comprehensive CatchmentManagement Plan

Development East Tamaki

Manukau City Council

2108771 Rev A L1:36127

R e p o r t

Comprehensive Catchment ManagementPlan: Development East Tamaki Area

Prepared for

M a n u k a u C i t y C o u n c i l

By

B e c a C a r t e r H o l l i n g s & F e r n e r L t d

In Association With

S t e p h e n B r o w n L a n d s c a p e A r c h i t e c t u r eN I W A

B i o r e s e a r c h e s L t d .

M a y 2 0 0 1

COMPREHENSIVE CATCHMENT MANAGEMENT PLAN:DEVELOPMENT EAST TAMAKI STUDY AREA

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Catchment Planning TeamThe Project Team included a range of technical experts from four different organisations,who provided various services and expertise at a number of points in the catchmentplanning process. The team is set out in the following table:

Team Position Person OrganisationMCC Project Leader Bruce Harland Manukau City CouncilJob Director Don Lyon Beca PlanningProject Manager, ClientLiaison / Senior Planner

Greg Pollock Beca Planning

Beca Job Manager Peter Burgess Beca Carter Hollings &Ferner

Stormwater Specialist Graham LevyPaul MitchellAmanda Hon

Beca Steven

In-stream ecologists,riparian managementand fisheries specialists

Ian BoothroydRichard Allibone

NIWA

Terrestrial Ecology Graham DonRhys Gardner

Bioresearches Ltd.

Landscape Architect Stephen Brown Stephen Brown LandscapeArchitect.

Asset management /Cost of Growth specialist

Chris Jenkins Beca Valuations.

GIS Kathryn CutlerJamie Bate

Beca Carter Hollings &Ferner

Verification Graham Levy and StephenPriestley

Beca Carter Hollings &Ferner


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Table of Contents

1 Introduction.................................................................................................................. 7

1.1 The Catchment Management Planning Process ................................... 81.2 Information............................................................................................... 11

2 Strategic Planning Framework .................................................................................13

2.1 Vision for the Catchment ....................................................................... 132.2 Integrated Management ......................................................................... 142.3 Regional Growth Strategy...................................................................... 152.4 DET Concept Plan ................................................................................... 172.5 Resource Management Act 1991 ........................................................... 212.6 District Plan.............................................................................................. 232.7 Regional Policy Statement...................................................................... 28

3 Catchment Analysis ..................................................................................................33

3.1 In-stream Habitat .................................................................................... 333.2 Land Use Assessment ............................................................................. 493.3 Landscape Inventory and Analysis ...................................................... 523.4 Terrestrial Ecology .................................................................................. 633.5 Hydrology ................................................................................................ 653.6 Stormwater Modelling............................................................................ 67

4 Catchment Planning Issues......................................................................................82

4.1 In-stream and Riparian issues ............................................................... 824.2 Stormwater Management Issues ........................................................... 824.3 Terrestrial Ecology .................................................................................. 824.4 Landscape Issues ..................................................................................... 834.5 Land Use Issues ....................................................................................... 834.6 Recreation ................................................................................................. 834.7 Receiving Environment, Water Quality and Chemistry ................... 834.8 Implementation ....................................................................................... 84

5 Consultation...............................................................................................................85

5.1 Consultation Parties................................................................................ 855.2 Consultation Techniques........................................................................ 85

6 Conceptual Catchment Management Framework...................................................88

6.1 The Concept for Development East Tamaki ....................................... 896.2 In-stream Management Strategy........................................................... 926.3 Stormwater Management Strategy ....................................................... 99

7 Catchment Management Objectives ......................................................................109


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7.1 Instream and Riparian Management.................................................. 1097.2 Stormwater Management Objectives ................................................. 1117.3 Terrestrial Ecology Objectives............................................................. 1137.4 Land Use Objectives.............................................................................. 1157.5 Landscape and Amenity Objectives ................................................... 1157.6 Recreation Objectives........................................................................... 1167.7 Implementation Objectives .................................................................. 1167.8 Receiving Environment – Otara Lake ................................................ 120

8 Implementation and Mitigation Framework...........................................................122

8.1 Stormwater Mitigation Options .......................................................... 1238.2 Environmental Corridor Zone............................................................. 1358.3 Enhancement of Upper Catchment .................................................... 1418.4 Staging Development of the Catchment ............................................ 1458.5 Funding Growth Development........................................................... 1548.6 Monitoring.............................................................................................. 177

9 Conclusion ...............................................................................................................181

9.1 Aims of the Study.................................................................................. 1819.2 Key Issues ............................................................................................... 1819.3 Conceptual Approaches ....................................................................... 1829.4 Catchment Objectives, Implementation and Mitigation ................. 1839.5 Sustainable Management and Conclusion ........................................ 183

FiguresFigure 1: Study Area Location Map .................................................................................................8

Figure 2: Approach to integrated Management for East Tamaki Catchment ManagementPlan............................................................................................................................................15

Figure 3: Central and Southern Section of Growth Concept Map to 2050 from the RegionalGrowth Strategy. .....................................................................................................................16

Figure 4: Development East Tamaki Concept Plan (June, 1999) ................................................20

Figure 5: Stream and Riparian Classification ...............................................................................36

Figure 6: Habitat assessment and Pfankuch bank stability scores for Otara Creek, Feb.-Mar.2000. ..........................................................................................................................................40

Figure 7; Macroinvertebrates taxa richness recorded from the Otara Creek catchment, Feb.-Mar. 2000. (refer to Map 1).....................................................................................................43

Figure 8: Macroinvertebrates Community Index (MCI) values recorded from the OtaraCreek catchment, Feb.-Mar. 2000. (refer to Map 1).............................................................44

Figure 9: Semi-quantitative Macroinvertebrates Community Index (SQMCI) values recordedfrom the Otara Creek catchment, Feb.-Mar. 2000 (refer to Map 1)...................................45

Figure 10: Number of Ephemeroptera, Plecoptera and Trichoptera (NoEPT) recorded fromthe Otara Creek catchment, Feb.-Mar. 2000 (refer to Map 1) ............................................45

Figure 11: Percentage of existing land use in catchment.............................................................50

Figure 12: Estimation of potential mix of future land use in catchment ...................................51

Figure 13: Seasonal variability of stream flows for the Hills Road and Bond Street Sites......67


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Figure 14: 100 Year ARI Hydrographs for Eastern and South-western Tributary ..................76

Figure 15: 100 Year ARI Hydrographs for combined Eastern and South-western Tributary 77

Figure 16: Variation of Total Sediment Yield During Development Phase..............................80

Figure 17: Banded kokopu habitat preferences curves, ..............................................................95

Figure 18: Low Flow Water Levels at Road Crossings................................................................97

Figure 19: 2 Year ARI Hydrograph for Subcatchment C5 Illustrating Effect of PondMitigation ...............................................................................................................................125

Figure 20: 100 Year ARI Hydrograph for Subcatchment C5 Illustrating Effect of PondMitigation ...............................................................................................................................125

Figure 21: 2 YR ARI Hydrograph for Subcatchment B1 Illustrating Effect of RiparianPlanting...................................................................................................................................126

Figure 22: 100 YR ARI Hydrograph for Subcatchment B1 Illustrating Effect of RiparianPlanting...................................................................................................................................127

Figure 23: Peak Flow for 100 Year Return Period – Effect of Low Impact Design ................129

Figure 24: Peak Flow for 2 Year Return Period – Effect of Low Impact Design ....................129

Figure 25: Anticipated Population Growth by Year ..................................................................158

Figure 26: Anticipated Cumulative Population Growth...........................................................158

Figure 27: Anticipated Pattern of Catchment Development.....................................................159

Figure 28: Total Area of each restoration category in ‘public’ portion of catchment. ...........165

Figure 29: Cost of Maintenance for Stormwater Ponds.............................................................168

Figure 30: Expenditure to Support Stormwater Management Requirements........................172

Figure 31: Stormwater Management Income/Expenditure Projections .................................173

Figure 32: Environmental Corridor and Reserves Development Expenditure......................173

Figure 33: Environmental Corridor/Reserves Income/Expenditure Projections ................174

TablesTable 1: Stream habitat, channel condition and biodiversity sample sites in the East Tamaki

Catchment Management Plan area, February/ March 2000. ............................................34

Table 2: Mean macroinvertebrate indicator scores for stream classifications in the OtaraCreek catchment, East Tamaki, Feb.-Mar 2000....................................................................46

Table 3: Fish species collected at each fishing site and the estimated abundance, ..................47

Table 4: Existing Land Use..............................................................................................................49

Table 5: Future Land Uses...............................................................................................................51

Table 6: Summary of Landscape Analysis ....................................................................................57

Table 7: List of Threatened Native Bird Species found in East Tamaki area............................64

Table 8: Otara Stream Flow Data....................................................................................................65

Table 9: Flood Peak Flows (m3/s) ..................................................................................................65

Table 10: Low Flows at Node 180 (Hills Road Flow Site) ...........................................................66

Table 11: TP 108 Soil Types and Permeability for Various Geological Layers.........................69

Table 12: Land Use / Percent Impervious.....................................................................................70

Table 13: East Tamaki Design Rainfall Depths.............................................................................71

Table 14: Calibrated Flows with Available Data..........................................................................73


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Table 15: Estimated Flows at Node 180 (Hills Road Flow Site) .................................................75

Table 16: Effects of Development on Timing ................................................................................76

Table 17: Assumed Contaminant Loading by Land Use.............................................................78

Table 18: Net Contaminant Yields for Study Area.......................................................................79

Table 19: Summary of Provisions of Draft Variation (Version 1.1, 12 October 2000)..............90

Table 20: Ability of Stormwater Devices To Achieve Stated Outcomes..................................104

Table 21: Representative Sub-catchments for Low Impact Design Investigations ................128

Table 22: Evaluation of Mechanisms to Secure Environmental Corridors in LowerCatchment ..............................................................................................................................137

Table 23: Species Composition for Lowland Catchment Restoration Area ............................140

Table 24: Species Composition for Upper Catchment Restoration Area.................................142

Table 25: Evaluation of Mechanisms to Secure Environmental Enhancement in UpperCatchment ..............................................................................................................................143

Table 26: Consistency with Staging Principles ...........................................................................153

Table 27: Restoration Category Broad Costing Estimates.........................................................164

Table 28: Environmental Corridor Restoration Costs................................................................165

Table 29: Estimated Cost of Stormwater Management Devices...............................................167

Table 30: Assessment of Possible Costs for Establishment of Key Open Space Nodes.........169

Appendices

Appendix 1 - Landscape Unit Assessment Sheets

Appendix 2 - Landscape Unit Photographs

Appendix 3 – Landscape Features, elements and nodes

Appendix 4 - Stormwater modelling results

Appendix 5 - Hills Road Mean Flows and Flow Distribution

Appendix 6 - Stormwater Management Options

Appendix 7 - Stormwater Mitigation Results

Appendix 8 - Results of Riparian and In-stream Ecological Assessments

Appendix 9 - Macroinvertebrates

Appendix 10 – Growth Strategy Principles

Appendix 11 - Species Lists for Murphy's Bush and 140 Jeffs Road Block.

Appendix 12 - Stream Photographs

Appendix 13 –“Green Finger” Cross Sections

Appendix 14 – Community Consultation Newsletters

Appendix 15 – Land Uses

Appendix 16 –Maintenance Costs for Stormwater Ponds


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MapsFor ease of cross-referencing, maps are bound as a separate document,including the following Maps:

Map 1 − Study Area and Sampling Sites

Map 2 − Stream Classification - Ecological

Map 3 − Existing Land Use

Map 4 − DET Concept Plan

Map 5 − Parcel Size Assessment

Map 6 − Landscape Analysis

Map 7 − Catchment Soils and Geology

Map 8 − Catchment Modelling

Map 9 − Stormwater Management Concept – Future Mitigated

Map 10 − 1% AEP Floodplain (Existing Land use)

Map 11 – Town Centre Mitigation Measures

Map 12 - Restoration Categories

Map 13 - Staging Units

Map 14 – Final Structure Plan / Catchment Management Plan Land UseConcept

Disclaimer

This report is based on the information supplied from the Manukau City Council’s GISdatabase, the District Plan, aerial photographs and a site walk over. This report andrecommendations are based on our understanding and interpretation of the availableinformation. The recommendations of the report are therefore subject to the accuracyand completeness of the information available at the time of the study. Should anyother information become available, then this report should be reviewed accordingly.

This is a strategic study for the Manukau City Council aimed at developing an overallmanagement plan for the catchment. The scope of the study and the informationavailable did not permit a detailed assessment of the stormwater system at all points.For individual sites it will be necessary to carry out site specific studies using thecatchment wide data provided in this plan.

It should not be copied or used or relied on for any purpose or by any person otherthan was originally intended. Any questions regarding the contents of this report orrecommendations therein, should be directed to a Director of Beca Carter Hollings andFerner Ltd.


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Report Prepared By: Greg Pollock

Senior Planner

Signed………………………………………………………….

Report Reviewed By: Graham Levy

Associate, Stormwater Specialist

Signed ………………………………………………………

Version: Final

Date: 31 May 2001

Introduction

Section 1


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1111 IntroductionIntroductionIntroductionIntroductionThe East Tamaki study area includes an area of approximately 1735 hectares of land. Thearea lies to the east of the Tamaki estuary, and adjoins existing developed parts ofManukau City, with Otara to the east, and Howick to the north (see Figure 1).

The study area, known as “Development East Tamaki” has been identified for futureurban purposes since 1973, and more recently, the Regional Growth Strategy has providedan impetus and mechanism to allow that zoning to be realise. Manukau City Council hasundertaken a visioning and structure planning exercise to provide greater certainty anddetail on how the area should develop.

In order to enable the DET area to be developed for urban purposes, and meet theobjectives of the Growth Forum, Auckland Regional Council and Manukau City, a numberof steps are required. The preparation of a concept plan has provided one of the first andmost significant steps in this process. The completion of this Catchment ManagementStudy is another significant input to that process. Both of these documents have ultimatelyprovided input to the draft variation which was circulated for public comment in October2000. A variation to the Proposed Manukau District Plan to rezone land and providedevelopment controls for the catchment will be notified upon completion of thatconsultation process. This should also coincide with another significant step, a change tothe Regional Policy Statement to move the metropolitan urban limits to the East Tamaki(Otara Creek) catchment boundary, with relevant staging of the MUL as appropriate.

Manukau City Council identified the aim of this project as being:

This aim has guided the development of the CMP and other associated work beingundertaken for Council. This study provides Council with an integrated framework for thesustainable management of the catchment both through the development phase and intothe future. The approach adopted by Council that in part sets a range of key targets for thestudy is:

“To achieve an integrated approach to stormwater management, improvingbiodiversity and integration of recreational and amenity values”.

“To manage the stormwater budget in an integrated manner to minimise risk offlooding and enhance the quality of water through innovative and effectiveengineering techniques which support a high quality environment based on theDevelopment East Tamaki Concept Plan.”



Figure 1: Study Area Location Map

1 . 1 T h e C a t c h m e n t M a n a g e m e n t P l a n n i n g P r o c e s s

Catchment management plans are non-statutory plans, which can be prepared forcatchments where issues arise which affect the use, development or protection of a rangeof natural and physical resources. CMPs have been prepared principally to managestormwater issues, although there is growing recognition of the need to address a range ofissues, such as ecology, landscape, amenity, recreation land use, transportation and soforth. The provisions of catchment management plans may be given effect throughresource consent processes, or their findings may be incorporated in regional, districtand/or annual plans.

The methodology and process followed to develop the CMP was required to take accountof the range of issues that needed to be addressed and the experiences of the organisations,tangata whenua and community stakeholders involved. The process followed needed tobe robust to ensure that this Catchment Management Plan provides strong guidance toManukau City Council in managing the growth and development of the East Tamaki area.In addition, the Beca Project Team recognised that innovation is critical in deliveringoutcomes which will meet the range of requirements for the area, and which will facilitatethe sustainable management of the catchment and study area.

The Project Team were guided by a number of principles which were established at theoutset as being important at a generic level to achieving a comprehensive approach tocatchment management planning. As comprehensive catchment management planning



requires different approaches in different catchments, and therefore, these principles arenot ‘rules’ but rather matters which were considered over the course of the project. Theseprinciples are as follows:

Create strong vision for future of catchment

Maintain or enhance ecological diversity and function

Recognise people as integral part of environment

Minimise environmental impact through a diverse range of management techniques

Recognise that change is inevitable

Local partnerships and commitment to vision crucial

Catchment specific solutions required

Investigate a range of options to address issues

Trade-offs may need to be made, optimise benefits from trade-offs

The process to develop the Catchment Management Plan followed four major stages. Theresults of each stage are reflect in the final CMP. The following diagram illustrates each ofthe four stages:



BASELINE INFORMATION:

Soils

Landuse

Stream and riparian characteristics

Water Chemistry

Stream flows

Biodiversity and Stream Biology

Landscape

ANALYSIS

Hydrologic/Hydraulic Model

Land use Assessment

Landscape Analysis

Subcatchment analysis

Riparian significance / enhancement opportunities

“Model” sites

Water chemistry

DESIGN

Stormwater management solutions

Riparian margins

Landscape / Amenity Solutions

Conservation areas

DRAFT CATCHMENT MANAGEMENT PLAN:

Water detention and quality issues

Financial issues framework

Subcatchment staging analysis

Approach to works

Recommended Development Rules

GIS

GIS

GIS

GISInput



Over the course of the project two significant reports have been produced:

Information and Data Summary, March 2000; and

Key Catchment Planning Issues and Analysis, July 2000

These reports form the basis for the final CMP in addition to the work carried out todevelop solutions to the issues identified in earlier stages.

1 . 2 I n f o r m a t i o n

For a project of this scale a range of information must be gathered to enable the policyframework and catchment planning recommendations to be formulated. Information hasbeen gathered from a number of sources including:

Field investigations carried out during February 2000

Reports and data held by Manukau City Council and Auckland Regional Council

Landowners in the Development East Tamaki (DET) Area

Discussions with tangata whenua representatives

Aerial photographs

The following key background information and reports have been referred to or providedby MCC in addition to the information included in this report:

Development East Tamaki Concept Plan, Manukau City Council, June, 1999.

Erosion and Sediment Control, Technical Publication 90, ARC, 1999

Guidelines for Stormwater Runoff Modelling in the Auckland Region, ARC TechnicalPublication No.108 (TP108) - BCHF April 1999

Stormwater Treatment Devices, Design Guideline Manual, Technical Publication 10,ARC.

Low Impact Design Manual, Technical Publication 124, ARC 2000

A Preliminary Visual and Ecological Landscape Assessment, DJ Scott Associates,August 1997

Barry Curtis Park Development Strategy, MCC, October 1997

City of Manukau - Otara Stream Flat Bush Catchment Study (White, Oldfield Dec.1990).

A development framework for a new town at Flatbush, East Tamaki. (MCC,September 1999).

Murphy’s Bush Management Plan (MCC, May 1999).

Otara Lake Improvement Project: Strategic Review, Worley Consultants, September2000

Otara Lake Water Quality: Technical Report, Worley Consultants, March 2000



Ten Year Development Strategy for Manukau City Parks: Discussion Document, MCC.

Concept/Structure Plan, including layouts for Town Centre and various iterations ofthe Concept Plan map.

Population Projections, MCC.

Draft Variation for Development East Tamaki (Version 1.1, 12 October, 2000), MCC.

Strategic Framework

Section 2



The purpose of this section is toprovide a description of the CatchmentManagement Plan process and theapplication of integrated managementto the process.

2222 Strategic Planning FrameworkStrategic Planning FrameworkStrategic Planning FrameworkStrategic Planning FrameworkThe strategic framework for thedevelopment of the East TamakiCMP is comprised of a range ofpolicy and regulatory documentsformulated under the RMA andother legislation. These strategicpolicy influences are as follows:

2 . 1 V i s i o n f o r t h e C a t c h m e n t

The vision for the catchment, which the strategic policy framework is ultimatelyattempting to achieve, is as follows:

DET Concept Plan

Strategic Plan

Regional PolicyStatement

Proposed District PlanRegional GrowthStrategy

LTFS / AssetManagement Plans

DETComprehensive

CMP

To achieve a sustainable community in the broadest sense. A

sustainable community is about using, managing and

protecting natural and physical resources in a way that

enables communities to develop economically, socially and

culturally - while safeguarding the life supporting capacity

of air, water, and ecosystems. A sustainable community must

also take into account not only the health and well - being of

the community but also the needs of future generations.



2 . 2 I n t e g r a t e d M a n a g e m e n t

One of the most significant principles driving the catchment management process, is thatof integrated management.

Integrated management is defined in the Auckland Regional Policy Statement (1999) asmanagement of natural and physical resources:

(a) “where decision-making about the use, development or protection of natural and physicalresources occurs in a holistic way;

(b) which takes into account the full range of effects which may stem from any such decision overthe short- and long-term; and

(c) which considers effects by referring to section 3 of the RM Act, and may include effects onnatural and physical resources and effects on the environment.”

There are a number of different environmental components and “inputs” to the catchmentplanning process for East Tamaki. To ensure the process results in a comprehensiveconsideration of catchment issues, all the individual components need to be broughttogether, analysed, and design solutions sought which meet multiple objectives.

Figure 2 illustrates the key inputs to the catchment planning process, from which anumber of environmental and development issues are identified. The issues are thenanalysed through a number of ‘filters’ which include developing design solutions whichenable land use, landscape, ecological and stormwater management objectives to be met.Design solutions, or mitigation measures are discussed later in the implementation sectionof this report. Meeting these objectives involves developing a range of mechanisms,including mitigation measures, an appropriate staging regime and a financial issuesframework.

Integrated management is not simply an outcome of the catchment management process,but is an ongoing principle for the future management of the catchment. While the currentcatchment and district planning process has identified a series of goals, objectives andmethods of implementation, there needs to be a significant level of certainty that thesemethods will be effective. Furthermore, it is important that theadministration/enforcement of the policy framework developed to date for East Tamakioccurs in an integrated manner.



Figure 2: Approach to integrated Management for East Tamaki Catchment ManagementPlan

2 . 3 R e g i o n a l G r o w t h S t r a t e g y

The strategic framework is strengthened by the Regional Growth Strategy, which wasformally adopted in August 1999. The Growth Strategy’s purpose is to ensure growth isaccommodated in a way that meets the best interest of the inhabitants of the Aucklandregion.

Three key themes emerge from the Strategy, which are optimising safe healthycommunities, the natural and physical environment, and accessibility. The Strategyincludes a number of principles and desired environmental outcomes (see Appendix 10),which are used for evaluating growth alternatives at a regional scale. These principlesprovide some guidance for more detailed catchment planning, and include priorities formanaging growth, and are therefore applicable to managing the development of areassuch as East Tamaki.

Inst

ream

Eco

logy

Identification of Key Development and EnvironmentalIssues

Management of Key Development and Environmental Issuesincluding; Mitigation and Enhancement Options,

Infrastructre Provision, levels of service and Staging ofDevelopment

Financial Issues Framework

Comprehensive Catchment Management Plan For EastTamaki

Cat

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Filt

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Sto

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Land

Use

Land

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Ter

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Consideration of these outcomes provides an excellent framework for a catchmentmanagement plan. While a number issues have been addressed in the development of theConcept Plan, the catchment management plan has focussed on specific areas to ensure anumber of outcomes are optimised. The outcomes identified in the RGS relate to:

Water quality Sustainable use of resources

Urban amenity Safe healthy communities

Cultural heritage Habitat

Open space Physical and social infrastructure

The RGS provided a comparative assessment of natural and physical resource constraintsin order to determine those catchments that were most suited to urban development. Thepurpose of the CMP for East Tamaki is to provide more detailed investigation and policydirection to ensure that development within the catchment meets the requirements of theRMA. While the focus of this project has been on the environmental parameters, social andaccessibility issues have been considered through the structure planning/variation processto ensure an integrated and comprehensive outcome.

Figure 3: Central and Southern Section of Growth Concept Map to 2050 from the RegionalGrowth Strategy.



2 . 4 D E T C o n c e p t P l a n

This section provides an executive summary of the DET Concept Plan. The Concept Planprovides a critical framework for the comprehensive CMP as it provides a vision,objectives, policies and key outcomes which have been though an extensive consultationprocess. The Development East Tamaki Concept Plan was adopted in June 1999.

The purpose of this Concept Plan is to:

Provide a vision for the future growth of the East Tamaki area

Provide the basis for the strategic co-ordination of private and public decision making, therebyminimising ad hoc decisions and promoting the sustainable development of natural, physicaland human resources

Provide an overall framework for assessing and evaluating land use and future developmentproposals.

Provide the basis for the detailed development of a variation to the Proposed District Plan

The Concept Plan is exactly that, a “Concept Plan” which was developed to provide abroad framework and strategic direction for the future planning and development of theFlat Bush - East Tamaki area. The Concept Plan cannot by its very nature contain all of thesolutions to issues that are raised in the Plan or by submissions to the Draft Concept Planwhich was notified in September 1997. At the time the Concept Plan was adopted, it wasacknowledged that further investigations would be required before any changes to theDistrict Plan could be introduced. These further investigations were identified as follows:

A detailed Catchment Management Study to examine how the conservation areasmight be achieved; including ownership issues, capital improvements, on-goingmaintenance, identification of boundaries including the adjoining urban zones andassessment of locations for flood management options. In addition this study wouldconsider in greater detail those parts of the catchment that may have physicalconstraints on development due to topographical, stability or conservation limitations.

A Town Centre Plan to determine the final location, function, size and relationship ofthe identified town centre with Ormiston Road and Barry Curtis Park

Development of Design Guidelines

Further consideration of Transportation Issues including the roading upgradesrequired and consideration of the costs and the appropriate locations for the currentlyunformed main road network identified on the plan.

Any changes introduced to the District Plan will involve full community participationincluding appeal rights to the Environment Court on any decision the Council may make.



2.4.1 Key Objectives/Goals

The DET Concept Plan included a number of objectives or goals. These are as follows:

To achieve an urban form that respects and works in harmony with the naturalenvironmental patterns that exist in the East Tamaki/Flat Bush area.

To promote the development of public values and recognition of the importance of thepublic realm in achieving healthy sustainable communities.

To reduce the reliance on the private motor car as a means of transportation.

To maximise “accessibility” for all ages and cultures, including accessibility to housingchoice, mobility, employment.

To achieve a reduction in travel demand and increase choice of travel modes.

To facilitate the establishment of a strong central focus for community and civic life.

To facilitate the establishment of a community that can celebrate its diversity andmaximise opportunities for innovation.

To facilitate an urban form that is flexible such that it can adapt to the constantlychanging values and pressures which shape our natural and physical environment.

2.4.2 Key Features of Adopted Concept Plan

A new community containing up to 50,000 residents.

Protection and enhancement of the natural gully/stream areas.

A new Town Centre based around a traditional “mainstreet” concept. The location ison the eastern side of Barry Curtis Park which provides a unique opportunity todevelop a focal point around which the Town Centre could develop. It is envisagedthat this Town Centre would contain a diverse range of activities including residential,retail, office, community and light industrial activities. The Town Centre would becharacterised by a compact pedestrian friendly environment.

Three Neighbourhood Centres are proposed which will provide for a diverse range ofactivities. They are strategically located throughout the area on main roads wherepublic transport options and accessibility will make them most viable. Neighbourhoodcentres are envisaged to be developed around the principle of being a pedestrianfriendly “mainstreet” based environment.

A range of residential housing types are envisaged including detached or semidetached dwellings, terrace housing, townhouses, and apartments. Overall thedensities suggested are higher than those found in traditional suburban areas. This isnecessary in order to utilise a finite land resource more efficiently in light of a rapidlygrowing population and to encourage an urban pattern that can support alternativeforms of transport including walking, cycling, and public transport. Higher averagedensities will result in a better range of services being available locally such as, shops,health and welfare facilities, recreation facilities, and child care.

Overall it is suggested that the following densities should be achieved:



– Low Intensity Residential / Rural area 5,000m2

– Medium Intensity Residential areas 15 dwellings per hectare (overall average)

– High Intensity Residential area 20 dwellings per hectare (overall average)

It is anticipated that residential densities would be highest closest to the Town Centreand Neighbourhood Centres.

Connectivity and permeability of the street system should be maximised in order topromote convenience, social interaction, and to enhance user safety in the street andsecurity of property.

Buildings should positively address the street and other public spaces by providinggood functional relationships to the public realm and providing opportunities forinformal surveillance.

Encourage along the main road corridors a wide range of activities including non-residential activities. These “mixed use” corridors will provide opportunities forresidential, employment, local convenience shopping, activities such as medicalcentres, and will support public transport options.

The following figure provides an illustration of the Concept as adopted in the June 1999.Subsequent work including investigations and analysis carried out for the CMP andstructure planning undertaken by MCC has fine tuned this initial concept.



Figure 4: Development East Tamaki Concept Plan (June, 1999)



2 . 5 R e s o u r c e M a n a g e m e n t A c t 1 9 9 1

The East Tamaki CMP is not a document required under the RMA. It is however adocument which has assisted Council in formulating its vision for the catchment, andensuring that the variation to the Proposed District Plan will promote the sustainablemanagement of the natural and physical resources of the catchment as it develops and intothe future.

2.5.1 Sustainable Management

Sustainable management is defined in section 5 of the Act as follows:

In this Act, “sustainable management” means managing the use, development, and protection ofnatural and physical resources in a way, or at a rate, which enables people and communities toprovide for their social, economic, and cultural wellbeing and for their health and safety while—

(a) Sustaining the potential of natural and physical resources (excluding minerals) tomeet the reasonably foreseeable needs of future generations; and

(b) Safeguarding the life-supporting capacity of air, water, soil, and ecosystems; and

(c) Avoiding, remedying, or mitigating any adverse effects of activities on theenvironment.

2.5.2 Matters of National Importance and Other Matters

In addition to section 5 of the Act that defines its purpose, section 6 identifies matters ofnational importance. In relation to East Tamaki, a number of these matters are important.While the decision to urbanise the catchment was made having regard to a wider regionalstrategic context, there nevertheless remains a need to ensure the process of urbanisationprotects those features of the catchment which would fall under the category of matters ofnational importance. Section 6 states that in relation to managing the use, development,and protection of natural and physical resources, the following matters must be recognisedand provided for:

(a) The preservation of the natural character of the coastal environment (including thecoastal marine area), wetlands, and lakes and rivers and their margins, and theprotection of them from inappropriate subdivision, use, and development:

(b) The protection of outstanding natural features and landscapes from inappropriatesubdivision, use, and development:

(c) The protection of areas of significant indigenous vegetation and significanthabitats of indigenous fauna:

(d) The maintenance and enhancement of public access to and along the coastal marinearea, lakes, and rivers:



(e) The relationship of Maori and their culture and traditions with their ancestrallands, water, sites, waahi tapu, and other taonga.

A number of these matters have been provided for through the concept developed for theEast Tamaki area. In particular, the preservation of the stream system in the catchment,areas of indigenous vegetation and the provision of access to the stream system providespractical recognition of these issues. Furthermore, the involvement of tangata whenua inthe concept and catchment planning exercises will ensure the relationship of Maori andtheir culture with the East Tamaki area is provided for.

Section 7 of the Act provides for a number of other matters which are to be givenparticular regard to when considering the use, development, and protection of natural andphysical resources. These matters include:

(a) Kaitiakitanga:

[(aa) The ethic of stewardship:]

(b) The efficient use and development of natural and physical resources:

(c) The maintenance and enhancement of amenity values:

(d) Intrinsic values of ecosystems:

(e) Recognition and protection of the heritage values of sites, buildings, places, or areas:

(f) Maintenance and enhancement of the quality of the environment:

(g) Any finite characteristics of natural and physical resources:

(h) The protection of the habitat of trout and salmon.

Comment on the consistency of the Catchment Management Plan and the overall conceptfor the future of the East Tamaki area with the purpose and principles of the Act isprovided in the conclusion and recommendation section.

2.5.3 Treaty of Waitangi

Section 8 of the RMA requires consideration to be given to the Treaty of Waitangi:

In achieving the purpose of this Act, all persons exercising functions and powers under it, inrelation to managing the use, development, and protection of natural and physical resources, shalltake into account the principles of the Treaty of Waitangi (Te Tiriti o Waitangi).

The following principles can be derived from the Court of Appeal decisions in relation tocases brought under s 9 of the State Owned Enterprises Act:

there is a duty on the two parties to the Treaty to act reasonably towards each otherand in utmost good faith;

the Crown must make informed decisions;



the Crown must not impede its capacity to provide redress for proven grievances;

there is a duty on the Crown to actively protect Maori interests.

One of the significant principles of good practice arising from resource management isthat tangata whenua should be consulted and have an active role in the process. Section 5provides a discussion on the consultation process with tangata whenua for the CMP,which is considered by Council to be ongoing.

2 . 6 D i s t r i c t P l a n

While the Development East Tamaki Concept Plan provides the framework for the futureof the East Tamaki area, an examination of existing District Plan provisions enables theexisting land uses to be better understood from a ‘historical’ perspective. The followingland use and planning assessment within the East Tamaki Catchment Study Area is basedon the provisions of the Manukau Proposed District Plan. The provisions of the ManukauTransitional District Plan have not been taken into account, given the dominant status ofthe proposed plan. The proposed variation will ultimately replace many of the existingprovisions to ensure the vision for the future of the catchment is achieved.

Map 3 provides the zoning under the Manukau Proposed District Plan for the CatchmentStudy Area.

The East Tamaki catchment area consists of large areas of Future Development (stages 1and 2) zoning, Main Residential, and Rural 2, 3 & 4 zonings. Smaller individual pockets ofland are zoned for recreational use as Public Open Space 1, 2 & 4. In addition, twoseparate parcels of land are designated for specific uses. These are a proposed extension ofthe Point View Drive reserve for public open space purposes, and the designation forwater supply purposes (reservoir and associated structures) of Watercare Services Ltdland, located off Gracechurch Drive between two Public Open Space 1 zones.

(a) Rural 2 Zone

The Rural 2 zone is a countryside living zone particularly aimed at part-time farming.This zone is designed to concentrate part-time farming / lifestyle block development inparticular areas of the City, to protect the resource and values of the wider rural area.

The zone is located within two areas of Manukau City - Flatbush (East Tamaki) andWhitford. The Flatbush area is located between the Future Urban Development zone andthe Rural 3 zone and is bounded by Jeffs Road to the north, Boundary Road to the south,Scenic Drive to the east and Murphy’s Road to the west.

This area has been identified as suitable for countryside living/part time farming as it islocated relatively close to the metropolitan urban area which reduces demand for urbanrelated facilities and minimises commuting distances. Furthermore, the area’s soils arerecognised as being of a mixed yet reasonable quality to enable part-time farming to becarried out. The ownership of land within this area is also somewhat fragmented which



creates constraints for productive farming activities. The area also has a history of part-time or lifestyle farming.

The range of activities permitted in the Rural 2 zone is more limited than that of the Rural1 or general rural zone, in order to minimise the range of environmental effects that a moredensely populated area may experience. Permitted activities within the zone includefarming, greenhouses, a single household unit on land which was held in a separatecertificate of title before 5 June 1989 or on a lot which was approved as a subdivisionwhere no additional lots were created (except if located within the airport outer controlarea), the repair of, or alteration to, an existing residential dwelling, Single household units(except if located within the airport outer control area), the clearance of a discrete parcel ofnative vegetation that does not exceed 250m2, produce stalls not exceeding 15m2 in floorarea for the direct sale of farm produce grown on the farm or holding on which theproduce stall is located.

Subdivision within this zone for the purpose of creating small holding lots will only bepermitted on land held in a separate certificate of title on 5 June 1989. The minimum lotsize for subdivision within the zone is 1.8 hectares and there is an average lot size of 4hectares when creating more than 3 lots.

(b) Future Development Zone (Stage 1 and 2)

The Future Development zone is a deferred development zone, which aims to protect ruralareas in the East Tamaki Corridor until such time as they are required for future urbanexpansion. The zone is divided into two stages, which largely reflect current urban growthdemand and the provision of services in the area. Dividing the zone into two stages alsoprovides for the progressive development of the City.

Stage 2 of the Future Development zone comprises the southern portion of the EastTamaki Corridor and is given second priority in terms of future urban development.Within the East Tamaki catchment, the zone is more specifically located between landzoned Main Residential and Rural 2, approximately in the middle of the catchment area.

The Future Development zone predominantly provides for rural activities such as farming(excluding pig keeping). However other permitted activities include a single householdunit (except within an airport outer control area), produce stalls not exceeding 15m2 infloor area for the direct sale of farm produce grown on the farm or holding on which theproduce stall is located and buildings accessory to any permitted activity.

Subdivision is strictly limited within the Future Development zone to ensure that futureurban development of the area is not jeopardised. Discretionary activity resource consentapplications are required for any subdivision activity and lots can only be created forcertain uses such as a cemetery or urupa, church or church hall, to contain a networkutility service, to protect a heritage item or for the purpose of a boundary adjustment. Nominimum lot size is prescribed for the Future Development zone.



This zone has in practice been effective in terms of maintaining a relatively rural land usepattern, which will not foreclose or limit the options for the future urbanisation of thearea..

(c) Main Residential Zone

The Main Residential zone applies to the majority of land zoned for residential purposes inManukau City and provides for medium intensity residential development while ensuringthe maintenance and enhancement of residential amenity values. In respect of the EastTamaki catchment area, land zoned Main Residential is located on the western edge of thecatchment between Te Irirangi Drive and the Future Development & Rural 3 zones.

The Main Residential zone includes four special policy areas, one of which is locatedwithin the East Tamaki catchment area. The Special Policy 2 area relates to a strip of landbetween Point View Drive and Browns Lane and is located adjacent to land zoned Rural 3.The additional provisions (density, height and yard setback rules) which apply to thisspecial policy area seek to mitigate the adverse effects of urban residential development onthe existing rural-residential amenity values in the neighbouring Rural 3 zone.

Permitted Activities within the Main Residential zone include accessory buildings(excluding buildings associated with horticulture and farm sales) not exceeding 81m2 grossfloor area, childcare services and facilities for up to 10 children, construction of singlehousehold units (except within the airport outer control area), demolition or removal ofexisting buildings, external additions or alterations to buildings (except for habitablerooms in the airport outer control area), farming including farm forestry, a minorhousehold unit, and residential centres accommodating not more than 10 persons inclusiveof owners, family and staff.

The minimum net site area for sites in the Main Residential zone is 400m2 wheresubdivision precedes the construction of a household unit(s) on these sites provided thatfor lots less than 600m2 the minimum average net site area is 500m2. In the Special PolicyArea 2 there is an exception where the minimum net site area shall be 750m2.

There is no minimum site area for sites in the Main Residential zone where buildingprecedes subdivision provided that the location of the site boundaries ensure compliancewith the development standards of the zone or are in accordance with a resource consent.In all cases the density of the Main Residential zone should not be exceeded (i.e. 1household unit per 400m2 for site less than 1000m2, 1 household unit per 300m2 for sites1000m2 and over).

(d) Rural 3 Zone

The Rural 3 zone is a low density countryside living zone located on the urban fringe andacts as a transition between the urban and rural areas. The zone is located on the edge ofthe catchment study area in 3 distinct pockets to the north, south and east. In the north thezone is located along either side of Gracechurch Drive and on the elevated slopes of PointView Drive. In the south the zone is situated on the slopes surrounding Redoubt Road



and in the east the zone follows the continuation of Redoubt Road into Scenic Drive untilthis meets Ormiston Road.

Parts of the zone are located within the sensitive ridgeline areas and are therefore subjectto additional controls designed to protect the visual, scenic and landscape qualities of theprominent ridgelines along Point View Drive, Redoubt Road and the proposed ScenicDrive, from the adverse effects of urban development. Buildings on sites within theSensitive Ridgeline areas require resource consent for a controlled activity.

