anderson park, neutral bay civil engineering report · taylor thomson whitting (nsw) pty ltd,...

Taylor Thomson Whitting (NSW) Pty Ltd, Consulting Engineers | ABN 81 113 578 377 48 Chandos Street, St Leonards NSW 2065 | +612 9439 7288 | ttw.com.au

Anderson Park, Neutral Bay

Civil Engineering Report

Prepared for EP (NSW) / 30 May 2018

TTW Job No: 171071

Document No: TTW-CV-RP01

Version: 1, Version Date: 29/08/2018Document Set ID: 7536122

Anderson Park 171071 Civil Engineering Report 30.05.18

Taylor Thomson Whitting (NSW) Pty Ltd 1 (Copyright 2016)

DOCUMENT REGISTER

PREPARED BY APPROVED BY STATUS ISSUE DATE

Kelvin Holey Paul Yannoulatos Review P1 30.05.18



Taylor Thomson Whitting (NSW) Pty Ltd 2 (Copyright 2016)

Contents

1.0 Executive Summary ............................................................................................... 1

2.0 Introduction ............................................................................................................ 1

2.1 The Park ................................................................................................................... 1

3.0 Existing Site ........................................................................................................... 4

3.1 Existing Services ...................................................................................................... 4

3.2 Existing Stormwater ................................................................................................. 5

3.3 Climate Change / Storm surge / Tidal Influences .................................................... 6

3.4 Salinity / Contamination ........................................................................................... 6

3.5 Geological conditions ............................................................................................... 6

4.0 Stormwater Design ................................................................................................ 8

4.1 Hydrology ................................................................................................................. 8

4.2 Hydraulics ............................................................................................................... 10

4.3 Environmental Flows and Onsite Stormwater Detention (OSD) ............................ 11

4.4 Flooding and Climate Change ............................................................................... 11

4.5 Water Sensitive Urban Design (WSUD) ................................................................ 11

4.6 Overland flow ......................................................................................................... 11

4.7 Stormwater Quality ................................................................................................. 12

4.8 Erosion and Sediment Control ............................................................................... 12

4.9 Riparian Zone and Watercourses .......................................................................... 12

5.0 Future Design ....................................................................................................... 13

5.1 Pavement Design ................................................................................................... 13

5.2 Existing Alluvial Material ........................................................................................ 13

6.0 Vehicle Site Access ............................................................................................. 13

6.1 Maintenance ........................................................................................................... 13

6.2 Bush Fire and Ambulance Access ......................................................................... 13

6.3 Oval Use ................................................................................................................. 13



Taylor Thomson Whitting (NSW) Pty Ltd (Copyright 2016)

1.0 Executive Summary

This report has been prepared by Taylor Thomson Whitting (TTW) to support the Anderson Park Plan of Management. The Plan of Management is intended to establish an overall vision for the park and to set out how the park will be used and managed by Council for the next five to ten years.

The aim of this report is to provide the following:

� Review and investigate the Water Sensitive Urban Design including stormwater and flooding,

� Identify existing issues in relation to geotechnical and contamination issues around the park.

� Propose potential strategies to mitigate these issues with consideration to the constraints of the park.

This report relates to civil elements and constraints for Anderson Park, Neutral Bay.

This report will review the civil engineering issues such as: stormwater, earthworks, contamination, and overland flow.

The key issues to be discussed include:

� Flooding and stormwater controls,

� Stormwater Quality, and

� Geotechnical and contamination ground conditions.

2.0 Introduction

Anderson Park, Neutral Bay is located on the lowest reach of a natural topography depression which flows into Middle Harbour.

The park is within North Sydney Council’s Local Government Area (LGA).

2.1 The Park

The park has an area of approximately 3Ha, this includes all area surrounded by Kurraba and Clark Roads. The ovals are generally fall towards Neutral Bay of Middle Harbour. There is one existing building located on the north side of the site between the oval and the bushland embankment. This building is a canteen with toilets, change rooms, and storage.

The upstream catchment from Anderson Park has an area of about 65Ha over a distance of 1.4km. The catchment flows around Anderson Park in a Sydney Water open concrete channel which is about 3.74m wide and 1.752m deep.

