PARTNERSHIP OF NORFOLK DISTRICT COUNCILS STRATEGIC FLOOD RISK ASSESSMENT SUBSIDIARY REPORT A NORTH NORFOLK DISTRICT COUNCIL AREA

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2 PARTNERSHIP OF NORFOLK DISTRICT COUNCILS STRATEGIC FLOOD RISK ASSESSMENT SUBSIDIARY REPORT A NORTH NORFOLK DISTRICT COUNCIL AREA DECEMBER 2007 REPORT REF: 7293A/21/CW/06-07/1778

3 PARTNERSHIP OF NORFOLK DISTRICT COUNCILS STRATEGIC FLOOD RISK ASSESSMENT SUBSIDIARY REPORT A NORTH NORFOLK DISTRICT COUNCIL AREA DECEMBER 2007 REPORT REF: 7293A/21/CW/06-07/1778 CLIENT: North Norfolk District Council ENGINEER: Millard Consulting The Atrium Merchants Court St Georges Street Norwich Norfolk NR3 1AB Tel: Fax: Report Prepared By:... Christopher Ward, BSc (Hons), CEng, MICE, MIHT, MCIWEM Report Checked By: Brian Coghlan, BSc (Hons), CEng, PhD, MCIWEM

4 REGISTRATION OF AMENDMENTS Revision and Date Draft 31/07/07 Second Draft 14/09/07 Final 21/12/07 Amendment Details Revision Prepared By Draft CDW JPC Amendments to text and plans CDW BC Final amendments to text and plans CDW BC Revision Approved By Ref: 7293A/21/CW/06-07/1778

5 SUBSIDIARY REPORT A: NORTH NORFOLK DISTRICT COUNCIL AREA CONTENTS 1. INTRODUCTION 1.1 Terms of Reference 1.2 North Norfolk District Council Area 1.3 Local Development Framework and Scope of Stage 2 SFRA 1.4 Shoreline Management Plan 1.5 Coastal Habitat Management Plan 1.6 Catchment Flood Management Plan 1.7 Internal Drainage Boards 1.8 North Norfolk Joint Flood Plan 2. SOURCES OF FLOODING IN NORTH NORFOLK 2.1 Coastal 2.2 Fluvial and Tidal 3. ENVIRONMENT AGENCY FLOOD ZONES 4. HYDRAULIC MODELLING AND FLOOD PROBABILITY MAPPING 5. COASTAL DEFENCE OVERTOPPING AND BREACH SCENARIOS 6. SUSTAINABLE DRAINAGE 7. RECOMMENDATIONS 8. SITE SPECIFIC FLOOD RISK ASSESSMENTS 9. CONCLUSIONS 10. REFERENCES 11. GLOSSARY APPENDICES A. CORRESPONDENCE B. INTERNAL DRAINAGE BOARDS C. PPS25 PRACTICE GUIDE: SITE SPECIFIC FRA PRO-FORMA Ref: 7293A/21/CW/06-07/1778 Page 1

6 PLANS (BOUND SEPARATELY) General 7293A/21/INDEX 1 NORTH NORFOLK DISTRICT COUNCIL: SFRA DRAWINGS INDEX SHEET A/21/INDEX 2 NORTH NORFOLK DISTRICT COUNCIL: SFRA DRAWINGS INDEX SHEET A/21/ A/21/ A/21/ A/21/203 NORTH NORFOLK DISTRICT COUNCIL: THE STUDY AREA RIVERS AND CATCHMENTS ENVIRONMENT AGENCY FLOOD ZONES AND EXISTING FLOOD DEFENCES WEST ENVIRONMENT AGENCY FLOOD ZONES AND EXISTING FLOOD DEFENCES EAST Flood Probability Maps (showing probability of flooding now and for the future climate change scenarios) 7293A/21/210 ALDBOROUGH ZONE 3b FUNCTIONAL FLOODPLAIN WITH/ WITHOUT CLIMATE CHANGE 7293A/21/ A/21/ A/21/ A/21/ A/21/215 ALDBOROUGH ZONE 3a HIGH PROBABILITY WITH/WITHOUT CLIMATE CHANGE ALDBOROUGH ZONE 2 MEDIUM PROBABILITY WITH/WITHOUT CLIMATE CHANGE ALDBOROUGH FLOOD PROBABILITY ZONES 2, 3a AND 3b WITH/ WITHOUT CLIMATE CHANGE CATFIELD ZONE 3b FUNCTIONAL FLOODPLAIN WITH/WITHOUT CLIMATE CHANGE CATFIELD ZONE 3a HIGH PROBABILITY WITH/WITHOUT CLIMATE CHANGE 7293A/21/216 CATFIELD ZONE 2 MEDIUM PROBABILITY WITH/WITHOUT CLIMATE CHANGE 7293A/21/ A/21/218 CATFIELD FLOOD PROBABILITY ZONES 2, 3a AND 3b WITH/ WITHOUT CLIMATE CHANGE CORPUSTY ZONE 3b FUNCTIONAL FLOODPLAIN WITH/WITHOUT CLIMATE CHANGE Ref: 7293A/21/CW/06-07/1778 Page 2