The Rural 3 zone has easy access to employment opportunities and urban facilities givenits proximity to the metropolitan area. Permitted activities within the zone are limited tominimise conflicts with the principal countryside living activity of the zone and to protectthe amenity values, landscape quality and semi-rural character of the area.

Permitted activities in the Rural 3 zone include farming, pig keeping on sites greater than 1hectare, the repair of, or alteration to, an existing household unit, the clearance of a discreteparcel of native vegetation that does not exceed 250m2, and accessory buildings for anypermitted activity.

Subdivision within the Rural 3 zones is provided for as long as a suitable buildingplatform of at least 250m2 can be identified within each site, taking into account naturallandform, soil stability and the capacity of the site for the disposal of stormwater andsewage. The establishment of household units on land zoned Rural 3 is a controlledactivity under the District Plan to ensure that stability and wastewater disposal issues areadequately addressed. The minimum lot size for the Rural 3 zone is 5000m2.

(e) Rural 4 Zone

Land zoned Rural 4 occupies a small part of the catchment area to the north of Jeffs Roadand south of Caldwells Road, which is unformed. This area of land is part of a larger areabetween Sandstone Road and Whitford Road that is subject to the Rural 4 zoning. TheRural 4 zone is characterised by a high degree of ownership and land fragmentation andcomprises moderate sized lots ranging between 3 and 10 hectares with steep terrain andlow soil quality resulting in limited productive potential.

The Manukau Proposed District Plan notes that the area zoned Rural 4 within the EastTamaki catchment is recognised as being very unstable and is also characterised by soilswith poor infiltration and high ground water levels. Development of this area thereforemay be constrained given that wastewater disposal is likely to be difficult.

The range of activities which can occur in the area is limited to avoid potential conflictsbetween activities resulting from more intensive development. Permitted activities withinthe zone include farming, pig keeping on sites greater than 1 hectare, greenhouses, theclearance of a discrete parcel of native vegetation that does not exceed 250m2, accessorybuildings for any permitted activity, a single household unit on land which was held in aseparate certificate of title on 5 June 1989 or on a lot which was approved as a subdivisionwhere no additional lots were created (except if located within the airport outer controlarea), the repair to, or alteration of, an existing household unit, and produce stalls not



exceeding 15m2 in floor area, for the direct sale of farm produce grown on the farm orholding on which the produce stall is located.

The Rural 4 zone will facilitate countryside living while recognising the rural characterand landscape quality issues as well as the stability and wastewater disposal constraints.Household units on existing lots and new subdivision proposals require restricteddiscretionary activity resource consents to ensure the above-mentioned issues areaddressed. Subdivision creating lots within the Rural 4 zone will only be permitted onland held in a separate certificate of title on 1 August 1995. Subdivision rules include aminimum lot size of 1 hectare with provision for an average lot size of 2 hectares.

(f) Public Open Space Zones 1, 2, & 4

The Public Open Space 1 zone aims to protect and enhance areas of significant landscapevalue as well as archaeological, geological, or other scientific features including indigenousflora and fauna and ecosystems. Activities on these public open space areas will bemanaged to ensure the protection of these heritage features. Permitted activities withinthis zone include farming and grazing (except pig, factory farming and horticulture),informal recreation and leisure, park furniture, and maintenance of buildings andgrounds.

Public Open Space 2 provides for passive outdoor informal recreation such as walking,resting, picnicking, enjoying nature or jogging. This open space area contributes to thegreening and beautifying of the urban environment and to the City’s walkway andcycleway network. Permitted activities include children’s playgrounds and relatedstructures, formed recreational walkways and cycleways excluding motorised vehicles,gardens, maintenance of buildings and grounds, park furniture, park depots includingimplement and storage sheds, public toilets, shelters, changing rooms and first aid rooms.

The Public Open Space 4 zone provides for community purpose buildings and indoorrecreation facilities. Local, regional and at times, national events will be held on thesesites. Public Open Space 4 zoned land is located in close proximity to public transportroutes, business areas and other community purpose buildings in order to enhance publicopportunities for use. Activities such as kindergartens, childcare facilities, kohanga reo,marae, community houses, halls, scout dens and guide halls, swimming pools, recreationcentres and arts and cultural centres can be located on land zoned Public Open Space 4.

Permitted activities include farming (except pig, factory farming, and horticulture),gardens, informal recreation and leisure, maintenance of buildings and grounds, parkfurniture, skateboard bowls, outdoor skating rinks, confidence courses, public toilets,changing rooms, and residential accommodation for a caretaker.

(g) Additional Constraints Applicable to the East Tamaki Catchment Area

Airport Outer Control Area

Parts of the East Tamaki Catchment Study Area are within the Airport Outer Controlboundary and hence are subject to additional constraints relating to aircraft noise. Theboundary of this Airport Outer Control Area extends through the middle portion of the



study area from Te Irirangi Drive(south-west of the catchment study area) to the north ofunformed Caldwells Road and proposed Scenic Drive (in the north-east part of thecatchment) and encompasses land zoned Main Residential, Future Development, andRural 2, 3, & 4.

The construction of household units or habitable rooms (space used for activities normallyassociated with domestic living including a bedroom but excludes a bathroom, laundry, orother space of a specialised nature occupied neither frequently nor for an extended period)within the Airport Outer Control Area requires a controlled activity resource consent toensure compliance with certain construction standards which attenuate aircraft noise andensure that the internal noise environment in habitable rooms does not exceed Ldn45dBA.

Flood Protection Area

Three distinct areas within the East Tamaki Catchment Area are subject to this overlay.These areas are located within the catchment as follows:-

an area of land located to the south of Flatbush School Road and west of Murphy’sRoad (see MCC Proposed District Plan Map No. 40)

an area of land located to the south of Flatbush School Road and to the west ofMcQuoids Road; (see MCC Proposed District Plan Map No. 55)

an area of land located between Te Irirangi Drive and Chapel Road and OrmistonRoad and an unformed section of Stancombe Road. (see MCC Proposed District PlanMap No. 39)

Land modification or development within these areas would be subject to a resourceconsent application for a restricted discretionary activity as they are located within the 1%Annual Exceedance Probability Floodplain.

2 . 7 R e g i o n a l P o l i c y S t a t e m e n t

The Auckland Regional Policy Statement is an important document and affects thedevelopment of a Catchment Management Plan in a number of ways. The purpose of thissection is to outline and identify key objectives from the RPS which will affect theconsideration of the CMP and future growth in the catchment.

One of the key issues facing the region is growth, and this chapter of the RPS, inassociation with the Regional Growth Strategy, provides a policy framework for managinggrowth. Chapter 2 sets a range of strategic objectives and policies for the region to assist inthe management of urban growth and its effects on the Regions environment. Thefollowing Strategic Objectives are important in relation to the East Tamaki CMP:

To ensure that provision is made to accommodate the Region’s growth in a mannerwhich gives effect to the purposes and principles of the Resource Management Act,and is consistent with these Strategic objectives and with the provisions of this RPS.



To protect the intrinsic values of the Region’s natural resource base, and to makeappropriate provision for the avoidance, remediation or mitigation of adverse effectson the Region’s environment, including the identification of significant naturalfeatures and landscapes, and areas of significant indigenous vegetation and habitat,and protection of these from inappropriate subdivision use and development.

To manage the Region’s natural and physical resources in an integrated manner.

To involve the Tangata Whenua as kaitiaki of the Region’s natural resources.

One key instrument used in the RPS are Metropolitan Urban Limits (MUL). In the EastTamaki catchment, the MUL is currently located on Murphy’s Road, east of which nourban development is currently permitted.

The Regional Growth Strategy has indicated that a more appropriate boundary for urbancontainment is the catchment boundary. The ARC is likely to initiate a change to the RPSto reflect the work being undertaken by MCC to provide for urban expansion in the EastTamaki area, and hence enable a number of regional growth objectives to be met. Theprogressive movement of the MUL in accordance with the staging approach proposedlater in the CMP could be an effective tool to ensure development of the area proceeds in amanner which protects the important values in the catchment. This would also enableMCC to plan the development of appropriate infrastructure to support development in anintegrated manner, as opposed to infrastructure being installed in an ad hoc manner bydevelopers.

The RPS also includes a requirement to prepare structure plans and catchmentmanagement plans for significant new areas of urban development. This investigation andthe earlier DET Concept Plan process will enable this requirement to be met.

Other important issues covered in the RPS relate to environmental issues for which theARC have responsibility under the RMA. Relevant objectives from the RPS are included inthe following table:



RPS Chapter Objective

No.

Objective

3.3-1 To sustain the mauri of natural and physical resources in ways

which enable provision for the social, economic and cultural

wellbeing of Maori.

Chapter 3: Matters of

significance to Iwi

3.3-3 To involve Tangata Whenua in resource management processes in

ways which:

take into account the principles of the Treaty of Waitangi,including rangatiratanga;

have particular regard to the practical expression ofkaitiakitanga.

Chapter 4:

Transportation

To avoid, remedy, or mitigate the adverse effects of transport on

the environment and, in particular:

to avoid, remedy, or mitigate the adverse effects oftransport on air quality and water quality;

6.3-2 To maintain, enhance or provide public access to the Region’s

heritage resources consistent with their ownership and

maintenance of their heritage value.

Chapter 6: Heritage

6.3-3 To protect and restore ecosystems and other heritage resources,

whose heritage value and/or viability is threatened.

Chapter 8: Water

Quality

8.3-1 To maintain water quality in water bodies and coastal waters

which have good water quality, and to enhance water quality

which is degraded particularly for the following purposes:

Estuaries and harbours: protection of aquatic ecosystems,recreation, fishing and shellfish gathering, cultural andaesthetic purposes.

Open coastal waters, including parts of the Hauraki Gulf:its natural state.

Groundwater: water supply.

Lakes, rivers and streams: protection of aquaticecosystems, recreation, food gathering, water supply,cultural and aesthetic purposes.

Wetlands: protection of aquatic ecosystems.

Chapter 9: Water

Conservation and

Allocation

9.3-1 To maintain water levels and flows sufficient to protect the:

natural character,

cultural, amenity and intrinsic values, and

aquatic habitats and ecosystems,

of streams, rivers, lakes and wetlands.

Chapter 11: Natural

Hazards

11.3 To avoid, remedy, or mitigate the adverse effects of natural

hazards on human life, property and the environment, while

minimising the adverse effects of measures implemented to reduce

the risks of natural hazards.

Chapter 12: Soil

Conservation

12.3-3 To avoid, remedy, or mitigate adverse effects of activities that

result in soil degradation. To minimise the effects of soil

degradation on the water quality of receiving environments.



In addition to the above objectives, the RPS has numerous methods which are of relevanceto the development of the CMP. One of the most significant issues raised by the RPS inrelation to land use intensification or urbanisation is maintenance of water quality andstormwater management. Policy 8.4.4 provides that where:

Land use intensification in urban areas shall only occur where adequate provisionis made for:

(i) control of sediment discharges;

(ii) control of stormwater discharges;

(iii) collection, transport, treatment, purification and disposal of sewage;

(iv) protection of the quality of groundwater recharge especially into aquifers used for watersupply purposes;

(v) protection of water quality and riparian margins;

Furthermore, Method 8.4.5-2 states that

”Where land use intensification is proposed, the need to prepare a catchmentmanagement plan or structure plan (see Appendix A) will be determined byconsultation and agreement between the ARC, relevant TA and persons initiatingthe proposal. The need for a plan will be determined by assessing the proposal interms of the following criteria:

(i) the scale of the proposal;

(ii) the sensitivity of the receiving environment;

(iii) the potential for adverse effects, particularly cumulative adverse effects towater quality.

The catchment management plan or structure plan will include the measureswhich are necessary to address the matters set out in Policy 8.4.4 -1 and theimplementation of those measures will be secured by means of resource consentsand related conditions, and/or measures in district plans and/or regional plans.

These policies and methods clearly establish the need for a comprehensive CMP for theEast Tamaki catchment. Appendix A to the RPS also includes a definition of whatcatchment planning should achieve. While this description is not necessarily definitive, theARC have been involved in the catchment planning process at key stages to ensure thelevel of analysis and recommendations are likely to meet requirements for any futurecomprehensive stormwater discharge consent application made by MCC. The followingtable is reproduced from the RPS to provide generic description of catchmentmanagement planning:



Type of process Responsibility General scope and outputsCatchmentmanagementplanning

ARC, TAs ormajor developers(under thesupervision ofthe ARC).Normally,catchmentplanning will beundertaken atthe initiative ofthe ARC.

Identifies and describes the important characteristics of acatchment in which resource management problems alreadyexist or may occur as a result of expected changes. Theexpected changes may include urban development orredevelopment, or other major changes in activity patterns.Catchment management planning will:

identify the natural resource values which should beconserved or preserved;

identify actual and potential resource managementproblems (such as demands for natural water resourceswhich exceed sustainable supply, flooding, landstability, effects of sediment laden stormwater onestuarine areas, or pollution from urban stormwater);

describe alternative futures (scenarios) and analysis oftheir consequences;

identify and evaluate the cost/effectiveness ofalternative means or avoiding or mitigating adverseeffects on the environment, and of protecting andenhancing conservation values and amenity values;

propose preferred means for addressing issues.Catchment planning produces guidelines and programmesto address resource management issues in ways which giveeffect to the purposes and principles of the RM Act, and arecost-effective. Outputs will normally be non-statutory plansto guide decisions about resource allocation or use. The non-statutory plans may provide:

the basis for promulgation of regional plans under theRM Act;

guidance for the ARC in exercising consentresponsibilities;

recommendations to be effected through district plans;

recommendations to be effected through ARC and TAannual plans.

Catchment Analysis

Section 3



3333 Catchment AnalysisCatchment AnalysisCatchment AnalysisCatchment Analysis

This section identifies the relevant environmental and ecological information collatedduring the ‘baseline information’ gathering phase of the CMP. Reference is made tomethods, relevant data, site visit records, and photographs in the appendices throughoutthis section.

3 . 1 I n - s t r e a m H a b i t a t

3.1.1 Study Sites

Sampling was restricted to the Development East Tamaki area, identified in the DETConcept Plan as bound by Te Irirangi Drive in the west, the proposed scenic road along theridgeline to the east, Redoubt Road to the south, and Point View Drive to the north. A visitto the estuary was undertaken on one occasion to view the weir established as part of theTamaki Power Station development.

A total of 27 sites were visited in February/March 2000 (See Map 1 and Table 1). Of these,four were not sampled (but visual observations were noted), seven were sampled for bothfish and macroinvertebrates, and a further four sites were visited for macroinvertebratesamples and habitat assessments. The remaining seven sites were sampled only for fish.

The purpose of this section of the report is to describe the keycharacteristics of the catchment relating to the in-steam habitat,existing land use, landscape and amenity values, terrestrialecology, water chemistry and stormwater.



Table 1: Stream habitat, channel condition and biodiversity sample sites in the EastTamaki Catchment Management Plan area, February/ March 2000.

SiteNo.

LaboratoryReferenceNumber

GridReference(260-R11)

Fish Macro-invert-ebrates

Riparian/Habitatassessment

Comment

1. O1/F1 820 677 Y Y Y

2. O2/F2 833 672 Y Y Y3. O3 830 683 Y Y4. O4/F3 816 688 Y Y Y5. O5/F8 814 675 Y Y Y6. O6 818 685 Y Y7. O7 810 679 Y Y8. O8 805 706 Not sampled, visual

observations9. O9/F15 805 694 Y Y Y10. O10/F18 825 687 Y Y Y11. O11 817 703 Y Y12. O12/F12 827 662 Y Y y13. O13 805 681 - - - Not sampled, visual

observations14. O14 801 683 - - - Not sampled, visual

observations15. O15 809 688 - - - Not sampled, visual

observations16. F4 830 675 Y - -17. F5 828 678 Y - -18. F6 829 679 Y - -19. F7 820 678 Y - -20. F9 816 667 Y - -21. F10 822 664 Y - -22. F11 823 661 Y - -23. F13 803 689 Y - -24. F14 805 692 Y - -25. F16 804 704 Y - -26. F17 803 698 Y - -27. F19 809 680 y - -

3.1.2 Methods

(a) Water and sediment chemistry

Urban development typically results in changes to water chemistry in the receivingenvironments. A summary of existing water quality information was compiled andimportant contaminants identified, as well as locations where accumulation is most likelyto occur.

(b) Channel condition and habitat assessment



The channel and habitat condition is an important determinant of the ecology andinstream values associated with aquatic habitats. Habitat assessments were carried outfrom visual estimates of instream aquatic habitat, bank stability and ripariancharacteristics within a 30 m reach of stream. The ARC Habitat Assessment method wasused to estimate habitat characteristics. This assessment leads to a single score that can beused for comparative purposes. The maximum score is 140 (high quality habitat), and theminimum is zero (low quality habitat). Additional quantitative and semi-quantitativemeasurements of 5 channel transects throughout the reach were also undertaken. A copyof the habitat assessment forms are also included in Appendix 8.

(c) Riparian characterisation

The riparian characteristics were first classified using a stream and riparian classificationrecently developed for use by Environment Waikato (Quinn 1999). Streams were classifiedvisually in accordance with 9 categories (Figure 5). Additional information of the structureof the riparian communities within the sample reach was also recorded to allowcomparison between sites. Additional information on local land use and riparianprotection was also obtained.

(d) Bank stability

The Pfankuch bank stability assessment (Pfankuch, 1975) is a standard method forassessing bank and channel stability based on observations at each site. This method hasbeen adapted for New Zealand conditions (Collier 1992, see Appendix 8 for assessmentforms). The assessment leads to a single score that can be used for comparative purposes.The maximum score is 152, which indicates poor channel and bank stability, and theminimum score is 38, which indicates excellent bank and channel stability.



Entrenched floodplain EF

V-shaped entrenched VE

Upper floodplain low relief UFL

Upper floodplain high relief UFH

U-shaped hill valley UHV

V-shaped hill valley VHV

Shallow V-shaped rolling SVR

Vegetated drain VD

Headwater wetland HW

Lower floodplain LF

Figure 5: Stream and Riparian Classification



(e) Macroinvertebrates

Stream macroinvertebrates are widely used as indicators of water and habitat quality, andoverall stream health. Macroinvertebrates were sampled from a 30 m reach at each site.Samples were taken with a 250 µm mesh kick net and from each habitat in proportion to itsoccurrence within the reach. Macroinvertebrates were sorted and identified in thelaboratory to appropriate taxonomic level and abundance was recorded using a codedabundance system as follows:

>500 individuals per sample - Very very abundant (VVA);

100-499 individuals per sample - Very abundant (VA);

20-99 individuals per sample - Abundant (A);

5 - 19 individuals per sample - Common (C)

1-4 individuals per sample - Rare (R).

A benefit of using macroinvertebrates as indicators of ecosystem health is that a number ofindices can be used to analyse and interpret the data. Four measures were calculated inorder to summarise the macroinvertebrate dataset:

taxonomic richness,

Macroinvertebrate Community Index (MCI) (Stark 1985; 1993),

the semi-quantitative version of MCI (SQMCI) (Stark 1998),

Number of Ephemeroptera, Plecoptera and Trichoptera taxa excluding Hydroptilidae(No.EPT).

Hydroptilidae were excluded from the calculation of the No. EPT index because thisfamily is often associated with degraded habitats.

(f) Fish

A fish population survey of Otara Creek for areas upstream (east) of Chapel Road wascarried out during February 2000. Sites were fished using electric fishing and fish trappingin the majority of tributary streams of Otara Creek and in Otara Creek itself. The NewZealand Freshwater Fish Database (NZFFD) was used to locate any previous records forthe Otara Creek. The NZFFD was also used to investigate the fish fauna of adjacentcatchments to determine if fish species might have been absent from Otara Creek that froma regional perspective could have been expected to be present.

3.1.3 Water Chemistry

The ARC have monitored a number of parameters in the vicinity of the East TamakiCatchment, include 2 saline sites and 6 freshwater sites, 2 of which are directly relevant tothe present study. The parameters for which monitoring data is available includes:

Colour

pH,



non filterable residue,

turbidity,

dissolved oxygen (DO),

biological oxygen demand (BOD5),

conductivity,

chloride,

ammonia,

total oxidisable inorganic nitrogen (nitrate, nitrite),

total phosphorus,

soluble reactive phosphorus,

total coliforms and faecal coliforms,

temperature.

The 2 sites where this data exists are East Tamaki Rd and Middlemore Cresent (ARWB1987, 1988, ARC 1992) and only at the former since 1992 (ARC 1999). The following tableprovides the locations of other monitoring sites relevant to the Tamaki estuary

No. Catchment Site Map Ref. Lat. Long.TAM 01 Otara Creek Power Station R11: 762 713 36o 56’.48 S 174o 51’.41 ETAM 02 Otara Creek East Tamaki Rd R11: 778 693 36o 57’.52 S 174o 52’.48 ETAM 03 Pakuranga Stream Greenmount

DriveR11: 799 725 36o 56’.06 S 174o 54’.10 E

TAM 04 Pakuranga Stream Guys Rd R11: 804 727 36o 56’.00 S 174o 4’.30 ETAM 05 Pakuranga Stream Botany Rd R11: 812 747 36o 54’.54 S 174o 55’.01 ETAM 06 Tamaki Estuary Panmure Bridge R11: 759 751 36o 54’.45 S 174o 51’.26 ETAM 07 Omaru Creek Taniwha St.

ReserveR11: 771 786 36o 52’.50 S 174o 52’.12 E

TAM 08 Otaki Creek Middlemore Cres. R11: 747 689 36o 58’.07 S 174o 50’.43 ETAM 09 Tamaki Estuary No. 7 Buoy R11: 797 792 36o 52’.29 S 174o 53’.56 E

Earlier surveys (e.g. Auckland Regional Council, 1992) indicate that water quality isgenerally poor in this region. Long term trends suggest an increase in DO, temperatureand pH, and this has been attributed to a loss of shade (riparian vegetation) and anincrease in aquatic weeds. Soluble Reactive Phosphorus (SRP) and nitrate levels aretypical of a stream draining agricultural or urban areas, and SRP levels have shown anincrease over 1985 – 1997. Ammonia levels are low indicating little or no contaminationfrom sewage and/or dairy shed washings.

Data is available form the ARC in relation to the water quality parameters which havebeen monitoring in the catchment since 1985 (pers. comm. McCarthy, April 2001). Whilethis information provides a valuable baseline, it is of little consequence in makingcatchment planning decisions for East Tamaki, as the land uses, and therefore pollutionsources are fundamentally different for a rural catchment versus a developing or fullyurbanised catchment.



Otara Lake sediments were examined for heavy metal and persistent organic pollutant(POP) contamination (Kingett Mitchell & Associates, 1996). Sediments appeared to bequite anoxic (olive black) and had elevated levels of Copper, (Cu), Lead (Pb) and Zinc (Zn).The levels suggest that the lake is enriched with organic matter. Heavy metal levels wereconsistent with the lake acting as an effective trap for urban-derived contaminants – aswould be expected. Concentrations of POP were not especially high and typical of manyother urban estuary sites.

3.1.4 Stream And Riparian Character

Four representative stream and habitat types were recognised in the Otara Creekcatchment (upstream of Chapel Road):

shallow lowland rolling streams (SR), and

valley headwater (HW),

hill valley (HV),

lowland first order streams (LFO).

The classification of the catchment streams into four types was based on thevalley/channel cross-sections, the stream/habitat characteristics, and themacroinvertebrates communities present. Results of the habitat and riparian assessmentfor each site are provided in Appendix 8. The four classifications were based on fourvalley/channel cross-sections: V-shaped entrenched headwater streams (VE), V-shapedhill valley (VHV), U-shaped hill valley (UHV), and shallow lowland V-shaped rolling(SVR), while the first order lowland streams were identified as ephemeral waterbodies (seeFigure 5). As the hill valley types were very similar and sufficiently distinct from the twoother categories it was decided that for the purposes of the East Tamaki CMP, these streamtypes would be combined to form hill valley streams. A brief summary of each of thestream types follows (see Map 2 for the spatial definition for each stream type within theEast Tamaki stream network).

(a) Shallow lowland rolling streams (See Appendix 12, Plates 1-4)

These zones occurred along streams meandering gently through gently rolling land withgentle-moderate slopes down to the stream edge. The stream channels were slightlyincised in the valley bottom, with low banks. The channel slopes were lower than in hillvalley streams and the streambeds were generally silt/mud/sand with between 10-40%woody debris cover. The stream banks appeared to be poorly consolidated, generallygentle in slope, or a composite of gentle to moderately steep. Vegetation neverthelessappeared to prevent excessive slumping or scour (bank erosion 10-20% of reach at mostsites). No additional stabilisation of the stream banks was noted. Riparian vegetation washighly mixed and included native (average 30% of the sites visited), exotic vegetation(30%), and grass (22%). The dominant species at most sites appeared to be crack willow(Salix spp.), and the roots and trunks of these trees often blocked the flow causing nil waterflow in some areas, which was especially evident during periods of low flow.



Land use surrounding these stream types was generally pasture, with stock access to moststreams, and some stock damage to the stream banks was evident. Fencing of streams wasgenerally minimal. Stream channel width varied from 1.5 – 8.6 m, and habitat availabilitywas minimal, generally with 50-100% of the reaches visited forming slow flowing shallowpools/runs and no riffles were observed. Observed water clarity was moderate to poor inmost cases, due to suspended algal blooms, flocs of algae floating on the surface of thestreams, and surface scums. Habitat assessment scores ranged from 51-73, and werealways less than half of the maximum score (140 = high quality habitat) in these streamtypes, and lower than those recorded at hill valley and headwater streams sites. Pfankuchscores ranged from 97-123, and were up to three times the minimum (excellent condition)score, and similar to hill valley streams (see Figure 6).

Figure 6: Habitat assessment and Pfankuch bank stability scores for Otara Creek, Feb.-Mar. 2000.

Hab=Habitat assessment, pf=Pfankuch score. Sr = Lowland rolling streams; Hv = Hillvalley streams; Hw = Headwater streams.

0

20

40

60

80

100

120

140

1 4 6 7 9 2 3 5 10 11 12

Site

Hab

itat A

sses

smen

t and

Pfa

nkuc

h Sc

ore

HabPf

(b) Hill valley streams (See Appendix 12, Plates 5-6)

These areas occur along moderate-slope streams in V-shaped and U-shaped valleys,generally in the foothills of Otara Creek catchment. The streambeds comprisesilt/mud/sand, with small cobbles in some cases. Only 5-20% instream woody debriscover was observed, and periphyton growths ranged from 5-20% at the sites visited. Thestream banks were poorly consolidated, generally gentle in slope, or a composite of low tomoderately steep. Bank undercutting is evident in some sections of the stream. Nostabilisation of the stream banks was observed. Riparian vegetation is dominated by native(average comprising 60% at each site visited), and exotic vegetation (25%).

Sr Hv Hw



Land use surrounding these stream types included pasture, exotic plantation andrecreational reserve. Less stock access is evident compared to the lower reaches. Streamchannel width varied from 1-2 m, and riffle areas comprised 5-60% of the available habitat,and generally 50-100% of the reaches visited formed slow flowing shallow pools/runs.Observed water clarity was good to slightly turbid.

Habitat assessment scores were higher in these hill valley stream types (range 81-92), andPfankuch scores ranged from 94-124.

(c) Valley headwater streams (See Appendix 12, Plates 7-8)

Valley headwater streams occur in the upper reaches of Otara Creek and include tributarystreams, especially in the southern and northern parts of the catchment. In these reachesthe channels were entrenched in steeper sided-vertical sided valleys. The stream channelswere slightly incised in the valley bottom, and the channel slopes were greater than in hill-valley and shallow rolling streams, with stream substrate generally comprisingbedrock/boulder/cobbles with between 15-30% instream woody debris cover. The streambanks were poorly consolidated, with slumping or scour (20-40% at most sites) occurring,and exposed soil and litter was evident. No additional stabilisation of the stream bankswas observed. Riparian vegetation is dominated by woody and non-woody nativevegetation (average 65% of the sites visited). Land use was pasture and native bush.Fencing of streams was generally more prevalent than in other parts of the catchment.Stream channel width varies from 0.5 – 2.5 m, and instream habitat included riffles (15-20%) and deeper pools (50-80%). Observed water clarity is moderate to good in most cases.

Habitat assessment scores were greater than in other parts of the catchment (range 67-97),but still fell short of the maximum score (140) for high quality habitat sites. Pfankuchscores ranged from 83-104, and still high compared to high quality bank stability scores.

(d) Lowland (mostly first order) streams (See Appendix 12, Plates 8-10)

Unlike the mainstem streams described above, these streams arise in the lowland rollingarea, and exist for only a short distance before joining the mainstem. Typically, at the timeof sampling, these streams contained no permanent water, and following ARC policy havebeen categorised as ephemeral. Thus no sampling or habitat assessments were undertaken.However, these small catchments are included here for complete catchment planning.

Despite containing no permanent water, the lowland first-order streams all retained adefinable course and channel area. Typically these dry courses were fringed and/or filledwith wetland plants such as reeds and rushes. In some cases these watercourses have beendammed to form small farm ponds, and in other cases, have been furnished with poorlyconstructed culverts.

3.1.5 Macroinvertebrates

The two macro-invertebrate indices used, Macro-invertebrate Community Index (MCI)and Semi-quantitative version of MCI (SQMCI) are regularly utilised in stream assessmentthroughout New Zealand. Their use in this report should be viewed in two ways:



as an assessment of pollution in Otara Creek; and

as a comparative exercise within the catchment.

The pollution indications are limited by the fact that the method was developed for stonybottom streams, and as such it has to be treated with caution. However, no soft bottomstream macro-invertebrate pollution assessment methodologies exist. Other pollutionassessment methods such as the % EPTs (Ephemeroptera Plecoptera Trichoptera –discussed later in this section) are also limited in their application in soft bottomed streamsas the absence of pollution intolerant taxa (such as EPTs) is often the result of the lack ofappropriate habitats, not of pollution. This is a recognised limitation to which no solutionis as yet available.

(a) Macroinvertebrates diversity and distributions

Most macroinvertebrate taxa found in the catchment were commonly occurring typesfound in a variety of stream habitats throughout New Zealand. One exception was thepresence of the mayfly Isothraulus, which has been recorded only in the Auckland area(Towns 1996). All other species have been recorded from lowland streams or low-lyingcatchments in the Auckland or Waikato regions (Collier et al. 1998, Boothroyd,unpublished data). The caddis fly, Polyplectropus, worms (Oligochaeta), amphipods, andthe snail Potamopyrygus antipodarum were abundant throughout the catchment. None ofthe macroinvertebrates taxa are classified as rare or threatened. Aquatic insects formed themajority (33) of these taxa with most belonging to orders Diptera (two-winged flies) (14),Trichoptera (caddis flies) (8), and Hemiptera (true bugs) (4). Amongst the non-insects,Crustacea provided most taxa groups (5). A full list of the macroinvertebrates recorded ateach site is given in Appendix 9.

Taxa richness varied from 8 (Site 9) to 22 (Site 1), (see Figure 7), was highly variableamongst the stream types, and did not clearly differentiate streams in different parts of thecatchment. The lowland shallow rolling streams might be expected to have lower taxarichness, a phenomenon commonly attributed to lowland streams in general. However,recent studies have indicated that lowland streams can have a high biodiversity (Collier etal. 1998).



Figure 7; Macroinvertebrates taxa richness recorded from the Otara Creek catchment,Feb.-Mar. 2000. (refer to Map 1)

0

5

10

15

20

25

1 4 6 7 9 2 3 5 10 11 12

Site

Taxa

num

ber

(b) Macroinvertebrate indicators of stream health

The MCI and SQMCI were developed as indicators of water quality and can be assignedthe following criteria (from Stark 1998):

MCI SQMCI

Clean water >120 >6

Doubtful quality/mild pollution 100-120 5-6

Probable moderate pollution 80-100 4-5

Probable severe pollution <80 <4

Mean MCI values in the Otara Creek catchment indicate moderate pollution throughout,while the SQMCI values suggest a gradient of pollution from mild pollution in theheadwaters, moderate pollution in the hill valley segments, and severe pollution in thelowland rolling areas. However, there was not a great difference in MCI values betweenstream types. Overall, the MCI did not indicate grossly polluted streams, but in the lowerreaches MCI and SQMCI values may have been elevated by the presence of the highscoring caddis fly (Polyplectropus). Furthermore, these levels must be treated with cautionas the MCI and SQMCI (and macroinvertebrate pollution tolerance scores) were developedfor use in stony bottom Taranaki streams and have not been evaluated in soft-bottomedlowland catchment streams. Nevertheless, observations and the stream and habitatassessments suggest that the lowland rolling segments of the streams are subject to greaterinfluence from stock, contain turbid waters and their slow-flowing nature and lowgradient increase the risk of poor water quality. Evidence of surface scum and algal flocswere found at these sites during sampling.



Differences between the two indices (MCI and SQMCI) at the same site reflect the differentways the indices are determined, but are not anomalies. The MCI, as stated in the methodis an assessment of taxonomic richness, hence the more taxa the higher the index.Furthermore this index assigns scores (of 1-10 for pollution tolerance) to taxa and thepresence of a single individual of a taxa will mean the taxa’s score is included in the total.The SQMCI is designed to accommodate species abundance into the index. Thereforecommon species at a site have a greater influence on the index value than rare taxa.Differences between the indices scores at the same site reflect this difference.

Figure 8: Macroinvertebrates Community Index (MCI) values recorded from the OtaraCreek catchment, Feb.-Mar. 2000. (refer to Map 1)

0

20

40

60

80

100

120

1 4 6 7 9 2 3 5 10 11 12

Site

MC

I val

ue



Figure 9: Semi-quantitative Macroinvertebrates Community Index (SQMCI) valuesrecorded from the Otara Creek catchment, Feb.-Mar. 2000 (refer to Map 1)

0

1

2

3

4

5

6

7

1 4 6 7 9 2 3 5 10 11 12

Site

SQM

CI V

alue

Figure 10: Number of Ephemeroptera, Plecoptera and Trichoptera (NoEPT) recorded fromthe Otara Creek catchment, Feb.-Mar. 2000 (refer to Map 1)

0

1

2

3

4

5

6

7

1 4 6 7 9 2 3 5 10 11 12

Site

Num

ber o

f EPT



Table 2: Mean macroinvertebrate indicator scores for stream classifications in the OtaraCreek catchment, East Tamaki, Feb.-Mar 2000.

SR = Lowland rolling streams; HV = Hill valley streams; HW = Valley headwater streams.

TaxaNumber

MCI SQMCI NoEPT %EPT Habitat Pfankuch

SR 13.4 81.4 3.8 1.4 7.8 63.8 112.8HV 17.0 96.7 4.7 3.7 20.3 86.3 105.7HW 14.3 92.0 5.2 2.7 19.3 84.0 92.0

3.1.6 Fish and their distributions

Nineteen sites were visited around the Otara Creek catchment of which three where notfished as the streambed contained no water (Sites 16, 18 and 19). Six species of fish;shortfin eel, longfin eel, banded kokopu (see Plate 1), Crans bully, mosquito fish and koicarp; were confirmed as being present with the Otara Creek catchment. A seventh species,goldfish, was possibly present as a single individual at one site (see Table 3). The mostwidespread fish was the shortfin eel (Anguilla australis), which was found at fourteen sites(see Table 3) and also appears to be the most abundant fish species.

Plate 1: Banded Kokopu

The New Zealand Freshwater Fish Database (NZFFD) has seven records for Otara Creek,from 1996 or 1997. The seven sites are all immediately west of Chapel Road, and were justoutside the area of the present survey. These records recorded three species; shortfin eel,longfin eel and mosquito fish, which were all recorded during this present survey. All therecords also note that the areas fished appeared to be in degraded stream reaches,suffering from the impacts of stock trampling and weed infestations.

In adjacent catchments, the NZFFD has fifteen records, Pakuranga Creek (four) andTuranga Creek (eleven), from surveys carried out between 1992 and 1999. Shortfin eelsare the most common fish, banded kokopu and longfin eels occurred regularly, but are notabundant, and mosquito fish are noted as present in Pakuranga Creek. One record fromPakuranga Creek indicates common bully is present at a site. Common bullies were notfound in Otara Creek, however common bully and Crans bully are often confused and it ispossible that the Pakuranga Creek bullies are in fact Crans bully. Finally, in TurangaCreek, a single redfin bully has been recorded, a fish not encountered anywhere in the



Tamaki River or its tributaries. Overall it is concluded that the fish present in Otara Creekrepresent the expected fish fauna for this region.

Table 3: Fish species collected at each fishing site and the estimated abundance,

r = rare, o = occasional, c = common,, a = abundant.

Site Shortfineel

Longfineel

Bandedkokopu

Cransbully

Mosquitofish

Koicarp

Goldfish

1 o - - - - - -2 - - r c - - -4 c - - - - c -5 a - - - - - -9 o - - - - - -10 r o - c - - -12 - - - - - - -16 c - - - - - -17 a - - - - - ?18 c - r - - - -19 c - o - - - -20 o o r c - - -21 r - r - - - -22 o - r - - - -23 c - - - c - -24 - - - - - - -25 - - - - - - -26 - - - - - - -27 c - - - - - -

(a) Fisheries values

The fish present in the Otara Creek catchment represent a range of fisheries values and fallinto a range of different legally-defined groups. The two eels species are of commercialvalue and of significance as recreational/food fisheries. The landowner at site 14 indicatedthat locals from nearby residential areas fished his stream for shortfin eels. Therefore, itshould be recognised that the streams, despite their apparent poor water quality dosupport a limited recreational fishery. It is unknown how widespread this fishery iswithin the catchment. Longfin eels may also contribute to the eel harvest within thecatchment, but probably on a small scale because of their limited abundance anddistribution. Banded kokopu, a threatened whitebait species (Tisdall 1994), occurs in mostof the upper reaches of streams within the catchment. However, it is unlikely that awhitebait fishery exists within the catchment. It is usual that such fisheries are for themost part, supported by inanga (G. maculatus) and other Galaxid species not recorded inOtara Creek. Crans bully, the other native fish in the catchment has neither a fisheriesvalue nor is it considered threatened.

Koi carp are classified as a noxious fish (Conservation Act 1990) and their presence withinthe catchment would appear to be the result of an illegal introduction. The introductionmay have come about from the desire to create a fishery for koi carp in the creek, or to



clear weed from the streams. The fish caught and observed in the creek attained sizes of0.5 m and could be considered of value as a food fish. However the possession of koi carpis illegal and any fishery is therefore also illegal.

Mosquito fish and goldfish are introduced, but are neither managed under the sports fishregulations or the noxious fish regulations. Mosquito fish are, however, increasinglyviewed as a potential pest species due to it ability to displace small native fishes, both inNew Zealand and internationally.

(b) Fish passage requirements

Both the eel species and banded kokopu are diadromous species and require passage toand from the sea to complete their respective life cycles. These species are all known fortheir ability to climb wetted vertical surfaces and juvenile fish are regularly recordedabove natural waterfalls. For example in the Otara Creek catchment, banded kokopu andshortfin eels were caught at site 2, a site that is immediately upstream of an approximately8 m high waterfall. The wide distribution of eels with the Otara creek catchment and thepresence of banded kokopu in headwater streams indicate fish passage is readily availablein most areas. This also indicates that there are no fish passage problems in the lowersections of Otara Creek downstream of the survey areas. Site 1, although having very goodwater quality and habitat structure, had no fish. It was noted that in this region there werea number of natural waterfalls and may act as fish barriers.