Access to Anderson Park is from the at grade intersection of Clarke and Kurraba Roads.

On the southern side of the park are mature fig trees that listed on the heritage register.

Close to the water is a footpath and vertical rock sea wall.

Shown in Figure 1 below is a recent satellite image of the site. Figure 2 shows a 1943 satellite image of Anderson Park.




Figure 1- Anderson Park, Neutral Bay (SIX 2017)




Figure 2 – Anderson Park, Cammeray 1943 (Spatial Information Exchange (SIX) 2017)

NORTH




3.0 Existing Site

3.1 Existing Services

Existing services have been investigated through Dial Before You Dig. Anderson Park has several service constraints. Service diagrams indicate that Sydney Water has a sewer pump station in the north east corner of the park as well as the Sydney Water channel located on the southern edge of the park, between the road and tree line. North Sydney Council has stormwater pipes connect to the harbour in the north east corner of the oval. Ausgrid has an underground power supply traverses the middle of the oval and probably connects to the existing building. Telstra and NBN are located below the embankment on the northern side of the oval and goes around the rear of the building. Sydney Water did not indicate water supply services even though the amenities and canteen buildings, as well as park bubblers indicate there is water supply. Additional services investigation will be required for any future development.

Figure 3 - Ausgrid Cables Traverses Anderson Park




Figure 4 - Sydney Water Services

3.2 Existing Stormwater

The existing oval building collects stormwater and conveys the flows to the harbour. Figure 5 below shows North Sydney Council stormwater assets. Water that falls on the oval will make its way to the channel as either overland flow or as groundwater flows, prior to discharge to the ocean




Figure 5 - North Sydney Council stormwater services

3.3 Climate Change / Storm surge / Tidal Influences

The Intergovernmental Panel on Climate Change (IPCC) (Fourth assessment Climate Change 2007) has indicated that sea levels will rise in the range of 0.18m to 0.58m by 2100. Increase in sea level rise coupled with high tides will lead to occasions of inundation and closure of ovals.

3.4 Salinity / Contamination

The Anderson Park is affected by contamination. Investigations indicate that the following contaminates have been identified:

• Polycyclic aromatic hydrocarbons (PAHs), including

• Benzo(a)pyrene,

• Naphthalene,

• Mercury,

• Tributyltin.

The above contaminates are not suitable for reuse of excavated material which includes after digging for new landscaping. The above contaminates provide a relatively moderate risk to the site receptors (humans, flora, fauna).

3.5 Geological conditions

Based on Sydney Soil Landscape Geological Map (NSW Department of Land and Water Conservation), Map can be seen in Figure 7. Sydney Soil map categorises the oval as disturbed land, refer to Figure 6 for the soils description.




Figure 6 - Sydney Soil Landscape Geological Map soil description

As the fill is likely to be variable, to varying depths, future building works are likely to need piled foundation systems. Sandstone rock outcrops can be seen around the field, with the depth to rock at the maximum along the tree line. Further, it is expected the site is fill material is founded over sand/silty clay, over sandstone bedrock improving strength with depth.

Possible batters for work in cutting these materials are given in Table 1.

Table 1 - Minimum Temporary Batter Slopes (Argus 2011)

Material Temporary (H:V)

Sandy silt 3.0:1.0

Very Stiff/ Hard Silty Clay 2.0:1.0

Distinctly Weathered Sandstone 1.0:1.0

Slightly weathered Sandstone or better 0.5:1.0

Any clay/silt is likely to be highly reactive and any earthworks within clay subgrade will need

protection from rain and moisture. Should the silty clay subgrade become wet, bearing

capacity will be reduced leading to the requirement to dry, replace, or mediate the material to

continue construction progress.

In addition, it is likely that the fill material is of poor quality and unstable. Any development on fill material will need be investigated with the likely outcome being removal and replacement with better material, or rework of the existing material until stable. If buildings are proposed on fill material then a footing system (CFA piling, screw piles, timber bores etc.) are incorporated; generally the taller the building coupled with building proposed use, with a big building footprint, leads to a deep foundation system i.e. piles to bedrock at 15m depth.

