greater nottingham strategic flood risk assessment...

Greater Nottingham

Strategic Flood Risk Assessment

Summary of Key Findings for Nottingham City Council

July 2008

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GREATER NOTTINGHAM STRATEGIC FLOOD RISK ASSESSMENT

Summary of Key Findings

Document issue details: B&V project no. 120986 Client’s reference no. BV-N2/MDC/00026

Version no. Issue date Issue status Distribution

1 October 2007 Draft Report (Electronic copy only)

Nottingham City Council Environment Agency Nottingham Regeneration Ltd. (digital copy only)

2 July 2008 Final Report Nottingham City Council Environment Agency Nottingham Regeneration Ltd.

Version no. Principal Authors Principal Checker Principal Reviewer

1 Naomi Wing, EA Lisa Roche, NCC Ian Vernalls, NCC

Jenny Palmer, B&V Naomi Wing, EA Lisa Roche, NCC Ian Vernalls, NCC

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Naomi Wing, EA Lisa Roche, NCC Ian Vernalls, NCC

Peter Savill, EA Naomi Wing, EA Lisa Roche, NCC Ian Vernalls, NCC

Notice:

This report was prepared by the Environment Agency and Nottingham City Council solely for use by Broxtowe Borough Council, Environment Agency, Erewash Borough Council, Gedling Borough Council, Nottingham City Council, Nottingham Regeneration Limited, Nottinghamshire County Council, Rushcliffe Borough Council and Severn Trent Water (the Greater Nottingham SFRA Partnership). This report is not addressed to and may not be relied upon by any person or entity other than the Greater Nottingham SFRA Partnership for any purpose without the prior written permission of BVL. BVL, its directors, employees and affiliated companies accept no responsibility or liability for reliance upon or use of this report (whether or not permitted) other than by the Greater Nottingham SFRA Partnership for the purposes for which it was originally commissioned and prepared.

Whilst all reasonable care has been taken in this assessment we cannot guarantee that during the lifetime of the flood risk assessment water levels may not exceed those stated. The report has addressed the risk of flooding from the River Trent, River Erewash, River Derwent, River Leen, Fairham Brook, Nethergate Brook, Day Brook and other watercourses/sources specifically mentioned only, and the conclusions stated in it are based on our best estimate using available data with a precautionary approach taken where possible. We have not assessed flood risks from sources other than those specifically referred to. We must make it clear that the assessment of weather generated flooding is inexact and that analysis is limited by the accuracy and availability of recorded data. Higher water levels may occur in the future due to the actions or omissions of third parties, or to poor maintenance, blockage, storm events in excess of the design standard quoted, inaccuracy or unavailability of data. Flooding beyond that estimated in this report may also occur due to climate change.

In producing this report, BVL has relied upon information provided by others. The completeness or accuracy of this information is not guaranteed by BVL.

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Note for Developers/Landowners The Greater Nottingham Strategic Flood Risk Assessment (SFRA) and River Leen SFRA represent the best currently available flooding information for the City of Nottingham. They should be read in conjunction with the Environment Agency’s Flood Zone Maps as described in Paragraph 5.3 of this document. Together these two documents should be the starting point for establishing the risk of flooding to sites in the City. However, the SFRA does not replace the need for a site-specific flood risk assessment to look at the flood risk and mitigation options for your individual site. Further advice on the process for undertaking a site-specific flood risk assessment is included in Section 4 of this document. It is important that when considering flooding to your individual site, you give due regard to climate change and the impact of proposed flood mitigation measures on flood risk to land elsewhere. Further advice on flood protection measures can be found in the Department of Communities and Local Government (DCLG) publication entitled ‘Improving the Flood Performance of New buildings’ available at http://www.planningportal.gov.uk/uploads/br/flood_performance.pdf and Office of the Deputy Prime Minister (ODPM) publication ‘Preparing for Floods’ available at http://www.planningportal.gov.uk/uploads/odpm/4000000009282.pdf?lang=_e The Environment Agency will expect a site-specific flood risk assessment to consider sustainable forms of surface water management (e.g. SUDS) in preference to traditional forms of drainage. Further advice can be found in the Construction Industry Research and Information Association (CIRIA) publication ‘SUDS Design Manual for England and Wales’ or www.ciria.org/suds/ A site specific flood risk assessment will need to conform with the advice contained in Planning Policy Statement 25: Development and Flood Risk (PPS 25). Excerpts of PPS 25 are included in Appendix B of this document. The Environment Agency encourages pre-planning discussions, in particular of major developments, in order to establish the constraints to delivery of sites at the earliest opportunity. You should also discuss application of the flood risk Sequential Test with the Planning Case Officer at Nottingham City Council.

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GREATER NOTTINGHAM

STRATEGIC FLOOD RISK ASSESSMENT

Summary of Key Findings

Contents 1. Introduction 1 1.1 Project Outline 1 1.2. Planning and Legislative Context 3 2. Study Area and Methodology 4 2.1. Study Area 4 2.2. Existing Flooding Information 4 2.3. Methodology 6 3. Results 8 3.1 Executive Summary 8 3.2. River Trent Corridor 9 3.3 Fairham and Nethergate Brooks 13 3.4 Other Sources of Flooding 13 3.5 River Leen and Day Brook 14 4. Site-Specific Flood Risk Assessments 14 4.1 Advice for Undertaking a Flood Risk Assessment 14 5. Development Control Guide 16 5.1 Guidance 16 6. Glossary of Terms and Abbreviations 18 7. Related Documentation 23 Appendix A – Detailed Methodology 30 Appendix B – Planning Policy Extracts 32

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1. Introduction 1.1 Project Outline 1.1.1 This document is designed to communicate to planners, landowners

and developers the key findings of the study as they relate to land use planning within Nottingham City Council area.

Background and Partnership

1.1.2 In December 2006, Black and Veatch (B&V) commenced a study into

flood risk from the River Trent and its key tributaries through the Nottingham Core Housing Market Area on behalf of the Greater Nottingham Strategic Flood Risk Assessment Partnership (GNSFRA), which comprises:

• Broxtowe Borough Council • Environment Agency • Erewash Borough Council • Gedling Borough Council • Nottingham City Council • Nottingham Regeneration Limited • Nottinghamshire County Council • Rushcliffe Borough Council • Severn Trent Water.

1.1.3 The Strategic Flood Risk Assessment (SFRA) draws upon updated

river modelling and survey data to predict how the River Trent and its key tributaries will react during various storm events, including the key planning benchmark - the 1 in 100 annual chance flood event1.

1.1.4 For Nottingham City Council, the SFRA primarily consolidates and

expands upon existing flooding information to provide a more complete picture of flood risk and its impact on planning.

Project Purpose

1.1.5 The purpose of the SFRA is to:

• provide a map-based planning tool that can be used by planning officers to inform the Local Development Framework (LDF) process and individual planning applications;

• inform and anticipate the Environment Agency’s response to the various stages of the planning process;

1 Probability of flooding is expressed in terms of the statistical likelihood of an event being exceeded in a given year, such as “the 1 in 100 annual chance flood event” or similar. This is often abbreviated as the 1 in 100 year flood. It is essential to appreciate that the 1 in 100 chance flood may re-occur in less than 100 years.