3.1.7 Otara Creek Catchment Issues

The composition of the fish fauna of Otara Creek is essentially as could be expected forthis type of catchment in the Auckland area. However the stream as a whole could beconsidered degraded for much of it length. The lower reaches are either unshaded orchoked with crack willow trees. Farm stock (cattle) have caused some bank damage,especially on the smaller tributary streams. Further siltation may result from the ongoingurbanisation in the catchment (including upper catchment). Algal blooms (suspended andfilamentous algae) were also present at a number of sites and indicate possible waterquality problems. The abundance of shortfin eel as opposed to other fish species in thecatchment is indicative of poor habitat, including poor water quality. This species is themost tolerant freshwater fish in New Zealand and therefore its presence and the absence ofother species indicates degraded habitats.



3 . 2 L a n d U s e A s s e s s m e n t

A land use assessment has been carried out to determine the predominant existing landuses of the catchment (See Map 3 and Figure 10). The catchment study area is dominatedby pastoral uses, with areas of relatively recent countryside living subdivision in the upperparts of the catchment along ridgelines. Small pockets of urban residential exist within thecatchment study area, although these are not significant from a land use perspective.

An assessment of future land use has also been carried out (see Map 4). For the catchmentstudy area, the future land use is based on the DET Concept Plan. Some areas outside the

catchment study area also needed a future land use assessment for stormwater modellingpurposes. The proposed Manukau District Plan provided the basis for future land use inthese areas. Map 4 provides the future land uses derived from the DET Concept Plan forthe upper parts of the catchment, and District Plan for those areas ‘downstream’ of theDET area.

Table 4 provides a summary of the key present land uses within the catchment boundariesidentified for stormwater modelling purposes. While the study area is approximately1735ha, the stormwater modelling boundaries include areas outside the ‘catchment studyarea to enable the stormwater model to be calibrated. These boundaries are clearly shownon the Map series, in particular, see Maps 3 or 4.

Table 4: Existing Land Use

Landuse Existing (ha) % of catchmentIndustrial/Commercial 93 3.5Motorway 11 0.4Pastoral 1467 55.0Public Open Space / Urban Park 58 2.2Residential 554 20.8Residential (undeveloped) 18 0.7Rural-Residential 138 5.2Rural-Residential (undeveloped) 48 1.8School 43 1.6Vegetation, Bush, Conservation etc 153 5.7Roads 85 3.2Total 2668 100.00



Figure 11: Percentage of existing land use in catchment

��

��

��

Motorway�� Pastoral

Public Open Space / Urban ParkResidentialResidential (undeveloped)��Rural-ResidentialRural-Residential (undeveloped)School��Vegetation, Bush, Conservation etcRoads

The future land use of the catchment will change significantly as a result of the DETConcept Plan, which provides a range of future land uses, dominated by a mix of urbanresidential uses and conservation areas. These are likely to include the following land usetypes:

Town Centre and Business areas

High density residential areas

Medium density residential areas

Low density (countryside living) areas

Conservation areas; and

Barry Curtis Park

This means a number of changes in land use as the areas moves from an essentially rural toa largely urban future. Some change in land use will occur in the ‘downstream’ parts of thestormwater catchment areas shown on Map 4 due to development of new industrial,commercial and other uses. Table 5 provides indicative future land use areas for thecatchment, as determined by Map 4, which for the purpose of modelling for Phase 1stormwater modelling (see section 3.6 for further explanation of stormwater modelling)early in the development of the Catchment Management Plan was the land use proposedin the Concept Plan. It is noted that some changes have occurred to the final areas of futureland uses as the CMP and structure plans have been further developed from theconceptual framework contained in the DET Concept Plan (June, 1999).



Table 5: Future Land Uses

Landuse Future (ha) % of catchmentIndustrial/Commercial 223 8.4Public Open Space / Urban Park 225 8.4Residential 535 20.0School 50 1.9Vegetation, Bush, Conservation etc 334 12.5Roads 241 9.0High Intensity Residential 455 17.0Low Intensity Residential 316 11.8Medium Intensity Residential 289 10.8

Total 2668 100.00

Figure 12: Estimation of potential mix of future land use in catchment

��

��

Public Open Space / Urban Park

��Residential

School

Vegetation, Bush, Conservation etc

Roads

High Intensity Residential

��Low Intensity Residential

Medium Intensity Residential

The DET Concept Plan (see Section 6.1utlines the proposed densities and keycharacteristics of each of these areas in greater detail. Table 9 provides greater detail onsome of the assumptions for each of these areas in terms of likely impervious surface areas.

Appendix 15 provides a breakdown of the existing and future land use areas bysubcatchment. It should be noted that the boundaries of future sub-catchments differ fromexisting sub-catchments due to the requirements of the stormwater management regimeoutlined in this CMP.



3 . 3 L a n d s c a p e I n v e n t o r y a n d A n a l y s i s

Initial analysis of the East Tamaki catchment has been directed at identification of thoseelements, features and qualities that might carried over from the present 'pre-urban'situation into its future urban form as the basis for landscape and amenity enhancement,and the retention of a sense of place and identity appropriate to the locality. Thesefeatures, elements and patterns are divided into two basic groupings:

geophysical components: which contribute to the basic structure of the currentenvironment - terrain, the existence of stream corridors, vegetation, etc; and

amenity characteristics: those components which contribute to landscape patterns,points of interest and focus, and spatial structure which directly influence visualidentity and character.

The attached worksheet lists these key components of the landscape 'inventory'. At thesame time, it highlights the fact that the initial survey of East Tamaki addresses theidentification of landscape or planning units at two levels: broader scale identity areas,which are primarily distinguished by terrain and general land / vegetation cover, andmore fine tuned landscape units, which reflect a wider array of influences - from types ofvegetation and vegetation patterns to slope angles, aspect, insolation, and even the visualfocus afforded different localities at present.

The five identity areas identified to date comprise:

The Point View Drive Ridge Area - embracing the area east of the Dannemora Estate,the Gracechurch subdivision and Point View Reserve extending towards the Jeffs Rdextension (see .

The Redoubt Rd Ridge - extending southwards from Hilltop and Adamson Rd tocapture the main ridge and 'roll over' into a pastoral valley that forms part of TotaraPark.

The Ormiston Rd Saddle - encompassing the lower profiled ridge and rollingsequence of ridges and gullies either side of Ormiston Rd , between the two identityareas already described.

The East Tamaki Valley - from Murphys Bush Scenic Reserve and Road towards themargins of the 'Ormiston Rd saddle' around the end of McQuoids Rd.

The East Tamaki Flats - covering the main alluvial west of Murphys Bush Reserveand Road, extending towards East Tamaki Rd and Springs Roads.

These areas are identified on Map 6.

The Point View Drive, Redoubt Rd and East Tamaki Flats identity areas are already verysignificantly influenced by urban development, with major change evident throughoutmost of the corridor around Chapel Rd and the recent completion of Te Irirangi Drive.While the East Tamaki Valley identity area and Ormiston Rd Saddle retain significantpastoral qualities, it is clear that pressure for change is already starting to influence the



character of these areas as well, with the recent Tuscany Estates subdivision overlookingthe southern reaches of both.

The following are summary findings in relation to each identity area. PanoramicPhotographs of each area are included in Appendix 2.

3.3.1 The Point View Drive Ridge Area

Marked by moderately to quite steep terrain, this area is a key focal -point for the mainEast Tamaki 'plain' directly below. It is hallmarked by a diversity of vegetation cover,much of it comprising exotic amenity planting, although the area is also interspersed withremnant pine and macrocarpa shelterbelts, and the slopes and gullies leading down fromPoint View Reserve into the Gracechurch Reserve are notable for remnant bands / pocketsof kahikatea, manuka, nikau, puriri, some rimu, totara and taraire. These have alreadyprovided a natural starting point for amenity planting in and around homes atop the ridgeand around the Gracechurch block. They lend the locality a sense of maturity lacking frommost of the adjoining lowland areas and reinforce the partial containment and seclusionafforded by the topography. Although stream corridors provide the basis for thisvegetative and (in part) the physical structure of the land they remain either largelyhidden under the canopy of native vegetation accompanying them or - on steeper slopes -are ephemeral in nature. As such, they have little appreciable visual presence in their ownright.

A key feature of the ridge is its high level of visual exposure to the broad matrix of EastTamaki, with views stretching to Mangere Mountain, the Manukau Harbour and Heads,the Awhitu Peninsula and Waitakere Ranges. This suggests that even though internalcharacter will remain a significant component of the area's identity, it will also be stronglyinfluenced - as it already is - by the nature of development on the 'apron' in front of it andbeyond.Key landscape attributes of the ridge area therefore include its actual ridgelineprofile (in relation to viewers out side the identity area), the two existing reserves, thestream and vegetative paths down and through the main slopes, and some isolatedpockets of bush outside these stream / gully corridors.

3.3.2 The Redoubt Rd Ridge Area

Similar features are evident more sporadically within this area, although the historicclearance of vegetation on the northern side of the ridge diminishes its sense of maturity,distinctiveness and overall appeal. In a similar vein, local stream systems are visually quitesubdued, with few obvious 'markers' other than localised changes in landform andsporadic vegetation within the stream margins (little of any real note). This quite sparselyvegetated profile contrasts with the much more verdant ridge crest, notable for a widerange of old shelterbelt and amenity planting, from macrocarpa and pine to oaks, eugenia,eucalypts, cypress, even some totara and pohutukawa. South of the ridge crest, within partof Totara Park, the landscape again has a more open pastoral quality, although the



retention of pine shelterbelts and the prevalence of manuka and totara within the park'stwo main stream gullies helps to provide a degree of containment and internal focus.

Again, the ridge area has a strong external focus, with the East Tamaki Flats veryprominent in the immediate foreground.

Unlike the Point View Dr area, this ridge does not enjoy a sequence of strong features -other than the relatively vegetated profile of the actual crest - to provide a platform forfuture open space development and amenity enhancement. Although a number of streamsthread their way down the northern face of the ridge, these remain largely ephemeral andsubordinate to the general (largely open) terrain. Any, or all, of these would have to besignificantly revegetated to become features in the future. Rather, future open spacedevelopment may be reliant upon a combination of stream retention / enhancement, theretention of some pockets of existing trees (mostly amenity planting around individuallarge lot properties) and the associated development of open spaces that are strategic interms of future urban development.

3.3.3 The Ormiston Rd Saddle

Comprising gently rolling to rolling country, largely in pasture, this identity area isnotable for its clear sequence of spurs and ridges (running towards the valley floor below)and the related interplay between grassed open space and a varied matrix of trees: pocketsof totara and manuka high up, with kahikatea and puriri starting to emerge lower down.Shelter belts of Chinese poplar, and stands of the ubiquitous macrocarpa and pine are alsoregularly visible. In one or two locations, pockets of broadleaf forest - including a mix ofpuriri, taraire, rimu and nikau - extend out of the gullies onto the main slopes.

Streams provide the physical focus in virtually all gullies and although (once more)typically subordinate to the accompanying vegetation and topography, are more visuallyapparent than on the steeper ridge units.

Framed either side by the two ridges just described and with a north-south alignment, thesaddle has a strong focus towards the eastern margins of the East Tamaki Valley and Flats,and - beyond both towards the Waitakere Ranges and Manukau Heads. Even so, thehigher level of visual and physical containment generally evident means that there isstrong internal focus and interaction with the nearby valley and flats. There is also strongvisual connection with both the Point View Drive ridge (in particular the reserve at itsouthern end) and the Redoubt Rd ridge. The combination of vegetation and topographylends the general locality a reasonable sense of containment and seclusion, although this isless apparent on some of the higher, more exposed, slopes.

As a result of this physical structure, the locality has a significant level of amenity andmany of the elements that contribute to this - a relatively undeveloped main ridgeline(except for Tuscany Estates), the main stream and vegetative corridors, some of the openspurs between these and the odd stand of remnant forest - could provide a foundation forfuture open space development, linkage and general amenity enhancement in the future.



3.3.4 The East Tamaki Valley

Strongly framed and delimited by the three identity areas already described, this area isfurther characterised by other key features: the transition into a gently undulating, alluvialterrace, landform; the continued prevalence of stream courses throughout the valley; andthe strong presence of trees. Most notably, these include the large stands of kahikatea,puriri and even some rimu around Murphy’s Bush Reserve, Murphy’s Rd and McQuoidsRd - primarily south of Ormiston Rd. The area is also very strongly dissected byshelterbelt planting, with old hawthorn hedges and the more recent introduction ofChinese poplars especially evident.

The landscape enjoys a comfortable level of physical and visual containment that,combined with the strong presence of stream systems and vegetation, lends it the strongestinternal character of the five identity areas under review. In this context, the kahikateadominated stands of native forest found throughout most of the identity area areespecially important, creating a local identity that is probably only matched (regionally) bya similar composition of landform and vegetation within parts of the Clevedon Valley.There is also a natural linkage with the stream systems and patchwork of vegetation at thefoot of the Ormiston Rd saddle.

This sequence of native vegetation and streams provides a foundation for both thelocality's identity and any future open space network, although the gently rollingtopography and physically sheltered nature of the locality also suggests the potential forintegration with spaces designed to cater for a range of more active recreational pursuits.

3.3.5 The East Tamaki Flats

Hemmed in by the quite distinctive identity areas already described, but also by urbandevelopment to the west, and now subject to considerable internal modification, landclearance and development, this area of alluvial flats is largely devoid of significantlandscape features. Although dissected by a sequence of stream courses, and stillcontaining a sporadic collection of old farm trees and shelterbelts - mostly pine andmacrocarpa, although some Eucalypts and Cupressocyparis are also occasionally visible - thearea has a markedly barren feeling. Many of the aforementioned trees are old and inserious disrepair, while the stream margins are rarely marked by much more than ascattering of crack willow and tobacco weed. An increasingly fragmented network of oldhawthorn hedges is also apparent; but both they and the larger remnant pockets of moremature trees are increasingly consolidated along the eastern margins of the identity area,next to the Point View Drive and east Tamaki Valley identity areas.

As whole, therefore, the flats have an excessively open, expansive quality, with their'denuded', transitional, quality amplifying a relatively featureless topographic profile.Only the rounded form of Hampton Park, with a scattering of mature trees across it,provides any sort of internal focal point, while the Point View Drive and Redoubt Rdridges are prominent as nearby external focal points. The stands of kahikatea aroundMurphys Rd and Flat Bush Rd provide an additional external influence, but do little todissipate the qualities already described.



In looking to the future, it may be that the stream courses will provide a strong focus forwider landscape enhancement, as with Logan Carr Park next to the Dannemora Estate.Indeed, unless such enhancement occurs and the width of individual stream corridors issignificantly expanded to embrace swathes of open space either side of the actual watercourses, the stream network will remain subservient to the often quite high density,development surrounding it. Although individual trees and the odd stand of vegetationmay also be conserved in the course of urbanisation, more widespread amenityenhancement cannot generally rely on the landscape elements found within this identityarea at present, and will also largely depend upon future development - parks, streamsand stormwater networks and streets - to expand their influence and impart a sense ofcharacter and quality to the area.

3.3.6 Analysis

The following table provides a more detailed breakdown of the core characteristics of all17 landscape units, in turn describing:

Each unit's location;

Key landscape features identified - those existing components of the landscape thatshould be the focus of conservation management, e.g. through the establishment ofreserves and public spaces, and the application of protective covenants;

Significant landscape features and elements - those existing components of thelandscape that could be help to structure and define the emerging urban scenethrough a mixture of conservation management and active rehabilitation, includingthe provision of open space networks, parks, etc;

Potential future features and linkages - primarily associated with establishment of astormwater / open space network;

Potential landscape / open space focal point or nodes - that might provide the focusfor both passive and active recreation within the East Tamaki area in the future;

Key tree species within each unit - recognising that trees are critical to the retention ofan endemic character.

In addition to the assessment included in this section of the report, Appendix 1 contains arecord of the field investigations for each landscape unit, Appendix 2 includes panoramicphotographs of each landscape unit, and Appendix 3 includes four figures that identify:

the Key Landscape Features and Elements;

Significant Landscape Features And Elements; and

Potential Open Space Focal Point; and

Vegetation restoration catchments.

The figure in Appendix 3 which defines the upper and lower catchment vegetationrestoration areas is referred to specifically in relation to species lists appropriate to eacharea in Sections 8.2 and 8.3.



Table 6: Summary of Landscape Analysis

LandscapeUnit:

Unit Location & BriefDescription:

Key Landscape Features: SignificantLandscapeFeatures /Elements:

Potential landscapeFeatures &Linkages:

Potential OpenSpace Nodes:

Key(Conservation)Tree Species:

Point View Drive Ridge1A The main westward facing

slopes and a vegetatedcentral gully below the PointView Drive ridge crest

The central gullysystem andremnant nativevegetation

Potential connectionbetween the ridgecrest / Point ViewDrive Reserve andthe flats of Unit 5A

RewarewaManukaPonga

1B The Gracechurch Block andits rural -residential(typically 1:5000 sq m)properties south-west of theRedoubt Rd ridge, includingGracechurch Reserve - asequence of shallow spursand gullies with extensivevegetation

Two stream corridors through theupper part of the GracechurchBlock, with the stream course andremnant forest within GracechurchReserve (the more eastern of thetwo water courses, extendingdown from the Point View DriveReservoir) crossing GracechurchDr and extending towardsBaverstock Rd

Some of the openpasture andscrubland framingthe forest remnantsand stream coursesbelow the PointView Dr reservoir

KahikateaNikauPuririRimuTaraireTotara

1C The Redoubt Rd ridgeline -its crest and immediatesurrounds with large lotsections divided up byplanting and shelter belts

1D The southern end of themain ridgeline aroundRedoubt Rd Reserve andwater reservoir - aprominent knoll and mainspur with remnant and re-emergent native forest in

The Point View Dr Reserve withassociated remnant forest

Some of the openpasture andscrubland framingthe forest remnantsaround the PointView Dr Reserveand reservoir

Potential connectionbetween the ridgecrest / Point ViewDrive Reservethrough Unit 1Awith the flats of Unit5A

ManukaNikauPuririRewarewaRimuTaraire



LandscapeUnit:






pockets TotaraRedoubt Rd Ridge2A The open northern slopes

below the main ridge crest -a sequence of shallow spursand water courses

Large stream corridor and remnantnative forest east of Murphys Rdextending down from just belowthe Redoubt Rd ridge crest

Four streamcorridors emergingjust below the crestof the Redoubt Rdridge andextending acrossThomas Rdtowards the flats ofunit 5A

Continuation of astream connectionnorth of Thomas Rdinto 'Donegal Park'

Ponga

2B The main ridge crest and itsimmediate surrounds, withpredominantly large lotsections divided up byplanting and shelter belts

Top of major stream course andremnant native forest east ofMurphys Rd

Pockets of remnantforest and streamsystems extendingup to just belowthe ridge crest

Oak

2C The Totara Park valleysystem immediately south ofthe ridgeline with a centralstream corridor and pocketsof remnant vegetation

The central streamcorridor and someremnant pockets ofvegetation

Connection withridge crest Kahikatea

ManukaTotara

EucalyptMacrocarpa

Ormiston Rd Saddle3A The main ridgeline north-

west of Ormiston Rd -shallow open slopes withsome water course gullies,shelter belts and largelyisolated stands of remnantforest

Stands of remnant native forestand stream course with nativeforest remnants north and west ofOrmiston Rd

Ormiston Rdridgeline

KahikateaPuririRewarewaTaraireTotara

3B A large, enclosed valley Forest remnants in three stream The main ridgeline;



LandscapeUnit:






system immediately east ofupper Ormiston Rd - a seriesof spurs and gullies withsome remnant forest liningthe main water courses

courses the remainder ofthe existing streamcorridors withsemi-scrub /pastoral fringes

KahikateaTotara

3C The main body of the saddlefrom south-east of OrmistonRd to Tuscany Estates - themain ridge crest, open spursdescending from it, and aseries of gully systems,including a network ofremnant forest and scrubfollowing the main streamcourses

Main stream courses and pocketsof remnant native forest

The main ridgelineand top of somespurs; theremainder of theexisting streamcorridors and semi-scrub / pastoralfringes

KahikateaManukaPuririTotara

EucalyptMacrocarpa

3D A lower part of the saddleimmediately south ofOrmiston Rd - subdividedby shelter belts and remnantforest around a central steamcorridor

Core stream system and associatedstands of native forest on (oftenquite) steep embankments framingthe stream system

The remainder ofthe existing streamcorridor and semi-forest /horticulturalfringes

KahikateaPuririRimuTotara

East Tamaki Valley4A Gently sloping land

straddling lower OrmistonRd - subdivided by shelterbelts and some bands ofremnant forest followingstream corridors

The combination ofa major streamcorridor andremnant pockets ofnative forest northof Ormiston Rd

KahikateaPuririRewarewaRimuTaraireTotara

4B Gently rolling landstretching in a band fromJeffs Rd to Murphys BushScenic Reserve - 'hall

Outstanding remnant stands ofkahikatea dominated forest andassociated stream corridors

Stream corridorsbetween the majorforest stands,leading up the

A node basedimmediatelysouth and eastof Jeffs Rd:

KahikateaNikauPuriri



LandscapeUnit:






marked' by large stands ofremnant forest and anetwork of stream courses

valley towards the"Ormiston Rdsaddle" units

combiningoutstandingstands oflowland forestwith streamcourses andpockets ofpasture - bothvisually andphysicallycontained bythe forestmarginsA node within acontained, lowlying, area of(present)pasture nearMurphys Rd -framed by a keystream corridorand a majorstand ofremnantlowland forest

TotaraChinese poplarOaks (bothpotentially inconjunction withopen space /recreation areadevelopment)

4C A shallow spur immediatelyeast of Murphys Rd andsouth of Flat Bush School Rd- dominated by open pasture(including an ostrich farm)broadly framed by theremnant forest on its fringes

Stands of kahikatea dominatedforest and stream systems on theouter margins of the unit - towardsMurphy Rd (Unit 4B) andMcQuoids Roads (Unit 4D)

The remainingstream corridorconnecting thekahikatea forest(on the unit'seastern flank) withthe water coursesand remnant

A node utilisingexisting pastureframed bymajor stands ofKahikateadominatedforest - towardsMurphys Rd,

KahikateaTotara



LandscapeUnit:






vegetation in Unit3C (in the directionof Tuscany Estates)

within MurphysBush ScenicReserve andalong thestream coursemargins at theinterface withUnit 4D

4D Gently rolling land aroundMcQuoids Rd and the end ofFlat Bush School Rd -subdivided by shelter beltsand occasional band ofremnant forest- mostlytowards its margins

The stream margins and nativeforest remnants abutting Unit 3D

Remaining streamcorridors includingone that crossesMcQuoids Rd

A nodeimmediatelynorth of the endof Flat BushSchool Rd - onslopes thatgently descendand facetowards majorstream corridorand large standof remnantforest on theedge of Unit 3D

KahikateaPuririTotaraChinese poplarOakPlane (potentiallyin conjunctionwith open space/ recreation areadevelopment)

East Tamaki Flats5A A large area of gently

undulating pasturestretching from East TamakiRd to Thomas Rd (north tosouth) and from Preston Rd/ Springs Rd to Murphys Rd(west to east) - displaying anexpansive, open, naturesporadically dissected byremnant hedgerows, stream

The bulk ofexisting streamcorridors visiblydenoted byexisting vegetation

Other recognisablestream corridors

A node near thejunction ofOrmiston andChapel Roads -at a strategiclocation wherea number ofstreamcorridorsconverge

Norfolk pines (2)



LandscapeUnit:






courses and the odd stand oftrees

5B A gently rolling localityaround Stancombe andChapel Roads - displaying aslightly greaterpreponderance of remnanthedgerows and shelter belts.

A small stand of remnant nativeforest near Stancombe Rd

Existing streamcorridors visiblydenoted byexisting vegetation

Other recognisablestream corridors

KahikateaPuriri



3 . 4 T e r r e s t r i a l E c o l o g y

3.4.1 Background Information

(a) Vegetation

The most significant area of vegetation is Murphy’s Bush in Murphy’s Road, which is subject toa current management plan. No recent reports or information is available on the study area,however, a species list is available for Murphy’s Bush and is contained in Appendix 11. ARCofficers have also recently carried out an investigation into a significant block at 140 Jeffs Road,and a species list is included in Appendix 11 also.

Department of Conservation records indicate that no at risk plant species have been recorded inthe area. A rare carex (Carex subdola) has been recorded nearby near Flat Bush, outside thepresent study area.

While there are additional tracts of remnant vegetation (e.g. kahikatea stands) within thecatchment, no detailed formal botanical assessment has been completed in the study area. Map3 provides an overview of the existing land use in the catchment, which includes a number ofother significant areas of native vegetation. These areas, while not necessarily studied from abotanical perspective, will form a valuable component of the conservation areas identified inthe DET Concept Plan.

(b) Wildlife

Advice from the Department of Conservation is that there are no SSWI’s (Sites of SpecialWildlife Interest) within the catchment. No reptiles are noted by the Department ofConservation records, however, several relatively common species are likely. Notable birdspecies, which have been reported (confirmed and unconfirmed), in the area, or in immediatelyadjacent areas, are shown below in Table 7. The species are classified according to threat, andwhile all species with a national ranking are threatened, the degree of threat varies as does theirpriority for conservation:

Category A - highest priority threatened species

Category B – second threatened species

Category C - third threatened species



Table 7: List of Threatened Native Bird Species found in East Tamaki area.

Common Name Latin Name DescriptionNew Zealandpigeon

(Hemiphaganovaeseelandiaenovaeseelandiae)

Category B species in terms of national conservationpriority; would utilise, in particular, upper Catchmentnative forest remnants (e.g. tawa and kahikatea).

New Zealanddabchick

(Poliocephalusrufopectus)

Category C species; reported from the lowland area butmay have been confused with Australasian little grebe(Tachybaptus novaehollandiae novaehollandiae), a self-introduced species. NZ dabchick, however, have beenrecorded in the broad South Auckland area for manyyears where they utilise farm ponds, dams and oxidationponds.

White heron (Egretta alba modesta) A Category O species (i.e. threatened in NZ but knownto be secure in other parts of its range outside NZ);reported from lowland area where it would utilisepaddocks and wet swampy habitats.

North Islandkaka

(Nestor meridionalisseptentrionalis)

Category B species; likely to be an intermittent visitor toremnant forest stands on occasions particularly in theMay to July period when juveniles often disperse fromGreat Barrier and Little Barrier Islands where they arerelatively common. Kaka are known to travel widely,for example, Little Barrier to Gisborne, especially duringthe winter period.

Generally the Catchment supports a wide diversity of mostly common introduced and nativebird species as a result of its remaining high diversity of habitat types i.e. grazed pasture tosmall forest remnants. Murphy’s Bush is the most significant area of native bush in publicownership, and supports a number of bird species. These are also listed in Appendix 11).

3.4.2 Management Issues

The existing database for the terrestrial flora and fauna (i.e. vegetation and wildlife) in theCatchment is poor and requires resolution via field survey. While information for the onlyreserve area, Murphy’s Bush, is adequate, the main deficiency relates to areas of forest andshrubland remnants on private property.

The location and protected status of these areas needs to be identified so that their potential forintegration with riparian vegetation and/or as vegetated corridors can be explored.

In principle, it should be noted that any area of native vegetation where it lies within theproposed ecological corridors is worthy of protection, and should be physically integrated,where possible, with the conservation or riparian zone areas identified in the Concept Plan. Adetailed survey of these areas at some future point will assist in identifying appropriate actionsto protect and enhance these areas to achieve the intended ecological corridors as expressed inthe concept plan and this Catchment Management Plan. Such a survey would identify thecurrent status of native vegetation, its significance, whether it is under threat, and provide abaseline for future monitoring. The significance of remnant areas needs to be viewed in thecontext of potential linkages throughout the catchment..



Once the nature and significance of the remnant habitats has been determined there are anumber of management issues which would need to be addressed to (a) enhance or secureexisting values and (b) ensure those values were maintained or enhanced. While none of theseissues, will be able to be resolved in an appropriate manner in the absence of baseline resourceinformation, it will be feasible that rules in the proposed variation to the District Plan can dealwith some of these issues. Key management issues from an ecological perspective include thefollowing:

stock exclusion and fencing. maintenance or enhancement of hydrologye.g. with regard to kahikatea stands.

plant pest control. set-back distances for urban areas androadways.

animal pest control. determination of optimum size (a few largeor several small areas).

provision of buffer zones. provision of particular habitat zones e.g.upland game species; rough scrubland.

provision of vegetated linkages. provision of habitat diversity - forestremnants, vegetated wetland, riparianshrubland etc.

enhancement aimed at particular speciese.g. New Zealand pigeon.

Recreation infrastructure (e.g. walkways)

retention of typical amenity plantings, bothnative and exotic.

Appropriateness of recreation activities.

Public access

3 . 5 H y d r o l o g y

3.5.1 Flood Flows

Stream flow data from two sites obtained from the ARC is detailed in Table 8. The modelling isprimarily examining flood flows. In addition, historical flood data is contained in the OtaraStream Flat Bush Catchment Study (refer White / Oldfield Dec. 1990). Table 9 shows the floodpeak flows extracted from the available record as described in Table 8.

Table 8: Otara Stream Flow Data

Site Name Site Number Map Reference Period of RecordOtara at Bond Street 8204 R11: 779 690 5/6/80 - 6/4/93*Otara at Hills Road 8208 R11: 780 697 28/4/92 - 7/1/00

* Site Closed

Table 9: Flood Peak Flows (m3/s)

Years (ARI) ReturnPeriod

2 5 10 20 50 100

Hills Road 20 32 41 49 59 67Bond Street 12 19 23 27 33 37

Note: The shortness of the record means that estimates for return periods greater than about 20 years are notreliable.



The Bond Street site does not include the study area, but provides data for the developedsouthern tributary of the Otara Stream. The Hills Road site includes most of the study area,plus additional catchment downstream of the study area.

3.5.2 Mean and Low Flows

(a) Mean and Low Flow Hydrology

i. Mean Flows at Hills Road

The mean flow measured at the Hills Road site from April 1992 to January 2000 isapproximately 0.3 m3/s (300 L/s). A plot of the flow distribution, and tabled mean monthlyflows for the site is given in Appendix 5.

ii. Low Flows at Hills Road

Analysis of the annual series of 7 day low flow (minimum moving mean) at the Hills Road siterevealed that there is a residual flow at the flow site, however, upper areas are most likelyephemeral. A summary of the analysis is included in the following table:

Table 10: Low Flows at Node 180 (Hills Road Flow Site)

Low Flow EventAnnual Exceedance Probability

(% AEP)Average Recurrence Interval

(ARI) – Years

7 Day Low FlowMinimum Moving Mean

(L/s)

50 2 10.320 5 7.110 10 5.75 20 4.72 50 3.71 100 3.0

The ‘5 year, 7 day low flow’ is typically quoted as a measure of the low flow characteristics of astream or catchment. The East Tamaki catchment area draining to Hills Road is approximately19km2 and hence this equates to approximately 0.38 L/s/km2.

The average size of the subcatchment areas is around 60ha (0.6 km2), which will typically yieldslightly more than 0.2 L/s for the 5 year 7 day low flow event. This will vary throughout thecatchment and it is most likely that the steeper areas and/or areas with poorer draining soilswill hold little if any residual flow during dry periods. Thus the headwater and hill valleystreams will probably be confined to pools for some period of time in most years.

3.5.3 Seasonal Variability of Stream Flows

Figure 13 illustrates the seasonal variability of stream flows based on the flow records at theHills Road and Bond Street sites.



Figure 13: Seasonal variability of stream flows for the Hills Road and Bond Street Sites

05

101520253035404550

Janu

ary

Febr

uary

Mar

ch

April

May

June July

Augu

st

Sept

embe

r

Oct

ober

Nov

embe

r

Dec

embe

r

Mon

thly

Mea

n Fl

ows

(L/s

/km

2) Hills Road ('rural')

Bond St ('urban')

The Bond Street site is characteristic of an urban catchment where as the Hills Road site ischaracteristic of a rural catchment. It should be noted that the following is an approximatecomparison only. The area and geology of the catchment feeding into each site differs, 18.9km2

and 5.3km2 for the Hills Road and Bond Street site respectively. In addition, the flow records ateach site are for different period with only a few months of overlap (See Table 8).

A comprehensive near surface groundwater model was not carried out in the modellingexercise, therefore it is not possible to quantify and comment on low flow variability during theyear and the expected effect on aquatic ecology due to urban development. It is normallyexpected that low flows reduce in the dry season due to development. However, the abovedata generally indicates higher dry season flows from the urban catchment. The reasons for thishave not been explored as they are beyond the scope of this study.

3 . 6 S t o r m w a t e r M o d e l l i n g 1

3.6.1 Modelling Assumptions

(a) Data Collection

The initial phase of the modelling exercise involved data collection. In particular GIS layersprovided by MCC and ARC were used to develop the models including:

Digital Cadastral Data Base

1 Note – A glossary of important stormwater modelling terminology is included at the rear of this report.



Roads

Contours (0.5m intervals)

Streams

Stormwater pipe networks

Land use and development concept plans

Aerial photographs

Data from other sources has also been used to develop the models including:

Geological /soil maps (refer Map 7)

Previous reports

Hydrological data

(b) Design Criteria and Modelling

The modelling was carried out using the graphics-based stormwater modelling softwarepackage XP-SWMM32. It was used to model both catchment runoff and to simulate thehydraulics of the open channels. XP-SWMM32 has three layers, each used to simulate adifferent part of the stormwater process. The runoff layer is used to simulate the rainfall-runoffprocess, while the hydraulics layer simulates the conveyance of the runoff through the drainagesystem.

For this exercise the SCS rainfall-runoff model (refer ARC TP108, April 1999) was applied in therunoff layer. For AEP of 50% to 1% (2-100 year return period), the model can be expected to liewithin ±25% at a confidence level of 90%. Further confidence can be placed in the resultsthrough calibration of the model to local flow records. This is discussed further in a laterSection 3.6.2.

An assessment was made of the following characteristics for each of the subcatchments asshown on Map 8 (for existing) and Map 9 (for future mitigated):

Area (ha)

Length (km)

Slope (m/m)

Geology / soil type

Land use and percent impervious (existing and future)

(c) Catchment Geology

The geological map is used in the CMP to identify areas of clearly different permeability, i.e.low, medium or high permeability. Materials exposed within a few metres of the groundsurface are soils and weathered rock. The soils, other than where man-made fill is placed, arederived from weathering of the underlying rock. The properties (including permeability) ofsoils derived from weathering of a rock-type are characteristic of that rock type. Mapped



Quaternary age geological units within the Auckland area (covering a large part of thecatchment area considered) have not generally been lithified and are soils both at the surface,and at depth. Hence, the geological map is considered to be an appropriate data source for thispurpose.

Table 11 relates the different geological layers provided in Map 7 to their corresponding soilcategory and permeability as defined in TP 108.

Table 11: TP 108 Soil Types and Permeability for Various Geological Layers

Description of Geological Layers Soil Groupbased onTable 3.3, TP108 1.

Permeability

Urban Refuse: Crushed and buried accumulations ofrefuse

B-C Medium to Low

Construction fill: Recinoacted clay to gravel-sizedmaterials. May include demolition debris

C Low

Undifferentiated alluvium: Mud, sand and gravel B MediumBasalt and Basanite lava: Grey, dense, fine-grainedlava

CN 17 Very High

Basalt and Basanite Scoria: Red, grey and black,angular to subrounded, vesicular pebble to bouldersized fragments

A High

Lithic Tuff: Thin graded beds of grey, mud to sand-sized fragments of country rock (mainly sandstone,mudstone, alluvium, micaceous sand) together withbasalt and basinite fragments

A High

Light grey to orange brown, pumiceous mud, sandand gravel, with black muddy peat and lignite

B-C Medium to Low

Light grey, massive to finely laminated, mud tosand-sized pumice: includes non-welded ignimbrite,tephra and alluvial pumice deposits (mainly coastalexposures)

B Medium

Greenish grey alternating muddy sandstone andmudstone

C Low

1. Group A = Volcanic Granular Loam, Group B = Alluvial, Group C = Mudstone / Sandstone

Impervious proportions have been defined for each major land use (see Table 12), and whereavailable these were calculated from aerial photographs. In the ‘future’ scenario, however,impervious proportions were defined for each land use after discussion with Manukau CityCouncil and ARC staff.



Table 12: Land Use / Percent Impervious

Percent ImperviousLand useExisting Future

Vegetation (Bush), Conservation, Stream, Gully,Wetland, Flood retention

0 0

Pastoral 4 -Public Open Space / Urban park 5 5Rural-Residential (undeveloped) 9 -Rural-Residential 18 -Residential (undeveloped) 29 -School 30 30Existing Residential 47 47Industrial/Commercial 75 75Low Intensity Residential - 20Medium Intensity Residential - 55High Intensity residential - 60Neighbourhood Centre - 75Town Centre - 75Main Road Network - 90

It is noted that the impervious assumptions are generic to the wider catchment, and that thedraft variation proposes specific precincts in each area (see Table 19). In particular, the precinctsurrounding the town centre is likely to have a higher level of imperious coverage than theaverage for the zone (Flat Bush 1 Residential Zone). However, these “discrepancies” inimpervious surface coverage are of minimal effect in respect of the overall stormwater“budget” for the catchment. In addition, the pond performance criteria specified will ensure theoverall effect of any localised increase in impervious surfaces will be mitigated by larger pondsto ensure the pond performance criteria area met.

The above catchment characteristics were used to define the following key inputs into therunoff layer of the XP-SWMM model:

Weighted Curve Number CN (defining runoff characteristics)

Time of concentration

Initial Losses Ia

The TP108 methodology recommends that ‘connected’ (piped) and ‘unconnected’ (e.g.driveways, paths etc) impervious areas are treated separately. We have therefore made anassessment of this breakdown relative to total impervious proportions. Our analysis or‘sampling’ of developed areas within the study area shows that for a typical urban catchment,approximately 30% of the total impervious area will be unconnected. For commercial areas androads we have assumed that the impervious proportion of these areas will be 100% connected.On this basis we have calculated separate sub-catchment flows in the model to allow for:

connected impervious (CN98) areas, and

unconnected impervious, and



pervious areas (weighted curve number).

(d) Rainfall

24 hour design storm depths were derived from the TP108 rainfall contour maps for the EastTamaki catchment for each of the 50%, 20%, 10%, 2% and 1% AEP rainfall events. A standardstorm shape for the Auckland Region encapsulating shorter duration design intensities hasbeen applied to the 24 hour rainfall depths shown in the table below:

Table 13: East Tamaki Design Rainfall Depths

Design Rainfall EventAnnual Exceedance Probability

(% AEP)Average Recurrence Interval

(ARI) – Years

TP108 24 Hour DesignRainfall Depth (mm)

50 2 8320 5 12010 10 1502 50 2001 100 230

(e) Channel Hydraulics

i. Channel Cross-Sections

Channel cross sections were determined from 0.5m contour maps provided by MCC. For eachlength of channel between two nodes, a channel cross-section which best represented thetypical channel section between these two nodes was selected. Care was taken so that cross-section between two parallel reaches does not overlap. Additional storage where there wereoff-channel ponding areas was also taken into account in the model by measuring these storageareas from the 0.5m contour maps and assigning them to the appropriate nodes in the model.

ii. Channel Roughness Coefficient

To determine the channel roughness coefficients (Manning’s n) for the main channels, a sitevisit to the area was undertaken. Photos of various channels in the East Tamaki area weretaken. These photos, published data from “Roughness Characteristics of New Zealand Rivers”(Hicks & Mason, 1991) and experience/engineering judgement were used to assign a typicalManning’s n to each main channel represented in the model.

Table 6.1 in Appendix 6 shows the typical Manning’s n assigned to the main channels in themodel. Photos from the site visit and their corresponding estimated Manning’s n are alsoincluded.