Future testing will be required.




Figure 7 - Sydney Soil Landscape Geological Map (NSW Department of Land and Water Conservation)

4.0 Stormwater Design

In general, any new building works, roof stormwater will need to be collected in roof gutters and downpipes and conveyed to the in-ground pipe system. Surface stormwater will be collected in pits. The in-ground stormwater should be connected to Stormwater Quality Improvement Devices (SQIDs) prior to discharge into the Harbour or Flat Rock Creek.

There is no expectation to modify the existing culverts under the oval. The culvert entry should be improved to benefit fish breeding as per the current intention.

4.1 Hydrology

The volume of rain is dependent on the storm duration and storm intensity. Storm duration and intensity data has been obtained from the Bureau of Metrology and can be seen below in Figure 9 and Table 2. This data is used to determine pipe capacities, overland flow rates, and OSD tank volumes.

Anderson Park




Figure 8 - Intensity Frequency Duration chart




Table 2 - Intensity Frequency Duration table

4.2 Hydraulics

Any new pipes and pits will need to be designed to satisfy the minimum provisions of AS 3500.2. They should be designed to convey, at least, the 5% Annual Exceedance Probability (AEP) flows.

Pipes 225mm diameter and greater must be class 2 concrete or better, laid at a desirable minimum fall of 1 in 100. As subsidence from the variable nature of the oval fill, slip joint pipes is recommended. Pipes within road ways or affected by service vehicle loads should be class 4.

Where pipe capacity is exceeded i.e. greater than 5% AEP, stormwater will need to be conveyed as overland flow. Overland flow paths are to be designed to convey at the minimum 1%AEP stormwater flows.

New building downpipes will be connected to surface pits. Between the base of downpipe and the top of the in-ground pit it is recommend there be an air void of about 50mm. The air void is to prevent the downpipes surcharging into the building should the in-ground drainage block and also to make any maintenance and access easier.




4.3 Environmental Flows and Onsite Stormwater Detention (OSD)

Catchment management is required to be in accordance with North Sydney Council’s Development Control Plan and Australian Rainfall and Runoff publications.

In addition, due to urbanisation or the replacing of permeable areas with hardstand (roof areas, pavements), stormwater runoff times are reduced which equates to the downstream catchment receiving stormwater sooner thus increasing flooding risk. Usually to remove this risk, slowing down of hard stand surfaces flow is required by the incorporation of Onsite Stormwater Detention. However, due to proximity to the receiving waters of Middle Harbour, stormwater attenuation for any new development at this oval will not mitigate flooding and is unlikely to be necessary.

To protect the downstream ecosystems from pollution, pollution control and pollutant removal is required to be provided. The Stormwater Quality Improvement Devices (SQIDs) should meet or exceed NorBen (Neutral or Beneficial) and Council pollutant removal rates.

4.4 Flooding and Climate Change

During storm events in the Anderson Park catchment, water is conveyed to Middle Harbour in the Sydney Water open channel. In large storm events, water can overtop the channel and flow across the oval

North Sydney Council LGA Flood Study indicates flooding for the 1%, 2% and 5% AEP storm events. The 1% AEP flood map is shown in Appendix A.

Flooding will impact the design of new buildings, as well as for infrastructure like substations. Flood levels need to be taken into consideration for setting of floor levels as well as the incorporation of appropriate freeboard.

Flood events coupled with: sea levels rise, storm surge, and high tides will impact the park leading to field, recreation, and parking area inaccessibility as well as oval use restrictions due to field condition.

4.5 Water Sensitive Urban Design (WSUD)

Water Sensitive Urban Design includes water reuse, pollutant removal via natural systems, and the minimisation of hard structures to control stormwater and improve environmental, aesthetic, and recreational appeal.

Where open space exists, an attempt to incorporate WSUD principles into the stormwater design. Although, as standing water poses waterborne health risk, careful attention to the WSUD type and how it is incorporated is required.

Anderson Park has opportunities for the incorporation of WSUD which includes bioretention swales and basins which can be incorporated into landscaped outcomes.