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• help steer new development away from areas of highest risk; and

• assist with emergency planning.

Primary Outputs 1.1.6 The primary outputs of the SFRA are:

• more accurate flood maps indicating areas of flooding at the 1 in 20, 1 in 100, 1 in 100 plus climate change and 1 in 1000 annual chance flood events with both the existing and proposed defences;

• flood dynamic plans illustrating depths and direction of anticipated flows shown on Maps 4–NCC–01 to 06;

• flood hazard maps providing information on the varying degrees of risk within the floodplain based upon the predicted depths and velocities of flood water (see Table 2.1 for further information on flood hazard ratings) shown on Maps 4–NCC–07 to 18;

• breach maps showing the impact of failure of the flood defences on flood risk shown on Maps 1–FDP–30 and Map 1–FDP–33; and

• other sources of flooding map consolidating factual and anecdotal evidence held by a variety of organisations on sources of flooding other than from rivers within the Nottingham City Council area e.g. sewer flooding, drainage issues, groundwater flooding etc. shown on Map 1–OTH-03 and Table 6.1 at the end of the report.

1.1.7 The SFRA will be reviewed when significant events occur, which

require updates to the mapping (e.g. flood event, changes to planning policy, defence works or development affecting major floodplain compensation/ storage areas etc).

Relationship between the SFRA and Existing Flood Zone Mapping

1.1.8 The SFRA differs from the Environment Agency’s Flood Zone Maps by

providing flood mapping taking into account existing flood defences. The Flood Zone Maps (as published on the Environment Agency’s web site) ignore the presence of man made structures (e.g. flood defences, railway embankments etc.).

1.1.9 The SFRA provides more refined flooding information for the River

Trent and its key tributaries and the SFRA should be used to compliment the Flood Zone Maps. Watercourses not specifically referred to are not included within the SFRA study. A limited study of flooding from other sources (e.g. sewer flooding, drainage issues, groundwater flooding etc.) has been made.

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1.2. Planning and Legislative Context 1.2.1 In 2004 the Planning and Compulsory Purchase Act introduced

comprehensive reforms to the planning system which replaced Local Plans with Local Development Frameworks (LDFs). LDFs are a ‘portfolio’ of documents known as Local Development Documents (LDDs), which outline the spatial planning strategy for the local area.

1.2.2 LDDs should reflect the Government’s policies for sustainable

development, which includes avoiding new development in areas at risk of flooding and taking climate change impacts into account in the location and design of development (PPS 25/Annex A3).

1.2.3 National planning policy on flooding is contained within Planning Policy

Statement 25: Development and Flood Risk2 (PPS 25) and its accompanying Practice Guide, which requires planners to take account of flood risk at all stages of the planning process in order to avoid inappropriate development in areas at risk of flooding and to steer new development toward areas of lowest flood risk (PPS 25/Paragraph 5). Please see Appendix B for further excerpts of PPS 25.

1.2.4 PPS 25 requires Local Planning Authorities (LPAs) to demonstrate that

a risk-based sequential approach to the allocation of development within LDDs has been implemented. This risk-based sequential approach states that development should first take place in areas of lowest flood risk. Where there are no lower risk sites reasonably available, development proposals need to be safe taking into account the vulnerability of land uses to flooding (PPS 25/Paragraphs 16 and 17).

1.2.5 The SFRA is a non-statutory document and does not itself provide a

sequential approach as required by PPS 25. The SFRA provides the evidence base needed to inform the application of a sequential approach and undertake the sequential test both in the allocation of development sites in LDDs and in the determination of individual planning applications. Nottingham City Council will therefore have due regard to PPS 25 and the results of the SFRA when considering the future use of land.

1.2.6 In terms of the PPS 25 Practice Guide, this SFRA constitutes a Level 2

assessment and provides a comprehensive assessment of the risks of flooding both now and with an allowance for climate change; detailed flood hazard information; breach mapping; and an appreciation of the varying degrees of flood risk within a flood zone. A full list of the expected outputs of a Level 2 SFRA can be found in Paragraph 3.57 of the PPS 25 Practice Guide.

2 PPS25 = Planning Policy Statement 25: Development and Flood Risk, CLG, 2006. This has an accompanying Practice Guide published in June 2008.

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1.2.7 The SFRA does not replace the need for developers to prepare site–specific flood risk assessments but rather it provides an overview of flood risk at a catchment-wide scale. Further advice on the requirements of site-specific flood risk assessments is included in Section 4.

1.2.8 A key decision-making principle of the recently published Planning

Policy Statement on Planning and Climate Change3 is that new development should be planned to minimize future vulnerability in a changing climate. The SFRA provides information of the likely impact that climate change will have on flood risk through Nottingham to inform land use planning decisions.

1.2.9 The Environment Agency has project managed and given technical

advice to the GNSFRA Partnership. However, as a specific consultation body, this involvement does not guarantee that the Environment Agency will support LDDs, rather it opens dialogue and helps identify at the earliest possible stage in the plan-making process areas of concern.

2. Study Area and Methodology 2.1. Study Area 2.1.1 A location plan showing the study area, key watercourses and

associated flood zones is shown on Map 4 –NTS –01. 2.2. Existing Flooding Information

River Trent Corridor and Proposed Flood Alleviation Scheme 2.2.1 In March 2005, the Environment Agency produced the River Trent

Fluvial Strategy which assessed the risk of flooding from the fluvial stretch of the River Trent from Stoke on Trent to the tidal limits at Cromwell Lock, downstream of Newark on Trent.

2.2.2 The Strategy established that the current flood defences through

Nottingham do not provide the standard of protection required and recommended that new defences be constructed.

2.2.3 The Environment Agency completed the West Bridgford Flood

Alleviation Scheme (FAS) in 2007, which provides protection against flooding to Wilford and Silverdale in the Nottingham City Council area for up to a 1 in 100 year standard.

3 PPS1 = Delivering Sustainable Development, CLG, 2005. This has a supplementary document entitled Planning Policy Statement: Planning and Climate Change, CLG, 2007.

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2.2.4 The Nottingham Trent Left Bank FAS covers some 27 km, beginning at Sawley and ending at Radcliffe Railway Viaduct in Colwick. It is designed to protect over 15,000 homes from flooding of the River Trent.

2.2.5 The Environment Agency is currently considering the alignment and

height of these proposed defences and their impact elsewhere. Subject to obtaining the appropriate permissions and funding, it is envisaged that construction of the Nottingham Trent Left Bank FAS would start sometime after 2009.

2.2.6 Further information on the proposed Nottingham Trent Left Bank FAS

can be obtained from the Environment Agency. 2.2.7 National guidelines on the standard of protection offered by flood

alleviation schemes are set by the Department for Environment, Food & Rural Affairs (Defra). It is unlikely that the new defences through Nottingham will provide protection against flooding during a climate change scenario. In the context of the SFRA this means that, even after the construction of the FAS, new development proposals will need to give careful consideration to the increased risk of flooding with climate change. It may be that some development is not appropriate or sustainable even if it is located behind the new defences.