3.6.2 Model Calibration

Flow data from the two guage sites has been analysed and assessed for its suitability forcalibration of the ‘Existing’ hydrological model. The flow data has been used to calibrate themodel at Nodes 180 and 200 (Hills Road and Bond Street, respectively). Although both recordsare short, they have been of value in determining design flows. These data have been used in



association with our assessment of similar gauged catchments (e.g. Puhinui) and also designflows tabled in previous reporting (White / Oldfield Dec. 1990).

Details of an existing detention dam were made available by MCC and have been included inthe existing and future mitigated models. The detention dam is located at Node 165,downstream of the study area, but upstream of the Hills Road flow site. We understand thatthe detention dam is a recent development and hence has not affected the historic flood flowrecord. We have therefore excluded the effects of detention when calibrating the model to theflows from the Hills Road site.

We also made an assessment of available rainfall records, however, these did not providesufficient detail to improve our assessment of long term flows. Where suitable long-termrainfall records were available these were daily manual gauges (and hence of limited valuewhen assessing shorter duration storm events) or shorter automatic records and hence of littlevalue for extending the flow record.

The main study model includes a simplified representation of the additional catchmentbetween the study area and the gauge site, to enable model calibration. In addition we havecombined this with the developed south-western tributary catchment draining to the BondStreet site. This will assist in calibrating the model for the ‘Future Unmitigated’ developmentscenario.

In calibrating the model, we adopted an approach that takes a reliable estimate of design stormrainfall, and applies that to the catchment to achieve a flood of the same frequency ofoccurrence. This method is recognised as sound, and is the method used for development ofthe TP108 guideline.

Overall, three independent methods were used to determine the design flood flows. There arethe flow gauge records (Table 9), the model itself (based on the ARC guidelines) andindependent work by White/Oldfield (December, 1990) on the “Otara Stream Flat BushCatchment Study”. Details on the calibration are included in the following.

Calibration of the model was carried out for the existing scenario without the extendeddetention dam in place. Hydrological (curve numbers, time of concentration, initial losses) andhydraulic (channel roughness coefficient, and cross sectional profiles) parameters as discussedin Section 3.6 were entered into the appropriate XPSWMM layer. In addition, potential offchannel ponding areas measured from the 0.5m contour map were inserted into correspondingnodes as storage nodes. The model was simulated and calibrated by comparing the flowpredicted at the conduit between node 180 and 220 (See Map 8 & 9) with the flow data availablefrom the flow gauge records at the Hill’s Road site and design flows from previous reports byWhite & Oldfield.

The table below shows the results of the calibrated flow with available data.



Table 14: Calibrated Flows with Available Data

100yr ARI Flood Flows (m3/s)by White & Oldfield (1990)

ARI Existing ModelCalibrated Flows

(m3/s)

RecordedFlood Flows

(m3/s) Method Used ExistingCatchment Flow

2 yr. 17 205 yr. 30 32

Modified TechnicalMemorandum 61 Method

82

10 yr. 41 41 Rational Method 8550 yr. 71 59

100 yr. 89 67Regional Flood Estimation

Method50

It is noted that the length of flow records for the Hill Road site is approximately 8 years. Thisimplies a lower level of reliability of the flow records for predicting larger floods, in this casereturn periods greater than 10 years (See Section 3.6. for further discussion).

Further details of the catchment modelling and nodal layouts are shown on Map 8 and inAppendix 4. Nodes are the points that have been selected to assist in defining the hydrologicalanalysis. Typically, nodes are points where significant tributary streams combine, or wherespecific information on the flows at that point is required. Nodes define the downstreamportion of a sub-catchment for modelling purposes (e.g. a bridge site, a possible futurestormwater pond).

In order to assess the timing of peaks from the ‘developed’ south-western and ‘future’ easterncatchments, the model has been extended to immediately downstream of their confluence(Node 220). The timing of peaks in the lower catchment is discussed further in Section 3.6.

3.6.3 Model Limitations

The following discusses the limitations of the current XPSWMM model:

The future mitigated model is representative of the conventional method of using pondsfor detention and flood attenuation. It does not incorporate low impact design (sourcemitigation options) and therefore will set the upper limit for sizing detention ponds.

It should be recognised that the short time frame of the CMP was not adequate to set uprainfall gauges to characterise specific storm events in relation to the flood flow. As aconsequence, rainfall data used to simulate the design storms were derived from the TP108rainfall contour map for the Auckland region. In addition, there were limited historicaland reliable rainfall data available (See Section 3.6.).

The model was simulated for design storm intensities for 24 hours storms only. Stormduration longer than 24 hours were not simulated. This is appropriate as the catchmentresponse time, even with ponds in place, is within the 24 hour storm tested.

The shortness of flow gauge records (approximately 8 years) for the Hills Road siteconsequently reduce the reliability for predicting larger flood flows, in this case, floodflows for return period greater than 10 years. This implies that calibration of the model for



the larger return period could not be accurately validated with the existing flood flowrecords. Flood flows for return period greater than 10 years should be used with caution.The direct implication of this short flow record is that flood plain widths derived from the100yr flood flows may be overestimated. For the purpose of planning, this is consideredconservative.

Cross sectional profiles of the conduits were generic to one location between thecorresponding upstream and downstream nodes representing that whole channel profile.Cross sectional profiles were also extracted from 0.5m contour maps limiting its resolutionaccuracy to +/- 0.25m. Implications of using these cross sectional profiles are as follows:

– Less reliable for smaller flow which are contained “in the channel” due to the limitedresolution of contours to detail of the exact channel’s section beyond he 0.5m contour.

– Reasonable for larger flows over extensive flood plains.

– Reasonable for the planning stage but not the design of detailed flood levels.

A free outfall control was used at the downstream end. While this means that the accuracyof flood levels at this end of the model is less reliable, extending the model to well belowthe study area compensated for this. Any effects from this assumption will

Lack of flood level data for calibration implies that no independent check was available onthe whole flow and flood level modelling. Flood levels predicted from the flows from themodel could not be validated.

3.6.4 Modelling Results

The stormwater modelling was developed in two stages:

Phase 1: developing and calibrating a hydrologic and hydraulic model for the existingsituation, then imposing land use changes on it; and

Phase 2: using the model to develop stormwater management measures (primarily ponds)to mitigate the effects of development.

These two phases are outlined below:

(a) Estimated Flows – Phase 1

The purpose of Phase 1 of the modelling was to determine the runoff characteristics of the EastTamaki catchment under two different scenarios:

1. Existing, i.e. existing drainage system and existing land use2. Future Unmitigated, i.e. existing drainage system and future land use, with no specific

stormwater management measures in place.Estimated flows for East Tamaki catchment are given in the table below for the ‘Existing’ and‘Future Unmitigated’ scenarios.



Table 15: Estimated Flows at Node 180 (Hills Road Flow Site)

Design Storm Flow (m3/s) for Land Use Scenario

Annual ExceedanceProbability (% AEP)

Average RecurrenceInterval (ARI) – Years

Existing Unmitigated(includes existing

detention)

Future Unmitigated(includes existing

detention)50 2 17 2220 5 30 3810 10 43 512 50 69 781 100 82 92

Subcatchment E1 is a part of the study area, but does not drain to the Hills Roads site and hencedoes not contribute to the flows in Table 11 above. There is already significant development inthe catchment and hence for these areas the changes in future flows will not be as significant asfor the undeveloped areas.

A summary of the catchment characteristics and model outputs for each of the 50%, 20%, 10%,2% and 1% AEP events (existing and future scenarios) is given in Appendix 4.

(b) Phase 2 Stormwater Modelling

To model future mitigated, pond sites were identified and preliminary siting undertaken. Themodel was then run, and the pond characteristics modified until an appropriate level ofmitigation was achieved. This was that frequent floods were significantly attenuated and the 2and 100 year floods did not exceed pre-development peaks. The result from the modelling isoutlined in Appendix 7, which includes the following tables:

Table 6.3 compares peak channel flows in the main channels between the existing andfuture mitigated model for 100yr, 50yr, 10yr, 5yr and 2yr ARI.

Table 6.4 outlines the pond characteristics required for mitigation.

Table 6.5 compares the peak velocities in the main channels for the mitigated scenario for100yr, 5yr and 2yr ARI. Velocities above 1.5m/s are considered significant in terms ofpotential channel erosion. From the table, these “erosive” velocities should not be aproblem in the more frequent storms. However, in the less frequent 100yr storm there areseveral channels which indicate potential “erosive” velocities. The channel stability of thesechannels should be addressed in more detail during the design phase.

(c) Lower Catchment Peaks

This section assesses the possible changes in the timing of peak flows brought about by adeveloped eastern catchment. ARC are concerned that as the eastern catchment develops, therate of runoff may increase with the overall effect of reducing the time to peak in the lowercatchment. The possible scenario of having two developed catchments (the eastern and south-western) peaking simultaneously could have adverse flooding and erosion effects in lowercatchment areas.



Our preliminary analysis (refer Table 16 below and Figure 15) compares the runoffcharacteristics of the existing catchment against the future unmitigated scenario. The latterscenario is effectively the ‘worst case’ as mitigation measures planned for the eastern catchmentwill have the effect of attenuating peak flows and increasing the time to peak.

Table 16: Effects of Development on Timing

Catchment Characteristics Eastern Tributaryat Node 220

South-western Tributaryat Node 220

Existing FutureUnmitigated

FutureMitigated

Existing FutureUnmitigated

FutureMitigated

Max Flow (m3/s) 82 92 80 68 72 67Time of Peak for Flow (hrs) 16.25 16.00 16.8 14.3 14.2 14.25% Area Impervious 9 40 40 39 51 51Total Area (ha) 1888 1888 1888 932 932 932Weighted CN 71 80 79 79 82.5 82.5Ia (mm) 4.6 3.0 3.0 3.1 2.4 2.4Length (km) 10.4 10.4 10.4 5.2 5.2 10.4Slope (m/m) 0.0061 0.0061 0.0061 0.0089 0.0089 0.0061Time of Concentration (hrs) 4.2 3.8 3.8 1.8 1.7 1.7Time of Concentration (min) 255 227 229 105 100 100

Figure 14: 100 Year ARI Hydrographs for Eastern and South-western Tributary

The TP108 methodology routes a 24 hour storm (which includes a central ‘peak’) through eachsub-catchment of the model. The times of peak of the eastern and south-western catchments inthe existing scenario are 16.3 and 14.4 hours, respectively. This implies that the developedsouth-western catchment will peak approximately 1.9 hours earlier than the eastern catchmentin the standard 24 hour storm. The times of concentration calculated on a ‘lumped’ basis for

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each catchment confirm that the developed south-western catchment will peak around 2 hoursahead of the eastern catchment. The humps in the hydrographs illustrate the different timingfrom the connected reticulated areas, the unconnected reticulated areas and the pervious areain the catchment.

The future unmitigated scenario shows a similar trend, with the developed south-westerncatchment peaking between 1.8 to 2 hours ahead of the eastern catchment. However, there is anearly rise to a secondary peak, reflecting the increased impervious area. As mentionedpreviously, it is likely that the mitigation measures (e.g. flood detention, water quality pondsand swales etc) employed in the eastern developing catchment will extend the time to peakgiving a longer duration at high flows, but no higher peaks than existing. The timing of peaksin the lower tidal catchment, therefore, are likely to be at least two hours apart.

The direction of storms will have an influence on the timing of peaks from the two tributaries.It is probable that, for example, a tropical storm approaching from the north-east would passover the eastern catchment first increasing the likelihood of peaks coinciding in the lowercatchment. This will occur naturally in the existing situation, and the proposed developmentsin the eastern catchment are only likely to ‘assist’ the probability of this coincidence by some 15or 20 minutes.

Figure 15: 100 Year ARI Hydrographs for combined Eastern and South-western Tributary

Figure 15 provides the combined hydrographs for the eastern and south-western tributary.These combined hydrographs show that the overall effect of development in the easterncatchment is to increase the peak and bring it earlier. The mitigation measures (i.e. ponds,discussed in detail in Section 8) reverse this, with the peak being lower and later than for theexisting.

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(d) Sediment and Contaminant Loads

A lumped model was prepared to identify loading of various contaminants under the existing,development phase, and developed condition of the catchment. This included modelling theeffects of the proposed ponds in reducing contaminants. The model identifies total area indifferent types of land use, and the typical yield of various contaminants from each. It alsoidentifies a percentage removal if ponds were in place. The assumed yields from different landuses are shown in the following table:

Table 17: Assumed Contaminant Loading by Land Use

Landuse TSS(kg/ha/yr.)

TPH(kg/ha/yr.)

TP(kg/ha/yr.)

TN(kg/ha/yr.)

Copper(kg/ha/yr.)

Zinc(kg/ha/yr.)

COD(kg/ha/yr.)

TreatedbyPonds

Low densityresidential

500 4 1 8 0.02 0.25 100 No

Mediumdensityresidential

350 16 0.8 8 0.15 1.4 150 Yes

High densityresidential

350 20 0.8 8 0.20 2 150 Yes

Existingresidential

350 12 0.8 8 0.09 0.75 150 No

Conservationareas

150 0 0.55 3 0 0 100 No

Reservenetwork

150 0 0.55 3 0 0 100 No

Urban park 500 2 1.0 8 0.01 0.1 100 No

Public openspace

500 2 1.0 8 0 0.1 100 No

Business /commercial

500 20 1.0 8 0 2 150 Yes

Vehicleorientedbusiness

500 20 1.0 8 0 2 150 Yes

Roadway 500 20 1.0 8 0 2 150 Yes

Contaminantremoval rateby ponds

75% 65% 40% 35% 65% 65% 30% -

Abbreviations:TSS = Total Suspended SolidsTPH = Total Petroleum HydrocarbonTP = Total PhosphorusTN = Total NitrogenCOD = Chemical Oxygen Demand

The development phase results in higher unit sediment yields off areas undergoingdevelopment, even when treatment is in place. However, at any one time only a small portionof the total catchment is undergoing earthworks, so the overall effect is small. It was assumed



in the analysis that earthworks areas were only open for 6 months of the years, and that theannual earthworks area was the same for that used for development staging (see Section 8.5).The net contaminant yields for the study area for each of these stages is shown in Table 18. Inaddition, the progressive change in sediment yield through the development period isillustrated in Figure 16. Initially, there is a slight increase in sediment yield as developmentcommences. However, as more land progressively turns from pasture to urban, sediment loadsdecrease, until they approach the long-term developed rates.

It should be noted that, despite the mitigation measures, there could still be some adjustment tostream channels as a result of the change in riparian character. This has the potential to generateof the order of 500 tonnes per year of additional sediment over a 20-year period. Thisdemonstrates the importance of careful attention to the nature and methods of riparianplanting.

The table below also shows that while sediment loads will decrease in the long term, someother contaminants (Such as TPH, Copper and Zinc) will significantly increase despite thetreatment by ponds.

Table 18: Net Contaminant Yields for Study Area.

Scenario TSS(kg/yr.)

TPH(kg/yr.)

TP(kg/yr.)

TN(kg/yr.)

Copper(kg/yr.)

Zinc(kg/yr.)

COD(kg/yr.)

UntreatedExisting 816,000 3,760 1,680 13,270 21 200 178,000Developmentphase (average)

935,000 - - - - - -

Fully developed 630,000 17,300 1,430 12,200 161 1,590 219,000TreatedDevelopmentphase (average)

704,000 - - - - - -

Fully developed 405,000 7,480 1,160 9,870 64.9 647 182,000

Abbreviations:TSS = Total Suspended SolidsTPH = Total Petroleum HydrocarbonTP = Total PhosphorusTN = Total NitrogenCOD = Chemical Oxygen Demand



Figure 16: Variation of Total Sediment Yield During Development Phase

Impending future development will change the catchment characteristics. It is important torealise that the model used in this report applies catchment characteristics based on the currentStructure Plan proposal and provides only a framework for strategic planning.As the catchment changes, further updates on the model should be done to reflect these actualchanges to the catchment. In general, it is not recommended that the model be updated in ahaphazard or frequent manner, as the changes to the catchment become available. Rather, it isrecommended to log and compile all changes to the catchment in a systematic manner andcarry out a more comprehensive update, at a frequency of 5 to 10 years, depending on howquickly the catchment develops. This will also provide for inclusion of a reasonable length ofmonitoring data.

The following monitoring and recommendations are proposed:

Rain gauges should be installed as the present model applies 24hr design storm depthswhich were derived from the TP 108 rainfall contour map for the Auckland region. Thiswill enable:

– More accurate design rainstorms to be established. However, these design rainstormsare limited to the length of record available and would therefore need correlation toexisting long term gauges

– Modelling of significant storms

The flow gauge at Hills Road should be maintained. Longer flow gauge records will enablethe model to be calibrated more reliably for the larger return period. It is recommended aslonger lengths of flow record is available, the model be recalibrated for the 50 year and 100year ARI.

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Maximum flood level gauges should be installed at key locations. The correlation ofrainfall, flood level and flow data from the rain, flood level and flow gauges will enable amore robust calibration of the model. The flood level gauges will also allow anindependent check on the flood levels and flows predicted from the model, and thereforegreater confidence in the model predictions.

As detailed channel cross-sections become available during the development stage, it isrecommended that these new profiles be included into any updated models of thecatchment. MCC could prepare a log of all new detailed cross sectional profiles to ease theprocess of incorporating these new profiles into the next model update.

Catchment PlanningIssues

Section 4



The purpose of this section isto provide an overview andunderstanding of the keycatchment planning issues forthe DET study area.

4444 Catchment Planning IssuesCatchment Planning IssuesCatchment Planning IssuesCatchment Planning IssuesIn July 2000 a report was issued by the BecaCatchment Planning team titled “East TamakiCatchment Management Plan – Key CatchmentPlanning Issues and Analysis. This identified arange of important issues to which solutionsneeded to be developed in thedesign/mitigation phase of the process. This

section provides a summary of those key catchment planning issues. The conceptualapproaches and mitigation measures are discussed in detail in section 6 and 8 of this CMP.

A number of key issues have been identified in the analysis sections of this report. These issuesneed to be addressed to achieve the objectives outlined in this report. The next stage of thecatchment planning process will provide solutions to these issues. It is noted that the analysiscarried out to date based on the land use concept contained in the DET Concept Plan has notraised any fatal flaws from a catchment planning perspective.

4 . 1 I n - s t r e a m a n d R i p a r i a n i s s u e s

The key issues for in-stream ecology and riparian areas are ensuring that the development ofthe catchment occurs in such a manner as to protect instream fauna and ecosystems and topromote riparian enhancement. In particular, protecting and enhancing the existing bandedkokopu population needs to be addressed by other inputs, such as land use and stormwatermanagement. An appropriate riparian enhancement and management framework needs toaddress these issues.

4 . 2 S t o r m w a t e r M a n a g e m e n t I s s u e s

The key issues for stormwater management in the catchment are closely related with theinstream and riparian issues. The management of the volume and peak flow rate of stormrunoff to avoid flood risk and limit stream erosion will be a critical and underlying issue. Inaddition, reducing contaminants in runoff reaching high value receiving environments andproviding appropriate protection and enhancement of waterways identified as having highactual or potential value will be significant issues to consider in developing the stormwatermanagement approach and detailed design elements.

4 . 3 T e r r e s t r i a l E c o l o g y

Terrestrial ecological values are not well catalogued in the catchment at present. With theexception of Murphy’s Bush, little is known about the species composition of other areas ofnative vegetation in the catchment. However, the key management issues that arise relate toprotecting the existing areas from stock, pest and development threats.



4 . 4 L a n d s c a p e I s s u e s

A number of landscape issues have been identified through the first two stages of thecatchment management process. The most significant issues are the identification andestablishment of appropriate areas of open space to serve the future communities requirements,and ensuring the enhancement of riparian areas occurs in a manner that enhances the visualand landscape values in the catchment. The protection of specific existing views and landscapefeatures is also a relevant issue.

4 . 5 L a n d U s e I s s u e s

The DET Concept Plan adopted by MCC in June 1999 proposes an urban land use pattern forthe catchment, which is based on protecting important natural features and providing a rangeof land uses and environments. While some minor changes to the land use pattern proposed inthe DET Concept Plan would be required to manage stormwater, the initial analysis suggeststhat the basic land use concept does not raise any unmanageable or fatal issues from acatchment planning perspective.

4 . 6 R e c r e a t i o n

The urban form being promoted through the Concept Plan relies heavily on the environmentalcorridors to provide urban amenity and recreation opportunities. The corridors are intended tobe ‘multi-functional’ in the sense that they will provide for urban amenity, water quality,stormwater management and landscape outcomes. The new area must also provide forrecreation and leisure opportunities, including for both active and passive recreation. Ensuringthat the environmental corridors, and any other local reserve areas, provide for this range offunctions is an important issue for the future community.

4 . 7 R e c e i v i n g E n v i r o n m e n t , W a t e r Q u a l i t y a n dC h e m i s t r y

It is important to examine water quality issues when considering the impact of urbanisation onaquatic ecosystems. Key issues will include managing increased suspended sedimentconcentrations, particularly during development, and increased general contaminants. Inaddition, the increased potential for contaminants or spills (e.g. pesticides, sump oil) needs tobe addressed through the rules established in the variation. An integrated approach tocatchment management requires the receiving environment to be considered in all aspects ofcatchment planning. Otara Lake has been the subject of other Council studies in conjunctionwith the local community and the ARC, and a range of objectives and management measureshave been put in place to improve the quality of water in the Lake and estuary.



4 . 8 I m p l e m e n t a t i o n

The implementation of the provisions of the catchment management plan requires acombination of tools and techniques available to Council under a range of legislation,principally the RMA 1991 and LGA 1974. One of the key issues is securing the environmentalcorridors in the upper and lower catchments, and ensuring that the flow of ‘financialcontributions’ from development will enable the enhancement of those corridors to achieve themultiple objectives that are identified in this CMP and the Concept Plan. There are a range ofoptions to secure the corridors in the lower catchment, such as vesting or designation.

Securing environmental enhancement in the upper catchment has been identified as a keyimplementation issue. Ensuring the planning framework put in place through the variation,and subsequent resource consenting secures the areas for replanting and steep slopestabilisation is critical for a number of outcomes. The upper catchment restoration area (seefigure in Appendix 3) also frames the entire catchment from a landscape and visual viewpoint,and thus the form of countryside living development in the upper catchment is important.

The control of development in the remaining parts of the catchment will also be an importantimplementation issue, as there are a range of options which can be implemented to achievebetter outcomes specifically from a stormwater management viewpoint.

Identifying the costs of growth and ensuring that the cash flow and financial contributionframework is able to manage and apportion those costs in an equitable and transparent manneris also a significant issue. The key cost issues associated with the CMP relate to the purchaseand enhancement of the environmental corridors, and stormwater management devices.

Consultation

Section 5



5555 ConsultationConsultationConsultationConsultation

5 . 1 C o n s u l t a t i o n P a r t i e s

Consultation is an important part of any resource or environmental management process. ForEast Tamaki there is a wide range of people and organisations interested in the future of thecatchment, many of whom have extensive and important knowledge of the area. People ororganisations with an interest in the area include:

landowners;

tangata whenua:

– Huakina Development Trust

– Ngai Tai ki Tamaki Tribal Trust

– Ngai Tai ki Umupuia

– Ngati Paoa Whanau Trust Board

– Ngati te Ata - Awaroa ki Manuka

Watercare Services Limited

Environmental groups

Development Companies.

MCC Asset Managers

Adjoining residents and ratepayer groups

5 . 2 C o n s u l t a t i o n T e c h n i q u e s

The process of consultation has been ongoing for over three years as the formulation of theConcept Plan was initiated following hearings on the Future Urban Zone in February 1997. Thedevelopment of the DET Concept Plan included a series of workshops and discussions with anumber of groups. Following on from the success of the Concept Plan, the CatchmentManagement Plan has also attempted to maintain momentum in terms of consulting with thecommunity. Over the course of the CMP project a number of tools have been used to provideinformation, receive feedback and set strategic direction for the project arising from the issuesraised by the community.

This section outlines the approach taken in consulting the rangeof interested parties and tangata whenua. Consultation has beenan integral component of the catchment and structure planningprocess for the area.



5.2.1 Newsletters

Newsletters have been sent to the community at two key stages, firstly prior to fieldinvestigations getting underway in mid February, and secondly in July following theidentification of key catchment issues and analysis.

The first newsletter sent out to landowners and other parties on 14 February 2000 requestedfeedback on the important environmental values worthy of protection in the catchment. Thesecond newsletter in July provided a progress report to landowners and discussed proposedmanagement regimes for key issues. Newsletters are included in Appendix 14. Feedback wasagain requested in relation to the approach being proposed. The following issues and valueswere identified by respondents:

Questioned scope of CMP, sought assurance that range of issues including cost ofinfrastructure, ecological enhancement, and managing the effects of subdivision would beincluded in the process.

Supports fundamental objective of environmental enhancement;

Greater recognition of visual and landscape issues, especially protection of features in themid and upper catchment;

Need to preserve extensive bush in the area;

Maintain open stream waterways for ecological purposes;

Need to value the bird life and create environment where co-existence is possible.

Supports need to preserve natural resources;

Need to preserve wildlife and bus areas as a priority.

Maintain important habitats by retaining natural contours, watercourses throughminimising earthworks;

Give priority to species which provide food for native birds

Support the need for environmental principles to guide development.

Provide a sufficiently detailed monitoring programme during development phase.

Eco-sourcing should be from Flatbush area, not the wider Tamaki Ecological District;

Loss of park area for town centre should be compensated for in another part of thecatchment, such as by providing a buffer to Murphy’s Bush to protect it from residentialdevelopment.

5.2.2 Tangata Whenua Workshops

Separate meetings were held with representatives of each tangata whenua at which thecatchment management plan process was discussed. All groups have indicated a desire to beinvolved, and it is anticipated that this process will be ongoing through the statutory processassociated with the proposed variation, and the implementation of various aspects of the CMP.Generally tangata whenua are supportive of the comprehensive approach proposed for the



management of the catchment. In particular, the protection and enhancement of the naturalstream systems is supported.

After these initial meetings, it was decided that there could be some advantage in organising ahui for all the tangata whenua representatives, including kaumatua. At the first of these hui, TeRoopu Kaitiaki was formed to represent the views of the tangata whenua to Council in relationto the DET project. While a range of broader relationship issues with Council were raised, aprocess for ongoing consultation with this group in relation to the CMP was established, andfurther presentations and reports have been issued to Te Roopu Kaitiaki.

5.2.3 ARC Workshops

A number of discussions and meetings have been held with officers from the ARC. Principally,the input from ARC has involved attendance at two early workshops, and comments on theIssues and Analysis report. It is anticipated that the ARC will review the final CMP, and thatthis will form the basis of an application for a comprehensive stormwater discharge consentapplication.

ConceptualCatchment

ManagementFramework

Section 6



6666 Conceptual Catchment ManagementConceptual Catchment ManagementConceptual Catchment ManagementConceptual Catchment ManagementFrameworkFrameworkFrameworkFramework

Conceptually, the process of developingobjectives for the management of thecatchment through the development phaseand longer term has involved a number ofsignificant inputs and stages. Thedevelopment of the structure plan and landuse framework as illustrated in the DET

Concept Plan provided the fundamental starting point for the catchment management process.A number of key catchment planning issues have been identified, and conceptual responsesdeveloped to ensure the urbanisation process occurs in a sustainable manner. The conceptualland use framework is therefore described in the first instance to provide a context, followed bya discussion of the approaches to managing two of the most significant issues: in-stream valuesand stormwater management. Finally, all of these approaches are drawn together into aframework of catchment objectives, which then form the basis of developing implementation ormitigation responses to meet those objectives. The key steps in this process are shown below:

Catchment objectives are included at the end of this section in relation to the key catchmentplanning issues. This section should be read in conjunction with section 7 and 8, which providea summary of catchment management objectives and more detailed implementationmechanisms respectively.

DET Concept Plan

Catchment ManagementIssue Identification and

Analysis

Catchment Objectives:

In-stream and riparian values

Stormwater Management

Terrestrial Ecology

Land Use

Landscape and Amenity

Recreation

Receiving Environment –Otara LakeImplementation

Draft Development EastTamaki Variation

This section provides an overviewof the broad strategies that havebeen developed to address thesignificant catchment planningissues.



6 . 1 T h e C o n c e p t f o r D e v e l o p m e n t E a s t T a m a k i

The final concept for the Catchment Management Plan is illustrated on Map 14. This has beendeveloped through a combined and concurrent structure and catchment planning exerciseundertaken by the Beca Project Team and Manukau City Council, in consultation with a rangeof parties.

The concept has not changed substantially from the DET Concept Plan adopted by MCC inJune 1999. The DET Concept Plan provides a framework for the environmental outcomes beingsought for the area. These have been included in the broader strategy for the area in the draftvariation to promote the achievement of a number of outcomes:

urban containment selective intensification

clustering and nodal development diversity of activities, including housingtypes

an integrated transport system thatpromotes a choice of travel modes

an integrated an multi functional publicopen space network

improved energy performance employment growth

ecological diversity improved water quality

sense of place and community focus safe environment

The catchment planning process has identified a range of issues that needed to be addressed inorder to ensure the broad conceptual framework provided in the Concept Plan and draftvariation can be implemented. Many of the outcomes listed above relate to the catchmentmanagement objectives identified later in this section of the CMP.

The DET Concept Plan has been discussed in section 2.4 of this report. The purpose of theremainder of this section is therefore to describe the final concept as modified through thecatchment planning and subsequent structure planning/urban design processes. The principlemechanism for defining the ultimate concept will be the variation to the Proposed District Plan.A draft version of the variation has been circulated on 12 October 2000 which includes adescription of the concept, relevant zones and the environmental outcomes sought. These aresummarised below to provide a reference for the catchment management objectives discussedlater.



6.1.1 Proposed Zones

There are a number of zones proposed for the DET area through the draft variation. Thesezones have been considered through the catchment planning process in terms of their location,extent, and potential effects on stormwater management, ecology and landscape. The followingzones are identified in the draft variation, and have been used for the purposes of stormwatermodelling and developing other catchment management objectives:

Town Centre Business Zone

Neighbourhood Centre Business Zone

Flat Bush 1 Residential Zone

Flat Bush 2 Residential Zone

Flat Bush Countryside Living Zone

Public Open Space 6 – Environmental Corridor Zone Overlying Zone

The following table provides the proposed objective and a brief description of the key featuresof each zone identified in the draft variation, including those features which may have animpact on catchment management:

Table 19: Summary of Provisions of Draft Variation (Version 1.1, 12 October 2000)

Zone Proposed objective for zone Description of key features of zone.Town CentreBusiness Zone

To achieve an integrated, compactpedestrian friendly town centre, thatprovides for a diverse range of activitiesand employment, and acts as a strongcommunity focal point.

Provides focal point for Flatbush/East Tamaki community;

Consists of main street, OrmistonRoad, Town centre Work – Live andTown Centre – Park Edge precincts:

Range of activities provided for,including commercial, office, lightindustrial, warehouse, education,health, community support,recreation and residential.

Impervious assumptions fromstormwater modelling equals 75%.

NeighbourhoodCentre BusinessZone

To achieve a number of integrated,compact pedestrian friendlyneighbourhood centres, that provides for adiverse range of activities andemployment, and act as localneighbourhood community focal points.

Three local neighbourhood centresidentified;

Provides for a range of activitiesincluding local shops,restaurants/cafes, supermarkets, daycare, medical and communityservices, high density residential;

Provide for excellent passengertransport linkages to wider area.


Flat Bush 1Residential Zone

To achieve an integrated, high densityresidential environment with high levels of Generally surrounds town centre;

Consists of General, Central,



Zone Proposed objective for zone Description of key features of zone.amenity that supports a range travelmodes and allows for a range of livingopportunities and incorporatesopportunities for compatible small scaleemployment in appropriate locations.

Arterial, Barry Curtis Park and LocalCentre precincts;

Provides for a range of activities,such as small business, but primaryfocus on residential.

Promotes high density residentialdue to proximity to town centre, andneed to promote urban sustainabilitythrough ensuring long term viabilityof town centre and alternativetransport (e.g. walking).

Lot sizes generally from 180-450m2


Flat Bush 2Residential Zone

To achieve an integrated medium densityresidential environment with high levels ofamenity that allows for a range of livingopportunities and incorporatesopportunities for compatible small scaleemployment in appropriate locations.

Generally located in mid-catchmentarea between high densityresidential and countryside livinguses in the foothills.

Consists of General and Arterialprecincts;

Promotes lower density residentialthan FB1 Residential Zone.

Provides for a range of housing typesfrom detached housing to 3 storeyapartments, but majority anticipatedto be detached housing.

Lot sizes generally from 250-550m2


Flat BushCountrysideLiving Zone

To achieve development within the flatbush countryside living zone thatmaintains and enhances the landscapequality, water and soil resources and therural amenity values of the area.

Located in the upper part of thecatchment in the foothills, and acts astransition from urban to rural uses(in the adjoining Clevedon area).

Aims to protect and enhanceenvironmental qualities;

Development restricted due toenvironmental constraints;

Provides for low-density residential

Range of lot sizes from 2000-5000m2

and above, but overall average atleast 5000m2 to be achieved.


Public OpenSpace 6 –EnvironmentalCorridor ZoneOverlying Zone

To integrate the management ofstormwater runoff with the maintenanceand enhancement of natural waterways,provision of passive recreationalopportunities and pedestrian and cycleaccess.

Overlying zone adjoining the mainwaterways in the lower catchment,but not including the 100 year floodplain;

Land to be acquired throughsubdivision process.

Provides for a range of functions,including active/passive recreationand leisure activities, amenity,



Zone Proposed objective for zone Description of key features of zone.mitigation of effects of urbandevelopment, water quality,ecological enhancement andbiodiversity,

Some activities provided for withinzone, but must be forpublic/community purposes.

6.1.2 Environmental Outcomes Sought

A number of key outcomes have been identified throughout the consultation, technicalinvestigation and other work. The anticipated environmental results for the Development EastTamaki area of the City have been derived from these inputs, and are listed in the draftvariation as follows:

Protection and enhancement of the terrestrial and aquatic ecology, including remnantnative vegetation and waterways.

A diversity of housing types.

A choice of transportation options including walking, cycling and passenger transport

Residential neighbourhoods with a sense of place/identity.

A vibrant ‘public realm’ with an integrated network of open space including parks andstreets.

An environment of high amenity values including:

– Generous provision of open space;

– Street trees and gardens;

– Easy and safe access to shops and services by a choice of transport options.

Safe Environment.

Energy savings.

While not all outcomes are entirely relevant to the consideration of the catchment planningissues, it is important to ensure the decisions made in relation to catchment management issues,solutions and implementation/mitigation measures refer to these wider outcomes. This willensure the integrated management of the development process, and ultimately a moresustainable outcome.

6 . 2 I n - s t r e a m M a n a g e m e n t S t r a t e g y

A range of physical and chemical variables control the environmental quality of rivers, streamsand lakes, and the ecosystems they support. Different combinations of these variables result ina wide range of available habitats and associated biological communities in most water bodies.Varying habitat and community composition means that a range of values (ecological,



aesthetic, recreational etc.), may be present and these values need to be considered andmanaged in catchment planning.

In order to manage ecological values, catchment management processes need to:

identify what ecological values are likely to be present and their significance;

identify the pressures which adversely affect these values;

set management objectives for these values;

determine the requirements (physical and chemical) to meet these objectives;

monitor to determine whether the management objectives are being met.

It may therefore be useful for resource management purposes to be able to partition riversinto different habitats or reaches on the basis of their suitability for different communitiesso that variability can be reduced and the expected conditions more appropriatelymanaged.

Methods to identify what values are present, or should be present, in an ecosystem are notreadily available, and a variety of approaches have been undertaken (Rutherford et al. 1997).Whilst methods are currently being developed for a physically based method of classifyingriver ecosystems (Rutherford 1987, Snelder 1999), the approach undertaken in this case hasbeen to identify ecological communities and assess their habitat, and link similar sites toprovide a differentiation of habitat and community types in order to develop specific objectivesfor each as appropriate.

6.2.1 Instream Management Objectives (ISMO)

Establishing instream management objectives are seen as the most appropriate way to manageecological values in rivers and streams. They aim to integrate catchment, land and watermanagement to achieve a common goal. Instream management objectives, as for any form ofobjective, need to be realistic and achievable, and measurable of a pre-determined timeframe.With these criteria in mind it is considered that the most appropriate instream managementobjectives for the Otara Creek in East Tamaki are:

The Otara Creek catchment is managed in such a manner to sustain a viable bandedkokopu population, allowing or providing for:

– suitable adult banded kokopu habitat in the headwater and hill valley streams;

– passage of juvenile and adults of the species throughout the entire mainstem2 reachesof the river from headwater streams, hill valley streams and lowland rolling streamsto the river mouth;

2 mainstem refers to permanent Otara Creek streams which traverse the lowland rolling stream sections to hillvalley and/or headwater stream sections as a continuous body of water, notwithstanding the formation ofseparate pools during periods of low flows.



– sufficient deep pool habitat throughout the mainstem reaches from headwaters andhill valley sections, and throughout mainstem lowland rolling streams, especiallyduring low flows;

– improvement of water quality to reduce oxygen depletion, high water temperatures,and excessive algal production;

– improvement of bank stability, particularly in the headwater and hill valley streams,to minimise excessive siltation of stream substrate in the lowland rolling streams, andto minimise the infilling of pools and the smothering of substrates to improve habitat.

The mainstem lowland rolling streams of Otara Creek are managed in such a manner tosustain a viable eel (shortfin and longfin) population allowing for: passage of juvenile andadults of the species throughout the entire mainstem reaches of the river from headwaterstreams, hill valley streams and lowland rolling streams to the river mouth; providingsufficient deep pool habitat throughout the mainstem reaches of lowland rolling streams,especially during low flows.

The headwater and hill valley streams are managed in such a manner to sustain habitatsuitable for a diverse Ephemeroptera, Plecoptera and Trichoptera (EPT) population,generally greater than 3 species types, allowing for: habitat heterogeneity including runs,pools and riffles, as well as moderate instream woody debris; improvement of waterquality to reduce oxygen depletion, reduce high water temperatures, and excessive algalproduction; and improvement of bank stability to minimise excessive siltation of streamsubstrate and to reduce infilling of pools and the smothering of available substrates.

A summary of these objectives is included later in Section 7.

6.2.2 Stream And Riparian Enhancement

(a) General

Enhancement possibilities are available in the Otara Creek catchment and should centre onextending the range of the more sensitive fish species within the catchment. It is unlikely thatadditional migratory fish species will enter the catchment at present, given the limitation of thelocal fauna. Higher quality habitats and water were observed at a number of the upper(headwater valley) tributary sites. These areas were generally well shaded by native or exoticforest, had reduced silt loadings compared to lowland streams, prevention of stock access byfencing, and minor or no algal build up. Using these features as goals for the more degradedareas of the catchment should lead to better habitat and water quality. If no recruitmentlimitations exist, then it could be expected that Crans bully and banded kokopu could extendtheir distributions within the catchment.

There are, however, some limitations placed on the ability to enhance the streams of thiscatchment. Summer water flows may be the major limitation. Many areas visited during thissurvey had low or no flows. This increases the likelihood of high instream temperatures andlow oxygen levels, which will reduce the suitability of the stream for some fish species, as wellas macroinvertebrates.