7 7293A/21/ A/21/ A/21/ A/21/222 CORPUSTY ZONE 3a HIGH PROBABILITY WITH/WITHOUT CLIMATE CHANGE CORPUSTY ZONE 2 MEDIUM PROBABILITY WITH/WITHOUT CLIMATE CHANGE CORPUSTY FLOOD PROBABILITY ZONES 2, 3a AND 3b WITH/ WITHOUT CLIMATE CHANGE ERPINGHAM ZONE 3b FUNCTIONAL FLOODPLAIN WITH/WITHOUT CLIMATE CHANGE 7293A/21/223 ERPINGHAM ZONE 3a HIGH PROBABILITY WITH/WITHOUT CLIMATE CHANGE 7293A/21/ A/21/ A/21/226 ERPINGHAM ZONE 2 MEDIUM PROBABILITY WITH/WITHOUT CLIMATE CHANGE ERPINGHAM FLOOD PROBABILITY ZONES 2, 3a AND 3b WITH/ WITHOUT CLIMATE CHANGE FAKENHAM ZONE 3b FUNCTIONAL FLOODPLAIN WITH/WITHOUT CLIMATE CHANGE 7293A/21/227 FAKENHAM ZONE 3a HIGH PROBABILITY WITH/WITHOUT CLIMATE CHANGE 7293A/21/ A/21/ A/21/230 FAKENHAM ZONE 2 MEDIUM PROBABILITY WITH/WITHOUT CLIMATE CHANGE FAKENHAM FLOOD PROBABILITY ZONES 2, 3a AND 3b WITH/ WITHOUT CLIMATE CHANGE GIMINGHAM ZONE 3b FUNCTIONAL FLOODPLAIN WITH/WITHOUT CLIMATE CHANGE 7293A/21/231 GIMINGHAM ZONE 3a HIGH PROBABILITY WITH/WITHOUT CLIMATE CHANGE 7293A/21/ A/21/ A/21/ A/21/235 GIMINGHAM ZONE 2 MEDIUM PROBABILITY WITH/WITHOUT CLIMATE CHANGE GIMINGHAM FLOOD PROBABILITY ZONES 2, 3a AND 3b WITH/ WITHOUT CLIMATE CHANGE HICKLING ZONE 3b FUNCTIONAL FLOODPLAIN WITH/WITHOUT CLIMATE CHANGE HICKLING ZONE 3a HIGH PROBABILITY WITH/WITHOUT CLIMATE CHANGE Ref: 7293A/21/CW/06-07/1778 Page 3

8 7293A/21/236 HICKLING ZONE 2 MEDIUM PROBABILITY WITH/WITHOUT CLIMATE CHANGE 7293A/21/ A/21/ A/21/239 HICKLING FLOOD PROBABILITY ZONES 2, 3a AND 3b WITH/ WITHOUT CLIMATE CHANGE HORNING ZONE 3b FUNCTIONAL FLOODPLAIN WITH/WITHOUT CLIMATE CHANGE HORNING ZONE 3a HIGH PROBABILITY WITH/WITHOUT CLIMATE CHANGE 7293A/21/240 HORNING ZONE 2 MEDIUM PROBABILITY WITH/WITHOUT CLIMATE CHANGE 7293A/21/ A/21/ A/21/ A/21/ A/21/ A/21/ A/21/247 HORNING FLOOD PROBABILITY ZONES 2, 3a AND 3b WITH/ WITHOUT CLIMATE CHANGE HORSEY ZONE 3b FUNCTIONAL FLOODPLAIN WITH/WITHOUT CLIMATE CHANGE HORSEY ZONE 3a HIGH PROBABILITY WITH/WITHOUT CLIMATE CHANGE HORSEY ZONE 2 MEDIUM PROBABILITY WITH/WITHOUT CLIMATE CHANGE HORSEY FLOOD PROBABILITY ZONES 2, 3a AND 3b WITH/WITHOUT CLIMATE CHANGE HOVETON ZONE 3b FUNCTIONAL FLOODPLAIN WITH/WITHOUT CLIMATE CHANGE HOVETON ZONE 3a HIGH PROBABILITY WITH/WITHOUT CLIMATE CHANGE 7293A/21/248 HOVETON ZONE 2 MEDIUM PROBABILITY WITH/WITHOUT CLIMATE CHANGE 7293A/21/ A/21/250 HOVETON FLOOD PROBABILITY ZONES 2, 3a AND 3b WITH/ WITHOUT CLIMATE CHANGE INGWORTH ZONE 3b FUNCTIONAL FLOODPLAIN WITH/WITHOUT CLIMATE CHANGE 7293A/21/251 INGWORTH ZONE 3a HIGH PROBABILITY WITH/WITHOUT CLIMATE CHANGE Ref: 7293A/21/CW/06-07/1778 Page 4

9 7293A/21/ A/21/ A/21/ A/21/255 INGWORTH ZONE 2 MEDIUM PROBABILITY WITH/WITHOUT CLIMATE CHANGE INGWORTH FLOOD PROBABILITY ZONES 2, 3a AND 3b WITH/ WITHOUT CLIMATE CHANGE LANGHAM ZONE 3b FUNCTIONAL FLOODPLAIN WITH/WITHOUT CLIMATE CHANGE LANGHAM ZONE 3a HIGH PROBABILITY WITH/WITHOUT CLIMATE CHANGE 7293A/21/256 LANGHAM ZONE 2 MEDIUM PROBABILITY WITH/WITHOUT CLIMATE CHANGE 7293A/21/ A/21/ A/21/259 LANGHAM FLOOD PROBABILITY ZONES 2, 3a AND 3b WITH/ WITHOUT CLIMATE CHANGE LUDHAM ZONE 3b FUNCTIONAL FLOODPLAIN WITH/WITHOUT CLIMATE CHANGE LUDHAM ZONE 3a HIGH PROBABILITY WITH/WITHOUT CLIMATE CHANGE 7293A/21/260 LUDHAM ZONE 2 MEDIUM PROBABILITY WITH/WITHOUT CLIMATE CHANGE 7293A/21/ A/21/262 LUDHAM FLOOD PROBABILITY ZONES 2, 3a AND 3b WITH/ WITHOUT CLIMATE CHANGE MUNDESLEY ZONE 3b FUNCTIONAL FLOODPLAIN WITH/WITHOUT CLIMATE CHANGE 7293A/21/263 MUNDESLEY ZONE 3a HIGH PROBABILITY WITH/WITHOUT CLIMATE CHANGE 7293A/21/ A/21/ A/21/ A/21/ A/21/268 MUNDESLEY ZONE 2 MEDIUM PROBABILITY WITH/WITHOUT CLIMATE CHANGE MUNDESLEY FLOOD PROBABILITY ZONES 2, 3a AND 3b WITH/ WITHOUT CLIMATE CHANGE POTTER HEIGHAM ZONE 3b FUNCTIONAL FLOODPLAIN WITH/ WITHOUT CLIMATE CHANGE POTTER HEIGHAM ZONE 3a HIGH PROBABILITY WITH/WITHOUT CLIMATE CHANGE POTTER HEIGHAM ZONE 2 MEDIUM PROBABILITY WITH/WITHOUT CLIMATE CHANGE Ref: 7293A/21/CW/06-07/1778 Page 5