Fairham and Nethergate Brooks

2.2.8 The Environment Agency made ground level data and information held

on river channel sections for Fairham and Nethergate Brooks available to the SFRA as it was necessary to construct a model of these watercourses. Further information on the modelling is included in Appendix A and Volume 4 of the technical report. Flood outlines for Fairham and Nethergate Brooks are shown on Map 4–FDP–01 to 03.

Other Minor Watercourses 2.2.9 For Nottingham City Council’s area, the SFRA has concentrated on the

risk of river flooding from the River Trent, River Leen, Day Brook, Fairham Brook and Nethergate Brook. However, there are a number of smaller watercourses in Nottingham City Council’s area which present a risk of flooding such as Tinkers Leen, Tottle Brook and Robins Wood Dyke.

Other Sources of Flooding 2.2.10 Existing information has also been collated on other sources of known

flooding in Nottingham City Council’s area (e.g. sewer flooding, drainage issues, groundwater flooding etc.) from a variety of anecdotal and factual sources including Severn Trent Water, a Nottingham City Council Drainage Engineer. This information is shown on Map 1–OTH–03.

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River Leen and Day Brook 2.2.11 In July 2007 Nottingham City Council released the River Leen Strategic

Flood Risk Assessment (SFRA). Technical and non-technical flooding information for the River Leen and Day Brook is available in the separate River Leen SFRA, which can be obtained from the Environment Agency or Nottingham City Council.

2.2.12 The River Leen SFRA model has been incorporated into the Greater

Nottingham SFRA model of the River Trent in order to provide a holistic view of flooding within Nottingham City Council’s area and to utilise the best currently available flooding information.

2.2.13 Together the River Leen SFRA and Greater Nottingham SFRA provide

a comprehensive strategic assessment of flood risk to the City of Nottingham.

2.3. Methodology River Trent Corridor 2.3.1 In order to build upon the existing River Trent Fluvial Strategy for

planning purposes, it was decided to undertake a linked one-dimensional/two-dimensional modelling4 exercise for the River Trent through the study area. Detailed information on the methodology applied is included in Appendix A and reference should be made to Volume 4 of the technical report.

2.3.2 Paragraph 4 of PPS 25 advises that present and future flood risk

should be taken into account in order to avoid, reduce and manage flood risk through positive planning. To accord with these requirements, the model was run at a 1 in 20, 1 in 100, 1 in 100 plus climate change and 1 in 1000 annual chance flood event for the scenarios shown in Figure 2.1.

4 See Volume 1 of the technical report for details.

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Figure 2.1 – Scenarios Tested

2.3.3 The data on flood depths and velocities from each of the model runs

was then translated into a flood hazard rating by applying research undertaken by the Environment Agency and Defra5 (see Table 2.1). This information provides a greater understanding of the varying degrees of risk within a flood zone and informs emergency planning and evacuation decisions. The results are shown on Map 1–DEP–01 to Map 1–DEP–06 in Volume 1 of the technical report.

Table 2.1 – Flood Hazard Rating Table

Degree of Flood

Hazard Hazard Rating

Description

Low

<0.75

Caution

Flood zone with shallow flowing water or deep

standing water.

Moderate

0.75 – 1.25

Dangerous for

some

Danger: flood zone with deep or

fast flowing water.

Significant

1.25 – 2.50

Dangerous for most people

Danger: flood zone with deep

fast flowing water.

Extreme

>2.50 Dangerous for all

Extreme danger: flood zone with

deep fast flowing water.

5 Defra ‘Research on Flood Risks to People FD2321 Rev0.2 Phase2’ available at www.hydres.co.uk

With existing flood defences

With defences not breached

With defences breached

With defences not breached

With defences breached

With proposed flood defences

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Fairham and Nethergate Brooks

2.3.4 Details of the methodology used to construct the model of Fairham and Nethergate Brooks is included in Appendix A and Volume 4 of the technical report.

2.3.5 Once the model was constructed, it was run for the key planning

benchmark flood events described in Paragraph 2.3.2 and flood maps were produced.

2.3.6 The SFRA has provided flood mapping of Fairham and Nethergate

Brooks for the first time. However, the robustness of the outlines can be improved upon through the collection of river level data during future flood events.

Other Sources of Flooding

2.3.7 In order to understand all possible sources of flood risk to the City of

Nottingham, information was collated from a range of organisations as discussed in Paragraph 2.2.10 and Section 3.4.

River Leen and Day Brook 2.3.8 No further work was required to the model produced for the River Leen

SFRA and part of this model was incorporated into the SFRA model. 3. Results 3.1 Executive Summary 3.1.1 The existing River Trent flood defences provide protection against

flooding for up to about a 1 in 50 annual chance flood event. The Environment Agency propose to increase the standard of protection through Nottingham, as part of the Nottingham Trent Left Bank Flood Alleviation Scheme (FAS).

3.1.2 Once the Nottingham Trent Left Bank FAS is completed, the City of

Nottingham will benefit from flood protection up to a 1 in 100 year standard, based upon current understanding of the FAS and flood risk.

3.1.3 The flood defences on the right bank of the River Trent have already

been improved through West Bridgford, protecting Silverdale and Wilford within Nottingham City Council’s area.

3.1.4 The SFRA predicts that flooding will significantly increase with climate

change, such that the flood outlines closely resemble the 1 in 1000 annual chance flood event.

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3.1.5 During a climate change scenario, it is expected that the new defences will overtop and there will be major flooding of the City of Nottingham. Major infrastructure such as the A453 would also be affected.

3.1.6 If a 1 in 100 year event was to occur prior to the defences being raised,

the SFRA has identified a flow route into the City Centre using the Nottingham Canal and railway line which act as secondary channels. This is broadly similar to a flow route observed during the 1947 flooding.

3.2. River Trent Corridor 3.2.1 The results of the SFRA are provided below in the same sequence as

the scenarios outlined in Paragraph 2.3.2.

Scenario 1 – Flood Risk with Existing Defences 3.2.2 The purpose of testing this scenario is to understand the short term

flood risk to Nottingham City Council area until the flood defences from Sawley to Colwick have been completed.

a – 1 in 20 Annual Chance Flood Event

3.2.3 In a 1 in 20 annual chance flood event, flooding is limited on the right

bank to Clifton Grove and land between the River Trent and Clifton Wood, as shown on Map 4–NCC–01. On the left bank land to the south of Thane Road and around the Lenton Lane area (Map 4–NCC–02) as well as the Queens Drive Park and Ride facility (Map 4–NCC–02) is expected to flood during a 1 in 20 annual chance flood event. Pockets of flooding are also expected around the Park Yacht Club area in the Waterside Regeneration Zone (Map 4–NCC–03) and all of Colwick Country Park (Map 4–NCC–03) is predicted to flood.

b – 1 in 100 Annual Chance Flood Event

3.2.4 During a 1 in 100 annual chance flood event, flooding is predicted to

severely affect the Boots site with depths of flood water reaching over 1.5m deep, as shown on Map 4–NCC–01. University Sports Ground is also predicted to be badly affected with flood water also reaching over 1.5m deep, as shown on Map 4–NCC–02.