4.6 Overland flow

In the event that the channel or piped in-ground stormwater system fails due to blockage, obstruction, or insufficient capacity, stormwater flow will be required to be conveyed as overland flow. The overland flow is to be directed through Anderson Park and towards Middle Harbour. The water front path is in the direct path of stormwater overland flow posing a safety risk to users in this area during flood events.

Overland flow paths for any new development will need to be sized to accommodate at least the 1%AEP storm flows.




4.7 Stormwater Quality

The oval does not appear to have any water quality devices for collection of pollutants prior to discharge to the harbour.

Stormwater discharged from the development will be treated in accordance with North Sydney Council policy. The site stormwater will pass through suitable pollution control devices to achieve the required water quality removal rates. All inlet pits should have litter screens / traps.

The pollution control devices will require on-going maintenance. Pollutant removal devices will require at least a yearly inspection and maintenance.

4.8 Erosion and Sediment Control

During construction and while the site is disturbed, erosion prevention and sediment control measures will be required. Erosion prevention generally involves managing stormwater by diverting overland flow around construction areas as well as collecting stormwater within the construction zone and directing to sediment control devices. Devices likely to be incorporated are: silt removal like fences, hay bales, and grass lined swales; water flow dissipation and discharge control devices such as sand bags, pollution mattresses, and basins.

Erosion prevention and sediment removal strategies need to be inspected regularly during service and construction works, cleaned and maintained after storm events, and modified to suit construction work progress, decanting and demolition.

Erosion and sediment control is to be provided in accordance with Urban NSW’s publication Managing Urban Stormwater: Soils and Construction by the NSW Department of Housing.

4.9 Riparian Zone and Watercourses

NSW Department of Primary Industries (Water) have proximity restrictions to Riparian zones and watercourses which can be seen in Figure 13.

Figure 9 - Riparian Corridor

Development setbacks to Sydney Water channel and Middle Harbour are applicable for any future development.




5.0 Future Design

5.1 Pavement Design

Existing pavements will be retained where possible for traffic loading, with re-construction of existing surfaces likely to be required where deterioration is evident. Access roads may need to be upgraded to a new wearing surface. Any new on-grade carpark is likely to be constructed from asphalt.

Table 3 - Preliminary Pavement Design (1x105 ESAs)

Pavement options based on a 5% CBR for car loading only

Typical flexible pavement would include: Concrete pavement option would be:

40mm thick asphalt on

120mm thick densely graded base on

120mm thick densely graded subbase on proof rolled subgrade

170mm thick 32MPa concrete with SL82 mesh on

100mm thick densely graded base on proof rolled subgrade

Additional subgrade testing will be required to determine that 5% CBR is achievable under any existing buildings. Should low strength materials be found after demolition and excavation, stabilisation (cement) or material replacement will be required to improve the subgrade bearing capacity.

5.2 Existing Alluvial Material

Any new building/structure work will require geotechnical investigation to determine the ground conditions. As we are adjacent to a watercourse the ground conditions are likely to consist of variable fill and soft alluvial material unsuitable for direct bearing. Any construction over variable fill or alluvial material may require suspension with supports outside the alluvial zone, or supports deeper enough to bear on suitable strength bedrock.

6.0 Vehicle Site Access

6.1 Maintenance

Oval maintenance vehicles will access the fields via a driveway off the Kurraba and Clarke

Roads. Site access needs to be able to accommodate heavy ridged vehicles for

maintenance, especially for clean out Sydney Water sewer pump station. Small service

vehicle access will be required for the channel as well for other services within the park.

6.2 Bush Fire and Ambulance Access

Access for fire trucks and ambulances is required. NSW Fire and Rescue guidelines

indicates that roads are required to be suitable for all weather access which is 4m wide with

6m zones for set down of vehicle outriggers.

6.3 Oval Use

In the event that Anderson Park is used for fairs, festivals, carnivals, sporting presentations,

etc., where large vehicles are required to come onto the oval to setup, there will be

restrictions due to the variable ground conditions, amusement rides and other structures will

similar point loads need to be founded on stable ground.




Appendix A – North Sydney Council LGA Flood study 1% AEP


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Peak Flood Level Profile Locations

Anderson Park Branch

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1% AEP Extent

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