10 7293A/21/ A/21/270 POTTER HEIGHAM FLOOD PROBABILITY ZONES 2, 3a AND 3b WITH/WITHOUT CLIMATE CHANGE ROUGHTON ZONE 3b FUNCTIONAL FLOODPLAIN WITH/WITHOUT CLIMATE CHANGE 7293A/21/271 ROUGHTON ZONE 3a HIGH PROBABILITY WITH/WITHOUT CLIMATE CHANGE 7293A/21/ A/21/ A/21/ A/21/ A/21/ A/21/ A/21/ A/21/279 ROUGHTON ZONE 2 MEDIUM PROBABILITY WITH/WITHOUT CLIMATE CHANGE ROUGHTON FLOOD PROBABILITY ZONES 2, 3a AND 3b WITH/ WITHOUT CLIMATE CHANGE SCULTHORPE ZONE 3b FUNCTIONAL FLOODPLAIN WITH/WITHOUT CLIMATE CHANGE SCULTHORPE ZONE 3a HIGH PROBABILITY WITH/WITHOUT CLIMATE CHANGE SCULTHORPE ZONE 2 MEDIUM PROBABILITY WITH/WITHOUT CLIMATE CHANGE SCULTHORPE FLOOD PROBABILITY ZONES 2, 3a AND 3b WITH/ WITHOUT CLIMATE CHANGE STALHAM ZONE 3b FUNCTIONAL FLOODPLAIN WITH/WITHOUT CLIMATE CHANGE STALHAM ZONE 3a HIGH PROBABILITY WITH/WITHOUT CLIMATE CHANGE 7293A/21/280 STALHAM ZONE 2 MEDIUM PROBABILITY WITH/WITHOUT CLIMATE CHANGE 7293A/21/ A/21/ A/21/283 STALHAM FLOOD PROBABILITY ZONES 2, 3a AND 3b WITH/ WITHOUT CLIMATE CHANGE STIFFKEY ZONE 3b FUNCTIONAL FLOODPLAIN WITH/WITHOUT CLIMATE CHANGE STIFFKEY ZONE 3a HIGH PROBABILITY WITH/WITHOUT CLIMATE CHANGE 7293A/21/284 STIFFKEY ZONE 2 MEDIUM PROBABILITY WITH/WITHOUT CLIMATE CHANGE Ref: 7293A/21/CW/06-07/1778 Page 6

11 7293A/21/ A/21/ A/21/ A/21/ A/21/ A/21/290 STIFFKEY FLOOD PROBABILITY ZONES 2, 3a AND 3b WITH/ WITHOUT CLIMATE CHANGE SUTTON ZONE 3b FUNCTIONAL FLOODPLAIN WITH/WITHOUT CLIMATE CHANGE SUTTON ZONE 3a HIGH PROBABILITY WITH/WITHOUT CLIMATE CHANGE SUTTON ZONE 2 MEDIUM PROBABILITY WITH/WITHOUT CLIMATE CHANGE SUTTON FLOOD PROBABILITY ZONES 2, 3a AND 3b WITH/WITHOUT CLIMATE CHANGE THORNAGE ZONE 3b FUNCTIONAL FLOODPLAIN WITH/WITHOUT CLIMATE CHANGE 7293A/21/291 THORNAGE ZONE 3a HIGH PROBABILITY WITH/WITHOUT CLIMATE CHANGE 7293A/21/ A/21/293 THORNAGE ZONE 2 MEDIUM PROBABILITY WITH/WITHOUT CLIMATE CHANGE THORNAGE FLOOD PROBABILITY ZONES 2, 3a AND 3b WITH/ WITHOUT CLIMATE CHANGE 7293A/21/294 WALSINGHAM ZONE 3b FUNCTIONAL FLOODPLAIN WITH/ WITHOUT CLIMATE CHANGE 7293A/21/ A/21/ A/21/297 WALSINGHAM ZONE 3a HIGH PROBABILITY WITH/WITHOUT CLIMATE CHANGE WALSINGHAM ZONE 2 MEDIUM PROBABILITY WITH/WITHOUT CLIMATE CHANGE WALSINGHAM FLOOD PROBABILITY ZONES 2, 3a AND 3b WITH/ WITHOUT CLIMATE CHANGE Coastal Overtopping and Breaching 7293A/21/ A/21/ A/21/2902 SEA PALLING BREACH 1 IN 200 YR EVENT PLUS CLIMATE CHANGE MAXIMUM FLOOD DEPTH AND EXTENT SEA PALLING BREACH 1 IN 200 YR EVENT PLUS CLIMATE CHANGE HAZARD TO PEOPLE MORSTON BREACH AND OVERTOPPING 1 IN 200 YR EVENT PLUS CLIMATE CHANGE MAXIMUM FLOOD DEPTH AND EXTENT Ref: 7293A/21/CW/06-07/1778 Page 7

12 7293A/21/ A/21/ A/21/ A/21/ A/21/2907 MORSTON BREACH AND OVERTOPPING 1 IN 200 YR EVENT PLUS CLIMATE CHANGE HAZARD TO PEOPLE WELLS-NEXT-THE-SEA BREACH AND OVERTOPPING 1 IN 200 YR EVENT PLUS CLIMATE CHANGE MAXIMUM FLOOD DEPTH AND EXTENT WELLS-NEXT-THE-SEA BREACH AND OVERTOPPING 1 IN 200 YR EVENT PLUS CLIMATE CHANGE HAZARD TO PEOPLE WELLS-NEXT-THE-SEA OVERTOPPING ONLY 1 IN 200 YR EVENT PLUS CLIMATE CHANGE MAXIMUM FLOOD DEPTH AND EXTENT WELLS-NEXT-THE-SEA OVERTOPPING ONLY 1 IN 200 YR EVENT PLUS CLIMATE CHANGE HAZARD TO PEOPLE Sustainable Drainage 7293A/21/298 SUITABILITY OF SUSTAINABLE DRAINAGE ACROSS THE NNDC AREA Ref: 7293A/21/CW/06-07/1778 Page 8