3.2.5 Flood water enters the city from upstream through Beeston and flows

over the railway line, utilising Nottingham Canal and the railway line as a gateway for flood water into the City of Nottingham. The ability of the Canal to convey flood water has been identified using the more advanced two-dimensional model prepared for the SFRA.

3.2.6 Flood water is then predicted to follow the railway line and University

Boulevard flowing north eastwards and is able to flow below the A52

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and put parts of the Queens Medical Centre at risk, as shown on Map 4–NCC–02. The new Diagnostic Treatment Centre has been built at a high level in response to concerns about flood risk from the River Leen but it is unclear if the floor level is above possible flood levels from the River Trent.

3.2.7 During a 1 in 100 annual chance flood event, the flow route into the city

from upstream is predicted to run out of steam in Lenton and cause flood water to pond around the Leengate and Abbey Bridge area. Depths of flood water are generally expected to be less than 500mm, as shown on Map 4–NCC–02.

3.2.8 Nottingham Canal is a gateway for flood water to enter the City of

Nottingham and puts large areas of the City at risk. Initially, this affects properties at Castle Marina and Castle Meadow Retail Park, as shown on Map 4–NCC–02, from where flood water then spills over the railway line putting large parts of the New Meadows at risk. Depths of flooding in the New Meadows are generally less than 300mm with the exception of around Answorth Drive where up to 700mm of flood water is expected.

3.2.9 Flood water continues along Nottingham Canal and the railway line

putting large areas of the Southside Regeneration Zone at risk, including Nottingham Train Station, as shown on Map 4–NCC–02. Parts of the Eastside Regeneration Zone such as the Extended Island site and BioCity are also at flood risk as shown on the same plan. Depths of flood water at the Extended Island site are shown to be about 0.56m and up to 1.36m in the Eastside Regeneration Zone.

3.2.10 Flood water continues to utilise Nottingham Canal as a route for flood

water and puts areas around Meadow Lane and County Road (Map 4–NCC–02) at risk of flooding, including existing residential properties at Quayside Close.

3.2.11 Flood water also directly overtops the flood defences along Victoria

Embankment into the Embankment Recreation Ground and onto parts of the Old Meadows, from where it meets flood water coming from the north (Map 4–NCC–02). Depths of flooding in the Embankment playing fields are predicted to be over 2m in parts whereas depths of flooding in the Meadows are generally less than 300mm.

3.2.12 Separate areas of flooding occur around Nottingham Racecourse and

puts the existing residential properties at Candle Meadow at flood risk, as shown on Map 4–NCC–03.

3.2.13 On the right bank, Silverdale and Wilford are protected against flooding

during a 1 in 100 annual chance flood event by the West Bridgford Flood Alleviation Scheme, as shown on Map 4–NCC–02.

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3.2.14 The predicted depths and velocities of flooding have been translated into a flood hazard rating in accordance with Table 3.1 and are shown on Map 4–NCC–07 to 09. These flood hazard maps show that parts of the Boots site, University Sports Ground, areas around University Boulevard, Abbey Street in Lenton, Castle Marina, parts of New Meadows, Victoria Embankment in the Meadows, Meadow Lane, Southside Regeneration Area, Eastside Regeneration Area and a small area of Nottingham Racecourse have a significant and extreme hazard rating, which means that depths and velocities of flood water are so high that it presents a danger to most people. Generally, the remainder of land within the Nottingham City Council area has a hazard rating of low to moderate.

c – 1 in 100 Annual Chance Flood Event

Plus Allowance For Climate Change

3.2.15 During the climate change scenario, more flooding is expected to impact upon Old Lenton and parts of Lenton Industrial Estate. Larger parts of the NG2 Business Park, the Meadows, Southside Regeneration Zone, parts of the Waterside Regeneration Zone around Meadow Lane to Trent Basin and Nottingham Racecourse are also expected to flood.

3.2.16 There is little separating the flood outline for the 1 in 100 annual flood

event plus an allowance for climate change and the 1 in 1000 annual chance flood event. This means that a climate change scenario has close to a 1 in 1000 year chance of occurring.

d – 1 in 1000 Annual Chance Flood Event

3.2.17 During a 1 in 1000 annual chance flood event, similar patterns of

flooding are expected as described in Paragraph 3.2.15 although more flooding is expected in Lenton Industrial Estate alongside Clifton Boulevard, NG2 Business Park, Old Lenton and at Little Tennis Street in the Waterside Regeneration Zone, as shown on Map 4–NCC–01 to 03.

Scenario 2 – Flood Risk with Existing Defences

Breached 3.2.18 The maximum flood envelope shows the area predicted to flood if the

flood defences failed during a 1 in 100 year flood and shows a maximum flood outline based upon the 14 breaches modelled. The probability of 14 simultaneous breaches occurring during a 1 in 100 year flood is extremely remote. However, it is difficult to predict the location and occurrence of a breach so the maximum flood envelope provides a good indication of the risk. The maximum flood envelope with the existing defences breached is shown on Map 1–FDP–30, which also includes average breach depths.

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Scenario 3 – Flood Risk with Proposed Defences 3.2.19 The SFRA has assumed that the proposed Nottingham Trent Left Bank

flood defences will provide a minimum standard of protection against overtopping of a 1 in 100 annual chance plus 200mm freeboard. Freeboard is an allowance added to flood defences to take account of a) uncertainty in assessing the flood levels (e.g. uncertainty in the flood modelling) and b) other physical effects (e.g. waves, settlement of flood banks) that have not been included elsewhere.

3.2.20 It is assumed that the new defences will not protect against

overtopping during a climate change scenario. 3.2.21 This scenario is important for land use planning in order to provide an

indication of flood risk in the longer term and to inform planning decisions to ensure that new development is sustainable.

a – 1 in 20 Annual Chance Flood Event

3.2.22 The only change that the Nottingham Trent Left Bank FAS has during a

1 in 20 annual chance flood event is to prevent the small pocket of flooding in the Waterside Regeneration Zone at Park Yacht Club, as shown on Map 4–NCC–06. Otherwise, there are no changes expected once the proposed flood defences have been completed.

b – 1 in 100 Annual Chance Flood Event

3.2.23 Once the proposed defences have been completed, the City of

Nottingham will be protected from flooding by the River Trent during a 1 in 100 annual chance flood event, based upon the assumed minimum standard of protection.

3.2.24 There are plans to utilise Nottingham Racecourse for additional flood

water storage and, if implemented, this would increase the depths of flood water expected to flood the racecourse in a 1 in 100 annual chance flood event, as shown on Map 4–NCC–06.

c – 1 in 100 Annual Chance Flood Event

Plus Allowance For Climate Change

3.2.25 During a climate change scenario, the proposed flood defences are expected to overtop and show similar patterns of flooding as predicted under the existing scenario with an allowance for climate change. This is because the proposed defences are unlikely to be built to prevent flooding during a climate change, which is close to a 1 in 1000 annual chance flood event and would require the height of the defences to be significantly raised. For a description of results see Paragraph 3.2.15.

d – 1 in 1000 Annual Chance Flood Event

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3.2.26 As stated in Paragraph 3.2.16, there is little separating the flood outline for the 1 in 100 annual chance flood event plus an allowance for climate change and the 1 in 1000 annual chance flood event. There is little difference between the existing and proposed defence scenarios during a 1 in 1000 annual chance flood event.