(b) Instream habitat management and enhancement

The physical and chemical habitat characteristics of a stream contribute to determining thestructure and composition of the resident and migratory biological communities. The diversity(number and type of taxa and structure of biological communities), is, in part, dependent on thehabitat structure and type. Amongst the functions relevant to the East Tamaki CMP and theinstream management objectives outlined above, instream habitat can be managed for:

improving available cover and refuge for fish and macroinvertebrates during periods ofinactivity, high or low flows;

increasing habitat diversity to increase the number and type of organisms present;

creating or improving pool/run habitat – pools provide refuge and cover for fish duringperiods of low flow;

Habitat suitability curves have recently been determined for banded kokopu (see followingfigure). The important factors to note are the preference for water deeper than 30 cm deep andfor low water velocity. This reflects their occurrence in pool habitats in small streams oftenwith little or no flow especially during low flow periods. These preference curves provide thebasis for recommending the retention of sufficient deep pool habitat throughout mainstemreaches of headwater and hill valley sections. This is particularly important during low flowperiods. Preference curves were developed from small Coromandel streams. Velocitypreference is for low water velocity, fine substrate classes –silt, sand, gravel are preferred tocobble boulder (1 being fine sediments – 8 coarse sediment) (Jowett, pers com).

Figure 17: Banded kokopu habitat preferences curves,

Sui

tab

ility

Sui

tab

ility

Sui

tab

ility

Depth (m) Velocity(m/s)

Substrate index

B anded K okopu (1+) McCullough

0.0 0.3 0.6 0.9 1.2 1.5 0.0 0.4 0.8 1.2 1.6 2.0

1 2 3 4 5 6 7 8

0.0 0.0

0.0

0.2 0.2

0.2

0.4 0.4

0.4

0.6 0.6

0.6

0.8 0.8

0.8

1.0 1.0

1.0

A further management issue is the control of the introduced fishes within the catchment. Thepresence of koi carp in Otara Creek indicates that at least one illegal transfer has occurred inthis catchment. At present removal of the koi carp is possible given the small numbers presentand their limited distribution. However, with increasing urbanisation of the catchment itshould be expected that further introductions of koi or other fish species will be attempted.Education measures should be undertaken in terms of the concepts of catchment protection andenhancement of instream values. Measures should also be taken to make riparian and instreamhabitat more suitable for desired native species and less suitable for undesired pest species



wherever practicable. The introduction of exotic species of plants and animals has the potentialto impact on the instream and riparian objectives. For instance the introduction of rudd, wouldhave substantial impacts on instream macrophytes and hence any objectives requiring theretention of macrophytes.

(c) Riparian management and enhancement

Improving the riparian margins is now widely recognised as a suitable mechanism for waterand ecological management in New Zealand and world-wide (Gregory et al. 1991; Quinn et al.1993, 1999; Rutherford et al. 1999). Riparian zones occupy a small proportion of the landscapeat the land-water interface, but have high recreational and aesthetic values and can perform avariety of functions that can be managed to protect the habitat and water quality of streams andrivers from the effects of land use (Quinn 1999). Amongst the functions relevant to the EastTamaki CMP and the instream management objectives outlined above, riparian zones can bemanaged for:

shading streams (reduction in stream temperature and reduction in light thus reducingexcessive algal and plant growth);

stabilising stream banks through tree and plant root structures holding bank materialtogether;

providing litter, woody debris (forming instream habitat and cover), and additional foodmaterial (terrestrial invertebrates)

providing a buffer and filtration interface between local land use (pastoral or urban) andthe removal and minimisation of contaminant entry to streams;

providing an overspill flood plain for excessive water during storm flows.

A number of recommendations for the enhancement of riparian vegetation and consequentlyinstream values are included in Chapter 8: Implementation and Mitigation Framework.

6.2.3 Transition period

An important finding of recent studies is that, for a given flow, forest streams are wider thanpasture streams. Dense riparian vegetation can shade out groundcover and may destabilisebanks, and Rutherford et al. (1999) forecast a transition period of up to 20 years, during whichtime the channel widens and bank erosion may contribute to sediment input. Thus care must betaken to ensure that riparian plantings are not undermined during this transition period, andsufficient space is given to new plantings. Enhancement and restoration will thus need to beplanned and staged over a considerable length of time. It should also be noted that othercatchment changes will affect the hydrology and therefore stream erosion patterns.

Rutherford et al. (1999) also concluded that to maintain bank stability, a compromise mightneed to be made between enough stream shade, without over-shading banks. Over shadingwill reduce the understorey and therefore the important bank stabilising plants will be unableto grow.



Improvements to riparian vegetation will change the manner in which streams transform andexport nutrients (Rutherford et al. 1999). Where a poorly shaded stream acts as a nutrientprocessor, a shaded stream acts more as a transporter, and any nutrient and contaminant runofffrom the catchment may have more significant impacts downstream.

6.2.4 Instream Crossings

There is a requirement to allow fish passage at all stream crossings within the catchmentbecause the important migratory species occur in the upper headwaters of Otara Creek. In thelower parts of the catchment this object is easily achieved by the use of bridges or largediameter culverts. Either form of bridging must be placed in the stream so that there is novertical drop at the downstream end. The culvert diameter or bridge capacity must be largeenough to accommodate flood flows but designed to concentrate water flow at low flow levels.To achieve this the large diameter culverts appear to be the most suitable mechanism. Theculverts should be placed so that the bottom of the culvert is below the stream level andtherefore natural substrates can cover the bottom of the culvert. The curved nature of culvertswill concentrate the water at low flows in the base of the culvert, but can still accommodatelarge flood flows (see Figure 18 below).

Figure 18: Low Flow Water Levels at Road Crossings.

Diagram showing the low flow water levels of culvert road crossing verses bridge crossing andthe benefits of the concentration of water in the culvert to retain deeper water through theculvert than the bridge.

Road

Culvert Bridge

Stream bedsubstrate

In the upper reaches of the catchment the higher stream gradients may make bridges the moreappropriate form of crossing. High gradient culverts tend to have high water velocities andhence impede or prevent fish passage. Bridge structures that retain the instream substratestructure should provide better opportunities for fish passage.

At the stream crossing sites the construction of low flow water retention areas could beconsidered. Lowering the stream bed on the upstream side of culverts could provide refugepool habitat for fish during periods of extreme low flow. These pooling areas would not draincompletely during low or no flow period as the stream bed level would be lower than the



culvert inflow. To construct such refuge areas and retain a bed load within the culvert (orbridge) pooling areas may need to be constructed a few meters upstream from the actualculvert entrance. An ongoing commitment to maintenance of these areas would be required toprevent sediments filling in the refuge pools areas over time.

6.2.5 Water Quality And Flows

The general changes in water quality of streams draining both urbanised and urbanisingcatchments are well known, and include increased high flows, decreased low flows, increasedsuspended sediment concentrations during development, increased general contaminants suchas Zinc (Zn), Copper (Cu) and PAH, and the increased likelihood of toxic spills (e.g., pesticides,sump oil) (ARC 1995). Changes in habitat (temperature, light, cover, depth) can also occur,depending on the way the urbanisation process is conducted.

Increased high flows may destabilise the stream and habitat, and accelerate channel shifts.Recommended riparian planting will take time to establish, so there is also the possibility ofvegetation being undercut to the point of collapse, and stream blockage leading to flooding.Decreasing low flows will cause a loss of habitat through changes in water depth, cover,temperature, and dissolved oxygen. Urban-derived contaminants may be toxic to EPT, butcurrent wisdom suggests that they are not toxic to fish, except for major spills.

To meet the three instream management objectives relating to the kokupu and eel populationsand EPT there are four major controlling factors which need to be considered in the stormwatermanagement strategy for the catchment. These are: ensuring the increase in storm flows whichtypically occur in developed catchments are minimised, minimising any drop in low flows(these two points are partially linked), reducing contaminant inputs to mainstem streams, andmaintaining or improving the instream and riparian habitat.

There are presently no quantitative guidelines to manage these controlling factors.3,4 It isconsidered, however, that there is sufficient knowledge and understanding of these issues toprescribe some general requirements.

Storm flow (and contaminants) should be attenuated as much as possible before the mainstemstreams. Ponds and wetlands on ephemeral streams provide flood storage, low flow release,and contaminant settling and adsorption. Other contaminant removal systems, e.g., grassyswales, wetlands and dry ponds would also serve these functions. Grassy swales and wetlandson side channels may be the best option for reducing the input of contaminants whilemaximising the input of dissolved organic matter, which binds contaminants and reduces theirbioavailability.

In-line ponds are possibly undesirable to maintaining a banded kokupu and eel populations,because ponds change the nature of the mainstream system and can create a barrier to fishmigration, although banded kokopu and eels have a strong ability to climb barriers.

3 However, they are currently researched in Public Good Science.4 Guidelines exist for the retention of 75% of contaminants within the catchment (ARC 1992).



At present, there is no guarantee that these management strategies will produce the desiredoutcome because of a lack of any validation by trials or experimentation. However, somegeneral comments about the risk of failure to reach the set objectives can be made. Fish andEPT are adapted to flashy New Zealand streams, so that the risk from more frequent floodingmay be least critical of the 4 controlling factors, as long as flood increases are not too great. Incontrast, the loss of habitat during summer low flows is critical to meeting all three objectives,and emphasis must be given to attenuating stormflows, recharging groundwater, andproviding shade and deep pools in the mainstem stream. EPT are the biota at most risk fromurbanisation (Wilder 1993), but the cause is not understood. It may be flow changes, SSincreases and/or contaminant effects – either from general impervious runoff (Zn, Cu andPAH) or spilt (e.g., oil, home pesticides). At present it is not known what level of treatment isrequired to maintain EPT, and all that can be said is that the use of the best practicable optionshould aim to reduce habitat modification. The EPT are not essential for the survival of nativefish (although they are preferred prey) because fish also feed on other benthic invertebrates andterrestrial insects.

6 . 3 S t o r m w a t e r M a n a g e m e n t S t r a t e g y

Development of the East Tamaki catchment will have a significant effect on catchmenthydrology. Unmitigated, this would lead to increased frequency and magnitude of flooding,stream erosion, reduced low flows, damage to freshwater aquatic habitat, accumulation ofcontaminants in the estuarine receiving waters and a general degradation of the environment.The encroachment of development on flood plains and stream margins would also lead toincreased risk of flood damage to property. Effective stormwater management is thereforecrucial to environmentally acceptable development.

6.3.1 Assessment for the East Tamaki area

There are a number of features of the study area and its proposed development which have asignificant bearing on the recommended approach to stormwater management. These includethe following.

The receiving environment at the outlet of Otara Creek into the Tamaki Estuary is of poorenvironmental quality. However, upstream development should not further impact onthis, or hinder any future attempts to improve the quality of the receiving environment.

The present stream environment is heavily overgrown and modified, and is very differentto what would have been its “natural” state. However, there remains a significant potentialto enhance the quality of the instream environment.

While fish species diversity appears to be low, there are migratory species present. Thusfish passage and maintenance of low flows are important in streams identified as havinggood upstream fish habitat. However, the species identified are good climbers, andtherefore there remains the possibility of being able to provide fish passage past facilitieswhich might be impassable to other species.



Based on the above point, while it is preferable that there be no instream structures on theprimary fish passage streams, they are not necessarily precluded.

6.3.2 Stormwater Management Outcomes

The development of an appropriate approach to stormwater management in the catchment iscentred around achieving the following key outcomes:

management of the volume and peak flow rate of storm runoff to avoid flood risk and limitstream erosion

management of contaminants and sediment in runoff reaching high value receivingenvironments

retention of stormwater in the catchment to assist in enhancing low flows

protection and enhancement of waterways identified as having high actual or potentialvalue.

In order to achieve these outcomes, there are a series of key management responses that havebeen identified:

manage storm flows such that the first 25mm of runoff can be retained and released over 24hours, and the 2 year Average Recurrence Interval (ARI) storm is significantly reduced;

manage storm flows such that larger events (10 through 100 year ARI) are no greater thanthose from the existing (predevelopment) catchment;

identify appropriate riparian corridors for designation, to protect the primary drainagepaths and provide for riparian cover;

identify flood plain areas, and put in place rules to avoid inappropriate development inthose flood plains;

provide as far as possible for enhancement of groundwater and interflow to assist inmaintaining stream base flows;

protect the important habitat qualities of streams including provision for fish passage;

plan for appropriate measures for both primary (on-site control) and secondary (off-siteback-up) management of erosion and sediment runoff during the development phases;

provide for both targeted source control of contaminants and for general catchment-wideremoval of contaminants in stormwater.

These stormwater management outcomes and responses are identified in the following sectionof the CMP as the key stormwater management objectives to guide the development of thecatchment.

6.3.3 Stormwater Management Options

There are a number of stormwater management tools which could be utilised in the EastTamaki Catchment. There is no one approach which is suitable throughout the catchment. The



steep upper areas, identified for low density development, will be suitable for one approach.The flatter downstream areas, identified for higher density development, will suit differentmanagement concepts. Some of the tools proposed for use within the East Tamakidevelopment area, and their advantages and disadvantages, are listed below.

(a) Low Impact Design

This is an approach to development which pulls together a number of stormwater andenvironmental management tools into a comprehensive approach to development. Some toolsare already incorporated into the Structure Plan or the assessments in this Catchment Plan.Others are included are those outlined below.

Key features of low impact design are identification and protection of natural features (streams,bush, wetlands etc), reduction of impervious areas, increased infiltration, increased use of greenopen space, a comprehensive approach to the total development and use of a range ofstormwater management tools including many of those listed below.

(b) Identification and protection of flood plains and secondary flow paths

The current Structure Plan has identified significant riparian corridors. However, these do notnecessarily reflect the full flood plain area. Identification of the flood plain is important inprotecting property against flood risk, both within the area and downstream. Within the area,it provides a mechanism to ensure that buildings are not put in a flood risk area, and otherstructures which might impede the flow and cause upstream rises in flood level are also notbuilt. In addition, ensuring that there is no earthworks filling or reduction of flood plainstorage volumes avoids resultant increases in downstream flood flows and levels. This toolrequires a combination of hydrologic and hydraulic analysis to define the flood plans, andappropriate mapping and rules to protect the flood plain areas. Existing flood plains areidentified in Map 10.

Similar issues apply in protecting secondary flow paths. These will often be modified byearthworks, so mapping at this predevelopment Catchment Plan stage is not appropriate.However, rules can require that during site development the secondary flow paths be identifiedin each subdivision, and protected from inappropriate development. This will typically includemarking them on a hazards map, and ensuring that buildings are not placed at risk within aflow path, and fences or other structures do not block the flow paths and direct flow intobuildings.

(c) On-site stormwater and wastewater disposal

In lower density areas, on-site disposal of stormwater runoff from all paved areas, and also ofwastewater which has received some form of primary treatment, can reduce storm flowimpacts and help to maintain stream base flows during dry periods. Care needs to be takenwith these approaches, especially in steeper areas, to minimise the concentration of flows and toavoid the risk of slope instability.



(d) Swales

Swales are grassed waterways of low gradient, which provide for removal of contaminants.They are distinct in shape and concept from drains, in that they have a flat bottom typically 1-2m wide, with a dense grass sward of at least 100mm length. They may be used for drainage ofstreets or major roads, and also as a means of treatment of runoff from other paved surfaces.

(e) Wetlands

Wetlands can be effective in removing sediment and some attached contaminants (e.g. heavymetals), as well as providing some bio-treatment. They can also become valuable habitats andamenity or landscape features, as part of a wider reserve development. One disadvantage isthe risk that they may become breeding grounds for mosquitoes and other insects. They alsorequire significant land areas.

(f) Wet ponds

These are primarily for removal of sediment and associated contaminants, and have similarcharacteristic to wetlands, but with less bio-activity. They are typically 1-2m deep, and as suchare less likely to harbour mosquitoes. One concern in areas with only a small urban catchment,is the maintenance of adequate water quality. There is a risk that ponds will have minimalinflow in summer, with evaporation reducing the water levels. Algal bloom could occur, ascould anaerobic conditions, leading to odour problems. As a general rule, it is recommendedthat developed catchments less than about 50 hectares may not be suitable for wet ponds.However, if the source flow is perennial even after development then wet ponds could still beviable.

(g) Flood detention ponds

Typically these have been designed to maintain similar flood peaks to those from the pre-development situation, by holding back flood waters to attenuate the peaks. Both wetlands andwet ponds can be designed such that the water level increases significantly during flood events,providing for this attenuation to occur. Similarly, areas which are normally dry can be used tostore flood waters during large storm events (e.g. sportsfields, park areas).

(h) Extended detention ponds

These are in effect a form of flood detention ponds, but are designed to hold back the morefrequent storm events for a sufficient period (i.e. more than 24 hours) to achieve reduction insediment and contaminant loads and to reduce downstream erosion. They can also serve thepurpose of flood peak attenuation, including achieving the standards set out in the keyoutcomes above. They can in part also fulfil multiple uses, although cognisance does need to betaken of the fact that sediment and contaminants will collect in them to a greater degree thanwould be so for normal flood detention ponds.

(i) Infiltration and soakage

In areas where there is good ground soakage, this can be an important mechanism for reducingstorm runoff in frequent events, and maintaining stream base flows.



There are a number of types of proprietary units available which enable low-trafficked areas toremain permeable. With appropriate design, these can be structurally sound yet retain similarrunoff characteristics to pervious surfaces. This is of significant benefit in reducing the effectsof storm runoff

(j) Erosion and sediment control

The greatest risk of sedimentation occurs during the development phase, but the effects cancontinue to be felt in the middle and lower catchment for many years, as sediment clogs thestream channel. Effective reduction of erosion and control of sediment is essential to minimisethis impact. This applies not only to the earthworks and subdivision stage, but equally to thesubsequent building and development on individual lots.

(k) Riparian planting

Appropriate riparian planting improves the quality of the stream environment, and can assistin controlling water temperature. Further, if appropriate planting extends up onto the banksfor a sufficient distance, then it serves as a vegetative filter strip, trapping contaminants inoverland flow before they reach the stream.

(l) Other devices

In addition to the measures listed above, there are a range of proprietary devices available forsediment, litter and hydrocarbon removal. Some of these will be appropriate for use inindividual developments, particularly on sites where there is a high risk of stormwater pickingup contaminants (e.g. service stations, industrial sites, large carparks etc). They will not beaddressed in any detail in this report.

6.3.4 Assessment of devices against outcomes sought

The following table identifies the outcomes that are achieved by the implementation of eachdevice. Ultimately a mix of devices is the most appropriate and comprehensive strategy forstormwater management. Many of the options presented in this table form part of the “LowImpact Design” approach. Further information on Low Impact Design is contained in the ARCTechnical Publication No. 124.



Table 20: Ability of Stormwater Devices To Achieve Stated Outcomes

Stormwater Management OutcomesManagement of thevolume and peak flowrate of storm runoff to:

StormwaterManagementOptions

avoidflood risk

Limitstreamerosion

Management ofcontaminants andsediment in runoffreaching high valuereceivingenvironments

Retention ofstormwater in thecatchment to assistin enhancing lowflows

Protection andenhancement ofwaterwaysidentified ashaving high actualor potential value.

ReduceImperviousSurfaces

Yes Yes Yes Yes Yes

Identification andprotection of floodplains andsecondary flowpaths

Yes Minor No No Minor

On-sitestormwater andwastewaterdisposal

Yes Yes No Yes Yes

Swales Minor Minor Yes Minor MinorWetlands No Minor Yes Minor NoWet ponds No No Yes Minor NoFlood detentionponds

Yes Minor Minor No No

Extendeddetention ponds

Minor Yes Yes No Yes

Infiltration andsoakage

Yes Yes Yes Yes Yes

Erosion andsediment control

No No Yes No Yes

Riparian planting No Yes Minor No Yes

6.3.5 Conceptual approaches

There are number of ways in which the tools can be applied. The approach adopted will varywithin the catchment but will generally be a combination of methods. The two extremes formanagement of stormwater are to:

put the onus on each and every developer to fully and individually manage the effects onstormwater runoff of development on their site, or

allow developers a completely free hand in their stormwater management, and haveCouncil implement “end-of-pipe” solutions to manage the effects of development on thequantity and quality of stormwater.

Neither approach is, in the final analysis, particularly satisfactory, and some form of middleground is normally appropriate. In the context of the East Tamaki development area this islikely to include:

an overall comprehensive approach to stormwater management in the catchment (i.e. theoutcome of this Catchment Plan)



a strong focus on managing significant sources of contaminants and storm flow at source

a second tier of protective works to address more diffuse stormwater effects

robust and appropriate policies and rules to ensure that development is carried out in anappropriate manner

public education on the importance of stormwater management, and the measures thatindividuals can take to improve the environment.

6.3.6 Recommended approach

The approach outlined below has been identified in principle based on the data collected on theexisting natural physical environment, and on our assessment of the effects of development.An initial application of the approach to the study area is illustrated in Map 9. The factorsconsidered, and the details for each subcatchment, are tabulated in Appendix 6. The conceptinvolves providing ponds for all development areas, and specifying pond performance criteria.Mitigation modelling results to test the effect of low impact design in representativesubcatchments identifies a benefit from low impact design. The use of low impact design willtherefore mean that smaller ponds can achieve those criteria. A “conservative” approach hashowever been adopted to pond sizing which assumes no low impact design. The low impactapproach is in broad terms more aligned with the vision and strategy adopted in the DETConcept Plan in relation to protecting natural features and so forth.

(a) Use of ponds

An initial general comment is required on the use of ponds. The following general principleshave been used in identifying where ponds might be required, and the type of pond to use.

Where the stream is a major fish passage stream (headwater, hill valley or principallowland streams fed by the first two) then ponds will be off-line. They will typically belocated towards the confluence of major tributaries, and the stormwater drainage systemwill be brought to them from the adjacent catchment areas.

Where the stream is a lowland first order ephermeral stream, consideration will be given tobringing all drainage from that catchment to an on-line pond immediately upstream of thepoint where the tributary joins the main stream.

Where a pond is close to houses (i.e. less than 100m), or has only a small catchment, thenthe preferred pond type will be extended detention.

Where the pond is in a larger reserve area, has adequate catchment, and there is littlehousing expected within 100m, wetlands or wet ponds will be considered, where these fitin with landscape and amenity objectives for the reserve. In many cases these may inpractice be a series of small wetland areas along the watercourse.

(b) Upper catchment low intensity development

In this area, it will be important to maintain recharge to soil water, and minimise any increasein storm runoff. Measures which will achieve this include:



minimising the development of impervious areas, through setting low limits (e.g. less than20%) on roof and paved area coverage in the Rules, minimising road pavement widths andencouraging the use of grassed paving wherever possible

minimising earthworks

disposal of stormwater (including runoff from roads) and primary treated wastewater in adispersed manner to the ground surface or immediately subsurface

encouraging planting of trees, not only in the steeper valley sides, but also on the upperridge areas

fencing off the steep valley sides and stream bottoms to facilitate development of strongundergrowth.

Issues to be addressed to ensure these measures are successful include:

careful consideration of land stability issues

avoidance of flow concentration, channelisation and erosion

No specific large stormwater management devices are proposed for this area. Effectively, theemphasis is placed on developers and landowners to provide the appropriate managementmeasures.

(c) Medium density development in the lower hillslopes

The density of this development precludes significant on-site stormwater disposal, except inareas where soils indicate there may be potential for soakage. Even there, attention will need tobe given to identification and management of secondary flow paths. In some areas there maylocally be potential for drainage systems based on swales, to slow runoff and treat for relativelylow levels of contaminants. In other areas, piped systems with ponds will be more appropriate.

Ponds are assumed to be of the dry pond or extended detention type where they are in closeproximity to houses. Where the ponds are further from houses, e.g. as part of a reserve area,and there is sufficient catchment, then wet ponds or wetlands may be appropriate, forming awater feature as part of the reserve.

Within the development areas there will be a range of measures which can be implementedthrough rules, including:

keeping impervious areas on each lot low (e.g. <55%, refer to earlier assumptions onimpervious coverage in Table 12)

minimising road widths, and providing alternative parking surfaces such as permeablepaving

identifying and protecting flood plains and secondary flow paths

wherever possible within individual subdivisions, making use of infiltration, swales, andvegetated filter strips.



(d) High density residential

While these areas will have high density housing, they will also include significant areas ofgreen open space (up to 25%). The appropriate approach to stormwater management will be toallow high levels of impervious within the “hard” areas, and use some of the green space forinfiltration, swales and treatment. While swales are preferred for treatment, they will notalways be practicable. Kerb and channel will be acceptable so long as maximum use is made ofgreen space to teat stormwater and increase infiltration. Swales should be at least 60m longfrom pipe discharge to the stream or the swale outlet, and provide for detention as much as forconveyance. In other words, during a storm they should pond up and drain slowly, to providefor both settlement of sediment and attenuation of runoff peaks. However, they will also needto have at least some infiltration capacity (e.g. subsoil drains) to ensure that they dry out afterrain events, and do not become permanently wet.

Where the high-density residential areas do not have significant reserve areas nearby, greaterreliance will need to be placed on ponds for treatment and attenuation. It is recommended thatkey pond locations be identified and set aside as part of the Structure Plan, and that developersbe required to convey their stormwater drainage to these ponds. Widespread piping direct toponds should be a last resort.

(e) Commercial

Similar comments apply to the commercial area as to high density residential. This zone islargely surrounded by a large park, and the park concept should include swales as and whereappropriate to collect, treat and convey the stormwater from the adjacent commercial areas. Itwill also be appropriate in these areas to include filter bags within the pavement cesspits, toprovide a primary capture of litter and coarser sediment.

(f) Principle Roads

There is a principal roading grid which will carry significant traffic volumes, and thereforegenerate significant contaminant loads. The road pattern is a generally rectangular grid, whichcrosses the natural stream system at reasonably frequent intervals. In the lower areas fromMurphy Road west, gradients are sufficiently flat for swales to be effective in treatment ofstormwater. While it may not be appropriate to be applied in all situations where other issuesare of more importance, wherever practicable swales or similar vegetated channels andtreatment areas should be used.

(g) Adjacent to protected streams

While the conceptual stormwater management layout attempts to provide for treatmentdevices for all medium and high density residential areas, there will be some, close to streams,where it is not realistic to provide for gravity drainage to such devices. Provision shouldtherefore be made for these to drain to the streams, but through appropriate treatment areas.These areas could be included within the riparian buffer where this is feasible. This couldpotentially apply to properties either adjacent to or within one property width of the stream.Initial assessment of future development layouts indicates this could apply along much of thestream reserve margins.



The treatment devices would include swales or vegetative filter strips. Paved areas shoulddischarge to adjacent pervious areas where possible, or be conveyed, along with roof water, bypipe. The pipes must discharge into a swale, or through a device which spreads flow onto avegetated filter strip. In both cases provision must be made at the outlet to avoid erosion, suchas by minimising the concentration of discharge outfalls.

CatchmentManagement

Objectives

Section 7



7777 Catchment Management ObjectivesCatchment Management ObjectivesCatchment Management ObjectivesCatchment Management ObjectivesThe aim of the catchment management study is“To achieve an integrated approach to stormwatermanagement, improving biodiversity and integration ofrecreational and amenity values”. To achieve this aima series of objectives to guide the decision makingprocess in relation to future policy, assetmanagement, implementation works, and

monitoring have been developed. While the majority of these objectives relate to the key‘environmental’ outcomes associated with the protection of the important catchment valuesidentified through the technical investigations and consultation, a range of implementationobjectives are included. Each objective includes a series of key success measures that have beendrawn from the analysis and discussion in previous sections, and also influence the mitigationmeasures proposed in Section 8. While this section provides a strategic overview of catchmentobjectives and success factors, it does not attempt to summarise all of the detailed assumptions,requirements or recommendations contained in other sections of this CMP. Therefore, whilethis section provides a strategic framework, for the purposes of decision making the documentshould be considered in its entirety.

7 . 1 I n s t r e a m a n d R i p a r i a n M a n a g e m e n t

The following instream management objectives have been derived from instream managementstrategy identified earlier in the CMP.

7.1.1 Catchment Management Objective 1: Kokopu Population

(a) Key Success Factors

The above objective can be achieved by making provision for:

suitable adult banded kokopu habitat in the headwater and hill valley streams;

passage of juvenile and adults of the species throughout the entire mainstem5 reaches of theriver from headwater streams, hill valley streams and lowland rolling streams to the rivermouth;

5 mainstem refers to permanent Otara Creek streams which traverse the lowland rolling stream sections to hillvalley and/or headwater stream sections as a continuous body of water, notwithstanding the formation ofseparate pools during periods of low flows.

To manage the Otara Creek catchment in such a manner to sustain a viable bandedkokopu population.

This section provides asummary of the key planningissues and objectives that willguide the implementation andmitigation framework.



sufficient deep pool habitat throughout the mainstem reaches from headwaters and hillvalley sections, and throughout mainstem lowland rolling streams, especially during lowflows;

improvement of water quality to reduce oxygen depletion, high water temperatures, andexcessive algal production;

improvement of bank stability, particularly in the headwater and hill valley streams, tominimise excessive siltation of stream substrate in the lowland rolling streams, and tominimise the infilling of pools and the smothering of substrates to improve habitat.

7.1.2 Catchment Management Objective 2: Eel Fishery



Passage of juvenile and adults of the species throughout the entire mainstem reaches of theriver from headwater streams, hill valley streams and lowland rolling streams to the rivermouth;

Sufficient deep pool habitat throughout the mainstem reaches of lowland rolling streams,especially during low flows.

7.1.3 Catchment Management Objective 3: Diverse Ephemeroptera, Plecoptera and Trichoptera(EPT)



habitat heterogeneity including runs, pools and riffles, as well as moderate instream woodydebris;

improvement of water quality to reduce oxygen depletion, reduce high watertemperatures, and excessive algal production; and

improvement of bank stability to minimise excessive siltation of stream substrate and toreduce infilling of pools and the smothering of available substrates.

To manage the mainstem lowland rolling streams of the Otara Creek Catchment insuch a manner to maintain and enhance the viability of a viable eel (shortfin andlongfin) population.

To manage the headwater and hill valley streams of the Otara Creek Catchment in sucha manner to sustain habitat suitable for a diverse Ephemeroptera, Plecoptera andTrichoptera (EPT) communities, generally greater than three species types.



7.1.4 Catchment Management Objective 4: Enhancement of Instream and Riparian Habitat



The control of introduced fish species;

Self-colonisation of other native fish species by providing suitable instream habitat;

Establishing a range of native species as riparian planting to provide habitat, shading andbank stability;

Ensuring future management and maintenance of the environmental corridors andassociated local reserves (and other land use practices) does not create the potential forlethal risk to the instream habitat or fish populations.

Education measures which ensure future communities of the East Tamaki area are aware ofthe importance of land management (e.g. correct disposal of hazardous household wastes)to instream values.

Recognising the importance of the transition zone (approximately 20 years) in managingsteam bank stability and its relationship with other sediment generating activities (i.e.development).

7 . 2 S t o r m w a t e r M a n a g e m e n t O b j e c t i v e s

7.2.1 Catchment Management Objective 5: Stormwater Run-off



manage storm flows such that runoff from the 25mm of rainfall can be retained andreleased over 24 hours, and the 2 year Average Recurrence Interval (ARI) storm issignificantly reduced;

manage storm flows such that larger events (10 through 100 year ARI) are no greater thanthose from the existing (predevelopment) catchment;

identify appropriate riparian corridors and protect the primary drainage paths and providefor riparian cover;

To manage the volume and peak flow rate of stormwater runoff to avoid flood risk andlimit stream erosion.

To promote the enhancement of riparian areas in the lower and upper catchment toprovide a habitat with a diversity of species.



Identify flood plain areas, and put in place rules to avoid inappropriate development inthose flood plains.

Design key or strategic arterial roads in the catchment to provide protection from the 100year ARI flood plain.

Incorporation of the proposed development rules for stormwater management purposes(contained in the ‘Implementation Section’) in the draft variation, or their considerationthrough the ‘Section 32’ process where other more cost effective or efficient means areavailable.

7.2.2 Catchment Management Objective 6: Stormwater Contaminants



appropriate measures for both primary (on-site control) and secondary (off-site back-up)management of erosion and sediment runoff during the development phases;

providing for both targeted source control and contaminants and general catchment-wideremoval of contaminants in stormwater.

Staging the development phase to reduce the potential for significant sediment run-offacross different or ‘unprotected’ parts of the catchment.

Incorporation of the proposed development rules for stormwater management purposes(contained in the ‘Implementation Section’) in the draft variation, or their considerationthrough the ‘section 32’ process where other more cost effective or efficient means areavailable.

Ensuring that stormwater ponds are provided ahead of development to act as a backup tothe standard requirements of the ARC TP90 guidelines which developers will be requiredto observe.

7.2.3 Catchment Management Objective 7: Low Flows



Enhancement of groundwater and interflow to assist in maintaining stream base flows.

To ensure contaminants in runoff are managed and appropriate measures to preventthose contaminants reaching high value receiving environments implemented.

To retain stormwater in the catchment to assist in enhancing low flows.



Reduced Impervious areas

Maximum use of soakage and infiltration for disposal of stormwater.

Incorporation of the proposed development rules for stormwater management purposes(contained in the ‘Implementation Section’) in the draft variation, or there considerationthrough the ‘section 32’ process where other more cost effective or efficient means areavailable.

7.2.4 Catchment Management Objective 8: Waterway Enhancement



The protection of the important qualities of streams, including habitat values andprovision for fish passage.

Suitable planning mechanisms to secure access to corridors to enable stormwatermanagement and enhancement.

A suitable financial framework which will ensure catchment enhancement works (such asfencing, and replanting) within corridors occurs, ideally paid for by developmentcontributions.

Incorporation of the proposed development rules for stormwater management purposes(contained in the ‘Implementation Section’) in the draft variation, or there considerationthrough the ‘section 32’ process where other more cost effective or efficient means areavailable.

7 . 3 T e r r e s t r i a l E c o l o g y O b j e c t i v e s

7.3.1 Catchment Management Objective 9: Protection and Enhancement of Terrestrial Ecology



Purchase/protection of significant areas of terrestrial ecology as public open space.

To protect and enhance waterways identified as having high actual or potential habitatand instream value.

To protect and enhance terrestrial ecological values and investigate and actionopportunities to create linkages between areas and re-establish native habitat whereappropriate.



Stock exclusion and fencing around significant areas of native vegetation or wildlife habitatareas (current and future)threatened by domestic animals.

Undertaking and promoting plant pest control for both public and private property, bothpresent and future.

Undertaking and promoting animal pest control for both public and private property, bothpresent and future.

Buffer zones surrounding areas of significant ecological value, such as Murphy’s Bush, tominimise the potential effects of the urbanisation process, and subsequent effects arisingfrom close proximity of centres of population (e.g. domestic pets),

Maintenance or enhancement of hydrology e.g. with regard to kahikatea stands.

Set-back distances for urban areas and roadways.

7.3.2 Catchment Management Objective 10: Enhancement of Terrestrial Ecological Values



Provision of vegetated linkages between key areas of native vegetation;

Determination of optimum size of future native vegetated ‘blocks’ (i.e. a few large orseveral small areas).

Provision of a range and diversity of habitat types e.g. upland game species; roughscrubland.

Enhancement, such as planting food species, aimed at particular species e.g. kereru.

Retention of typical amenity plantings, both native and exotic.

7.3.3 Catchment Management Objective 11: Terrestrial Ecology Information



Gaining a greater understanding of terrestrial ecological values and species diversitythrough field surveys.

To enhance the existing terrestrial ecological values and biodiversity of the East Tamakiarea.

To ensure that adequate information is available when making detailed decisions on themanagement and enhancement of existing and future terrestrial ecological areas ofsignificant natural value.



Requiring development applications to provide assessments of ecological values,significance and management measures where appropriate.

7 . 4 L a n d U s e O b j e c t i v e s

7.4.1 Catchment Management Objective 12: Future Land Use



The range of land uses densities identified in concept plan which modelling and technicalinvestigations have confirmed through the catchment planning process as being able to bemanaged appropriately.

Ensuring land use management through the District Plan provides controls on imperviouscoverage associated with each land use type.

Ensuring the staging objectives are met by supplying a range of development opportunitiesat any particular point in time.

7 . 5 L a n d s c a p e a n d A m e n i t y O b j e c t i v e s

7.5.1 Catchment Management Objective 13: Landscape Features



The protection of the stream network within publicly owned land, and its enhancementthrough weed and pest control, replanting, and where necessary recontouring.

The protection of the integrity of significant areas of existing native vegetation (such asMurphy’s Bush and the Gracechruch Road block);

The protection of ridgelines which frame the catchment from inappropriate development;

To identify and protect key landscape features and elements to retain a sense of identity forthe East Tamaki area.

To provide for a range of land use types within the study area whilst ensuring that the effectsof urbanisation can be managed in a sustainable manner.



The development of ‘Barry Curtis Park’ in a manner which will ensure ‘an internationallyrenowned park which reflects the peoples and cultures of Manukau City’ and whichcreates a key focal point for both the catchment and the wider area.

Recognising the need to develop and integrate key open space nodes within the overallcatchment concept where possible. This is most likely to be successful by public purchaseof open space nodes, although other opportunities may be available to enable such areas tobe used for passive and active recreation. Where possible such areas should be containedwithin or linked to the ecological corridors.

7 . 6 R e c r e a t i o n O b j e c t i v e s

7.6.1 Catchment Management Objective 14: Recreation and Leisure



Walkways and cycleways along the ‘green finger’ network;

Safe and easy access to walkways through appropriate design measures;

Community recreation and leisure facilities within environmental corridors (provided theycomply with stormwater rules);

Community involvement in the enhancement of riparian corridors to develop a strongsense of community ownership and protection of corridors and other ecological features.

7 . 7 I m p l e m e n t a t i o n O b j e c t i v e s

7.7.1 Catchment Management Objective 15: Development Control



Protection of existing ecological, landscape and other environmental features;

Protection of floodplains from development;

To provide a diverse range of recreational opportunities in the catchment, including foractive and passive recreation and leisure activities.

To ensure Catchment Management Objectives and assumptions upon which these arebased are translated into workable development rules.



Low Impact Design measures, where appropriate, to minimised stormwater run-off andthe impact of site development on the stream ;

Asset management and infrastructure development to minimise the effects of development.

7.7.2 Catchment Management Objective 16: Acquisition and Enhancement of EnvironmentalCorridors



Acquisition of the environmental corridors, consisting of a stormwater management zoneand an overlying POS zone, in the lower catchment;

Protection of the environmental corridors in the upper catchment through environmentalenhancement measures combined with legal mechanisms to ensure enhancement occursand long term protection (e.g. through covenanting) is provided.

Ensuring the funding policy, asset management, district planning and other policies whichguide the future development of the area are aligned and a co-ordinated implementationprocess developed.

To ensure flexibility is provided in the acquisition and management of environmentalcorridors to enable Council to meet a broad range of outcomes.

7.7.3 Catchment Management Objective 17: Enhancement of Upper Catchment Area.



Rules in the variation which require environmental enhancement to be secured at the pointof subdivision in the upper catchment;

Flexibility in the design and layout of subdivision in the upper catchment to ensuresufficient incentive for ‘enhancement subdivision’ occurs to secure the outcome over theanticipated development life-span of the catchment;

To require additional information at the point of subdivision in relation to the ability of thearea to manage wastewater;

To secure the protection and enhancement of the environmental corridors in thelower catchment in perpetuity.

To secure, promote and recognise the importance of environmental enhancement of thestream margins and steep slopes in the upper catchment.



To develop an education and awareness programme to promote the benefits ofenvironmental enhancement in the upper catchment, and which recognises that a certainlevel of subdivision has already occurred in the area.

7.7.4 Catchment Management Objective 18: Managing Costs of Growth – StormwaterManagement



Establishing a register of projects to be implemented to achieve the stormwatermanagement policies.

Including in the register an up to date assessment of the costs of projects, including actualcosts of projects completed.

Establish a ledger of financial contributions received. The ledger is also to record the value(contract or agreed cost) of projects undertaken by developers and vested in council.