13 1.0 INTRODUCTION 1.1 Terms of Reference Millard Consulting were appointed to carry out the Stage 2 Strategic Flood Risk Assessment (SFRA) for the administrative areas covered by a consortium of District Councils consisting of Broadland District Council, North Norfolk District Council, the Broads Authority, Norwich City Council and South Norfolk Council. The particular Terms of Reference for this Stage 2 study are set out in the JBA Consulting document Stage 1 Inception Report and Terms of Reference for Stage 2 dated October The Stage I Study consisted essentially of the compilation of a data inventory together with a review of the various planning and development related flood risk matters considered important to the five authorities. The Stage 1 Study also set out a Scope for the Stage 2 work This Report covers the North Norfolk District Council area The SFRA is intended to be utilised as a planning tool to enable local planning authorities and others to meet the strategic objectives set out in the Department for Communities and Local Government Planning Policy Statement 25 (PPS25) Development and Flood Risk published in PPS25 requires each local planning authority to carry out an SFRA to inform the preparation of local development documents (LDDs), and to enable the LPA to apply the sequential approach in the site allocation process PPS25 covers the general scope of an SFRA in paragraphs E5, E6 and E7. Key paragraphs are: Decision-makers should use the SFRA to inform their knowledge of flooding, refine the information on the Flood Map and determine the variations in flood risk from all sources of flooding across and from their area. These should form the basis for preparing appropriate policies for flood risk management for these areas. The SFRA should be used to inform the Sustainability Appraisal (incorporating the SEA Directive) of the Local Development Ref: 7293A/21/CW/06-07/1778 Page 9

14 Documents (LDDs), and will provide the basis from which to apply the Sequential Test and Exception Test in the development allocation and development control process. Where decision-makers have been unable to allocate all proposed development and infrastructure in accordance with the Sequential Test, taking account of the flood vulnerability category of the intended use, it will be necessary to increase the scope of the SFRA to provide the information necessary for application of the Exception Test. This should additionally, consider the beneficial effects of flood risk management infrastructure in generally reducing the extent and severity of flooding when compared to the Flood Zones on the Flood Map. The increased scope of the SFRA will enable the production of mapping showing flood outlines for different probabilities, impact, speed of onset, depth and velocity variance of flooding taking account of the presence and likely performance of flood risk management infrastructure. There may be considerable benefits in several LPAs, within a catchment area of high development pressure or a designated development area, joining together to undertake a subregional Strategic Flood Risk Assessment. This will help LPAs to consider the issues raised by flooding on the wider scale (of the river catchment and/or coastal cell). This will enable them to contribute to, and take account of, the River Basin Management Plans required to be published by 2009 by the Environment Agency as part of the implementation of the EC Water Framework Directive Other guidance relating to the scope of the SFRA is contained in the February 2007 Communities and Local Government Web-based document Development and Flood Risk, A Practice Guide Companion to PPS25 Living Draft, A Consultation Paper. This document defines two Levels of SFRA, the Level 2 SFRA being more exhaustive than the Level 1 SFRA, each to be adopted in the following circumstances: In local authority areas where flooding is not a major issue and where development pressures are low, a less detailed approach will be required relative to that necessary in areas where there is high development pressure and flooding is a significant issue. A staged approach is therefore recommended in PPS25, designed to allow flexibility in the level of assessment required from one local authority area to another. Ref: 7293A/21/CW/06-07/1778 Page 10

15 Where the need to apply the Exception Test is identified, due to there being an insufficient number of suitably available sites for development within zones of lower flood risk, the scope of the SFRA should be widened. This increased scope SFRA, (see paragraph E6 of PPS25) is referred to a Level 2 SFRA. The PPS25 Practice Guide includes a list of the key outputs required from a Level 1 SFRA. Table 1.1 below shows the Practice Guide requirements and identifies where in this NNDC SFRA the required information can be found. The Practice Guide also includes at paragraph 2.41 a list of key outputs required for a Level 2 SFRA. Some of these outputs are relevant to this NNDC SFRA and Table 1.2 below identifies where in this NNDC SFRA these outputs can be found. Ref: 7293A/21/CW/06-07/1778 Page 11

16 Table 1.1: Required Level 1 SFRA Outputs Practice Guide Companion to PPS 25 Required Level 1 SFRA output Plans showing the LPA area, Main Rivers, ordinary watercourses and flood zones, including the functional floodplain where appropriate, across the local authority area as defined in Table D1 of PPS25, as well as all allocated development sites An assessment of the implications of climate change for flood risk at allocated development sites over an appropriate time period, if this has not been factored into the plans above The location of any flood risk management measures, including both infrastructure and the coverage of flood warning systems Locations where additional development may significantly increase flood risk elsewhere Guidance on the preparation of FRA s for allocated development sites Guidance on the likely applicability of different sustainable drainage systems (SuDS) techniques for managing surface water run-off at key development sites Section in this NNDC SFRA Flood Probability Maps and other Plans. Report Section 4. GIS layers. Flood Probability Maps. Report Section 4. GIS layers. Report Section 2 Report Section 7 Report Section 8 Report Section 6 Ref: 7293A/21/CW/06-07/1778 Page 12

17 Table 1.2: Required Level 2 SFRA Outputs Practice Guide Companion to PPS 25 Required Level 2 SFRA output An appraisal of the current condition of flood defence infrastructure and of likely future policy with regard to its maintenance and upgrade An appraisal of the probability and consequences of overtopping or failure of flood risk management infrastructure, including an appropriate allowance for climate change Maps showing the distribution of flood risk across flood zones Guidance on the appropriate policies for sites which satisfy parts a) and b) of the Exception Test, and requirements to consider at the planning application stage to pass part c) of the Exception Test Guidance on the preparation of FRA s for varying risk across the flood zone Section in this NNDC SFRA Not included Report Section 5 - Coastal Defence Breach and Overtopping Scenarios. Coastal Breach, Overtopping and Hazard Maps, and animations, which all include a climate change allowance Not included Not included Report Section The PPS25 Practice Guide also states: PPS25 requires that LPAs prepare Strategic Flood Risk Assessments (SFRAs) to an appropriate level of detail to allow the Sequential Test to be applied in the site allocation process. This is an essential part of the pre-production/evidence gathering stage of the plan preparation process. Consideration should be given to working jointly with other local authorities and stakeholders to prepare a sub-regional SFRA. The SFRA should take into consideration any regional guidance prepared by the Regional Planning Body. Ref: 7293A/21/CW/06-07/1778 Page 13