Scenario 4 – Flood Risk with Proposed Defences Breached

3.2.27 A maximum flood envelope has been mapped to show the impact on

flood risk if the proposed defences failed. This flood outline shows similar patterns of flooding to the breach scenario tested based upon the existing defences described in Paragraph 3.2.18 but shows more extensive flooding in the Waterside Regeneration Zone, as shown on Map 1–FDP– 33.

3.3 Fairham and Nethergate Brooks

3.3.1 During a 1 in 20 annual chance flood event, Fairham Brook is predicted

to overtop its banks and flood surrounding fields and Clifton Lane. No property flooding is predicted, as shown on Map 4–FDP–01.

3.3.2 In a 1 in 100 annual chance flood event, flooding is expected to parts of

Fairham Community College, Clifton Lane and the A453 with a few properties being at risk on Hyde Close near to The Spinney. The high ground on the right bank protects Wilford from flooding, as shown on Map 4–FDP–01 and Map 4 –FDP–02.

3.3.3 During both a climate change scenario and 1 in 1000 annual chance

flood event, more flooding is expected and high ground on the right bank close to The Down overtops. Most of the properties in Wilford to the west of Clifton Boulevard are at risk. Flows would also pass through the subways underneath Clifton Boulevard and Clifton Road and put the ambulance station and its access road at risk. Other properties near Bradbourne Drive and off Ruddington Lane are predicted to flood, as shown on Map 4–FDP–02.

3.3.4 The Nethergate Brook is mainly contained within its channel and

flooding is limited to the confluence with Fairham Brook.

3.4 Other Sources of Flooding

3.4.1 Anecdotal and factual information was gathered on other possible sources of flooding and this information is consolidated on Maps 1-OTH-01 to 03. These maps indicates areas of drainage and sewer problems, flooding from surface water, sites where sandbags have been provided and identifies key assets such as balancing ponds, flood storage lagoons and sewage pumping stations.

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3.4.2 For Nottingham City Council’s administrative area, a large area of rising groundwater levels has been identified in Old Basford which causes property flooding and a large area of flooding is expected from the River Trent in Wilford. Elsewhere, sewer flooding and highway drainage issues have been identified at Daleside Road, Clifton Boulevard, Queens Drive and Lenton Lane.

3.5 River Leen and Day Brook 3.5.1 Please refer to the River Leen SFRA for results of the risk of flooding

from the River Leen and Day Brook. 4. Site-Specific Flood Risk Assessments 4.1 Advice for Undertaking a Flood Risk Assessment 4.1.1 The outputs of the SFRA are focused upon establishing the risk of

flooding and improved flood mapping and modelling for planning purposes. These outputs are compatible with the requirement of Nottingham City Council to produce an SFRA to inform preparation of the LDDs, identify broad principles to assist the development control process and to quantify perceived constraints holding back redevelopment of inner city brownfield land.

4.1.2 The SFRA does not provide specific flood risk information for individual

sites. Therefore, those proposing development will need to utilise the flood dynamic plans, flood hazard information and general discussion in the SFRA as the starting point for considering flood risk to development proposals.

4.1.3 A site-specific flood risk assessment may need to involve river

modelling where built development and flood mitigation measures require testing.

4.1.4 However, it is envisaged that the number of site-specific flood risk

assessments needing to be supported by river modelling will be reduced because the SFRA provides greater flooding information than currently available and the LDF process will aim to steer development away from those areas of highest flood risk.

4.1.5 Paragraph 3.78 of the PPS 25 Practice Guide recommends that the

approach shown in Figure 4.1 is taken to scoping the requirements of a site-specific flood risk assessment.

4.1.6 The Environment Agency encourages pre-application discussion and

offers a pre-planning enquiry service were advice can be given on the preparation of flood risk assessments for development proposals. As a minimum, this service requires submission of a site location plan or other means of site identification such as postal address or grid

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reference. Where further information is available (e.g. development proposals, ground level data, statement of development principles etc.) this should be provided with the enquiry.

Figure 4.1 – Scoping of Site Specific Flood Risk Assessment

Development Description and Location

e.g. review LDD, flood risk vulnerability classification

Definition of Flood Hazard e.g. identify all flood sources and

existing surface water arrangements for the site

Probability e.g. information from the SFRA

covering the site

Climate Change e.g. effects of climate change on flood risk for the lifetime of the

development

Detailed Development Proposals

e.g. details of development layout

Flood Risk Management Measures

e.g. how will the site be protected from flooding

Off Site Impacts e.g. incorporate SUDS in overall design or justify why they are not

suitable

Residual Risk e.g. assessment of flood-related risks that remain after measures to protect

site

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5. Development Control Guide 5.1 Guidance 5.1.1 The SFRA is designed to provide a robust evidence base upon which

informed decisions about land use planning can be made. However, it must be stressed that the SFRA is not intended to replace consultation with the Environment Agency who remain the key custodian of flooding data and will continue to provide technical responses to planning consultations.

5.1.2 Therefore, for Development Control the key information will be the

flood dynamic plans for discussions with developers and landowners; understanding site constraints; and when to consult with the Environment Agency.

5.1.3 The Environment Agency’s existing Flood Zone Maps and the SFRA

should be looked at together when assessing the vulnerability of a development proposal to flooding. In general, the SFRA will provide more refined flooding information for the River Trent and its key tributaries than the Flood Zone Maps. The SFRA however, concentrates on only the major watercourses and omits flood risk from some local watercourses.

5.1.4 In some circumstances, the Flood Zone Maps will show a site to be at

risk and yet the SFRA shows the site not to be. This is because the SFRA has used more advanced modelling techniques and takes account of the presence of flood defences. However, it should not be assumed that a site-specific flood risk assessment is not required because as stated above in Paragraph 5.1.3 the SFRA does not show flood risk from local watercourses.

5.1.5 In these cases where a site is shown as being at risk of flooding on one

map but not the other, planning officers are advised to discuss the site with the local Environment Agency office. Developers are reminded that, where possible, flood risk matters should be considered at the earliest possible opportunity and the Environment Agency encourages pre-planning consultation and involvement.

5.1.6 The other maps produced as part of the SFRA (e.g. flood hazard maps,

breach maps, other sources of flooding maps etc.) may be useful to planning officers in cases where there are drainage or emergency planning issues. However, planning officers are not expected to become flooding experts and the SFRA does not replace the need to seek advice from relevant consultees.

5.1.7 A site specific flood risk assessment is required for any development

proposals in Flood Zones 2 or Flood Zone 3 and for developments over 1 hectare in Flood Zone 1, as set out in Paragraph 22 of PPS 25.

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6. Glossary of Terms and Abbreviations Brownfield Land Land which is or was occupied by a

permanent structure, including the curtilage of the developed land and any associated fixed surface infrastructure. Also referred to as developable previously-developed land.

Defra Department of Environment, Food and Rural Affairs.

