Greater Nottingham Strategic Flood Risk Assessment. Summary of Key Findings for Nottingham City Council

Transcription

1 Greater Nottingham Strategic Flood Risk Assessment Summary of Key Findings for Nottingham City Council July 2008

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3 GREATER NOTTINGHAM STRATEGIC FLOOD RISK ASSESSMENT Summary of Key Findings Document issue details: B&V project no Client s reference no. BV-N2/MDC/00026 Version no. Issue date Issue status Distribution Nottingham City Council 1 October 2007 (digital copy only) Draft Report (Electronic Environment Agency copy only) Nottingham Regeneration Ltd. 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 2 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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5 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 and Office of the Deputy Prime Minister (ODPM) publication Preparing for Floods available at 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 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. i

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7 GREATER NOTTINGHAM STRATEGIC FLOOD RISK ASSESSMENT Summary of Key Findings Contents 1. Introduction Project Outline Planning and Legislative Context 3 2. Study Area and Methodology Study Area Existing Flooding Information Methodology 6 3. Results Executive Summary River Trent Corridor Fairham and Nethergate Brooks Other Sources of Flooding River Leen and Day Brook Site-Specific Flood Risk Assessments Advice for Undertaking a Flood Risk Assessment Development Control Guide Guidance Glossary of Terms and Abbreviations Related Documentation 23 Appendix A Detailed Methodology 30 Appendix B Planning Policy Extracts 32 iii

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9 1. Introduction 1.1 Project Outline 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 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 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 event 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 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. 1

10 help steer new development away from areas of highest risk; and assist with emergency planning. Primary Outputs 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 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 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.) 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. 2

11 1.2. Planning and Legislative Context 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 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) National planning policy on flooding is contained within Planning Policy Statement 25: Development and Flood Risk 2 (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 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) 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 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, This has an accompanying Practice Guide published in June

12 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 A key decision-making principle of the recently published Planning Policy Statement on Planning and Climate Change 3 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 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 A location plan showing the study area, key watercourses and associated flood zones is shown on Map 4 NTS Existing Flooding Information River Trent Corridor and Proposed Flood Alleviation Scheme 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 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 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, This has a supplementary document entitled Planning Policy Statement: Planning and Climate Change, CLG,

13 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 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 Further information on the proposed Nottingham Trent Left Bank FAS can be obtained from the Environment Agency 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 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 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 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. 5

14 River Leen and Day Brook 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 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 Together the River Leen SFRA and Greater Nottingham SFRA provide a comprehensive strategic assessment of flood risk to the City of Nottingham Methodology River Trent Corridor In order to build upon the existing River Trent Fluvial Strategy for planning purposes, it was decided to undertake a linked onedimensional/two-dimensional modelling 4 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 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 See Volume 1 of the technical report for details. 6

15 Figure 2.1 Scenarios Tested With existing flood defences With defences not breached With defences breached With proposed flood defences With defences not breached With defences breached 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 Defra 5 (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. Degree of Flood Hazard Table 2.1 Flood Hazard Rating Table Hazard Rating Low <0.75 Caution Moderate Dangerous for some Significant Dangerous for most people Extreme >2.50 Dangerous for all Description Flood zone with shallow flowing water or deep standing water. Danger: flood zone with deep or fast flowing water. Danger: flood zone with deep fast flowing water. Extreme danger: flood zone with deep fast flowing water. 5 Defra Research on Flood Risks to People FD2321 Rev0.2 Phase2 available at 7

16 Fairham and Nethergate Brooks 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 Once the model was constructed, it was run for the key planning benchmark flood events described in Paragraph and flood maps were produced 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 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 and Section 3.4. River Leen and Day Brook 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 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) 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 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 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. 8

17 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 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 River Trent Corridor The results of the SFRA are provided below in the same sequence as the scenarios outlined in Paragraph Scenario 1 Flood Risk with Existing Defences 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 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 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 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 Flood water is then predicted to follow the railway line and University Boulevard flowing north eastwards and is able to flow below the A52 9

18 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 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 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 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 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 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 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 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

19 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 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 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 During a 1 in 1000 annual chance flood event, similar patterns of flooding are expected as described in Paragraph 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 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. 11

20 Scenario 3 Flood Risk with Proposed Defences 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 It is assumed that the new defences will not protect against overtopping during a climate change scenario 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 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 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 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 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 d 1 in 1000 Annual Chance Flood Event 12

21 As stated in Paragraph , 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 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 but shows more extensive flooding in the Waterside Regeneration Zone, as shown on Map 1 FDP Fairham and Nethergate Brooks 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 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 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 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 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. 13

22 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 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 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 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 A site-specific flood risk assessment may need to involve river modelling where built development and flood mitigation measures require testing 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 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 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 14

23 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 15

24 5. Development Control Guide 5.1 Guidance 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 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 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 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 the SFRA does not show flood risk from local watercourses 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 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 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

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26 6. Glossary of Terms and Abbreviations Brownfield Land Defra Exception Test Flood Dynamic Maps Flood Risk Assessment (FRA) 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. Department of Environment, Food and Rural Affairs. 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. A map showing the direction, average spot depth and cause of flooding. 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. 18

27 Functional Floodplain Greater Nottingham Strategic Flood Risk Assessment Partnership (GNSFRA) Left Bank LiDAR Local Development Documents (LDDs) 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. A collaborative project to produce floodplain mapping of the River Trent and its key tributaries. The river bank on the left side when viewed by a person stood facing downstream. A technique for obtaining ground level data, stands for Light Detection And Ranging. 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 Planning Policy Statement (PPS 1) 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. 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. 19

28 Planning Policy Statement 25: Development and Flood Risk (PPS 25) Planning Policy Statement: Planning and Climate Change - Supplement to Planning Policy Statement 1 Right Bank Sequential Test Strategic Flood Risk Assessment (SFRA) 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. 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. The river bank on the right side when viewed by a person stood facing downstream. The flood risk sequential test as set out in PPS 25 requires development to first take place in areas of lowest flood risk. 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. 20

29 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. 21

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31 7. Related Documentation Nottingham City Council s Corporate Plan 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. Climate Protection Strategy September 2006 The Nottingham Declaration on Climate Change August 2006 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. 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. 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. 23

32 Sustainable Development Guide Incorporating Sustainable Drainage Systems (SUDS) in Development in Nottingham City, Consultation Draft, May 2008 Breathing Space - A Strategic Framework for the Management of Nottingham s Open and Green Spaces 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. 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. 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 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. 24

33 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 Learning lessons from the 2007 floods by Sir Michael Pitt June 2008 Future Water The Government s water strategy for England February 2008 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. 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: eview.aspx 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: ater/strategy/index.htm 25

34 Making Space for Water Consultation July 2004 First Government response March 2005 Planning Policy Statement 25: Development and Flood Risk (PPS 25) December 2006 River Leen Hydrological and Hydraulic Modelling Study, Final Report April 2005 River Leen and Day Brook Strategic Flood Risk Assessment July 2007 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: ategy.htm 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: 5/PlanningPolicyStatement25Develop mentandfloodrisk_id pdf 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. 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. 26