Establish a ledger of stormwater growth expenditure. The ledger is to record actual cost ofprojects undertaken, interest charged on borrowings, value of land purchased or vested,and legal, consulting and management costs.

Establishing clear policies and guidelines for consenting officers to manage costs of worksundertaken by developers on behalf of council. The purpose is to ensure transparency inaccounting for meeting the costs of growth.

Undertaking frequent (at least 3 yearly) reviews of the status of anticipated expenditureand contributions received.

Undertaking frequent (at least 3 yearly) reviews of the amount of the financial contributionto be charged.

Implementation of clear policy statements in the District Plan and guidelines for consentingprocedures that require implementation of subdivision practices that conform to the “lowimpact design” philosophy.

To ensure adequate funding is provided to provide for implementation ofstormwater management policies.



To establish a staging regime that assists in managing the adverse effects ofdevelopment, promotes good financial management, and ensures development proceedsin a manner which will achieve the range of outcomes sought for the area.

7.7.5 Catchment Management Objective 19: Managing Costs of Growth Reserve Contribution



Establishing a register of land purchases and projects to be implemented to meet thereserve development requirements.

Including in the register an up to date assessment of the costs of projects, including actualcosts of projects completed.

Establish a ledger of reserve contributions received. The ledger is also to record the value(contract or agreed cost) of projects undertaken by developers and vested in council.

Establish a ledger of reserve growth expenditure. The ledger is to record actual cost ofprojects undertaken, interest charged on borrowings, value of land purchased or vested,and legal, consulting and management costs.

Establishing clear policies and guidelines for consenting officers to manage costs of worksundertaken by developers on behalf of council. The purpose is to ensure transparency inaccounting for meeting the costs of growth.

Undertaking frequent (at least 3 yearly) reviews of the status of anticipated expenditureand contributions received.

Undertaking frequent (at least 3 yearly) reviews of the amount of the financial contributionto be charged.

7.7.6 Catchment Management Objective 20: Staging of Development



An adequate supply of land is available to cater for population growth, including choice ofhousing types.

Suitable environmental mitigation measures are in place so that urban development willnot compromise important values within, or downstream of, the catchment;

Ensuring specific land use standards are met, such as appropriate densities.

To ensure adequate funding is provided to provide for implementation of reserves andrecreational facilities supporting the growth community.



To establish a robust monitoring framework which contributes to the management ofthe East Tamaki Catchment in a sustainable manner.

Ensuring any costs of growth incurred by Council can be recovered.

Minimising construction related sediment.

Minimising general disruption to the community from an uncontrolled stagingprogramme.

7.7.7 Catchment Management Objective 21: Monitoring



The development of a monitoring programme to meet the combined requirements of:

– monitoring compliance with any consents granted by the ARC,

– monitoring the effectiveness of the CMP, District Plan and any other assetmanagement strategies or plans for East Tamaki,

– gathering environmental information on the effects of urban development in thecatchment to enable the aforementioned; and

– regular reporting to inform the community on the success of implementation.

Providing sufficient resourcing, in conjunction with other organisations with particularinterests or responsibilities for monitoring in the area, to enable the monitoring programmeto be implemented in a robust manner.

Provide for regular review of progress and success of implementation, with a particularfocus on reviewing the environmental outcomes being achieved, potentially on an annualbasis.

7 . 8 R e c e i v i n g E n v i r o n m e n t – O t a r a L a k e

The receiving environment for the East Tamaki study area is the Tamaki Estuary, and the areaknown as Otara Lake in particular. The Lake is the subject of an ongoing study being carriedout for Council by Meritec to improve water quality. While the Development East Tamaki areais not the only catchment area draining into the Lake, it is an important input in that the landuse for DET area will change over the next 20 years through a significant development process.The development stage is critical as this is when the potential for high levels of sediment isgreatest. The development of the study areas is therefore most likely to be of concern in relationto the objectives for the Lake.

In 1994 the Otara Lake Accord, signed by the former ECNZ, Manukau City Council, AucklandRegional Council and members of the community provided a commitment to enhancing thewater quality, access and amenity of the Otara Lake. The accord provided for three goals, witha third added through consultation with the community subsequent to the accord being signed:



Integrated management of land and water with regard to Otara Lake and its margins;

Improve water quality to contact recreation standard by the Year 2000

Greater use of the lake and margins and improved relationship between Ngati Otara Parkand the Lake;

Investigation subsequent to the signing of the accord determined that it is unlikely to bepossible to achieve the goal of providing contact recreation water quality standards in the Lake.However, a number of improvements have been identified to ensure the Lake water quality isimproved to a secondary (non-contact) standard. A series of management objectives have beenidentified to assist the agencies responsible for improving the quality of water in the Lake.

As part of the implementation of the Accord, a strategic review was prepared for Council byMeritec. This review identified a range of issues which affect the quality of water in the Lake,and hence the ability to meet the goals of the accord.

Key issues in relation to the DET catchment management planning process include thefollowing:

Management of flood peaks;

In-stream erosion;

Stormwater quality, and sediment control.

Other sections of this CMP illustrate how these objectives can be met, specifically byimplementing a stormwater and staging management regime, combined with standardsediment control measures. It is noted that Council will need to provide careful management ofthe development process in conjunction with the ARC in relation to sediment yields.

Implementation andMitigation

Framework

Section 8



8888 Implementation and MitigationImplementation and MitigationImplementation and MitigationImplementation and MitigationFrameworkFrameworkFrameworkFramework

The purpose of this section is to provide detail on the implementation measures required toensure the catchment management objectives are achieved. The previous section outlined arange of catchment management objectives and key success factors. These have been developedover the course of the catchment management planning exercise to provide a strategicframework to the more detailed technical investigations.

Implementation means the ‘act of putting a plan into effect’. In achieving the vision for thefuture of the catchment it is important to ensure an integrated approach to implementation.While the focus of this document is on the implementation of those matters that are within thescope of this report, there have been a range of other processes occurring concurrently whichwill require certain tools to be used to achieve the ‘vision’.

Manukau City Council, as the agency with primary responsibility for the development of thearea has a number of roles to play. In summary, these may include:

establishing strategic direction for the future of the catchment and East Tamaki area;

being responsive to the democratic wishes of both present and future communities andacting on their behalf in the ‘public interest’;

regulator of the development process through land use and subdivision consents under theRMA;

asset manager of future community infrastructure, both social and physical;

landowner;

ensuring compliance with any comprehensive stormwater discharge consents granted toCouncil by the ARC;

monitoring the progress in implementing the vision.

The legislative basis for the implementation framework is comprised of both the RMA and theLGAct. The following table identifies the two primary pieces of legislation, and three ‘tiers’within this framework where different mechanisms operate.

This section identifies the implementation actions and mitigationmeasures necessary to achieve the catchment planning objectives. Itshould be read in conjunction with the catchment managementguidelines included at the beginning of this document.



Tier 1 Tier 2 (e.g.) Tier 3 (e.g.)

RMA Variation Consent conditions

Financial contributions

Monitoring andenforcement

LGAct Annual Plan

LTFS Rate relief

Funding provision / capex

Works

While legislation appears to imply a certain regulatory focus, it is recognised that in addition tothe more formal ‘regulatory’ or ‘structured’ mechanisms in the legislation, other means areavailable to Council to achieve the visions, which in many instances may be more effective that‘intervention’ approaches. Indeed, the RMA encourages Council to examine the range oftechniques that could be used to promote the sustainable management of the resources of thecatchment ahead of regulatory means. This may include education and raising awareness,establishing and supporting community based groups for conservation/protection of streams(e.g. landcare groups), providing information and assistance to developers in implementingalternative methods for developing sites (e.g. higher density or low impact design) and so forth.

The remainder of this section outlines the key implementation and/or mitigation measuresproposed (which would fall under the ‘third tier’ of implementation) to ensure the urbanisationof the Development East Tamaki area does not compromise those values identified as beingimportant. This is achieved primarily though identification of options, and recommendationson the most appropriate options for East Tamaki which meet the range of objectives set outearlier.

8 . 1 S t o r m w a t e r M i t i g a t i o n O p t i o n s

This section develops the stormwater management strategies discussed in Section 4 of thisreport and incorporates these design elements into the ‘Future Mitigated’ model. The results ofthe modelling are discussed here to define a preferred management approach to stormwatermitigation within the East Tamaki catchment.

8.1.1 Stormwater Design Options

There are a number of proven methods available to mitigate the effects of urbanisation onstormwater in a developing catchment. These include:

Low Impact Design (LID) techniques

Conventional design using ponds for stormwater treatment, and extended and flooddetention

A combination of the two approaches.

The approach has been to develop the mitigation options such that the peak flows and floodlevels (at key nodal locations) within the developed catchment are no worse than in the existing



situation as presented in this report. To achieve this, it is necessary for many subcatchments tobe managed so that peak flows are reduced below the pre-development rates.

No attempt has been made to model every possible scenario, but rather assess the generaltrends or reductions in runoff volume achieved through a variety of low impact designtechniques. The ‘Future Mitigated’ model does not incorporate these low impact designtechniques and hence sets the upper limit for sizing of detention ponds. In practice, a mixtureof low impact design and conventional design will prevail in the catchment. Water qualitybenefits can be achieved by greater use of LID across the catchment, and some attenuationbenefits can also be achieved for more frequent storms. Pond sizes may be smaller thandetailed in this report, as long as the overall flow rate management objectives are met in eachcatchment.

The assumptions made in the future mitigated modelling are set out in Appendix 6, and theresults of the modelling (Table 6.3), along with the required pond sizes and performance (Table6.4), are set out in Appendix 7. A brief comment on the model development is included inAppendix 6. Typical hydrographs from two sub-catchments (C5 and B1), illustrating the effectsof development and of the pond mitigation (C5) and riparian planting (B1) for the 2 and 100year ARI , are given in the following sections.

(a) Hyrdorgraphs for Subcatchment C5 (C5A)

This subcatchment comprises mainly medium and high intensity residential. An online pond isproposed to manage stormwater runoff in the future developed scenario.

From the hydrographs below (Figure 19 and 20), the following are observed:

Greater increase in peak discharge in the future unmitigated due to the larger imperviousarea from development. This effect of development is more evident in the 2 year ARI (≅1.75times greater than existing, Figure 19) than the 100 yr. ARI (≅1.4 times greater, Figure 20).

The rise to the peak flow from the highly reticulated environment in the future unmitigatedis quicker than from the existing. Runoff also starts earlier in the future compared to theexisting because a larger area has become impervious and will immediately start todischarge as the rain begins (Figure 19 and 20).

Greater runoff volume in the future again due the larger impervious area in the future.

Mitigation by the pond manages to reduce and attenuate the peak discharge to no worstthan the existing scenario. This is more evident in the 2 year ARI where the initial slowerand flatter rise in the future mitigated hydrographs illustrates the effect of extendeddetention as the pond slowly begins to fill. The faster rise that follows starts when the weircrest level has been exceeded.

Mitigation by pond alone does not change the total volume of runoff compared to the futureunmitigated. It does however, reduce and attenuate the peak discharge. Low impact designapproaches and/or extensive conservation planting on the other hand, can help to lower thetotal runoff volumes and peak discharges (See Figure 21 and 22 and discussion below).



Figure 19: 2 Year ARI Hydrograph for Subcatchment C5 Illustrating Effect of Pond Mitigation

Figure 20: 100 Year ARI Hydrograph for Subcatchment C5 Illustrating Effect of Pond Mitigation

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(b) Hyrdorgraph for Subcatchment B1 (B1A)

This subcatchment is comprised of low intensity residential and conservation area. Themitigation options for this subcatchment includes extensive conservation planting within theconservation area (modelled) and low impact design approaches (not modelled). Figures 21and 22 illustrate the effect of incorporating extensive conservation planting into thesubcatchments, and the following can also observed from these hydrographs:

Extensive conservation planting in the upper reaches can help reduce the peak dischargebut it does not attenuate (slow) the rise to peak. This is more evident in the 2 year ARI. Thefaster initial rise is due to greater runoff from the larger impervious area.

A slight reduction in total runoff volume in the future compared to the existing in the 100year ARI as a result of extensive conservation planting in the upper reaches.

Figure 21: 2 YR ARI Hydrograph for Subcatchment B1 Illustrating Effect of Riparian Planting

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Figure 22: 100 YR ARI Hydrograph for Subcatchment B1 Illustrating Effect of Riparian Planting

The framework for managing the type of stormwater techniques which are encouraged by theCMP consists of the District Plan and Councils Asset Management plans. Council maydetermine that LID techniques should be encouraged in certain situations (e.g. on roads whichrun adjacent to the ‘green fingers’), while in other circumstances (such as where access to, ormaintenance of, stormwater devices may cause future problems) LID may not be appropriate. Itis anticipated that Council would wish to retain flexibility into the future, and therefore themodelling has assumed a ‘worst case scenario’ of no LID for them purposes of determining anappropriate mitigation framework.

8.1.2 Low Impact Design

Low Impact Design is a design approach for site development that protects and incorporates natural sitefeatures into erosion and sediment control and stormwater management plans (ARC TP 124). Detailson LID are available from the “Low Impact Design Manual for the Auckland Region” by theAuckland Regional Council (ARC TP 124).

In the modelling process, the following LID techniques for new development have beeninvestigated:

Reduction of impervious area through the use of permeable paving for driveways, paths etc in newresidential areas (Option 1)

On-site stormwater disposal of roof water in new residential areas i.e. soakage (Option 2)

Biofiltration practices in the form of swales adjacent to major roads (Option 3)

The East Tamaki catchment varies in terms of land use, soil type and slope. Five representativesubcatchments (refer to the following table) were selected and modelled to evaluate the LIDapproach.

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Table 21: Representative Sub-catchments for Low Impact Design Investigations

Subcatchment Area(ha)

Land Use Soil Type(TP108 classification)

AverageCatchmentSlope (m/m)

B1 92.9 Low intensity residential andconservation

Group C Soils (poorlydraining)

0.031

B7 79.2 Medium intensity residential andconservation

Group C-B Soils (med-poor draining)

0.022

B9 162 Mix of mainly medium and highintensity residential, conservationand small low intensity residential


0.024

C4 40.8 High intensity residential andconservation

Group B Soils (mediumdraining)

0.011

C5 57.5 High intensity residential,conservation and small low intensityresidential


0.038

The following LID approaches have been investigated for each subcatchment:

Effect on volume reduction and peak reduction for a 24 hour design storm using theXPSWMM model for the 2 and 100 year ARI storm events.

Effect on the average annual total runoff, baseflow and stormflow using the ARC RunoffVolume model (BCHF February 2000). This model simulates the catchment runoff volumebased on 26 years of daily rainfall data for the Auckland region and allows comparison ofdifferent land uses within the same subcatchment e.g. existing and future.

In analysing the effects above, each subcatchment has been separated into pervious, connectedimpervious (e.g. roof, roads etc) and unconnected impervious (driveways, paths etc) areas. Thecontributing area, curve number and response time is then entered for each according to theoptions analysed.

8.1.3 XP-SWMM Modelling Results

The graphs below show the reductions to the 100 year ARI and 2 year ARI peak flows whenapplying Options 1, 2 and 3. The results are presented as peak flow per unit area. For eachsubcatchment, the first column shows the unmitigated scenario, followed by the different LIDapproaches.



Figure 23: Peak Flow for 100 Year Return Period – Effect of Low Impact Design

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Figure 6.1 - Peak Flow for 100 Yr Return Period

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Figure 24: Peak Flow for 2 Year Return Period – Effect of Low Impact Design

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Figure 6.2 - Peak Flow for 2 Yr Return Period

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(a) Option 1: Reduction of Impervious Area

The reduction of impervious area will enable more infiltration of stormwater into the ground,with a corresponding decrease in total runoff volume and peak flow expected.



Figures 23 and 24 show that for each of the catchments there is a consistent reduction in peakflows in both the 2 year and 100 year events due to reduced impervious areas.

Typically, the best results will be gained where the catchments are flatter, there is potential for highimpervious and where soils are medium or well draining (i.e. in the medium and high intensityresidential areas in the middle and lower catchment).

(b) Option 2: On Site Disposal of Roof Water

The effect on peak flow reduction by on site disposal is small in larger storm events but is morenoticeable in the 2 year ARI event. This implies that there will be a greater reduction in peakflows during the more frequent events, when the soil has not yet reached saturation. The slightincrease shown for example in Subcatchment B1 (upper catchment low intensity) in the 2 yearand 100 year ARI events is most likely an issue of the timing of peak flows from the perviousand impervious areas in the model. In practice, runoff from these steep upper catchment areasis not likely to increase above the unmitigated scenario through the use of on site disposal.

On site disposal of roof water will therefore have beneficial effects in reducing peak runoff in the morefrequent rainfall events e.g. ≤2 year ARI. While the upper catchment has water supply, it would bebeneficial to require some on site disposal of roof water, or to encourage rainwater reuse through storagetanks.

(c) Option 3: Biofiltration Practices in the form of Swales for Roads

The use of swales has been recommended within the catchment in conjunction with roads,where grades are no steeper than 4%. There will be a small locally beneficial response in termsof attenuation, however, this is not evident over the whole catchment, as swales will only beused adjacent to roads where the grade is appropriate. The primary benefits from the use ofswales are in water quality improvement, which are not reflected here.

8.1.4 Results from the ARC Runoff Volume Model

The ARC Runoff Volume model allows a comparison of the effects of development on theannual volume of baseflow, storm flow and total runoff. Baseflow is the sustained residualflow in streams due to groundwater inflow or release of flow from the soil. Storm flow is thedirect runoff that is generated during a storm event.

Urbanisation or development of a catchment tends to decrease baseflow, while increasing stormflow and total runoff volume. Incorporating LID will assist in reducing the negative effect ofdevelopment by addressing:

The reduction in baseflow, and the

Increase in storm flow and total runoff volume.

The use of LID techniques will reduce runoff volumes and hence the required size of waterquality / flood detention ponds and resulting Council infrastructure start-up costs within thecatchment, with more of the costs being incorporated within each development site. Reducing



the increase in storm flow and total runoff volume will reduce the effects on stream erosion andsedimentation. Similarly, maintaining baseflow is desirable (particularly during low flowperiods) as this will reduce the impact (e.g. increased temperature, reduced habitat) on thefishery and aquatic ecosystems.

The benefit of reduced impervious areas and discharge of stormwater from roofs and pavedareas to ground is that the stormwater has a chance to permeate the upper soil layers. Thisresults in a decrease in storm runoff during wet periods and a corresponding increase in streambaseflow during dryer periods. Typically, the best results are obtained through reducedimpervious area (particularly in the flatter, high intensity, well draining areas), with similarresults achieved through discharge to ground. Swales have a more localised effect and aremost suitable in flatter areas (grade ≤4%). Total annual runoff volume will show slightreductions for all three LID options.

8.1.5 Preferred Approach to Flood Mitigation Design

The preferred approach to mitigating the increase in flood flows is through the use of lowimpact design wherever practicable. Stormwater detention ponds should be used as a backupto the LID techniques i.e. to provide the remaining mitigation that is not achievable throughLID alone. Mitigation design must ensure that peak flows and flood levels within thedeveloped catchment are no greater than in the existing situation as presented in this report.

8.1.6 Town Centre

It was established in the preliminary stages of this study that part of the planned Town Centre,and in particular a significant part of the adjoining residential area, is located in a floodplain(refer Map 10). We have therefore assessed mitigation measures in detail in this area to enablethe Town Centre area to proceed largely as proposed in the DET Concept Plan and subsequentTown Centre Plan.

The mitigation measures have effectively attempted to divert upstream flows away from theTown Centre and raise the Town Centre above the flood level. Measures for achieving thisinclude:

Diversion of the local catchment (future subcatchment B11B, refer Map 9), which currentlydrains through the Town Centre, and discharging it to the main stream channel.

Filling of the Town Centre to a level 0.5m above the 1% AEP floodplain (existing land use).

Mitigation measures identified in the modelling have sized flood detention ponds such thatstream flows and flood levels through the Town Centre are no greater than in the existingsituation. The diversion of the local subcatchment (B11B) to Node 70 has slightly increasedflows at this point (refer Appendix 7, Table 6.2), and the filling of the Town Centre has alsocreated a restriction in the stream channel.

In the model we have effectively moved back the limit of the Town Centre by 10m from that inthe draft Structure Plan, over a length of approximately 500m (i.e. from Node 70 to 80). A



minimum channel cross sectional area of approximately 120m2 is required at the 1% AEP floodlevel at Node 70 to the stream junction at Node 80, and approximately 150m2 is required belowa 1% AEP flood level below Node 80. It is recommended that the channel width and crosssectional area be maintained, otherwise the Town Centre would require raising by a further0.3m to stay above the flood level. Fill levels for the Town Centre are detailed on Map 11.Finished floor levels, however, will need to be up to 0.5m higher than the fill levels to provideprotection from local overland flow.

Flood levels calculated during the mitigation modelling confirm that the Town Centre area willrequire fill material of approximately 250,000m3 at a cost of $7.5 Million (30 per m3). Drainagerequirements for the local catchment (B11B) diverted to Node 70 in the future mitigatedscenario are also detailed on Map 11.

Typically, where floodplain areas are reduced (e.g. roading projects) then minimum crosssectional areas will need to be maintained at these locations. Site specific surveys should beundertaken such that the 'developed' cross sectional area is no less than the 'existing' for thegiven flood level. The effect of reducing cross sectional areas would be twofold i.e. flood levelswould rise upstream of the constriction, and flows would increase downstream. The effects ofany proposed change in stream cross sectional area should be assessed at each location prior toallowing any development to proceed.

8.1.7 Development Rules and Other Measures Required for Stormwater Management Purposes

It is recommended that the following conceptual rules be applied to all development within theEast Tamaki catchment:

Site coverage assumptions made in this report (refer Table 12) are maxima and reducing orlimiting these should be the goal wherever possible;

Low impact design should be encouraged as appropriate over the whole of the catchmente.g.

– In the low intensity zone, discharge of stormwater to ground with no reticulatedstormwater;

– Middle and lower catchments (medium and high intensity), the use of permeablepaving to reduce runoff, soakage used wherever practicable / soils suitable;

– Swales on the flatter (<4%) roads will provide treatment;

All floodplains must be protected from development and remain free of any obstructions tothe flow i.e. no development, buildings, fences, etc. This includes:

– Earthworks filling of the principal floodplain in the flood protection areas (part of theenvironmental corridors) is not allowed, as this will increase flooding in adjacent anddownstream areas. Minimum channel widths and cross sectional areas are required tomaintained channel capacities.

– Finished floor levels should be set above the 1% AEP flood levels, typically withfreeboard of 0.5m to 1.0m. They will also need to be up to 0.5m higher than groundlevels to cope with localised overland flow issues.



– In flood plain areas outside the stormwater reserves, ground reshaping associatedwith development may result in a change to the location and shape of the flood plain.However, the development must recognise the presence of a flood plain or secondaryflow path, and ensure that it is protected so there is a clear flow path withoutobstructions, and houses are not flooded. The new (post-development) floodplainmust be defined and included on an updated flood hazard map.

For any development area secondary flow paths need to be identified, and rules requirethat during site development the secondary flow paths be identified for each subdivision,and protected from inappropriate development. This will typically include:

– Identifying them on a hazards map

– Ensuring that buildings are not placed at risk within a flow path, and

– Fences or other structures do not block the flow paths and direct flow into buildings.

The pond layout given in Map 9 is based on the protection of important streams, and providingmaximum capture of runoff from development areas. It is able to achieve the managementplan objectives. In the event of multiple ownership and development in a sub-catchment,Council is able to put the pond in prior to development, and require each development toconnect to the pond as and when that development occurs. In the case where a single ownerdevelops most of a sub-catchment, they may prefer to develop the pond themselves, as part oftheir overall work on the site. In either case, there is the opportunity for the pond layout to bechanged, so long as the following criteria are met:

– There must be no reduction in the total development area captured to ponds

– The pond performance in aggregate should be equivalent to that indicated inAppendix 7 for the pond(s) that the alternate layout replaces;

– Land ownership must be resolved such that Council has ownership or easement rightsover the new pond site(s), sufficient for access and maintenance;

– If the reserve land previously identified for the pond is no longer needed with the newpond arrangement, that it not be retained as stormwater reserve unless there are otherspecific reasons for doing so.

The modelling carried out in this report is based on the use of existing 0.5m contourinformation only. Flood levels given in this report are therefore indicative only, theyshould be used as a guide and cannot be relied on for design. For better local definition ofthe floodplain, a site-specific survey should be undertaken to estimate the local hydraulicconditions, which may change as a result of development. Development must not result inhigher levels than shown. Council should require detailed stormwater reports as part ofany development applications to confirm flood hazards, flood levels and the ability tomanage stormwater (and development phase sediment) within a site.

The hydraulic modelling for the flood plains did not include specific modelling of culvertscrossings. In many cases these culverts are likely to be undersized for the standardsrequired for urban development, and probably result in spill over the road more frequentlythan is acceptable. Further, there will be additional crossings as yet not identified or sized.The flood plain model therefore provides indicative levels assuming appropriatelydesigned crossings, and design flows are also provided in Appendix 7. These should be



used in the design of culverts and stream channel improvements (related to riparianplanting and stream enhancement) to ensure that they are built to an appropriate standardto cope with the design flows and to not exceed the indicative flood levels.

Stormwater discharge from all development areas to be treated in accordance with ARCTP10 as a minimum. Attenuation of runoff from 25mm of rainfall to be held and releasedover 24 hours. Flood peaks in the 100 Year ARI events to be attenuated in accordance withthe specific subcatchment requirements of this plan.

As development proceeds there will be new information on the channel and crossings,which can be used to update the model and ensure that the design flood levels reflectreality. This should be undertaken whenever significant changes have occurred to theconveyance system, and the result updated on the Council GIS.

(a) Future Subcatchment

It should be realised that the proposed future drainage sub-catchments provide for a strategicoverall framework for the planning of development. Omitting to attenuate adequate runoffvolume from one or part of a subcatchment during development is possible, however, thedetention volume which has been omitted needs to be catered for further downstream or inadjacent sub-catchments and the consequence from the unmitigated portion of the runoff mustbe clearly documented. This is a key role for the catchment manager.

(b) Stormwater Pond Location

In setting the pond locations, ponds were located only in the designated green finger corridor,and efforts made to ensure they did not impact on any existing land use. This assumes that thedesignated green finger corridors by MCC do not encroach on any existing houses in the area.There may be some locations where green finger corridors could impinge into existing houses.It is noted however that ponds were assigned at a strategic level only and hence, there will bepoints of detail that should be addressed and resolved as development progresses.

In identifying the environmental corridors, tentative ponds sites were also included as part ofthe green finger corridors. It is noted that during the final placement of ponds from themitigated model results, some ponds were smaller than originally anticipated, and thereforemay have moved slightly from the original tentative pond site. One example is the pondtreating subcatchment B10B. In these cases, there is an opportunity to tighten the green fingersfurther. This has not been included in the current mitigated model, however the approachadopted by Council in vesting areas for environmental corridors provides some flexibility withrespect to those areas surrounding ponds.



8 . 2 E n v i r o n m e n t a l C o r r i d o r Z o n e 6

8.2.1 Functions of Environmental Corridors

The green fingers form a range of functions during both the development phase, and long term.These areas have been a part of the vision for the future of the catchment since the early stagesof the concept planning undertaken by Council. The DET Concept plan recognises the range offunctions these corridors will have, including:

protection and enhancement of the biodiversity of the study area

protection and reinstatement of sensitive marginal areas from inappropriate development

flood protection / storm water disposal

water quality control

multiple recreational functions including

– passive reserve,

– integrating with neighbourhood reserve,

– walkways, cycle ways, bridle trails

high quality amenity for the surrounding urban environment

providing a strong legible natural element for the wider built environment.

Throughout the catchment management process the functions of these green fingers have beenclosely examined. The preservation of stream systems in urban environments has historicallybeen relatively poor in Auckland, with many stream systems used for direct and uncontrolleddischarge of stormwater from roads, residential, industrial and commercial areas, car parks andso forth. This has created in many instances degraded and polluted waterways of littleecological or habitat value. The protection of the stream system, including the 100 year floodplain and a significant adjoining corridor for public open space purposes will result in a muchimproved approach to stormwater and stream system management. The approach adopted isconsistent with the purpose and principles of the RMA, the RPS and other documentscomprising the strategic framework for the development of the CMP.

While alternative approaches to stormwater management are available, these would notachieve the same degree of flood plain protection or stormwater quality treatment. In addition,more conventional approaches would not resolve the need for other outcomes to be achieved inthe catchment, such as increasing biodiversity, creation of urban amenity, meeting the passiveand active recreation needs of the community and so forth. The green fingers therefore performa range of functions, and represent a change towards a more appropriate and ultimatelysustainable urban form.

6 Throughout the consultation process, these zones have been referred to as “green fingers”. This term is usedgenerically in this report to refer to the restoration areas in the upper and lower catchment.



8.2.2 Determination of Environmental Corridors

This CMP identifies a range of landscape, amenity, water quality, flood attenuation and generalcatchment management requirements of the environmental corridors. In setting the greenfinger corridors, the following basic framework was used:

First order streams/upper catchment/low density - 50m minimum width

Second order streams/medium/high density - 80m minimum width

Third order streams (main streams)/lower catchment/high density - 100m minimumwidth

In addition, the following allowances were also included:

Pond locations. Initially, 2% of future subcatchment drainage area was used toapproximate the pond size. The pond sizes were confirmed with the final mitigation model.

Protecting headwater streams

Protecting existing major bush areas

Incorporating riparian planting in the green finger corridors to the top embankment. Thisincludes ensuring planting continues along all steeper banks and areas which are too steepfor building roads. Roads were assumed to be constructed adjacent to and along theriparian corridor.

Overall, to decide the width of the riparian corridor, it was ensured that the riparian corridorwould

encompass the modelled 100 year existing flood plain

meet the respective minimum corridor widths (50m / 80m / 100m) set above

include any steep areas with planting up to the top of embankment

include areas which are too steep for roads i.e. road (cross slope) steepness of minimum1(V):5(H)

The original environmental corridors identified in the DET Concept Plan have been reworkedusing the specifications discussed above. Where the original corridor met all the abovespecifications, it has been maintained (i.e. it was not changed). In a number of situations, theposition of the original environmental corridor was either "misaligned” with the streams or didnot meet these specifications. In these situations, a new alignment of the environmentalcorridor which meets the above specifications was identified. It is noted that the "new"environmental corridor identified in this CMP does not include the road reserve that isproposed alongside a number of corridors by MCC through the concept/structure planningexercises undertaken for the development of the Draft District Plan Variation.



8.2.3 Securing the Environmental Corridors

One of the key catchment management objectives is “to secure the protection and enhancementof the ‘green fingers’ in the lower catchment”. In relation to the lower catchment securing theenvironmental corridors is important, as these areas provide the basis for stormwatermanagement, ecological enhancement, amenity and so forth.

A range of mechanisms are available to Council to secure the environmental corridors. Beforeconsidering these mechanisms, it is important to note that the corridors consist of two parts:

The 100 year flood plain, which would not be suitable for residential urban development(or habitable buildings); and

The public open space component, which overlies an underlying urban zone, and whichenables additional amenity, landscape, recreational, and water quality objectives to be met.

While these two parts of the corridor can be distinguished, for the purposes of securing thesecorridors, and to ensure they are seen as an integrated package, they are considered as a single‘land use’.

(a) Options

Table 22 identifies a number of mechanisms that could be utilised to secure the environmentalcorridors. A brief description of each mechanism is provided, and an assessment of the keyadvantages and disadvantages of each mechanism to Council. The key mechanisms examinedare:

Do nothing;

Public Open space zoning;

Deferred POS Zone and designation with staging;

Designation;

Vesting through subdivision process.

Table 22: Evaluation of Mechanisms to Secure Environmental Corridors in Lower Catchment

Mechanism Description Pros ConsDo Nothing Rely on subdivision

process to set asidegreen fingers to anappropriate ‘width’.

Potentially lowest costimplications forCouncil providedreservation of greenfingers does not goabove reasonable level(e.g.7%).

No certainty

Take longer time toachieve

No environmentalprotection in placefor developmentstage.

No integratedmanagement.

Receivingenvironmentcompromised.

Public Open SpaceZone

Zone land as POS,and limit thepotential for

Zoning does notcreate purchaserequirement.

Floodplainsprotected on privateproperty – no control



Mechanism Description Pros Consdevelopment withinthe zone. Enablesome developmenton the edge of thezone.

Can managefloodplain throughconsent conditions(e.g. prohibitingstructures).

over management.

Reasonable use (s85)and ‘expectation’argument may beraised.

Difficult to ensurereplanting as cost ofenhancement maynot be appropriatefor one developer.

Deferred POSzone anddesignation withstaging

Deferred POS zoneimposed invariation.Designation andpurchase to followas staging unitsreleased.

Provides certaintythat corridor will befor POS once stagingunit released fordevelopment.

Deferred POS zonewill ensure noactivities in zonewhich wouldcompromise itsintended future use.

Purchase programmecan be managed withdevelopment asdesignations proceed.

Future urban zonewell tested in terms of‘holding’development.

Administration ofdistrict planprovisions mustensure no furtherdevelopment.

Designation Designate land forwater managementand POS/ amenityunder RMA.

Land secured.

MCC gains access andcontrol over long termmaintenance ofstormwater system.

Environmentalprotection works canbe carried out withindesignation area.

Certainty forlandowners.

Flexibility oncedesignated remanagement of‘margins’.

Need clear definitionof which areasrequired for whichpurpose.

Cost of land high,cost may increase ifdevelopment anddesignation staged.

Requirement topurchase can beinvoked bylandowner oncedesignated.

Significantimplications forfunding andmanaging cash flow.

Vesting at point ofsubdivision

At point ofsubdivision eachlandowner with anarea of corridor intheir block isrequired to vest that

Council not liable forfunding corridorsfrom date of operativezoning.

More flexibility in

No certainty forlandowners orCouncil on whenaccess to corridorwill be achieved;



Mechanism Description Pros Consarea with Council location of green

fingers for developersand Council.

Rate of developmentcontrols rate ofvesting and henceenhancement.

Council maintainssome control onlocation and directionof developmentthrough provision ofinfrastructure.

Less ability forCouncil to intervenewhere specific areasof corridors arerequired to facilitatedevelopment (e.g.pond locations);

No certainty on rateof enhancement.

(b) Recommendations

From the above table it can be demonstrated that a range of planning mechanisms exist whichwould enable to green fingers to be secured. The difference between many of these mechanismsis the degree of confidence in the outcome, and also the degree of certainty provided by Councilto landowners and the community in terms of ‘if’, ‘when’ and ‘how’ the green fingers are to beacquired.

The vesting process provides Council and landowners with a great deal of certainty over theprocess for acquiring the corridors. While Council is in one sense unable to control the rate ofdevelopment, and hence the rate at which land is added to the POS network, this places asignificant degree of certainty in the hands of the landowner. Furthermore, the underlyingresidential zoning means landowners with an existing expectation of future urban developmentpotential will not have a perception of lost ‘value’ where their land is above the 100 year ARIfloodplain.

The deferred POS zone following by designation is also an approach which has significantmerit. This would ensure that the areas required for management of stormwater and provisionof future urban amenity functions are secured at the outset. Some staging of thedesignation/purchase of these areas could occur to ensure Council is able to fund the purchaseof the green fingers through development contributions. The use of the designation procedurein the RMA also provides Council with the ability to overcome any issues which may occur inrelation to the direction or rate of development, where landowners chose to avoiddevelopment, thereby creating an ad hoc green finger network. There are also a number ofinherent difficulties with this process which are discussed later in section 8.5.

8.2.4 Design of Corridors – Riparian Recommendations

The design and function of the environmental corridors are critical, as these areas form one ofthe fundamental components of the future urban fabric of the DET area. Indicative crosssections that illustrate how the ‘green fingers’ could look once the ecological restoration andother works have been carried out are included in Appendix 13.



The results of the riparian and instream ecological study provided a number ofrecommendations for riparian enhancement as follows (refer to Map 2 for streamclassifications):

(a) Hill valley streams

maintain riparian vegetation as both woody and non-woody native vegetation;

retain shade at 70-100%;

encourage planting of native understorey to encourage stabilisation of banks;

encourage fencing of stream margins to prevent stock access.

(b) Lowland rolling streams

staged removal of crack willow and replacement with a mixed native/deciduous riparianmix;

aim for stream shade > 70%;

retain existing sinuous stream channel;

retain wide floodplains, these can be grassed and used for additional amenity value,and/or stormwater treatment; and migration of natural stream channel;

retain first order lowland streams as wetland areas.

8.2.5 Species Composition

The following table provides the recommended list of species for the valley or lowlandcatchment restoration area (see Appendix 3 for definition of this area), which is comprisedpredominantly of those areas within the environmental corridor network. In addition to theenvironmental corridor network, there will be other areas which will be replanted, such asprivate developments, local urban parks, schools and so forth. This species list could thereforebe provided to other landowners or developers as a preferred list. It is noted that some interestgroups would prefer to use locally sourced plants for the enhancement of the area.

Table 23: Species Composition for Lowland Catchment Restoration Area

Species Common NameCanopy TreesAlectryon excelsus TitokiBeilschmiedia tarairi TaraireB. tawa TawaCordyline australis Cabbage TreeCorynocarpus laevigatus KarakaDacrycarpus dacrydioides KahikateaDacrydium cupressinum RimuDysoxylum spectabile KohekoheKnightia excelsa RewarewaKunzea ericoides KanukaPodocarpus totara TotaraPseudopanax crassifolius Horoeka (Lancewood)



Species Common NameVitex lucens Puriri

Sub-Canopy TreesCoprosma arborea MamangiHedycarya arborea Porokaiwhiri (Pigeon Wood)Melicope simplexMelicytus macrophyllusM. micranthusM. ramiflorus MahoeMyrsine australis MapouRhopalostylis sapida NikauNestegis Lanceolata Maire

Understory Trees &ShrubsCorpodetus serratus PutaputawetaCoprosrna areolataC australis RaurekauC rhamnoidesC. spathulataCyathodes fasciculata MingimingiGeniostoma ligustrifolium HangehangeLeptospermum scoparium ManukaMyrtus bullata RamaramaMacropiper excelsurn KawakawaPittosporurn tenuifolium Kohuhu

Ferns & FlaxCyathea dealbata Silver FernC.rnedullaris MamakuPhormium tenax Common FlaxPhormium cookianum Mountain Flax

8 . 3 E n h a n c e m e n t o f U p p e r C a t c h m e n t

The enhancement of the upper catchment is a critical outcome in relation to the success of theobjectives for protection of instream and terrestrial ecological values. The headwaters are alsoidentified as being important in terms of maintaining water quality.

8.3.1 Design of Corridors – Riparian Recommendations

The following recommendations are made in relation to the enhancement and futuremanagement of the valley headwater streams (identified on Map 2).

(a) Valley headwater streams:

maintain riparian vegetation dominated by woody and non-woody native vegetation;

retain and enhance shade to 50-70%;



ensure full planting of steep-sided slopes of entrenched streams to prevent erosion of upperbanks;

include planting of native understorey to encourage stabilisation of banks;

encourage fencing of stream margins to prevent stock access.

8.3.2 Species Composition and Future Management

The following table provides a species list for those species which should be included in theupper catchment restoration area (see Appendix 3 for a definition of this area).