Exception Test The Exception Test as set out by PPS 25 requires development to provide wider sustainability benefits that outweigh flood risk, be on developable previously-developed land and be supported by a satisfactory flood risk assessment.

Flood Dynamic Maps A map showing the direction, average spot depth and cause of flooding.

Flood Risk Assessment (FRA)

A study to assess the risk to an area or site from flooding, now and in the future, and to assess the impact that any changes or development on the site or area will have on flood risk to the site and elsewhere.

Freeboard The design of an asset will include an allowance (known as the freeboard allowance) for uncertainty in design and construction to ensure the completed asset can withstand the design flood (say, a 2% or 1 in 50 year flood). The design freeboard will allow for uncertainty in water levels and settlement of embankment materials and foundations.

Flood Zone Maps

Map published by the Environment Agency on the internet showing flood risk separated into three zones as defined in PPS 25. It does not show other sources of flooding such as surface water, groundwater, sewers, canals and reservoirs which also need to be included in the flood risk assessment which is needed to support a planning application.

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Functional Floodplain An area that would naturally flood during an event up to and including a 1 in 20 annual chance flood event. However, areas that are prevented from doing so by existing infrastructure or solid buildings will not normally be defined as functional floodplain, in accordance with Paragraph 3.15 of PPS 25 Practice Guide.

Greater Nottingham Strategic Flood Risk Assessment Partnership (GNSFRA)

A collaborative project to produce floodplain mapping of the River Trent and its key tributaries.

Left Bank The river bank on the left side when viewed by a person stood facing downstream.

LiDAR A technique for obtaining ground level data, stands for Light Detection And Ranging.

Local Development Documents (LDDs)

Planning documents which form part of the Local Development Framework.

Local Development Framework (LDF) A folder of Local Development Documents prepared by district councils, unitary authorities or national park authorities that outline the spatial planning strategy for the local area.

Other Sources of Flooding Maps A map showing anecdotal and factual information on known sources of flooding other than rivers and streams e.g. sewer flooding, drainage issues etc. included in Volume 1 of the technical report.

Planning Policy Statement (PPS 1) A statement of policy issued by central Government setting out overarching planning policies on the delivery of sustainable development, supplemented by a Planning Policy Statement on Planning and Climate Change.

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Planning Policy Statement 25: Development and Flood Risk (PPS 25)

Sets out Government policy on development and flood risk. Its aims are to ensure that flood risk is taken into account at all stages in the planning process to avoid inappropriate development in areas at risk of flooding, and to direct development away from areas of highest risk. Where new development is, exceptionally, necessary in such areas, policy aims to make it safe, without increasing flood risk elsewhere, and, where possible, reducing flood risk overall.

Planning Policy Statement: Planning and Climate Change - Supplement to Planning Policy Statement 1

Sets out how planning, in providing for the new homes, jobs and infrastructure needed by communities, should help shape places with lower carbon emissions and resilient to the climate change now accepted as inevitable.

Right Bank The river bank on the right side when viewed by a person stood facing downstream.

Sequential Test The flood risk sequential test as set out in PPS 25 requires development to first take place in areas of lowest flood risk.

Strategic Flood Risk Assessment (SFRA)

A high-level document that strategically appraises all sources of flood risk impacting upon a study area and provides a planning tool to inform the planning process.

Sustainability Appraisal (SA) A statutory document under the Planning and Compulsory Purchase Act 2004 which requires LDD to be tested against sustainability criteria.

Sustainable Drainage Systems (SUDS) A collection of management practices and control structures designed to drain water in a more sustainable manner than some conventional techniques and replicate natural patterns of drainage.

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1 in 100 annual chance flood The probability of flooding is expressed in terms of the statistical likelihood of an event being exceeded in a given year, such as “the 1 in 100 annual chance flood event” or similar. This is often abbreviated as the 1 in 100 year flood. It is essential to appreciate that the 1 in 100 chance flood may re-occur in less than 100 years.

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7. Related Documentation Nottingham City Council’s Corporate Plan 2006 - 2011

Nottingham City Council’s Corporate Plan sets out the medium and long terms goals for 2006 until 2011 for achieving a safer, cleaner ambitious Nottingham – a city we’re all proud of. The corporate plan theme ‘Respect for Nottingham’ sets out the approach to delivering a cleaner, greener Nottingham and cites the Green and Open Space Strategy and Climate Change Strategy as key milestones to achieving respect for Nottingham. An addendum was added in April 2007 covering changes to certain measures and targets in the Corporate Plan in line with the refresh of the Local Area Agreements and review of local indications in the Plan.

Climate Protection Strategy September 2006

This appendix to the Corporate Plan aims to put Nottingham on the path toward a low carbon future by reducing carbon dioxide emissions and adapting to the impacts of climate change. A priority for adapting to climate change is to assess the likely impacts of climate change on Nottingham and put in place measures that reduce risk, improve resilience and maximize benefit. This will involve a programme of work on the adaptation agenda to ensure that the Council, its service, the City and its residents are better prepared for climate change impacts.

The Nottingham Declaration on Climate Change August 2006

This document acknowledges the evidence to show that climate change is occurring and sets out the commitments of Nottingham City Council at reducing emissions and addressing the associated risks.

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The declaration welcomes local opportunities to adapt to the impacts of climate change and to improve the local environment. It promises to work with partners and local communities to progressively address causes and impacts of climate change to secure maximum benefit for the community. The declaration also commits to assessing risk associated with climate change and the implications for the Council’s services and communities and adapting accordingly.

Sustainable Development Guide Nottingham City Council publication providing information on the basic principles of sustainable design and advice on saving energy and water in extensions, new builds and general home improvements.

Incorporating Sustainable Drainage Systems (SUDS) in Development in Nottingham City, Consultation Draft, May 2008

This report proposes the adoption of planning guidance to encourage the provision of Sustainable Drainage Systems (SUDS) and their incorporation through such measures as green roofs in developments in the City. The guidance will be used as an adjunct to the existing statutory policy base at national, regional and local level until replaced by planning policies in the emerging Core Strategy.

‘Breathing Space’ - A Strategic Framework for the Management of Nottingham‘s Open and Green Spaces 2007 – 2017

‘Breathing Space’ forms the basis of the City Councils Strategic Framework for the future management of the City’s open and green spaces. Work is currently ongoing to audit existing open space and asses needs in relation to current and future provision of open space. Once this work is finalised, it will be used to develop ‘Breathing Space’ further.

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‘Breathing Space’ will eventually comprise a long-term plan which aims to; provide city residents and visitors with accessible good quality open and green spaces, involve local people and communities, development and management of safe and accessible green spaces, protect open and green spaces now and into the future by raising environmental sustainability, promoting biodiversity, and supporting wildlife and developing open and green spaces to mitigate against and adapt for climate change.

Corporate Biodiversity Statement As part of a review of the Nature Conservation Strategy, the Parks and Open Space Development Service are proposing a biodiversity statement which flags up the City Council’s commitment to fulfilling its responsibilities under the Natural Environment and Rural Communities Act.