18 The SFRA will provide useful baseline information to the Sustainability Appraisal scoping and assessment stages and will also provide the evidence base for application of the Sequential Test and the Exception Test in the land use allocation process. The LPA should demonstrate that it has considered a range of options in conjunction with the flood zone information from the SFRA and applied the Sequential Test, and where necessary the Exception Test, in the site allocation process. This can be undertaken directly or, ideally, as part of the Sustainability Appraisal. Where other sustainability criteria outweigh flood risk issues, the decision making process should be transparent in the Sustainability Appraisal report. The process should take account of any locational criteria included in guidance prepared by the Regional Planning Body The Stage 1 Study says that the NNDC SFRA is required to: provide a reference and policy document to inform Local Development Frameworks and any subsequent plans; ensure that the Planning Authorities meet their obligations under the latest planning guidance; provide a reference and policy document to advise and inform private and commercial developers of their obligations under the latest planning guidance The particular Scope relevant to the NNDC area, as set out in the SFRA Stage 1 study, is itemised in paragraphs and below. 1.2 North Norfolk District Council Area North Norfolk District covers an area of sq km with a coastline of 82.6 km. The area is very diverse; the predominant land use is arable farming with some livestock. Other major land uses include forestry, gravel and sand working, nature reserves on the coastal plain and tourism. The western and central areas are predominantly arable and characterised by heathland, valley mires, woodland, and coastal cliffs. The topography has a greater relief than other areas of Norfolk; the Holt-Cromer ridge, formed of sands and gravels, reaches an elevation of 100 m near Sheringham. The major part of the coastal strip is designated as an Area of Outstanding Natural Beauty, containing several SSSIs, and is recognised as one of Ref: 7293A/21/CW/06-07/1778 Page 14

19 the finest natural coastlines in the British Isles. It includes large areas of saltmarshes developing behind sand dunes and shingle with extensive areas of intertidal sand and mudflats. The eastern area is rather bleaker, with less woodland, and the coast fringed with cliffs of varying height and composition. Coastal erosion is a feature of the North Norfolk coastline. The dynamic processes involved and the policies associated with the management of the retreating coastline are covered in the Kelling to Lowestoft Ness Shoreline Management Plan (SMP), which is currently under review To the south and east of the North Norfolk area lie the Norfolk Broads, the premier wetland within the UK, associated with the Rivers Ant, Thurne, Bure. Where the Broads Authority area overlaps the North Norfolk District Council area, the Broads Authority is the local planning authority There is a thriving tourism industry in North Norfolk, principally centred around the wildlife habitats of the coastal areas, the seaside towns, and the towns and villages associated with the Broads North Norfolk is bounded by Kings Lynn and West Norfolk Borough Council to the west, Breckland District Council and Broadland District Council to the south and Great Yarmouth Borough Council to the south east. Kings Lynn and West Norfolk Borough Council adopted an SFRA in SFRAs also exist for Great Yarmouth Borough Council (Great Yarmouth and Gorleston Strategic Flood Risk Assessment Capita Symonds June 2006) and for Breckland (Breckland Strategic Flood Risk Assessment Mott Macdonald June 2005). Both the Kings Lynn and West Norfolk Borough Council SFRA and the Great Yarmouth and Gorleston SFRA are being updated to be PPS25 compliant. There are no plans to update the Breckland SFRA. 1.3 Local Development Framework and Scope of Stage 2 SFRA The NNDC LDF Core Strategy submission document is now complete. The Examination in Public is scheduled for December The NNDC LDF Submission document (June 2007) proposes that most of the new development in North Norfolk should be concentrated in four of the larger towns of the District, ie Cromer, Fakenham, Holt and North Walsham, which are identified as principal settlements. A lesser level of development is proposed in Ref: 7293A/21/CW/06-07/1778 Page 15

20 secondary settlements identified as Hoveton, Sheringham, Stalham, and Wells-Next-The- Sea. In addition, the Core Strategy proposes that some small scale development is necessary to meet local needs in some of the larger villages and that the service role of these villages should be protected and enhanced. These villages are nominated as service villages, identified as Aldborough, Briston and Melton Constable, Catfield, Corpusty and Saxthorpe, Horning, Little Snoring, Little Walsingham, Ludham, Roughton, and Southrepps. Some of these villages have proposed housing allocations and others will only be permitted infill development in designated areas Five Coastal Service Villages, Bacton, Blakeney, Happisburgh, Mundesley, Overstrand and Weybourne are also identified The LDF Site Specific Proposals Preferred Options Consultation Document (for consultation 25 September 2006 to 6 November 2006) identifies the preferred options (residential, retail, employment, etc) on specific sites associated with these settlements, selected on the basis of a range of criteria, including sustainability The Stage 1 SFRA report inspected each of these preferred option sites against the Environment Agency Flood Zone Maps, which do not take account of climate change, or defences, or hydraulic structures, and determined that on the basis of these maps all but three appeared to be totally within PPS25 Flood Zone 1, ie for which there is no significant risk of flooding from main rivers or sea and which could therefore be considered sequentially preferable to all others. The proposed allocation in Ludham that is partly in Flood Zone 2 is intended for housing. The site in Wells similarly affected is intended as a car park, but is at risk only in the event of breaching or overtopping of the defences This analysis, made in the Stage 1 SFRA on the basis of the Environment Agency Flood Maps, is of limited usefulness, because PPS25 requires that the spatial planning process should take account of climate change. It is conceivable that some sites currently within Flood Zone 1 may be in Flood Zone 3 in the future. This Stage 2 SFRA, which includes an assessment of climate change, is intended to determine whether sites might be at a higher risk than previously identified. Ref: 7293A/21/CW/06-07/1778 Page 16

21 1.3.6 The Stage 1 SFRA study included a review of the apparent flood risk at each of the settlements identified in the LDF consultation. The following scope for the Stage 2 SFRA work was set out: determine and map the PPS25 Zone 3b functional floodplain (the 1 in 20 year return period flood event), the Zone 3a floodplain (the 1 in 100 year return period event), and the Zone 2 floodplain (the 1 in 1,000 year event), with and without the PPS25 allowance for climate change (appropriate to residential development), at the following settlements: Fakenham, Hoveton, Stalham, Sculthorpe, Roughton, Mundesley, Corpusty, Horning, Ludham, Thornage, Erpingham, Gimingham, Stiffkey, Langham, Potter Heigham, Hickling, Horsey, and Ingworth. The modelling and mapping was intended to utilise the existing Environment Agency hydraulic models (prepared by other consulting engineers) and where models had not been constructed, the Stage 1 document noted that: an alternative approach will be needed including possibly some model development. The modelling and mapping was required to represent the with defences scenario, and to include hydraulic structures such as bridges and defences. This is opposed to the Environment Agency Flood Zone Maps which do not account for all of these structures; carry out breach and overtopping modelling to produce maximum extent, depth and hazard maps at three locations along the North Norfolk coast, at Sea Palling, Blakeney/Morston and Wells-Next-The-Sea, the exact location to be agreed with NNDC and the EA; carry out a general assessment of areas being considered for the LDF in the context of the Sequential Test, covering surface water drainage and sustainable drainage The exact scope of this Stage 2 SFRA was refined during the early period of the work to take into account the more detailed requirements of NNDC (see Appendix A). 1.4 Shoreline Management Plan NNDC, together with Great Yarmouth Borough Council, Waveney District Council, the Environment Agency and Natural England are joint sponsors of the Kelling to Lowestoft Shoreline Management Plan (SMP). This second generation SMP is one of several Ref: 7293A/21/CW/06-07/1778 Page 17