Table 24: Species Composition for Upper Catchment Restoration Area

Species Common NameCanopy TreesAgathis australis KauriAlectryon excelsus TitokiBeilschmiedia tarairi Taraire [in gullies and near streams]B. tawa TawaCordyline australis Cabbage TreeCorynocarpus laevigatus KarakaKnightia excelsa RewarewaKunzea ericoides KanukaPodocarpus totara TotaraPseudopanax crassifolius Horoeka (Lancewood)Vitex lucens Puriri

Sub-Canopy TreesCoprosma arborea MamangiMelicytus macrophyllusM. micranthusMyrsine australis Mapou

Understory Trees &ShrubsCorpodetus serratus PutaputawetaC. australis RaurekauC. rhamnoidesC. robusta KaramuC. spathulataCyathodes fasciculata MingimingiLeptospermum scoparium ManukaMyrtus bullata RamaramaMacropiper excelsurn KawakawaPittosporurn tenuifolium Kohuhu

Ferns & FlaxCyathea dealbata Silver FernC.rnedullaris MamakuPhormium tenax Common FlaxPhormium cookianum Mountain Flax



8.3.3 Securing Environmental Enhancement in the Upper Catchment

The methods for securing the protection of these areas however differ from the lowercatchment, as the areas will not be retained in public ownership. Rather, the preferred approachis to secure the enhancement and protection of the green fingers at the point of subdivision, anduse mechanisms such as consent conditions, bonding, and covenants to ensure enhancementoccurs longer term. The level of development contemplated for the upper catchment isreflective of the constraints imposed by the topography and stability of the area. In addition,the ridge restoration catchment identified in the landscape study recognises the area as beingimportant for framing the entire catchment.

Therefore, while the outcomes sought in the upper catchment are ultimately similar to thelower catchment, leaving the area in private ownership means enhancement must be securedthrough other means.

(a) Options

The range of options which may be pursued in relation to the upper catchment area:

Do nothing;

Consent conditions

Bonding;

Education / Awareness

Incentives;

Monitoring and Enforcement.

The following table identifies a number of mechanisms that could be utilised to secure theenhancement of the areas identified in the structure plan / catchment management plan. Abrief description of each mechanism is provided, and an assessment of the key advantages anddisadvantages of each mechanism to Council.

Table 25: Evaluation of Mechanisms to Secure Environmental Enhancement in UpperCatchment

Mechanism Description Pros ConsDo Nothing Rely on landowners

/developers to replant andenhance stream corridors asa part of improving their site.

Area may slowlybecomereforested atlittle or noexpense toCouncil.

No certainty

Take longer timeto achieve.

ConsentConditions

Include provision invariation which requiressteam/steep slopereplanting/enhancement attime of subdivision.

Providescertainty.

Can be securedat time ofsubdivision.

Can be enforced.

Othermechanismssuch as bonding

Does notguaranteeoutcome will beachieved, relieson subdivisionoccurring.

Enforcement canbe costly.



can be utilised toensurecompliance.

Bonding Associated with condition ofconsent. Requires bond to beheld by Council to be used inthe event replanting fails oris not carried out.

Providescertainty thatoutcome will beachieved.

Costly toadminister.

Long termmaintenancedifficult toenforce onceestablished andbond released.

EducationAwareness

Encourage landowners toreplant steep slopes/streams.

May achieve agreater level ofbuy-in andawareness forlonger termmanagement.

No certainty.

Not necessarilygoing to convinceall people.

Incentives Provide rating relief,discounted material (e.g.plants) to those landownerswho choose to replant.

Providesfinancialassistance toachieve outcome.

Providing plantsensures speciesand sourcesuitable.

Recognises that acertain level ofexistingsubdivision hasoccurred inupper catchmentwhich would nototherwise beenhanced.

Likely to meanlandowners/developers recogniseCouncils thrustto achieveoutcome – mayachieve morebuy-in.

May be perceivedelsewhere inMCC as being a‘subsidy’ – otherlandowners whohave done thesame thing mayrequest rate reliefor other sucheconomicincentive.

Difficult tobudget for.

May placeincreasedemphasiselsewhere onfinancialcontributions.

Covenant Attaching notices to titlesthat future subdivision is notpermitted, or that certainareas of the land parcel areprotected as open space.

Provides highlevel of certaintythat oncesecured throughsubdivision,further land useconsents cannotjeopardiseenvironmentalgains.

Can limitflexibility forfuturelandowners.

Monitoring andenforcement

Required on any option toensure outcome beingachieved.

Enforcementprovidesbackstop toregulatory

Can be costly,and requiresconsistentapproach.



means.

Often onlyrequired for 5%of cases.

Provides recordof effectivenessof differentapproaches andattainment ofoutcome.

(b) Recommendations

The most proven and viable mechanism for securing the enhancement of identified areas in theupper catchment is through subdivision consent conditions. In practice, a range of mechanismscan be used in combination to provide a suite of measures in recognition of the range ofcircumstances and pressures present in the upper catchment. For example, there has alreadybeen a degree of subdivision in the upper catchment, and thus consent conditions cannot beimposed retrospectively. This requires a more considered approach, which may includeseducation and awareness programmes, incentives and so forth.

One of the key issues in the process of securing enhancement through subdivision is that thereplanted areas are maintained over time to provide the environmental enhancement andmitigation that is anticipated. Council could provide information on species composition,management of replanted areas, weed and pest management and so forth. It is recommendedthat each subdivision application should include a management plan for the planting andmaintenance of any such areas proposed. Bonding should be used where possible to ensure theoutcomes stated in the management plan are achieved before allowing development toproceed. Over the longer term, covenants are a useful tool to secure the ‘open space’components of the subdivision, whether part of the private green finger network or otherwise,as future decision making on resource consents cannot be guaranteed.

Communal ownership of planted areas is one approach that could enable integratedmanagement of the replanted areas into the future. While this is likely to have benefits, Councilmay be limited in its ability to “impose” communal ownership, except through covenanting atthe point of subdivision, where the limit would be on the extent of area proposed to besubdivided at any one time. The development of management guidelines for replanted areasfor all landowners in the upper catchment may reduce the need for communal management toa degree, as all landowners will have the opportunity to adhere to similar standards ofmaintenance of the areas on their respective properties.

8 . 4 S t a g i n g D e v e l o p m e n t o f t h e C a t c h m e n t

‘Staging’ is the process whereby Council manages the release of land in ‘staging units’ for urbandevelopment. This may be achieved in a number of ways, such as leading developmentthrough provision of infrastructure, however the District Plan is considered to be the most



effective mechanism to achieve staging. Two key issues arise in respect of staging, and theseare:

The principles used to determine ‘when’ areas of land (“Staging Units”) are released forurban development; and

The principles used to define the ‘extent’ of Staging Units areas.

8.4.1 Staging Objectives

The reason staging of development needs to be considered in East Tamaki is to ensure theobjectives sought for the area are achieved, and also to assist Council in managing the costs ofgrowth. Staging of catchment development may therefore achieve a number of goals,including:

Ensuring an adequate supply of land is available to cater for population growth, includingchoice of housing types.

Ensuring suitable environmental mitigation measures are in place so that urbandevelopment will not compromise important values within, or downstream of, thecatchment;

Ensuring wider strategic goals of Council (or the ‘Southern Sector’ of the Region) are ableto be met;

Ensuring specific land use standards are met, such as appropriate densities.

Ensuring any costs of growth incurred by Council can be recovered.

Minimise construction related sediment.

Minimise general disruption to the community from an uncontrolled staging programme.

8.4.2 Approaches to Staging

The staging of development is inevitable even without Council intervention. Market andpopulation pressures are not likely to result in the East Tamaki area being urbanised within ashort period of time (e.g. 5 years). Managing the staging and release of staging units, and theenvironmental effects associated with that development will be an important role for Council.

As noted above, there are a number of goals that can guide the staging of growth anddevelopment in the East Tamaki Catchment. These goals could be achieved using a number ofdifferent conceptual approaches to staging, including:

Capacity based staging: new areas of land are released for development once the existingurban area has reached capacity for accommodating growth. This is essentially demanddriven.

Time based staging: new areas of land area released for development at a specific point intime identified in the District Plan.



Value or Constraint based staging: new areas of land are released as appropriateenvironmental enhancement or mitigation measures are in place to protect specified values(e.g. water quality) to a specified standard.

In practice, the most appropriate staging strategy will need to involve a combination of theseapproaches, in addition to relying on a number of different RMA or other tools to achieve theoutcomes required (e.g. environmental protection). Therefore, each approach establishes aparticular ‘bottom line’ that needs to be identified and established in the District Plan as themeans by which staging is controlled.

From a broader perspective, staging must be growth or capacity based, to ensure an adequatesupply of land is available to cater for growth, which may occur at greater or lesser thanpredicted levels. Servicing growth will also be a key consideration. Some parts of thecatchment are likely to be able to meet their own servicing requirements, and thus someadvantage may accrue from allowing these areas to be developed first. In particular, thoseparts of the upper catchment, where countryside living is proposed may enable replantingriparian areas in these crucial headwater streams.

Identifying sub-catchments and utilising these as a basis for staging development will ensurethe financial contribution framework is able to deal directly with relevant environmental issuesas they arise. Identifying the most beneficial use of financial contributions will also form asignificant component of the staging strategy.

8.4.3 Identifying Staging Units

Identifying the spatial extent of staging units requires consideration of a range of factors. Thefollowing principles or factors were considered to provide a suitable basis for defining theboundaries and areas of staging units within the catchment:

“Future” stormwater sub-catchment boundaries used as a basis for determiningboundaries,

Boundaries to follow ‘land parcels’ where practicable to acknowledge likely developmentsequences associated with land ownership;

Provision of open space focal points;

Provision of a range of land use types (e.g. high density, medium density areas)

Provision of appropriate primary transport network, including ability to service area withappropriate passenger transport services;

Provision of and/or proximity to appropriate social and community services (e.g. schools,town centre).

Ability to manage effects associated with construction and development of staging unitwithin the unit itself or the upper catchment (e.g. sediment loading).

Proximity to adjoining urban areas (i.e. avoid ‘pockets’ of urban areas developing in uppercatchment in isolation);

Ability to fund the costs of growth.



Sufficiency of size to provide an adequate land bank for development , but not too muchland as to ‘swamp’ the market.

Two key considerations emerge in terms of managing the environmental effects of urbanisationin this catchment. These are staging issues associated with stormwater management, and themanagement of sediment generation as each staging unit is developed.

(a) Stormwater Management - Staging issues

There is some flexibility in staging, in respect to stormwater management. Key requirementsfor an area to be developed are:

appropriate Rules be in place to control the development and ensure designs meet thestormwater management objectives

any major stormwater management devices (e.g. ponds, swales) required to serve asubdivision area be in place prior to any development on that area, or be incorporated aspart of that development.

It is desirable that replanting in the upper catchment commence early in the developmentprogramme. However, there is no specific requirement that it be complete prior to downstreamdevelopment. The measures proposed for the upper catchment do not include any majordevices, and therefore development can proceed according to demand, subject to replantingand other on-site stormwater management measures being part of each development.

Proceeding with the downstream development on a catchment-by-catchment basis would bedesirable, but not essential. This approach would facilitate the inclusion of the streamenhancement as part of the development in each catchment, providing a more coherentapproach. In this respect, development could proceed on a radial basis, with a band from theCentre to Gracechurch Dr moving progressively south, and one from the Centre to RedoubtRoad moving progressively north. This would provide for a catchment based developmentwhich also maintained a range of development densities and market choices available at anytime. However, the establishment of mitigation measures at the lower end of eachsubcatchment could enable development to proceed in any order from a stormwaterperspective. Consideration of other infrastructure provision would however likely require amore planned approach to staging.

“Future subcatchment” areas are defined as those draining to a particular stormwatermanagement device. In many instances these vary from existing subcatchments, e.g. indownstream areas each side of the stream must be treated separately, but it is possible tocombine flows from two tributaries into a device at the confluence. These “futuresubcatchments” provide a basis for building up development parcels to manage the staging andrelease of land for subdivision.

(b) Managing effects of Development

The effects of sediment generated during the development phase and managing those effectsthrough appropriate construction techniques are relevant issues that need be addressed by theCatchment Management Plan.



i. Effects of sediment inputs

The effect of sediment inputs on the receiving environment of the East Tamaki catchment is amatter that Council has a particular responsibility for addressing when proposing a variation tothe District Plan which will enable urbanisation of the area. Tables 17 nd 18 give a broad-brushassessment of the likely effects of sediment inputs during earthworks construction associatedwith each staging unit. The sediment yields need to be considered by Council in the context ofthe goals that have been agreed with the Community for the Otara Lake. Within the catchment,this effect is dependent on the existing stream characteristics – for example, lowland streamswith fine sediment beds are likely to be less vulnerable to sediment inputs than cobblestone-bedded streams with good pool/riffle runs.

ii. Construction management

All site development must be done in accordance with ARC requirements, specifically TP 10.In addition, the run-off from each development site must pass through a stormwater pondbefore reaching the stream wherever practicable. This will provide backup to the TP10requirements, as well as covering the “building” period of development. Constructionmanagement may include a number of measures to reduce the impacts of this key phase ofdevelopment on the receiving environment. The staging of development over a period of years,partly through the provisions of the District Plan and partly as a result of market demand,assists in “distributing” development and hence its effects over a period of time. It is recognisedthat the Auckland Regional Council will play a significant role in this aspect of managing thedevelopment of the catchment.

iii. Timing Flexibility

In relation to the flood peak attenuation and stormwater quality treatment devices proposed(primarily ponds) there is some flexibility in terms of the timing for the completion of these.During the development phase, these stormwater ponds will provide a backup to the TP90sediment management requirements which all developers should meet, and will also attenuatethe flood peaks off the bare land under earthworks. As such, each pond should be in placeprior to development occurring in its contributing subcatchment. The timing of construction ofthese ponds is dependant on the timing of development in the subcatchment concerned. Insome situations, Council may need to take a lead role in facilitating the construction on pondsidentified in this CMP where indicative pond locations are owned by landholders who havediffering development timeframes to those ‘upstream’. In other situations, where a singledeveloper holds all the affected land it is likely to be more cost-effective that the developerbuild the ponds as part of their earthworks and site development.

8.4.4 Population Growth Forecasts

The population forecasts for the East Tamaki area assist in providing a framework fordetermining the ultimate level of development for the catchment. This will enable amongstother things:

Estimation of the level of community facilities to be provided;



Estimation and long term asset management to enable infrastructure provision capable ofmeeting needs of both the population and the environment.

Estimation of the cost of growth and determination of the financial contributions.

The growth predications provided in the following graph for East Tamaki have been suppliedby Manukau City Council and are based on a medium growth rate projection:

Note that for 2001 the 500 person increase is in the main residential areas on the fringe of the DET area. For

2002 it is estimated that 500 persons would be in the fringe Main residential areas.

8.4.5 Development East Tamaki Staging Units

Two staging units have been identified for the Development East Tamaki area. These havebeen determined using the above principles. Initially, a series of smaller staging units wereidentified based on drainage sub-catchments. Analysis of the financial and infrastructurerequirements for the development of each of these units, plus the forecasted populationpressures required the amalgamation of smaller units into larger ones. The extent of eachstaging unit is illustrated on Map 13.

(a) Staging Unit 1:

This staging unit consists of two key ‘sub-areas’, the upper and the lower catchments. Firstlythe main component of the staging unit which consists of the area in the north of the catchmentwhich has been identified for medium and high density residential development, and whichalso includes the town centre. While the development of the town centre may not progressimmediately, due to the need to ensure sufficient population exists to support the centre, thereare currently pressures in this part of the catchment for residential development. This part ofthe catchment also includes one of the most significant parts of the stream system, and as such,release of this area early in the development process will ensure the protection and

DET Population Growth

0

5000

10000

15000

20000

25000

30000

35000

40000

45000

50000

2000

2002

2004

2006

2008

2010

2012

2014

2016

2018

2020

2022

2024

2026

2028

year

pop

ula

tion

.



enhancement of riparian margins, the stream system, and other important environmentalvalues.

The following table provides the land uses, corresponding zones and area of land included inthe lower catchment component of staging unit 1:

Land Use Corresponding Zone (whereapplicable)

Area(ha)

Urban Park Existing 105.2Conservation Public Open Space 6 – Environmental

Corridor Zone Overlying Zone84.8

Medium Intensity Residential Flat Bush 2 Residential Zone 110.1High Intensity Residential Flat Bush 1 Residential Zone 246.5Existing School Existing 2.4Vehicle Orientated Retail Existing 2.0Town/Neighbourhood Centre Town Centre Business Zone

Neighbourhood Centre BusinessZone

22.7

Total Stage 1 Area (Lower Catchment) 573.7

The second part of staging unit 1 relates to the upper catchment. This area has been identifiedfor countryside living purposes, with lot sizes ranging from 2-5000m2 or above. This part ofthe catchment includes some relatively steep and unstable slopes, the prominent ridgeline, anda number of important headwater streams. The protection of steams and steep slopes in theupper catchment is an important component of the overall catchment management plan, asthese areas have an important influence on ecological diversity, water quality and provideimportant habitat for kokopu and eel amongst other species. Securing the protection andenhancement of these areas will be through subdivision consents and conditions attached tothose consents. These areas are released in the first stage as it is anticipated that the rate ofdevelopment in this zone is likely to take some time, perhaps as long as 15 years. It is thereforeadvantageous to allow this to occur as soon as possible, and enable the ecological enhancementassociated with subdivision to be secured. As with the enhancement elsewhere in thecatchment, the environmental benefits that are associated with replanting in the uppercatchment will increase with time as vegetation matures.

The following table provides the land uses, corresponding zones and area of land included inthe upper catchment component of staging unit 1:


Area(ha)

Existing POS Existing 17.5Conservation Conservation/Stormwater

Management Overlying Zone178.6

Low Intensity Residential Flat Bush Countryside Living Zone 358.6Total Stage 1 Area (Upper catchment). 554.7



(b) Staging Unit 2

Staging Unit 2 is located in the southern part of the catchment. It includes the most significantnatural area in the catchment, Murphy’s Bush. In addition, this staging unit includes asignificant amount of stream system. Of particular importance is that the stream system in thisstaging unit will ultimately provide a linkage from the upper catchment to the lower catchmentand beyond to the receiving environment (Tamaki Estuary). Again, the basis for theboundaries of this staging unit are future subcatchment boundaries, with some adjustment toenable development to occur in relation to existing land parcels.

The following table provides the land uses, corresponding zones and area of land included inthe lower catchment component of staging unit 1:


Area(ha)

Existing POS Existing 18.3Conservation Public Open Space 6 –

Environmental Corridor ZoneOverlying Zone

118.3

Medium Intensity Residential Flat Bush 2 Residential Zone 232.7High Intensity Residential Flat Bush 1 Residential Zone 153.6

Total Stage 2 Area 522.9

(c) Capacity of Staging Units

In order to ensure the staging units are of the right order in scale, it is important to establish thecapacity of each staging unit and attempt to correlate this with projected population growth.The reason for this is that the Council must provide sufficient land to accommodate anticipatedgrowth. Manukau City Council aims to have sufficient land zoned for urban purposes for 16years supply. While the availability of land across the City is not a consideration for thecatchment study, the DET area provides a significant contribution to that 16 year goal.

Analysis presented in Section 8.4 confirms that the target population for the catchment ofapproximately 45,000 people is achievable. Staging Unit 1 can accommodate about 22,000people, which based on population projections, would mean that it would be nearing capacitywithin 10 – 11 years. Staging Unit 2 can accommodate a population of about 20,000, and usingCouncil population projections, this would mean the catchment could be fully developedwithin about 20 years. About 3,000 people would be accommodated in the upper catchmentareas released concurrent with stage 1.

8.4.6 Consistency with staging principles.

The following table provides an assessment of the staging unit boundaries proposed (see Map13) against the principles identified earlier in this section.



Table 26: Consistency with Staging Principles

Assessment of Proposed Staging Units Against PrinciplesStaging PrincipleStaging Unit 1 Staging Unit 2

“Future” stormwatersub-catchmentboundaries;

Boundaries have been determined using sub-catchment boundaries andadjusted to follow existing land parcel boundaries to ensure developmentcan be easily managed. Where areas are inside or outside subcatchmentboundaries, a decision on whether they should be within staging unit 1 or2 was made based on the ability to mitigate the effects of thatdevelopment through the pond system.

Provision of open spacefocal points;

Barry Curtis Park is a significantfeature of this staging unit. Inaddition, a significant area ofenvironmental corridors isincluded.

Murphy’s Bush and the surroundingarea to be included in theenvironmental corridors provides asignificant focal point for this stagingunit.

Provision of a range ofland use types (e.g. highdensity, mediumdensity areas)

Staging Unit 1 provides for thegreatest diversity of land uses,as it includes the town centre,low, medium, and high intensityresidential land uses. Thedevelopment of higher densityresidential development alongthe environmental corridors andin areas adjacent to accesscorridors and thetown/neighbourhood centresshould also ensure an earlyindication of the success of theDistrict Plan and overallconcept.

Staging Unit 2 provides for a range ofresidential development, althoughprincipally medium and high densityresidential. While the countrysideliving areas in the upper catchmentare released with staging unit 1, it isanticipated that there will be capacityin this area remaining when stagingunit 2 is released.

Provision ofappropriate primarytransport network,including ability toservice area withappropriate passengertransport services.

Both staging units are well served by access corridors. Existing roadswould be progressively upgraded as development proceeds, andneighbourhood centres have been located through the structure planningprocess to ensure passenger transport services can operate efficientlythough them and surround neighbourhoods. The development of TeIrirangi Drive will assist in the accessibility of both this area and thecorridor from Manukau City Centre through Botany Downs and furthernorth.

Provision of and/orproximity toappropriate social andcommunity services(e.g. schools, towncentre).

The provision of community facilities is a matter, which will occur asdevelopment proceeds. There are no restrictions to the availability ofland for these facilities. The draft variation also enables certaincommunity activities to occur in the environmental corridors whereappropriate. Co-locating community facilities adjacent to or within theenvironmental corridors will create an advantage in terms of maximisingthe use of open space. This is a matter to be considered and addressed asdevelopment occurs.

Ability to manageeffects associated withconstruction anddevelopment of stagingunit within the unititself or the uppercatchment (e.g.sediment loading).

The presumption in relation to the boundaries established for eachstaging unit is that the effects of development within each subcatchmentcan effectively be managed/mitigated within that subcatchment. Pondslocated at bottom of each subcatchment within the green finger networkwould be required ahead of any development in a particularsubcatchment to the size and performance standards specified in thisCMP.

Proximity to adjoiningurban areas (i.e. avoid‘pockets’ of urban areas

The greatest pressure fordevelopment is presentlyoccurring in the north of the

The second staging unit is slightlymore ‘isolated’ from currentdevelopment pressures, and also from



Assessment of Proposed Staging Units Against PrinciplesStaging PrincipleStaging Unit 1 Staging Unit 2

developing in uppercatchment in isolation).

catchment. Enablingdevelopment to occur in thenorthern part of the catchmentin the first staging unit shouldenable Council and otherinfrastructure providers tomanager expenditure andinfrastructure provision in anefficient manner. While it isanticipated that developmentwill progress from the north intothe catchment, pockets of urbandevelopment across the stagingunit should not pose a risk tothe overall concept as thestructure planing process hasbeen relatively detailed and setsclear performance requirementsfor developers.

other centres such as Botany Downs.The eastern part of the staging unitwhich is the majority of the area ispresently outside the MUL and hasnot been identified in the District Planas being for future urban purposes.

Ability to fund the costsof growth.

Staging unit 1 includes the upper catchment area and a portion of thelower catchment areas. Staging unit 2 includes the ‘upstream’ portions ofthe lower catchment. Each contains a diversity of features intended toenhance the development of the catchment as a whole. The lowercatchment portion of stage 1 has a predominance of the stormwatermanagement devices serving the needs of the catchment as a whole.Stage 2 includes a predominance of the environmental corridors. As aconsequence it is appropriate that the approach to assessing financialcontributions is applied to the catchment as a whole. This approach willensure an equitable assignment of growth costs to the communitiescausing the effects.

Sufficiency of size toprovide an adequateland bank fordevelopment, but nottoo much land as to‘swamp’ the market.

Both staging units are of significant size, and based on the capacitycalculations recorded in the previous section, staging unit 1 would reachcapacity in 2010, and staging unit 2 would reach capacity in 2020.

8 . 5 F u n d i n g G r o w t h D e v e l o p m e n t

8.5.1 Features of development

The Structure Plan for proposed development of the East Tamaki area breaks the available landinto two broad categories.

Developable land.

Land excluded from development.

The 1613 ha of land within the study area is divided as follows:

(a) Developable land

i. High density (Flat Bush 1 Residential Zone)



About 423 ha located generally on the present flat to moderately rolling pastureland are to bezoned high density. An anticipated yield of 20 lots per hectare (equivalent to a net lot area ofabout 250m2 per lot7) is proposed. With an assessed occupancy rate of 2.7 persons per lot thiswill provide for a population of about 22,830.

ii. Medium density (Flat Bush 2 Residential Zone)

A further 343 ha also located generally on the present flat to moderately rolling pastureland areto be zoned medium density. An anticipated yield of 15 lots per hectare (equivalent to a net lotarea of about 400m2 per lot8) is proposed. With an assessed occupancy rate of 3.0 persons perlot this will provide for a population of about 15,420.

iii. Low density (Flat Bush Countryside Living Zone)

The steeper land at the headwaters to the East Tamaki catchment has been zoned low density.The 537 ha in this zone is generally steeper land in pasture and bush. An anticipated yield of2 lots per hectare (equivalent to a net lot area of about 4,500m2 per lot) is proposed. With anassessed occupancy rate of 3.0 persons per lot this will provide for a population of about 3,225.The form of the subdivision has not been dictated.

(b) Land Excluded from Housing Development

i. Creation of Environmental Corridors

A significant feature of the proposed development is the setting aside of an extensiveenvironmental corridor network. These provide ecological and pedestrian linkages through thecatchment and are based on the present primary watercourses and as such double as providingprotection of the residential areas from flooding. It is proposed that these corridors will beimproved through replanting with native vegetation as development proceeds to recreate anappropriate ecological environment. In parallel with the stream bank improvements andreplanting, a network of pathways will be established enabling the corridors to serve aspedestrian linkages through the new community. This environmental corridor networkcomprises about 382 ha (including 178 ha in the low density upper catchment areas) of theavailable land area.

The environmental corridors in the lower catchment will be vested to council through thesubdivision process and remain in public ownership. The corridors in the upper catchmentwill be identified and may be covenanted through the subdivision consents process, howeverthe land will remain in private ownership.

ii. Other Land Uses

Land within the catchment is set aside for recreational purposes ranging in size from theextensive 106 ha (approx.) Sir Barry Curtis Park to small neighbourhood reserves. The existing

7

8 The net lot area has been assessed based all lots facing onto a 20m road reserve widths; no rear lots have beenconsidered. Land contour flat to rolling. Introduction of rear lots and cluster development with commonaccessways would increase the net lot area per dwelling.



native bush area known as Murphy’s Bush is to be set aside as an extension to theenvironmental corridor network.

Adjoining the proposed Sir Barry Curtis Park, within the high density zone, land will be setaside for commercial/retail development including provision for very high density, multilevelresidential development.

iii. Management of Flood Plains

Throughout the catchment it is proposed that residential development will not be permittedwithin the 1% AEP floodplain. The proposed “environmental corridors” contain the majorityof the 1% AEP floodplain in the study area and therefore provide much of the flood protection.However, it is apparent that floodplains associated with lowland ephemeral streams willextend into the developable areas (See Maps 10 and 14). Developers will need to designsubdivisions to avoid the potential for flood hazards in those areas. This may result in thedeveloper piping the minor watercourses and forming secondary flowpaths clear of housingplatforms to achieve the protection required and the proposed residential densities.

iv. Extension of Environmental Corridors into Low Density Areas

It is proposed that controls will be placed on the low density development in the uppercatchment areas to require the land owners/developers to create building platforms clear ofecological corridors. This land may be covenanted through the subdivision consents process.In addition the land owners/developers will be required to replant and re-establish theappropriate ecological environment. Establishment and maintenance of planting will be theresponsibility of the landowner. No public access to these upper catchment corridors isproposed. A review of the structure plan in comparison with the current land boundariesindicates that in some areas it may be difficult to achieve the proposed 2 lots per ha. (seeMap 5).

8.5.2 Implementation of Development

(a) Residential Development

Dividing the area into three staging units will control the release of land within the catchment.The release of land for development in the lower catchment has been divided into two stageswith an anticipated delay of 10 years before the release of stage 2. It is anticipated thatdevelopment will extend generally towards the south east from the existing residential land tothe north and west of the area covered by the structure plan. Although some development may“jump” ahead. The staging will encourage development to extend into the catchment from thenorth. The rules and design criteria proposed in the draft Variation to the District Plan couldresult in different urban forms. The process of determining the financial contributions fromtime to time needs to acknowledge changes in the patterns of development with time.

The third staging unit represents the upper catchment low density areas. These will be releasedimmediately and allowed to develop in an “ad-hoc” manner in parallel with stage 1. Thisfollows current development patterns in this low density area. There is a strong “vision” andeffects or outcome based rule framework in the draft Variation to manage this development. It



is noted that the “ad-hoc” development will be constrained to some extent by the limitationsimposed by road creation and extension of services.

Exclusive of land to be set aside for arterial roads, the environmental corridor network andreserves about 379 ha will be available in stage 1. This is anticipated to provide for about 10years of development. Stage 2 will supply about another 386 ha. The population and lotcreation growth is summarised in the following figures (Figures 25, 26 and 27). These figuresassume a development pattern generally from the North West to South East based onsubdivision of existing land parcels. The progression of development has been based on anassessment of population growth provided by Manukau City. The purpose of defining thedevelopment pattern is to enable an assessment of expenditure requirements in each year.

(b) Environmental Corridor Network

This network is a significant feature of this catchment as it includes setting aside about 382 ha9

of land. This represents about 24% of the total land area available for development under themanagement of the structure plan.

The land set aside for the environmental corridors will have an underlying zoning equal to theadjoining land. As such there will be no requirement for Manukau City to designate the land.Within the lower catchment council propose to acquire the land through vesting at the point ofsubdivision. The primary advantage of this approach to Manukau City is that there will be norequirement to purchase this land in advance of development. This approach will providesome flexibility in the definition of the environmental corridor boundaries enabling the abilityto permit efficiency of development. That on the other hand will also require the establishmentof positive and effective rules consistently administered by council to ensure the purpose andintegrity of the fingers is maintained and not lost in the enthusiasm of developers to maximisetheir activities. (Refer also Section 8.5.3 which comments on the need for effective standards tocontrol the development).

9 Sum of environmental corridor areas in both the upper and lower catchments.



Figure 25: Anticipated Population Growth by Year

Figure 26: Anticipated Cumulative Population Growth

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MCC Projection

High Intensity

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MCC Projection



Figure 27: Anticipated Pattern of Catchment Development



New development will generally follow the pattern of existing land parcels. A consequencewill be that many parcels, and therefore developments, will not encroach onto theenvironmental corridors and conversely some parcels will be substantially absorbed into theenvironmental corridors. In the former case the reserves contribution would be limited to acash contribution. In the latter case the Council will need to set in place policies to manage theenvironmental corridor creation (refer Section 8.5.2(c)). Owners of parcels that are substantiallyengulfed by the environmental corridors will have little incentive to develop. Council mayhave little power to compulsorily purchase the environmental corridor portion of theseproperties. The result may be breaks in the ecological network and discontinuity in thelinkages. (Refer also Section 8.5.2(c)).

It is assumed as a general principal that Manukau City will purchase the land forenvironmental corridors within the high and medium density zones as development proceeds.(Purchase means acquire by way of either vested land or a cash contribution). Manukau Citywould also take responsibility for the improvements to the watercourses and establishment ofplanting, walking paths and the like and long term maintenance. The purchase value of theland would be based on the value of equivalent land with the same underlying zoning. Thisvalue would be influenced as appropriate by the fact that some of the land would be within the1% AEP flood plain and therefore not developable.

The environmental corridor network is made up of two elements.

Land within the environmental corridors that lie within the 1% AEP floodplain. Thisportion is to be set aside for stormwater management purposes and will be funded throughthe stormwater financial contribution charged as cash on each lot created.

Land outside the floodplain to be set aside for environmental corridors which will functionas ecological enhancement, landscape, amenity, and recreation linkages across thecatchment. This reserve development will be funded through the reserve contribution.Currently this contribution is 6% of the value of the lot created. The contribution may bepaid either as reserve land vested in Council or cash.

It is anticipated that the 6% reserve contribution provision of land/cash in the upper catchmentlow-density areas would be collected as cash. The funds created would then be put towards thepurchase and creation of the environmental corridors in the lower catchment areas. It is notedthat this may be seen as double counting to those newcomers to the upper areas. They will becontributing to provision of the environmental corridors in the lower catchment and berequired to invest in the continuation of those corridors through their own land. It is to berecognised that the reserve contribution serves a wider purpose than just the creation of theenvironmental corridors. Funds raised through this contribution will also apply to theestablishment of neighbourhood reserves, sports and recreational facilities and the likesupporting the range of recreational needs of the community.

The stormwater financial contribution collected from the upper catchment would supportdevelopment of the stormwater management devices and floodplains in the lower catchment.This would assist in protecting the residents in the lower catchment from flooding effects



arising from development (creation of roads, roofs and hard stand areas) in the uppercatchment areas.

(c) Policies to Manage Establishment of Environmental Corridors

i. General Approach

As development proceeds council will require vesting of land identified for theenvironmental corridors that lie within the parcel of land under development.

Where the parcel under development does not include land identified for theenvironmental corridor (or the value of the land vested is less than) the reservecontribution (or balance required) will be collected in cash. An exception to a full cashcontribution would be where council is planning “other recreational development”utilising land within the parcel. Vesting for those purposes would offset the cashcontribution required.

Where the value of the environmental corridor land within the parcel under developmentexceeds the reserve contribution the council will purchase the balance at market values.

Where the land required for the environmental corridor is a significant portion of the landthe council may, in agreement with the landowner, purchase the entire parcel.Subsequently remaining developable land would be made available for development inconjunction with adjoining subdivision activities.

Council will need to monitor progress of development and anticipate the need to acquireparcels that are substantially included in the environmental corridor. Early negotiationswith the landowners may avoid the risk that these areas are not developed and that gaps inthe environmental corridors occur.

ii. Discontinuities in the Environmental Corridors

Discontinuities in the environmental corridors will break the linkages and limit theimprovements in ecology that can be achieved by the proposed continuous networks. Thevision of sound ecological and stormwater management within the catchment will becompromised.

It is unlikely, but possible owners within the corridor would be reluctant to sell. A possiblereason would be the owner’s perception of high value of the land when in fact the risk offlooding actually diminishes its value.

A proactive policy of identification of parcels at risk of isolation, together with a clearidentification of the flood risks on the property, in advance of development would assist thecouncil in negotiating purchase. It would be unfortunate if council found itself obliged to usethe provisions of the Public Works Act to achieve the visions for this catchment.

(d) Creation of Stormwater Management Devices

The term stormwater management device generally refers to the formation of stormwatermanagement ponds. These ponds have a dual purpose – flood mitigation and water qualityimprovement. Therefore, it is essential that these devices be installed concurrent with, or inadvance of, development proceeding. A subdivisional policy requirement will be that



development cannot proceed until the devices serving the area proposed for development areimplemented. The stormwater management devices are generally located within theenvironmental corridor network and therefore are the responsibility of the Council to establish.

There are instances within the catchment where the creation of stormwater management pondsis required on land that is outside the boundaries defined by the structure plan. This mayimpact on the ability of the Council to acquire the land. In this case the land upstream wouldnot be permitted to develop until the downstream stormwater management devices were inplace. Ponds in Sir Barry Curtis Park and immediately downstream of the study area areobvious examples. Other instances will occur when development leaps ahead, or the pattern ofdevelopment encourages subdivisions in higher catchment areas upstream of planned pondlocations.

8.5.3 Need for clear defined standards for subdivision development.

The draft Variation desired outcomes from the development that will enable effectivemanagement of the ecology and floodplains. To achieve these outcomes it will be necessary todevelop guidelines and rules that define the manner by which subdivisions are permitted toproceed. In particular, a rule framework that encourages improvement of the quality ofstormwater discharged from the streets and residential areas into the ecological watercourseswill be an important issue.

Traditional management of engineering aspects of development is defined in the currentNZS 4404 “Code of Practice for Urban Land Subdivision”. Whereas these standards have goodfundamental objectives, current practices derived from the examples in these standards do notmake room for modern techniques for management and control of stormwater, in particularlow impact design. Ultimately current practices do not promote the sustainable stormwatermanagement outcomes adopted in the “DET Concept Plan” and Catchment Management Planto protect and enhance streams. An innovative approach is required. In order to change thepresent culture of development and achieve appropriate management techniques it will benecessary for Manukau City to develop and impose standards for subdivision specific to thiscatchment, as are proposed in the draft Variation.

It is critical to the success of the Catchment Management Plan that these rules and techniquesare retained through to the District Plan. Assuming the intent of these rules is retained aneffective consent administration, monitoring and asset management programme must be seenas part of the package of policy measures to implement the visions for the area.

8.5.4 Cost of Development

(a) Environmental Corridors

The need to develop the environmental corridor network to enhance and re-establish theecological and landscape values of the catchment has been outlined in earlier sections, and is afundamental objectives of the concept for the area. A range of improvement approaches is



presented as Restoration Categories ‘A’ through ‘H’ (refer Map of restoration Categories). Inorder to determine the cost of development, these costs must be identified.

i. Riparian Restoration

The following is a detailed breakdown of the 8 major categories of restoration through differentparts of the catchment and attached costs. These have been prepared on the basis of specificpercentages (and associated unit rate costs) for recontouring, vegetation removal, topsoiling,grassing and restoration planting in relation to each category. The overall costs were based ona 1 metre strip across each category of stream / open space corridor, with 50 metres total widthallowed - encompassing the actual stream course and open space either side. As the finalstream corridors are to be wider and narrower than the 50 metres allowed for, the relevantfigures have been extrapolated proportionally. Thus a 100 metre wide corridor would costtwice as much - on a metre length basis - than the 50 metre strip used as the base. The $ ratedetermined in relation to the average corridor width for a restoration category segment is thenmultiplied by the length of that segment. E.g. a segment of the 'open pasture' category with abase costing of $60 per metre length, an average width of 100 metres and a total length of300 metres would equate to $60 x 2.0 x 300 = $36,000.

The following table includes costings that relate to the 1m x 50m strip referred to above for eachcategory and show the contributing figures allowed for recontouring, vegetation removal,topsoiling, grassing and restoration planting. A per square metre costing is also included as afinal cost to be applied proportionally to each area identified.



Table 27: Restoration Category Broad Costing Estimates

Category PlanCode

Recontouring& Vegetation

Removal

TopsoilPlacement

Grassing RestorationPlanting

Total: Totalper m2

@$3.50/m2 @$2.20/m2 @$2.00/m2 @$8.00/m2

(shrubs, etc)$/m2

Open Pasture(minimal riparianvegetation)15% regrassing;15% replanting.

A 58.00 35.00 15.00 64.00 169 3.44

Pasture &RiparianVegetation40% removal;25% regrassing;15% replanting.

B 105.00 65.00 45.00 64.00 279 5.58

Pasture, Scrub &Weed80% removal;55% regrassing;25% replanting.

C 140.00 87.00 55.00 100.00 382 7.64

Scrub & RemnantForest40% retained;50% removal;30% regrassing;20% replanting.

D 87.00 55.00 30.00 80.00 252 5.04

Pasture &Remnant Forest50% retained;40% removal;25% regrassing;15% replanting.

E 70.00 45.00 25.00 64.00 204 4.08

Pasture, Scrub &Remnant Forest30% retained;30% removal;15% regrassing;15% replanting.

F 53.00 17.00 18.00 64.00 152 3.04

PredominantlyRemnant Forest80% retained;10% removal;5% regrassing;5% replanting.