‘Learning lessons from the 2007 floods’ by Sir Michael Pitt June 2008

The final report of the independent review into the lessons learned from the Summer 2007 floods, which contains 92 wide-ranging recommendations. The recommendations on building and planning reinforce the role of PPS 25 and presumption against building in high flood risk areas. Web Site: http://www.cabinetoffice.gov.uk/thepittreview.aspx

Future Water – The Government’s water strategy for England February 2008

The consultation document sets out the Government’s plans for water in the future, looking at the water cycle as a whole and every aspect of water use. Future Water builds upon the floods plan ‘Making Space for Water’ and sets out a new approach to managing surface water to promote sustainable drainage above ground. Web Site: http://www.defra.gov.uk/Environment/water/strategy/index.htm

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Making Space for Water Consultation July 2004 First Government response March 2005

Making Space for Water is the Government’s strategy for flood and coastal erosion risk management for the next 20 years. The aim of the strategy is to reduce threat to people and their property; and to deliver greatest environmental, social and economic benefit consistent with sustainable development principles. Web Site: www.defra.gov.uk/environ/fcd/policy/strategy.htm

Planning Policy Statement 25: Development and Flood Risk (PPS 25) December 2006

This planning document sets out the Government’s national policies on different aspects of land use planning with the aim of ensuring flood risk is taken into account at all stages of the planning process and to avoid inappropriate development in areas at risk of flooding. Supported by a Practice Guide to provide information on implementation of the policies set out in PPS 25. Web Site: http://www.communities.gov.uk/pub/955/PlanningPolicyStatement25DevelopmentandFloodRisk_id1504955.pdf

River Leen Hydrological and Hydraulic Modelling Study, Final Report April 2005

Partnership project looking at flood risk from the River Leen and Day Brook through Nottingham to establish standard of protection of flood defences and produce flood mapping.

River Leen and Day Brook Strategic Flood Risk Assessment July 2007

A Strategic Flood Risk Assessment for the River Leen and Day Brook produced in collaboration with Nottingham City Council, Nottingham Regeneration Limited and the Environment Agency.

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8. Further Information 8.1.1 The Environment Agency remains the key custodian of flooding

information and data. Copies of the full SFRA report containing comprehensive technical information on methodology, modelling data etc. are available for inspection at the Environment Agency’s offices in West Bridgford, Nottingham.

8.1.2 Copies of the technical and non-technical documents as they relate to

Nottingham City Council are also available for public inspection at the Reception of Environment and Regeneration at Exchange Buildings North. A text only version of the non-technical document will be made available to download on Nottingham City Council website and CD copies of the documents (including maps) will be available on request.

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Appendix A – Detailed Methodology A.1 A linked one-dimensional/two-dimensional model was developed for

the River Trent to provide more accurate information and representation of the floodplain. This level of detail is critical for planning purposes and also because of the complexity of the floodplain through Nottingham.

A.2 It was necessary to obtain ground level data using a technique known

as LiDAR (Light Detection And Ranging). LiDAR detects ground levels by measuring the delay between a pulse of light emitted toward the ground and the time taken to receive the reflected signal back in the aircraft. The data were filtered to remove buildings and trees in order to give ground levels. For the River Trent corridor, the LiDAR data has a vertical accuracy of +/-15cm. This is well within the Environment Agency’s tolerance of +/-25cm.

A.3 The LiDAR data were then reviewed and key structures that could

obstruct or convey flood water were highlighted e.g. canals, railway and road embankments etc. The consultants undertook site visits to record any key openings through the roads and railway embankments that may influence the flow of water in the floodplain. These structures and openings were then incorporated into the model.

A.4 Existing river models for the River Trent and its main tributaries through

the study area were then included into the SFRA model of the River Trent e.g. River Erewash, River Leen etc. so that a full picture of the risk of flooding and interaction of the River Trent with other watercourses could be formed.

A.5 The SFRA model was then run using flow data from the November

2000 flood event and the resulting flood outlines were compared against actual flooding data and photographs taken during November 2000. For the 41 observations that coincided exactly with the model predictions, there was an average difference in level of 158mm; the maximum was 379mm and the minimum 2mm. This exercise shows that the two-dimensional model calibrates well to the November 2000 flood providing confidence in the results and flood maps.

A.6 The calibrated and verified SFRA model was then run at a 50m coarse

grid size for general checks and testing and at a 15m fine grid size for producing the detailed floodplain maps.

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A.7 It was also necessary to construct a model of Fairham and Nethergate Brooks. First, likely flows in the watercourses were established for the key planning benchmarks – 1 in 20 year flood (functional floodplain), 1 in 100 year flood, 1 in 100 year flood plus climate change and 1 in 1000 year flood. This exercise was carried out using methods from the Flood Estimation Handbook by the Institute of Hydrology (1999) which is an industry recognized approach. Further details of this approach are set out in the accompanying Technical Report.

A.8 Next, the computer model was built using the river sections and LiDAR

data, the latter of which has a vertical accuracy of +/-15cm and is well within the Environment Agency’s standard tolerance of +/-25cm. The model was then verified against a series of sensitivity tests as there is an absence of historic flooding information available.

A.9 Further information on the methodology applied to the Greater

Nottingham SFRA is set out in Volume 4 of the technical report.

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Appendix B – Planning Policy Extracts

Other Sources of Flooding B.1 PPS 25 explains that all forms of flooding, and their impact on the

natural and built environment, are material planning considerations (Paragraph 3) and that a number of forms of flooding present a range of different risks (Paragraph C1).

B.2 PPS 25 is clear that flood risk assessments should consider all forms of flooding and Maps 1-OTH-01 to 03 provide the starting point for this appraisal.

Climate Change B.3 Paragraph 6 of PPS 25 states that policies should be framed for the

location of development which avoids flood risk to people and property where possible and manages any residual risk, taking account of the impacts of climate change.

B.4 A key decision-making principle of the PPS on Planning and Climate

Change is that new development should be planned to minimize future vulnerability in a changing climate and climate change considerations should be integrated into all spatial planning concerns (Paragraph 10).

B.5 A Working Draft of Practice Guidance to support the Planning Policy

Statement on Planning and Climate Change was published in March 2008 which provides guidance on how planning should secure new development and shape places resilient to the effects of climate change. The Working Draft Practice Guidance is available on the Department of Communities and Local Government (DCLG) website.

B.6 Map 4–NCC–01 to 06 show the current flood risk to the borough

together with the predicted increase under a climate change scenario with both the existing and proposed defences in place. Site-specific flood risk assessments should take account of this information in appraising flood risk both now and in the future and in the design of developments that are safe, taking full account of the likely impacts of climate change. Initially, such assessments should be based upon the allowances in Table B.1.

Table B.1 – Climate Change Allowances from PPS 25/Annex B

Parameter 1990 - 2025 2025 - 2050 2055 - 2085 2085 - 2115

Peak Rainfall Intensity

+5% +10% +20% +30%

Peak River Flow

+10% +20%

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B.7 Where the advice of the Greater Nottingham SFRA is superseded by scientific developments on climate change, this information should be used to compliment the SFRA.

Development Behind Defences / Embankments

B.8 PPS 25 advises that, following application of the Sequential Test and

Exception Test, development should not normally be permitted where flood defences, properly maintained and in combination with agreed warning and evacuation procedures, would not provide an acceptable standard of safety taking into account climate change (Paragraph G2).