22 compiled for various stretches of the UK coastline. The SMP is a coastal defence management document which aims to promote sustainable management policies, for a coastline for the 22 nd century, which achieve objectives without committing to unsustainable defences. It covers policies and scenarios for three epochs (time periods); 0 to 20 years, 20 to 50 years and 50 to 100 years. There are four main objective areas: the framework objective (policies to comply with current defence management framework associated with public funding), the technical objective (policies to have no adverse effect on any physical processes which bring benefits), the environmental objective (policies to take due consideration of biodiversity) and the socio-economic objective (policies to consider current regional development policies and statutory planning policies). The coastline is divided into particular cells to which are assigned coastal defence policies appropriate to the three epochs, which might be advance the (defence) line, hold the line managed retreat or no active intervention. The SMP Review was published in 2006 but its consequences have been considered to be so severe by many stakeholders that authorities are reticent to adopt and implement it until suitable mitigation measures are in place. 1.5 Coastal Habitat Management Plan NNDC, together with Defra, the EA, English Nature, the Natural Environment Research Council are joint sponsors of the North Norfolk Coast Coastal Habitat Management Plan Royal Haskoning Ltd 2003 otherwise known as ChaMP. It is prepared as one of the inputs to the SMP and is intended to direct the long term strategic view of likely losses and gains to habitats and species as a result of coastal processes, climate change and coastal defence policies. It seeks to optimise policies towards offsetting losses. It is linked to national obligations associated with the EU Habitats Directive, the EU Birds Directive and the Ramsar International Convention on Wetlands. 1.6 Catchment Flood Management Plan NNDC area is the subject of two ongoing Catchment Flood Management Plans (CFMP s). The work is being carried out for the EA by its framework consultants. CFMP s are broad scale strategic plans intended to assess how flood risks across a catchment might change and be sustainably managed over the next 50 to 100 years. The work usually considers fluvial catchment systems, across administrative boundaries, and is linked to the UK s obligations in Ref: 7293A/21/CW/06-07/1778 Page 18

23 respect of River Basin Management Plans under the EU Water Framework Directive. The Plans are intended to set out strategic guidance for future flood risk management but not to specify actual flood risk reduction measures or management approaches to be put in place. The date for final publication is uncertain. The two studies covering North Norfolk are: The North Norfolk Catchment Flood Management Plan, which covers the river systems draining northwards (including part of the Borough of Kings Lynn and West Norfolk), ie the Rivers Hun, Burn, Glaven, Stiffkey, Mun and Spring Beck. The settlements of Wells, Stiffkey, Little Walsingham, Blakeney, Langham, Thornage, Holt, Weybourne, Sheringham, Cromer, Mundesly, Bacton and Happisburgh are therefore covered by this Plan. The Broadland Rivers Catchment Flood Management plan, which covers all the river systems draining southward and eastwards towards the River Yare. This includes the Rivers Bure, Wensum, Ant and Thurne in North Norfolk. The settlements of Fakenham, Sculthorpe, Briston/Melton Constable, Corpusty/Saxthorpe, Roughton, Aldborough, Erpingham, Ingworth, North Walsham, Lessingham, Ingham, Horsey, Hickling, Stalham, Sutton, Catfield, Ludham, Horning, Hoveton and Potter Heigham are covered by this Plan. 1.7 Internal Drainage Boards An Internal Drainage Board (IDB) is a statutory public body operating under primary legislation to provide a water level management service within its prescribed drainage district. It raises income through the direct rating of agricultural land and buildings in its drainage district and recovers through a special levy placed on constituent district councils or unitary authorities an income in recognition of the benefit arising from its work to all nonagricultural land and property. The IDB owns, operates and maintains pumping stations, water control structures, sluices and other assets and has the power to designate watercourses (other than EA Main River) as Board Main Drains which it then maintains. It is the relevant operating and drainage authority within its district and can control third party works through its Byelaws made under the Land Drainage Act Ref: 7293A/21/CW/06-07/1778 Page 19

24 1.7.2 The IDB consortium operating in North Norfolk is the Water Management Alliance, based in King s Lynn and information relating to its areas and policies is included in Appendix B. The relevant Alliance members are: The Norfolk Rivers IDB formed in 2005 by the amalgamation of seven Boards (North Norfolk IDB, Upper Nar IDB, River Wensum IDB, Upper Yare & Tas IDB, Upper Bure IDB, and the gravitational areas of the Smallborough IDB and Middle Bure IDB. The Broads IDB first formed in 2005 by the amalgamation of eight Boards (Happisburgh to Winterton IDB, Repps, Martham & Thurne IDB, Muckfleet & South Flegg IDB, Lower Bure, Halvergate Fleet & Acle Marshes IDB and the pumped areas of the Smallburgh IDB and the Middle Bure IDB. The Lower Yare First IDB and the Lower Yare Fourth IDB also joined the Broads IDB; the new amalgamation is the Broads (2006) IDB The IDB s are not statutory consultees in the planning process, but the Environment Agency informs applicants and the Local Planning Authority that a particular development may lie within an IDB district and that its Byelaws will apply. The Water Management Alliance has a planning officer and planning applications are scrutinised regularly. An IDB is also entitled to receive payment in the form of a development contribution from any development either within its district, or from outside the district but within the catchment, for managing any additional flows. This charge is index-linked and is in the order of 40,000 per hectare of additional impermeable area In common with many authorities, IDB s support the principles of sustainable drainage systems as a method of reducing the impact of flooding. IDB s regard it as essential that agreement is reached between the developer, the Local Authority, IDB and Environment Agency, etc., in order to determine and secure the future maintenance of these systems. Ref: 7293A/21/CW/06-07/1778 Page 20