G 17.00 12.00 6.00 20.00 58 1.10

Remnant Forest /Reserves100% retained.

H - - - - - 0.00

Note these costs do not include allowance for Contractors establishment, access, and contract contingencies,design and supervision, consenting or owner administration costs. These costs can be in the order of 50-60%.



Map 12 illustrates the areas of each of the 8 categories that have been identified. These areas arebased on the stream corridors that are to be protected as part of the public systems, as these arethe costs that are of interest to Council. (Therefore, no category F areas have been included inthis assessment as these are all located within the upper catchment, which is to be restoredunder private management).

In addition, Map 12 identifies areas of vegetation outside the main environmental corridors,which have not been included in the above costing. It should be noted that some of these areasare pine forest, and may have little ecological value. The earlier recommendation in Section 3.4that a more detailed ecological survey be carried out may identify some areas of ecologicalimportance or value which should be protected by Council. In such instances, Council couldsecure the protection of these areas through negotiation with landowners, or provide incentivesfor their protection.

The following figure illustrates the total area of each restoration category identified above:

Figure 28: Total Area of each restoration category in ‘public’ portion of catchment.

Total costs of these restorations are summarised in the following table:

Table 28: Environmental Corridor Restoration Costs

Restoration Category Base Cost($/m2)

Total Cost($ per hectare)10

Area(ha)

A Open Pasture $3.44 $53,320 49.0B Pasture and Riparian Vegetation $5.58 $86,490 49.3C Pasture, Scrub and Weed $7.64 $118,420 11.9D Scrub and Remnant Forest $5.04 $78,120 26.1E Pasture and Remnant Forest $4.08 $63,240 14.9F Pasture, Scrub and Remnant Forest $3.04 $47,120 0

10 The total cost is derived by adding to the unit costs allowances for Contractors establishment, access, andcontract contingencies, design and supervision, consenting and owner administration costs.

0

100000

200000

300000

400000

500000

600000

700000

A B C D E G HRestoration Category

Sq.m



Restoration Category Base Cost($/m2)

Total Cost($ per hectare)10

Area(ha)

G Predominantly Remnant Forest $1.10 $17,050 21.7H Remnant Forest / reserves $0 $0 50.0Upper Catchment (owner managed) $0 $0 178.0

It is proposed that both the stormwater management land within the 1% AEP floodplain andthe reserve land making up the environmental corridors would receive the same restorationtreatment. The total cost of the restoration is:

Reserves $7,193,500

Stormwater Management Areas $7,298,000

Total $14,491,500

Land purchase of the reserve land is assessed to be $400,000 per ha based on the currentpurchase value of developable land. However, land within the environmental corridor that issubject to flooding would have been unsuitable for development and as a consequence have alower purchase value, $50,000 per ha. Manukau City has provided these values. These valuesprovided compare reasonably well with recent sales of developable blocks in the area. Sales in1998 and 1999 range from $275,000 to $385,000 per hectare. The higher values are adjacent tocurrent residential development, the lower values are in areas some 10 – 15 years fromdevelopment. The total value of the purchase of the environmental corridor network is:

Reserves $49,676,500

Stormwater Management Areas $5,476,500

Total $55,153,000

(b) Pathway Network

The environmental corridors will serve as an effective linkage between the various portions ofthe developed residential areas. For the purposes of this analysis it has been assumed that a1.5m wide concrete pathway will be established at least on one side of the watercourse for thefull 24 kilometre length of the environmental corridor corridors. The cost of the concretepathway linkages is estimated as $1,896,000.

(c) Stormwater Management Devices

A number of stormwater ponds are proposed providing flood mitigation, stormwater qualityimprovement and landscape features. Sediment control during earthworks would be providedseparately on the development sites. The locations of the stormwater management ponds areshown in Map 9. The total estimated cost of providing these ponds is $17,627,000.

The cost estimates for ponds are for forward planning purposes, and are based on a generic costrelationship with pond size. This has been derived from detailed studies in Manukau Cityprepared by BCHF (ARC TP52, February 1995). The pond estimates include design,construction, landscaping, and construction management. The pond estimates do not include



the cost of land. Costs for individual ponds may vary up to 50% from those quoted in the table,but the total development budget is expected to be within 15 to 20% overall. The estimatedpond costs are:

Table 29: Estimated Cost of Stormwater Management Devices

Number PondReference

Volumem3

Cost Number PondReference

Volumem3

Cost

1 A1A 7,700 $210,000 26 B8B 21,800 $499,0002 A1B 3,400 $123,000 27 B9A 11,800 $294,0003 A2A 26,000 $585,000 28 B9B 17,200 $405,0004 A2B 3,400 $123,000 29 B9C 40,600 $883,0005 A3A 14,200 $343,000 30 B9D 19,900 $460,0006 A3B 38,200 $834,000 31 B9E 8,000 $217,0007 B10A 15,700 $374,000 32 B9F 3,400 $123,0008 B10B 5,600 $168,000 33 C1A 10,400 $266,0009 B10C 7,100 $198,000 34 C1B 7,000 $196,00010 B11A 50,600 $1,069,000 35 C1C 24,500 $554,00011 B11B 32,700 $722,000 36 C2A 5,100 $157,00012 B13A 6,200 $180,000 37 C2B 13,500 $329,00013 B2A 9,800 $253,000 38 C2C 10,100 $260,00014 B3A 11,400 $286,000 39 C3A 9,700 $251,00015 B3B 3,800 $131,000 40 C3B 11,500 $288,00016 B3C 16,200 $384,000 41 C3C 1,100 $76,00017 B5A 10,200 $262,000 42 C3D 3,100 $116,00018 B5B 6,700 $190,000 43 C4A 7,700 $210,00019 B6A 12,800 $315,000 44 C5A 30,500 $677,00020 B6B 18,400 $429,000 45 C6A 15,700 $374,00021 B6C 4,300 $141,000 46 C6B 8,000 $217,00022 B7A 16,900 $399,000 47 D1A 9,400 $245,00023 B7B 15,100 $362,000 48 D2A 31,000 $687,00024 B7C 6,500 $186,000 49 E1A 57,800 $1,235,00025 B8A 14,100 $341,000

Total Estimated Cost of Pond Development $17,623,000

Cost estimates for maintenance of stormwater ponds have been derived from trials undertakenby the ARC in the Puhinui catchment, in Manukau City (ARC TP52, 1995). The likely costsidentified for maintenance are for sediment clearance and ground maintenance. The neteffective cost per hectare for maintenance has been estimated based on the level of treatmentrequired by TP10 (75%), and the size of the contributing catchment.

Sediment removal from ponds would be undertaken within the first 5 years of the pondsconstruction, and every 15 years thereafter on average, although more frequent clearing of theforebays will be necessary. It is preferable that the costs of the first sediment removal beattributed to developers. In the following graph these costs which could be passed on todevelopers are included to give an overall maintenance cost, however, it is recommended thatCouncil recover this cost through the financial contribution.



$0

$50,000

$100,000

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ost

Total Annual Cost

Average Total Annual Cost

Additional costs include ground maintenance. Again, this figure has been calculated based onthe size of the contributing catchment (which in turn provides the basis for pond size). Groundmaintenance includes vegetation maintenance, grass mowing, and general care for thestormwater pond. Appendix 16 includes a spreadsheet of stormwater maintenance costs. Thefollowing figure identifies stormwater pond maintenance costs described above.

Figure 29: Cost of Maintenance for Stormwater Ponds

(d) Other Recreational Development

Manukau City is proposing to purchase and develop other land within the catchment to serveas recreational reserves and sports fields. This may include for example the restoration anddevelopment of core open spaces identified in the landscape assessment and the figures inAppendix 3 ( 'Potentially Key Open Space Node' and four other 'Potential Open Space Nodes').By way of example, the following table provides a breakdown of the broad costs that might beassociated with restoration and development of these open spaces for both passive and activerecreational use. The costings are, however, limited to the same basic restoration measures ashave been identified for the restoration categories and do not extend to the provision ofdrainage and pond development, provision for vehicle circulation and parking, buildings,walkways or other structural elements. They also assume that in the region of 35 - 40% of eachnode would need to be cleared, recontoured and either grassed or replanted with the restretained for existing native forest, stream corridors or pasture that can be used for passiverecreation. In the case of the 'Potentially Key Open Space Node' near Chapel Rd however this'allowance' would increase to around 90% of the total site area.



Table 30: Assessment of Possible Costs for Establishment of Key Open Space Nodes

Open SpaceLocation

PlanCode

Area Recontouring& VegetationRemoval

TopsoilPlacement

Grassing RestorationPlanting

Total:

ha @$3.75/m2 @$2.50/m2 @$2.40/m2 @$9.00/m2

(shrubs, etc)Junction Of Chapel& Ormiston Roads(Key P.O.S.N. – Partof Barry CurtisPark)

1 22.8 812,250 297,825 207,936 487,350 $1,805,361

North Of OrmistonRd & East Of JeffsRd (Key P.O.S.N.)

2 16.4 246,300 123,150 102,460 177,336 $649,246

South of OrmistonRd & East OfMurphy’s Rd(P.O.S.N.)

3 10.1 128,775 75,750 58,176 109,080 $371,781

North Of Flat BushSchool Rd Extension(P.O.S.N.)

4 12.3 207,562 123,000 88,560 166,050 $585,172

East Of Murphy’sBush Reserve (KeyP.O.S.N.)

5 14.6 197,640 117,120 84,326 158,112 $557,198

Note these costs do not include allowance for Contractors establishment, access, and contract contingencies, designand supervision, consenting and owner administration costs. These can be of the order of an additional 50 – 60%of the costs quoted.

The cost would also include the provision of facilities, play apparatus, landscaping and passiveareas.

In the analysis it has been recognised that the requirement of a 6% reserve contribution exceedsthe expenditure requirement for the purchase and restoration of the environmental corridornetwork. The analysis assumes that this cash surplus will be applied to the creation of theseother recreational developments within the catchment. A uniform expenditure of $1,172,000per year for 20 years from 2003 to 2022 has been calculated as available for these activities. Thissum balances the excess funds available after environmental corridor development has beendeducted from the reserve contribution. It is noted that should development patterns andtiming vary from the trends assumed in this analysis then the excess funds available wouldvary from the $1,172,000 per year.

(e) Distribution of Expenditure with Time

The development pattern presented in Section 8.5.2(a) has been used as the basis fordetermining the annual expenditure requirement to support development. The environmentalcorridor development and restoration of floodplains has been assumed to occur concurrentlywith land development abutting the corridors. The establishment of the stormwatermanagement ponds has been timed to permit upstream development to proceed without delay.In some circumstances this requires purchase and establishment of these ponds two or threeyears in advance of the environmental corridor vesting and development. In these instances it



is recommended Manukau City make early progress on acquisition of this land. These pondslie within Sir Barry Curtis Park and outside the study area to the west. Other instances willoccur where development of upstream areas precedes earlier than downstream areas.Manukau City will need to monitor development patterns and anticipate the demand forimplementation of the stormwater ponds.

8.5.5 Analysis of the Financial Contributions

(a) General

Analysis of the financial contributions in this analysis is limited to:

The implementation of the primary stormwater management devices and purchase offloodplains.

The assessment of the portion of the reserve contribution required supporting the creationof the environmental corridors.

Larger stormwater pipe networks serving a number of developments are excluded. Stormwatermanagement practices and swales, drains etc. serving the primary road network are excluded.

Whereas the developers generally install the larger stormwater pipe networks, they are oftensuccessful in claiming provision of larger diameters or lengths to serve adjoining areas is a costto council. Recovery of these growth costs would be subject to an additional stormwaterfinancial contribution.

Development of primary water supply and wastewater networks, arterial roads andcommunity facilities are excluded. Other reserve development is anticipated within the studyarea, however this analysis is limited to determining excess funds available to support thecreation of these other areas.

This analysis has assumed that all transactions will be in cash. It is anticipated that councilwould wish to take advantage of efficiencies that can be achieved by careful management ofvesting of reserve areas and contractor implementation of landscaping and stormwater controldevices. Doing so would affect the result of this financial analysis as transactions without cashdo not attract the implications of interest on borrowing to meet shortfalls, or investing excessfunds.

All costs presented in this analysis are in year 2000 dollars. GST has not been included indevelopment of the financial contributions and would be charged extra to the amounts quoted.

(b) Use of Interest in the Analysis

Development will proceed over a period of about 20 years. It is apparent that income from thefinancial contributions will not balance expenditure in each year. The surplus income orexpenditure will attract interest on the investment of surplus funds or the borrowing to meetshortfalls. For this analysis an overdraft approach has been adopted to assess the impact ofinterest on the determination of the required contributions. Interest paid on borrowings hasbeen adopted as 8% and interest earned on credit balances has been adopted as 6%.



Each activity has been assessed separately. With respect to reserves inclusion of interest hashad a beneficial effect as overall the reserves fund is in credit most of the time. The bulk of theenvironmental corridor development is in the South East of the catchment coinciding with thelast areas to be made available for residential development. On the other hand stormwatermanagement generally requires early expenditure to permit development to proceed. Thestormwater financial contribution will attract interest to support early expenditure in advanceof income.

Changing the pace of development from the pattern anticipated would affect the interestcalculated in the analysis, and effect the financial contributions required.

(c) Future Reassessments of the Financial Contributions

With time a number of factors that have been used in this analysis to determine appropriatefinancial contributions will change. Knowledge of how the activities will be implemented willimprove. Current conceptual cost estimates will be replaced with detailed estimates andeventually actual costs. Other factors that will change will include:

The rate and pattern of development.

Inflationary effects on the estimates of cost.

Changes in engineering approach or technologies to achieve stormwater qualityimprovement.

Future variations in the District Plan.

Proportion of purchases and works undertaken without transfer of cash.

Fluctuations in the interest rates used in the analysis.

Each of these may have a significant effect on the financial contribution required to supportdevelopment. To ensure that the activities supported by the financial contributions remainadequately funded over time the draft Variation must make provision for Council to reassessthe financial contribution on a maximum of a three-year cycle.

Manukau City should not release land for development until the financial contributions are inplace under the provisions of an operative District Plan. The transitional plan provisionsrelating to short term identification of expenditure will limit the ability of council to considerthe costs of full development of the catchment. The result would be unbalanced assessments offinancial contributions benefiting some developments and penalising others.

(d) Stormwater Management Financial Contributions

Based on the population projections and land development progress described inSection 8.5.2(a) the following assessment of expenditure by year has been made (see followingfigure).



Figure 30: Expenditure to Support Stormwater Management Requirements

In assessing the financial contributions required from the growth community to support thisexpenditure it has been assumed that each development lot will contribute equally. In generalincreases in stormwater runoff from development are attributed to the increase in impervioussurfaces and the provision of stormwater drainage. Controls in the draft Variation will limitthe creation of the impervious surfaces and introduce measures to limit runoff. Progressingfrom high through medium to low density lots will generally produce an increase in theimpervious surfaces per lot, and a corresponding improved ability to introduce measures tolimit runoff. For example the large lots in the low-density areas have the potential to havegreater impervious surfaces than those lots in the medium and high-density areas. Howeverthese greater impervious areas are generally offset by onsite development controls to direct therunoff from the impervious areas across the land before entering open watercourses. For thisanalysis, it has been assumed that as each lot contributes to the demand for stormwatermanagement in a similar manner then the stormwater management financial contribution is thesame for each lot created.

A stormwater financial contribution of $2,800 per lot has been assessed. This assessmentincludes allowance for interest arising from borrowing to support early expenditure in advanceof income. The resultant cash flow is described in the following figure:

$0

$500,000

$1,000,000

$1,500,000

$2,000,000

$2,500,000

$3,000,000

$3,500,000

$4,000,000

2000

2002

2004

2006

2008

2010

2012

2014

2016

2018

2020

2022

2024

2026

2028

2030

Sir Barry Curtis Park, Stormwater ManagementLandscape/Restoration, Stormwater Management LandEstablish Stormwater Management PondsPurchase Land subject to flooding



Figure 31: Stormwater Management Income/Expenditure Projections

(e) Reserve Contribution

The total expenditure to support land purchase and restoration of the environmental corridornetwork (excluding the stormwater management areas) is $66,083,500. Funds available tosupport development of other reserves in the catchment as a result of the 6% reservecontribution exceeding environmental corridor development costs is $23,432,000. Totalexpenditure included in this analysis for reserve development is $89,515,500. This expenditureis summarised in the following figure:

Figure 32: Environmental Corridor and Reserves Development Expenditure

-$10,000,000

-$8,000,000

-$6,000,000

-$4,000,000

-$2,000,000

$0

$2,000,000

$4,000,000

2000

2002

2004

2006

2008

2010

2012

2014

2016

2018

2020

2022

2024

2026

2028

2030

Total Annual Expenditure

Total Annual Income

Cummulative Surplus / Deficit

$0

$1,000,000

$2,000,000

$3,000,000

$4,000,000

$5,000,000

$6,000,000

$7,000,000

$8,000,000

$9,000,000

$10,000,000

2000

2002

2004

2006

2008

2010

2012

2014

2016

2018

2020

2022

2024

2026

2028

2030

Other Recreational Development

Other Development

Pathway Network Development

Restoration of Environmental Corridors

Purchase of Environmental Corridors



Current Manukau City policy is for the provision of 6% of the value of the lots created as eithercash or land for the purposes of funding land purchase and development of reserves. The totalincome derived from the reserve contribution is:

High Density $40,589,000

Medium Density $26,216,500

Low Density $16,166,000

Total $82,971,500

This is equivalent to an average contribution of $5,650 per lot created. The contribution willfluctuate with time dependant on market variations in the value of land. The contribution canbe either as land vested in Council or as cash. Council will need to manage the income andexpenditure on this account to ensure sufficient funds are available and all reservedevelopment objectives are achieved.

As the income from the reserve contribution generally precedes expenditure on creation ofreserves this analysis recognises the interest earned and allows for a total expenditure of$89,515,500. The resultant cash flow is provided in the following figure:

Figure 33: Environmental Corridor/Reserves Income/Expenditure Projections

(f) Transparency and Auditability of Financial Contributions

The introduction of financial contributions has been in response to the pressures developmentplaces on Council resources to support that development. Historically the application has beeninconsistent and widely varying in approach between councils. Contributions for reservedevelopment have been supported by legislation, though the percentage of value applied variesbetween councils. For other activities a charge has been developed or a requirement for work(e.g. frontage development for roading) has been applied. Often the charge had little

-$10,000,000

-$5,000,000

$0

$5,000,000

$10,000,000

$15,000,000

$20,000,000

2000

2002

2004

2006

2008

2010

2012

2014

2016

2018

2020

2022

2024

2026

2028

2030

Total Annual Expenditure

Total Annual Income

Cummulative Surplus / Deficit



appearance of relating to the actual cost of growth and the existing community subsidiseddevelopment. Recent changes in legislation require councils to adopt an equitable approach tofunding their activities and a concept of intergenerational equity has been introduced. Ingeneral this requires councils to ensure each generation pays for the creation and consumptionof assets put in place to support them. This requires that councils accurately determine the costof providing services to support the development of the growth community and require thegrowth community to meet that cost. The process now in place is to charge developers afinancial contribution for each lot created. As service demands vary from area to area thefinancial contribution will vary depending on the asset and the area.

Council still retains the right to encourage growth by subsidising development with reducedfinancial contributions. However there is now a demand for clarity in the process. This leadsto the need to accurately determine the costs to support development and to match the level offunding or works required transparently to that cost. The existing community desires to knowhow much they are supporting growth and the developers are keen to ensure they are not overproviding. There is a tension here that places a responsibility on council to ensure the processis transparent and auditable.

The determination of the stormwater financial contribution in this analysis follows theassignment of costs of catchment improvements required to support development as thegrowth cost. The financial contribution is the growth cost divided by the number of lotscreated.

The reserve contribution has been assessed in this analysis following current council policy.The contribution is a percentage (6%) of the land value created. As can be seen this does notrelate directly to the cost of providing the reserves. To balance the analysis a sum of $1,172,00per annum has been allowed for “other (undefined) recreational development”. Weunderstand Manukau City is planning other recreational activities that may include therestoration of core open spaces referred to earlier and in Appendix 3. Whether this sum isadequate for the other recreational purposes has not been assessed. A more correct proceduremeeting the intentions of the new legislation would be a detailed assessment of growth cost anda matching of the financial contribution raised to that cost. The analysis of the cost of providingthe environmental corridors is an accurate assessment of one component of the cost ofproviding reserves to support the community. Manukau City will need to determine theremaining “other recreational development” costs and add these to the cost of growth. It ispossible that the 6% reserve contribution will not meet the full cost of providing reserves andtherefore the existing community may subsidise this activity.

8.5.6 Implementation of Development

The issue here is, “who does the work?” developer or council? This relates particularly to theimplementation of stormwater management devices. A number of possible implementationscenarios are feasible.

Council establishes.

Developer establishes and Council repays developer.



Council requires developer to establish.

Council permits developer to establish in lieu of financial contributions.

These options have implications on the net financial contribution the developer pays to council.The most transparent mechanism is for the council to collect financial contributions for each lotthe developer creates and for the council to implement the facilities necessary to support thatdevelopment. However practical issues intervene. The environmental corridors and in someinstances the stormwater management ponds abut development and the contractor has on sitethe necessary equipment to support implementation/improvement of the ponds/corridor.There is some efficiency in combining the two activities. The danger is that “horse trading”takes place and the transparency of the procedure supporting the financial contributions is lost.

Other issues arise when there is a mixed approach to implementation. For stormwater pondimplementation it is possible the contractor may wish to use these temporarily for sedimentcontrol. Maintenance a long term cleaning of these devices will be an issue if they are to beeffective as stormwater quality improvement devices.

Flexibility is important as it enables the council to take advantage of improved efficiency inimplementation of infrastructure. Council will need to develop sound policies to manage thisprocess and retain the transparency and confidence in the financial contribution policy.

8.5.7 Other Management Issues

(a) Mapping Stormwater Hazards

Outside the environmental corridor the subdivision development will modify ephemeralstreams and create secondary flowpaths and ponding areas. The result will be a need toidentify the flood hazards created by implementation of stormwater management within thesubdivisions. Manukau City will need to set in place through the consent processes tools torequire, collect and record these flood hazards.

(b) Cost of Restoration of Environmental Corridors in Upper Catchment

Development of the environmental corridors in the upper catchment is to be the responsibilityof the developers. This will entail a significant investment by the developers. There is a riskthat this investment will be difficult to police. Establishment of correct species with sufficientmaturity to survive and adequate maintenance to control weeds and ensure survival will becrucial to the success of the environmental enhancement. Scenarios to achieve theestablishment of these corridors include:

Trust.

Bonding the developers against the success of the measures required.

Council implementing.

Trust is a good principle, unfortunately marred by the few who make little attempt to supportsound community objectives.



Developers could be required to commit to a bond, either in cash or through an approvedbondsman, which would only be released once a satisfactory level of compliance withstandards set in consent conditions had been achieved. Clear standards defining land areas tobe restored, landscaping requirements, species (and proportions), maturity, weed control,mulching, maintenance, survival, time frames, etc. will be required to provide a measure ofcompliance. Standards will need to be consistent across all the upper catchment areas to ensureequity in approach. The value of the bond would need to reflect the cost of the council steppingin and implementing the restoration. These costs would include administration and legal costsassociated with calling on the bond.

Establishment of the environmental restoration would occur over a number of years whichwould be followed by continued maintenance in the future. The current policy is that thesecorridors would be retained in private ownership. Council implementation would thereforeoccur on both the subdivision and the resulting private land. Rights of access may be difficultto achieve. In establishing a financial contribution to support council implementation issues ofland betterment would need to be considered to ensure equity with the community establishingin the lower catchment areas. An alternative would be for council to purchase and manageoutright these corridors in the upper catchment areas.

About 178.6ha of land in the upper catchment has been identified for inclusion in theenvironmental corridors. As the land is in the steeper upper catchment areas the impact offloodplains on land value would be minimal. Therefore the purchase value of this land (at$400,000 per ha) would be $71,440,000. The anticipated total 6% reserve contribution($82,971,500) would be unable to support this level of expenditure in addition to thecommitments in the lower catchment.

The cost of restoration of the entire 178.6ha environmental corridor located in the uppercatchment is estimated to be $11,550,000. As a basis for establishing a bond this is equivalent to$21,500 per ha of the total developable land in the upper catchment, or $64,600 per ha of theenvironmental corridor sited within each development lot. That is on average a cost of $10,750per lot created.

Beyond the issues of establishing the environmental corridors in the upper catchment areas theCouncil will need to address long term maintenance. The land will be subject to pockets ofinstability that may move, damaging the corridor. Long term growth of some species willinterfere with view lines of established properties. In the medium and long term species willreach their natural lives and die out. One of the longer terms questions will be whether councilwill require replacement, or rely on natural regeneration to retain the nature of the corridor?Early advice of how these issues will be managed should be incorporated into the Variation toavoid future debate.

8 . 6 M o n i t o r i n g

One of the significant issues identified during the catchment planning process is the need todevelop a robust monitoring programme specific to East Tamaki. It is important to measure thesuccess of the implementation of the catchment management and concept plans. The concept



for East Tamaki is one which fully embraces the concept of sustainable management, andtherefore it is important that a process be established to measure and understand the effects onthe environment arising from the type of catchment development proposed. This will enableboth Council and other local authorities or environmental agencies to more fully understandthe effects of the urbanisation process, and thus ensure constant improvement in environmentalmanagement techniques.

The purpose of this section of the CMP is to identify an appropriate goal and objectives for amonitoring strategy for the East Tamaki area. An actual monitoring programme (i.e. theparameters to be measured and monitoring methods) cannot be prepared at this stage, as thereare a range of further steps to be taken to enable the development of the area. In particular thedraft variation to the Proposed District Plan needs to progress through a statutory process, andthis will include a range of monitoring requirements. In addition, Council will need to havediscussions with the ARC in relation to its monitoring programmes to determine the mostappropriate allocation of monitoring tasks.

8.6.1 Monitoring Requirements

The need to monitor can arise from three key sources; legislative requirements, policy and planrequirements, and good resource management practice. In this instance, while monitoringrequirements will be included in the draft variation, and Council has a range of responsibilitiesand existing programmes to monitor policy, the most significant driver for a robust monitoringprogramme arises from good resource management practice.

The following diagram illustrates the role of monitoring in the resource management processfor East Tamaki.



To establish a robust monitoring framework which contributes to the management of theEast Tamaki Catchment in a sustainable manner.

Figure 34: The Monitoring Process in Relation to East Tamaki

outputs

outcom es Develop EastTam aki CM P andDistrict Plan

Provisions/ReviewPolicy

Im plem ent

Catchm ent

M anagem entIssues

M ONITORReport

Monitor Performance of CMP / DistrictPlan Provisions:

• Plan Implementation & Effectiveness• Comprehensive Discharge Consent

Compliance• Enforcement of DP provisions• Transfers/Delegations• Resource User (public) Knowledge• Annual Plan Outputs, in particular

acquisition of Public Open Space(“Green Fingers”)

Responses:• Implementation Plan• District Plan• Transport Strategy• Pest Control Strategy for

East Tamaki• Annual Plan expenditure

Monitor State of the EastTamaki Environment:

• Baseline Monitoring• Impact Monitoring• Specific Issue

Monitoring• Research

State of Environment Reporting forEast Tamaki (in context of MCC)

• Technical Monitoring &Research Reports

• Annual Report – Outputs• District Plan Effectiveness• Consent Compliance Reports• Developer / Resident Surveys

8.6.2 East Tamaki Monitoring Strategy

While it is acknowledged that in relation to the East Tamaki area both the Manukau CityCouncil and Auckland Regional Council have monitoring functions under the RMA (Section35), the purpose of this section of the CMP is to define monitoring objectives which are specificto the area. Some of these objectives may form a part of any consent monitoring requirementswhich may be imposed by the ARC in relation to any comprehensive stormwater dischargeconsent for the catchment.

The catchment management objective for an East Tamaki Monitoring Strategy is:

From the perspective of catchment management planning, the purpose of environmentalmonitoring is to improve resource management practice by:



increasing information bases and knowledge of resources and process in the East Tamakicatchment;

enabling the measurement of the policies and methods (“tools”) identified in this CMPand the draft variation for effectiveness and performance, and thereby establish a processwhich reviews those mechanisms at appropriate and regular intervals;

increasing understanding of existing issues and highlighting emerging issues identifiedin this CMP, that is, state of the environment (SOE) monitoring which would incorporate:

– baseline monitoring

– impact monitoring (e.g. monitoring sediment generation and water quality over thedevelopment phase)

– specific issue investigations

– research

determining the effectiveness of current policies and practice - performance monitoring;

determining compliance with legislation, rules or standards, and consent conditions -compliance monitoring;

communicating information (reporting) to local communities, tangata whenua,developers and Council.

While a range of information has been collected from field investigations and research,ongoing monitoring over the development process will assist Council in monitoring theperformance of the environmental mitigation strategies suggested in this CMP. Over the firstten year period (approximately) the development of the Stage 1 area will occur. A robustmonitoring programme will ensure that any unforeseen environmental issues can be detectedand appropriately mitigated, and where necessary, improvements made to theimplementation framework or ‘toolbox’ of techniques used to manage the developmentprocess for the ‘Stage 2’ development area. Thus constant improvement in resourcemanagement techniques and ultimately outcomes can occur. This CMP provides the basis formonitoring specific parameters relating to instream ecology, terrestrial ecology, changes towater quality, water quantity and so forth. A number of ‘bottom line’ indicators for ecologicalhabitat will also ensure issues such as kokopu habitat and low flows are monitored andmaintained. It is therefore recommended that a comprehensive monitoring strategy bedeveloping by Council in association with the ARC which aims to achieve these broadobjectives.

Conclusion

Section 9



9999 ConclusionConclusionConclusionConclusion

9 . 1 A i m s o f t h e S t u d y

The process for the production of the East Tamaki Comprehensive Catchment ManagementPlan has been an iterative one involving consultation with tangata whenua (Te RoopuKaitiaki), landowners, and other interest groups. The progression of the ‘concept plan’ togreater levels of detail in conjunction with the technical catchment investigations has enabledthe consideration of a wide range of issues, the development of a range of solutions andagreement on the most sustainable solutions.

To conclude the CMP, it is important to refer back to the vision for the catchment which wasestablished through the DET Concept Plan, and which ultimately has been reinforced throughthe consultation undertaken throughout the course of this project. That is:

“To achieve a sustainable community in the broadest sense. A sustainable community isabout using, managing and protecting natural and physical resources in a way that enablescommunities to develop economically, socially and culturally - while safeguarding the lifesupporting capacity of air, water, and ecosystems. A sustainable community must also takeinto account not only the health and well - being of the community but also the needs offuture generations.”

The aim of the catchment study was “to achieve an integrated approach to stormwatermanagement, improving biodiversity and integration of recreational and amenity values”. This aimhas been achieved through a process of examining these issues, and ensuring the objectivesestablished for each specific outcome were complementary to other objectives. The approachadopted by the Project Team was “To manage the stormwater budget in an integrated manner tominimise risk of flooding and enhance the quality of water through innovative and effective engineeringtechniques which support a high quality environment based on the Development East Tamaki ConceptPlan.”

9 . 2 K e y I s s u e s

Following gathering and assessment of field and background information, a number of thekey issues in the catchment were identified. These included the following issues:

In-stream and Riparian

Stormwater Management

Terrestrial Ecology

Land Use

Landscape and Amenity

Recreation



Receiving Environment – Otara Lake

Implementation

9 . 3 C o n c e p t u a l A p p r o a c h e s

Conceptual approaches to enable a management approach which met the aims of the studyand addressed the key issues were developed. Again these approaches were the subject ofconsultation with Tangata Whenua (through Te Roopu Kaitiaki), ARC and MCC staff.Newsletters to all landowners also invited comment on the broad conceptual approaches, andgeneral support was received from a number of parties.

The conceptual approaches identified in Section 6 relate principally to instream and riparianoutcomes, and stormwater management. These two issues have driven the development ofthe CMP and the structure plan. Following initial analysis, it was determined that the landuse framework proposed by the DET Concept Plan (June, 1999) did not present any ‘fatalflaws’ with respect to the catchment planning approach, but rather promoted urbansustainability with respect to the key issues identified. Therefore, conceptual approacheswere developed to manage the effects of the urbanisation proposed in the Concept Plan.

In relation to the instream management strategy, the conceptual approach involved:

Identifying the ecological values present and their significance;

Identifying the pressures which adversely affect these values;

Establishing management objectives for these values;

Determine the requirements (physical and chemical) to meet these objectives;

The overall outcome of this component of the study is that the majority of the stream networkhas been protected in the environmental corridors, and a management regime for differenttypes of stream have been identified. This includes significant enhancement of riparianvegetation, enabling fish passage to the important headwaters of the catchment, and ensuringthe stormwater management regime will maintain and enhance the instream habitat.

In relation to the stormwater management strategy, the conceptual approach revolvedaround achieving a number of key outcomes, as follows:

Management of the volume and peak flow rate of storm runoff to avoid flood risk andlimit stream erosion;

Management of contaminants and sediment in runoff reaching high value receivingenvironments;

Retention of stormwater in the catchment to assist in enhancing low flows;

Protection and enhancement of waterways identified as having high actual or potentialvalue.



9 . 4 C a t c h m e n t O b j e c t i v e s , I m p l e m e n t a t i o n a n dM i t i g a t i o n

The approach to achieving these outcomes has been to develop a stormwater managementregime based around the protection of the 100 year ARI floodplains in the environmentalcorridors, including the use of ponds as a ‘backup’ to other stormwater managementtechniques which may be implemented by developers. The pond system provides securitythat the outcomes sought will be achieved, while also enabling the use of other techniques ondevelopable land. This provides developers with flexibility and room for creative solutionsfor future land development processes, provided the stormwater performance criteria aremet.

Modelling and experience indicates that the adoption of specific techniques, collectivelyknown as Low Impact Design, will enable greater stormwater “benefits” to be securedthereby further reducing the impact of development on the stormwater budget. The approachtaken has also been to enable flexibility and the best practicable option to be adopted forindividual developments. It is assumed that guidelines such as the ARC’s TP10 and TP90 willbe met by development.

Catchment management objectives, followed by detailed mitigation measures translatedthese conceptual approaches into a series of actions, recommendations and key successfactors which will assist Council in managing the urbanisation process in a sustainablemanner. Ensuring that the costs of growth arising from this process can be accounted for is amajor component of this approach. Managing the costs of growth ties in closely with thestaging regime proposed, which has the added benefit of enabling Council to manage theeffects of development, particularly on the downstream receiving environment.

9 . 5 S u s t a i n a b l e M a n a g e m e n t a n d C o n c l u s i o n

Ultimately the goal of the CMP will be to meet the tests of sustainable management asrequired by the Resource Management Act 1991. This document will be used for two majorpurposes:

To inform Council on the regulatory and other requirements which need to beconsidered in its implementation framework, which will enable the urbanisation of theEast Tamaki area in accordance with the vision developed in consultation with thecommunity;

To provide background information and assessment to enable Council to apply to theAuckland Regional Council for a comprehensive stormwater discharge consent

In assessing the CMP and Concept Plan against the test of sustainable management, it hasbeen demonstrated that a range of values have been protected and enhanced. In particular,protecting and enhancing the life supporting capacity of the stream system is a significantcomponent of the CMP. In addition to the protection of significant environmental values,



provision has been made for over 40,000 people to reside in the catchment by about 2020,enabling the community to provide for its wider social, economic and cultural needs. Thisalso meets Councils wider strategic goals associated with the Regional Growth Strategy.

In summary, it is concluded that the approach adopted in the CMP of containing urbandevelopment within the catchment, protecting the important environmental values withinthe catchment, and introducing a resource management regime will promote sustainablemanagement. In addition, to meeting the tests of the RMA, a range of Councils’ widerstrategic goals.

General conclusions are that:

The stream system of the East Tamaki catchment has a range of instream ecologicalvalues which are worthy of enhancement and protection as proposed;

The stormwater mitigation framework will enable stormwater and ecological objectivesto be achieved;

The development of environmental corridors and areas of open space, combined withprotection and enhancement of key parts of the upper catchments and ridgeline, willcreate a sense of identity for the area into the future, while providing valuable recreation,amenity and leisure open space;

The land use pattern proposed in the draft Variation, with appropriate environmentalcontrols, will enable the key catchment objectives and environmental outcomes to beachieved.

One of the next key stages in the process for enabling the development of the East Tamakiarea is the application to the ARC for a comprehensive stormwater discharge consent for thecatchment. Ensuring that developers are consistent with the ARC comprehensive dischargeconsent will be a policy significant issue to be addressed by the Variation.

The vision for the catchment which was developed in consultation with the local communitythought the DET Concept Plan (June, 1999) and the CMP can be achieved if the District Plan,Asset Management, Education, Monitoring and Enforcement programmes identified in thisCMP are put in place by Council.



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Regional Water Board Technical Publication No. 47.

Auckland Regional Water Board 1988: Tamaki Estuary Water Quality Survey 1987 – 1988. AucklandRegional Water Board Technical Publication No. 54.

Auckland Regional Council, 1992: Tamaki Estuary Water Quality Survey 1988 – 1991. Environment andPlanning Division Technical Publication No. 12.

Auckland Regional Council, February 1995 “Comprehensive Catchment Stormwater Treatment: PilotStudy, ARC Technical Publication no. 52.

Auckland Regional Council 1999: Tamaki Estuary Water Quality Survey 1985 – 1997. ARC TechnicalPublication No. 105.

Auckland Regional Council, "Guidelines for Stormwater Runoff in the Auckland Region", AucklandRegional Council Technical Publication No. 108

Collier, K. J.; Wilcock, R.J.; Meredith, A.S. 1998: Influence of substrate type and physico-chemicalconditions on macroinvertebrate faunas and biotic indices of some lowland Waikato, NewZealand, streams. New Zealand journal of marine and freshwater research 32: 1-20.

Collier, K. 1992 Assessing river stability: use of the Pfankuch method. Wellington, New Zealand:Department of Conservation.

Gregory, S.V.; Swanson, F.J.; McKee, W.A.; Cummins, K.W. 1991: An ecosystem perspective on riparianzones. Bioscience 41: 540-551.

Hicks, D.M. and Mason, P.D., " Roughness Characteristics of New Zealand Rivers", Water ResourcesSurvey, 1991, Wellington New Zealand.

Manukau City Council, Otara Stream Flat Bush Catchment Study, Prepared by J. White (B.E. (Hons).And J.S. Oldfield (C.Eng.MICE, MIPENZ) December, 1990.

Manukau City Council, June 1999, Development East Tamaki Concept Plan.

Maxted, J., and Evans, B 2000. Standard Methods for Macroinvertebrateand Habitat Assessment ofWadeable Streams in the Auckland Region. Internal report, Environmental Research,Auckland Regional Council.

NZS 4404: Code of Practice for Urban Land Subdivision.

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Appendices

Appendix 1 -LandscapeUnitAssessmentSheets

Appendix 2 -LandscapeFeatures,elementsand nodes

Appendix 3 -Stormwatermodellingresults

Appendix 4 -Hills RoadMean Flowsand FlowDistribution

Appendix 5 -StormwaterManagementOptions

Appendix 6 -StormwaterMitigationResults

Appendix 7 -Results ofRiparian andIn-streamEcologicalAssessments

Appendix 8 -Macroinvertebrates

Appendix 9 -GrowthStrategyPrinciples

Appendix 10- Murphy'sBushSpecies List

Appendix 11- StreamPhotos

Appendix 12- GreenFinger CrossSections

Appendix 13- Maps

Appendix 10:ConsultationNewsletters

comprehensive catchment management plan - … · 3 catchment analysis ... management plan for the...

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