B.9 Road and railway embankments and other linear infrastructure may

hold back water or create enclosures to form flood storage areas in addition to their primary function. This may or may not be a deliberate design. It is important that this is recognised, and where use of such infrastructure is proposed for flood management purposes, this should be discussed with the infrastructure owners (PPS 25/Paragraph G3 and PPS 25 Practice Guide/Paragraph 7.16).

B.10 The PPS 25 Practice Guide explains that previously, existing raised

embankments may offer a degree of flood protection. However, such structures should only be relied upon to protect new development following a flood risk assessment, which should investigate:

• whether the embankment is made of suitable materials to

prevent seepage of water through it, and is physically strong enough to maintain the pressure of water on one side;

• whether there are any culverts through the embankment or other gaps or holes that would let flood water through;

• the performance of the structure during any recorded historical flood event;

• the long-term Asset Management Plan provided by the owner of the embankment; and

• whether by holding water back, a structure may fall under the regulation requirements of the Reservoirs Act (1975).

B.11 However, both PPS 25 and its accompanying Practice Guide stress

that risks will be greatest close to flood defences and local planning authorities should seek opportunities to set back developments and site new development away from existing flood risk management infrastructure (PPS 25/Paragraph G2 and PPS 25 Practice Guide/Paragraph 7.12).

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Functional Floodplain B.12 The functional floodplain is an area that would naturally flood during an

event up to and including a 1 in 20 annual chance flood event. However, areas that are prevented from doing so by existing infrastructure or solid buildings will not normally be defined as functional floodplain (PPS 25 Practice Guide/Paragraph 4.81).

B.13 Table D1 of PPS 25 explains that only water compatible and essential

infrastructure uses are appropriate in the functional floodplain, subject to being designed and constructed to:

• remain operational and safe for users during times of flood; • result in no net loss of floodplain storage; • not impede water flows; and • not increase flood risk elsewhere.

B.14 Examples of water compatible uses are flood control infrastructure,

water treatment works, sewage treatment works, sand and gravel workings and amenity open space. Examples of essential infrastructure are electricity generating power stations, strategic utility infrastructure and mass evacuation routes (PPS 25/Table D2).

B.15 Those proposing development should utilise the flood dynamic plans to

establish whether the land falls within the functional floodplain, as defined above.

Access and Egress

B.16 PPS 25 requires that safe access and escape is available to and from new developments in flood risk areas (PPS 25/Paragraph 8). The PPS 25 Practice Guide explains that wherever possible, safe access routes should be provided which are located above design flood levels and where this is not possible limited depths of flooding may be appropriate provided that the proposed access is designed with appropriate signage etc. to make it safe (PPS 25 Practice Guide/Chapter 4/Paragraph 4.55).

B.17 Therefore, site-specific flood risk assessments should have due regard

to the depths and velocities of flood water as per Table 2.1 in Section 2 and to the hazard rating maps of the River Trent shown on Maps 4–NCC–07 to 18 prepared as part of the SFRA.

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B.18 In some exceptional cases, developments or redevelopments will be proposed where the building remains safe, but safe access cannot be guaranteed during a flood. In these cases, the Practice Guide advises that the potential implications of this should be considered when assessing the acceptability of the proposals and PPS 25 advises that the emergency services should be consulted on LDDs and planning applications where emergency evacuation requirements are an issue (PPS 25/H11 and Practice Guide/Chapter 4/Paragraph 4.58).

Surface Water Drainage in New and Redeveloped Sites

B.19 PPS 25 requires that, as a minimum standard, no major development

proposals within Nottingham City Council area shall exacerbate the existing flooding situation and that volumes and peak flow rates leaving a developed site should be no greater than the rates prior to the proposed development, unless specific off-site arrangements are made (PPS 25, Paragraph F10). Factual and anecdotal information on existing flooding problems is given on Map 1–OTH–01 to 03.

B.20 Nottingham City Council’s River Leen and Day Brook SFRA found that

flooding experienced in the City is attributed to a legacy of surface water run-off from urban development occurring within the catchment. Therefore, wherever possible, development proposals within this part of the city should seek to reduce volumes and peak flow rates to greenfield run-off rates (average taken to be 4 – 5 l/s/ha). This approach is also advocated by PPS 25.

B.21 Paragraph F6 of PPS 25 also advises that surface water arising from a

developed site should, as far as is practicable, be managed in a sustainable manner to mimic the surface water flows prior to the proposed development, while reducing the flood risk to the site itself and elsewhere, taking climate change into account.

B.22 Priority should be given to the use of Sustainable Drainage Systems

(SUDS) and green infrastructure in meeting the objectives of PPS 25 and should be considered as part of a site-specific flood risk assessment (PPS 25 Paragraphs 6, 8 and E3).

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MAPS Map 4-GEN-01 Watercourses covered in this volume Map 4-GEN-02 Fairham and Nethergate Brooks Location Plan Map 4-GEN-03 Fairham & Nethergate Brooks ISIS Hydraulic Model

Geographic Schematisation (1 of 3) Map 4-GEN-04 Fairham & Nethergate Brooks ISIS Hydraulic Model

Geographic Schematisation (2 of 3) Map 4-GEN-05 Fairham & Nethergate Brooks ISIS Hydraulic Model

Geographic Schematisation (3 of 3) Map 4-GEN-06 Fairham and Nethergate Brook Hydraulic Model Orthogonal

Schematisation Map 4-FDP-01 Flood Dynamic Plan for Fairham and Nethergate Brooks (1 of

3) Map 4-FDP-02 Flood Dynamic Plan for Fairham and Nethergate Brooks (2 of

3) Map 4-FDP-03 Flood Dynamic Plan for Fairham and Nethergate Brooks (3 of

3) Map 4-FDP-04 Flood Dynamic Plan for Tinkers Leen Map 1-FDP-30 River Trent Flood Dynamic Plan – Existing Defences Breached

(2 of 3) Map 1-FDP-33 River Trent Flood Dynamic Plan – Proposed Defences

Breached (2 of 3) Map 4-OTH-01 Robins Wood Dyke Plan Map 4-NCC-01 Flood Dynamic Plan of the River Trent (Existing Defences)

Nottingham City Council (1 of 3) Map 4-NCC-02 Flood Dynamic Plan of the River Trent (Existing Defences)

Nottingham City Council (2 of 3) Map 4-NCC-03 Flood Dynamic Plan of the River Trent (Existing Defences)

Nottingham City Council (3 of 3) Map 4-NCC-04 Flood Dynamic Plan of the River Trent (Proposed Defences)



Nottingham City Council (3 of 3) Map 4-NCC-07 River Trent 100yr Flood Hazard Rating Plan (Existing

Defences) Nottingham City Council Map 4-NCC-08 River Trent 100yr Flood Hazard Rating Plan (Existing





Defences) Nottingham City Council Map 4-NCC-13 River Trent 100yr Flood Hazard Rating Plan (Proposed

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Defences) Nottingham City Council Map 1-OTH-03 Other Sources of Flooding Western Area