25 1.8 North Norfolk Joint Flood Plan The NNDC Emergency Planning Section, together with other interested parties (the EA, the Police, Fire and Rescue Service, etc) has compiled the Seawitch Joint Flood Plan. It sets out warning and emergency evacuation procedures for all the settlements which are thought to be at risk of coastal flooding. It prescribes and nominates in specific detail all the individual responsibilities, the evacuation routes, the location of rest centres, and the operational procedures which will be triggered in the event of flooding along the coast. The document was issued in 2006 and is updated annually. Ref: 7293A/21/CW/06-07/1778 Page 21

26 2.0 SOURCES OF FLOODING IN NORTH NORFOLK 2.1 Coastal The North Norfolk coastline includes approximately equal lengths of eroding cliffs and low lying land which is susceptible to flooding. The low lying areas are found at each end of the central length (from Kelling Hard to Cart Gap). At the western end of this central stretch there is saltmarsh and the shingle ridge leading to Blakeney Point. In the east there are sand dune areas which protect the Norfolk Broads. All these low lying areas are vulnerable to coastal flooding, and encroachment into the Broads area remains possible. The worst coastal flood recorded is the well documented event of 31 January Where cliffs exist, erosion is the major problem. The cliffs are comprised of silts, sands, clays which are eroded by wave action. This, together with instability of the cliffs, results in the loss of material and retreat of the cliff line. Defences exist at the main settlements in order to limit coastal erosion and protect these settlements Coastal flooding exhibits the highest hazard in North Norfolk. Hazard is especially high where defence failure might occur as flood velocities and depths are likely to be extreme following any defence breach. 2.2 Fluvial and Tidal Fluvial flooding, or a combination of fluvial and tidal flooding, is a threat to settlements in North Norfolk particularly towards the east and south of the District where the Broads river system exists and where the tidal influence dominates. The onset of flooding is slow and is generally associated with tidal effects which are predictable and the subject of Environment Agency flood warnings. Flow velocities during flood conditions are relatively slow and depths relatively shallow. Ref: 7293A/21/CW/06-07/1778 Page 22

27 3.0 ENVIRONMENT AGENCY FLOOD ZONES 3.1 Flood Zones are defined in Table D.1 of PPS25 Development and Flood Risk. The zones delineate areas at risk of fluvial, tidal or coastal flooding. Table D.1 notes that these flood zones refer to the probability of river and sea flooding, ignoring the presence of defences. This is an important qualification, and it should be noted that the Environment Agency Flood Maps available on the EA website, and elsewhere, are drawn on this basis. The EA flood maps therefore give a worst case scenario. o Flood Zone 1 Flood Zone 1 (Low Probability) is defined in PPS25 as land assessed as having a less than 1 in 1,000 annual probability of river or sea flooding in any year (<0.1%). These areas are on higher ground than the areas defined by Zones 2, 3a and 3b. o Flood Zone 2 Flood Zone 2 (Medium Probability) is defined in PPS25 as land assessed as having between a 1 in 100 and 1 in 1,000 annual probability of river flooding (1% 0.1%) or between a 1 in 200 and 1 in 1,000 annual probability of sea flooding (0.5% 0.1%) in any year. o Flood Zone 3a Flood Zone 3a (High Probability) is defined in PPS25 as land assessed as having a 1 in 100 or greater annual probability of river flooding (>1%) or a 1 in 200 or greater annual probability of flooding from the sea (>0.5%) in any year. o Flood Zone 3b Flood Zone 3b (Functional Floodplain) is defined in PPS25 as land where water has to flow or be stored in times of flood. SFRAs should identify this Flood Zone (land which would flood with an annual probability of 1 in 20 (5%) or greater in any year or is designed to flood in an extreme (0.1%) flood, or at another probability to be agreed between the LPA and the Environment Agency, including water conveyance routes). Ref: 7293A/21/CW/06-07/1778 Page 23

28 3.2 PPS25 requires that SFRA s should adopt a more detailed and rigorous approach and take account of the presence of flood defences in flood zone mapping. The Flood Probability Maps included with this SFRA are therefore drawn on this basis, and the flood zones indicated, although using the same category designation (Zones 3b, 3a, and 2), do take account of the existing flood defences. This is noted on the drawings themselves. Ref: 7293A/21/CW/06-07/1778 Page 24

29 4.0 HYDRAULIC MODELLING AND FLOOD PROBABILITY MAPPING 4.1 In order to carry out the hydraulic modelling and flood mapping for this project, well established hydraulic modelling and flood mapping techniques were applied. This involved one- and two-dimensional (1-D/2-D) unsteady hydrodynamic modelling and the application of GIS techniques for further processing of the modelling results. 4.2 The flood mapping analyses the flood risk associated with North Norfolk river systems. T he maps therefore indicate the probability of flooding associated with the river systems, including where the rivers are tidally influenced. Certain coastal areas are also at risk of direct coastal flooding associated with failure or overtopping of coastal defences. Information relating to the risk of coastal flooding is available from the Environment Agency. These SFRA flood probability maps should therefore be read in conjunction with EA information relating to the probability of coastal flooding. 4.3 Most of the flood mapping was based on existing ISIS models prepared by others. These existing models were identified in the Stage 1 SFRA. For areas not already covered by one of the existing ISIS models, new hydrodynamic models were created. The level of sophistication of these 1-D models is appropriate to the strategic nature of this mapping exercise. 4.4 Some areas were modelled using ESTRY, the 1-D component of the TUFLOW modelling software. 4.5 The following settlements were identified in the Stage 1 Inception Report as requiring flood risk mapping and the delineation of the Functional Floodplain: Fakenham, Hoveton, Stalham, Sculthorpe, Roughton, Mundesley, Corpusty, Horning, Ludham, Thornage, Erpingham, Gimingham, Stiffkey, Langham, Potter Heigham, Hickling, Horsey and Ingworth. Table 4.1 below indicates the hydraulic model used for each. Ref: 7293A/21/CW/06-07/1778 Page 25

30 Table 4.1: Flood Mapping Locations and Hydraulic Models North Norfolk District Council Settlement Watercourse Model Model Type and Source Fakenham Wensum Upper Wensum 1-D ISIS Model/EA Hoveton BESL Broads Bure Model 1-D ISIS Model/Halcrow Stalham BESL Broads Ant Model 1-D ISIS Model/Halcrow Sculthorpe Wensum Upper Wensum 1-D ISIS Model/EA Roughton Bure Tributary Bure Tributary 1-D ESTRY Model/Millard Mundesley Mun Mun 1-D ISIS Model/EA Corpusty Bure Bure 1-D ISIS Model/EA Horning BESL Broads Bure Model 1-D ISIS Model/Halcrow Ludham Thurne/ BESL Broads Womack Water Model 1-D ISIS Model/Halcrow Thornage Glaven Glaven Tributary Tributary 1-D ISIS Model/Millard Erpingham Bure Tributary Bure Tributary 1-D ISIS Mode/Millard Gimingham North Norfolk Mun Rivers 1-D ISIS Model/EA Stiffkey North Norfolk Stiffkey Rivers 1-D ISIS Model/EA Langham Stiffkey Stiffkey Tributary Tributary 1-D ESTRY Model/Millard Potter Heigham BESL Broads Thurne Model 1-D ISIS Model/Halcrow Hickling BESL Broads Hickling Broad Model 1-D ISIS Model/Halcrow Horsey Horsey BESL Broads Mere/New Cut Model 1-D ISIS Model/Halcrow Ingworth North Norfolk Bure Rivers 1-D ISIS Model/EA 4.6 For each settlement affected by fluvial flooding there are individual maps showing the 1 in 20 year flood outline (Functional Floodplain Zone 3b), with and without climate change; the 1 in 100 year outline (Zone 3a High Probability), with and without climate change; and the 1 in 1,000 year outline (Zone 2 Medium Probability), with and without climate change. All the SFRA modelling and mapping takes account of the existence of flood defences, whereas, as noted above, the EA flood maps do not. 4.7 Where a particular watercourse reach is tidally influenced, the mapping shows the 1 in 20 year flood outline (Functional Floodplain Zone 3b), with and without climate change; the Ref: 7293A/21/CW/06-07/1778 Page 26

31 outline for a combination of the fluvial 1 in 100 year event combined with the 1 in 200 year tidal event (Zone 3a High Probability), with and without climate change; and the 1 in 1,000 year outline (Zone 2 Medium Probability) with and without climate change. 4.8 The climate change outline is that appropriate to the year 2115, appropriate to the design life of residential development. The climate change increment calculated for use in the hydraulic modelling is that recommended by PPS25, ie in fluvially dominated reaches an increase in peak fluvial flow of 20%. In tidally dominated reaches the tidal climate change increment appropriate to the year 2115 is calculated as set out in PPS25, Annex B, Table B.1. Where appropriate the fluvial and tidal climate change increments are added together in order to obtain the most conservative result. 4.9 There is also a map for each settlement showing all six flood outlines Map scales vary depending upon the size of each settlement and the intention has been to maximise the clarity of the mapping for the purpose of informing the strategic planning process and sequential test decisions The modelling and mapping take account of existing defences and structures whereas the Environment Agency Flood Zone Maps do not The maps are supplied as prints and as GIS layers compatible with MapInfo and ESRI GIS. Ref: 7293A/21/CW/06-07/1778 Page 27

32 5.0 COASTAL DEFENCE OVERTOPPING AND BREACH SCENARIOS Breach in Coastal Defences (200 year event with Climate Change) Residual Risk Mapping of Maximum Flood Depth and Extent 5.1 The Stage 1 Inception Report identified three locations where it was considered important to examine Residual Risk associated with the failure of coastal defences. Specific breach modelling was carried out at Sea Palling, Morston and Wells-Next the-sea. The locations were agreed with NNDC and the EA. The breach locations are chosen based on a qualitative judgement of the magnitude of consequences, rather than on a quantative assessment of the probability of failure of the defence. The Sea Palling breach location is chosen near to communities at risk. The land locally is slightly lower than the surrounding area and it is near to the end of the reef defences. At Morston the village is protected by a flood bank and the breach scenario assesses the effect on the village if the bank breaches. At Wells Next-The-Sea the breach location is chosen at the point in the West Bank which is known to have breached during the 1978 event. 5.2 The breach locations were chosen in consultation with the EA and the Coastal Planning Team at NNDC. A breach could occur at any location, and the probability of a breach occurring at any particular position is not possible to determine in any quantitative way, unless there are known defects or weaknesses or particular characteristics relating to a certain location. The probability of breach will be influenced by the design standard of defence, its condition and maintenance regime. Coastal erosion and loss of beach material are also factors. 5.3 The purpose of the breach analysis is to predict what would happen in this very worst scenario, for the purposes of emergency planning, and in order that planning decisions for areas that benefit from the defences, and decisions relating to the provision of funding for new defence infrastructure and for the maintenance and improvement of existing defences, can be made. Ref: 7293A/21/CW/06-07/1778 Page 28

33 5.4 The breach analysis provides detailed information indicating where the floodwater will go, at what speed, how deep it is, and how long it will take to get there, across the hinterland behind the defences. There will be a Rapid Inundation Zone immediately behind the defence where there will be an extreme degree of hazard to people and property (usually considered to be the general area which floods to a depth of 500mm within 30 minutes, unless otherwise analysed). The computer modelling is dynamic, ie it operates against time steps. The analysis produces maps of water depth and extent at any given time after the breach, together with water velocities, and an animation of the progress of the whole flood is produced. 5.5 If the whole coastline were to be analysed with breaches modelled at many points, the resulting flood line would be similar to the EA Flood Maps, which ignore the presence of flood defences. (Note that the breach analyses carried out in this SFRA include an allowance for future climate change, and therefore the extent of flooding from a series of breaches close together along the coastline would produce a worse flood outline than the EA Flood Maps, as these do not include climate change). Many areas of the North Norfolk Coastline are not at risk of flooding by breach of defences; many stretches of the coastline are high enough to be unaffected by breach or overtopping scenarios, even with the predicted sea rise associated with climate change. However the threat of coastal erosion remains in these areas of the coastline: this is not a topic covered by this SFRA and reference should be made to the SMP for guidance on policies and planning there. 5.6 The breach analysis also allows an assessment of Hazard to People on the basis that the combination of flood speed, and flood depth, will affect people more or less, depending upon physical strength and size. The analysis will produce Hazard Maps showing areas in which during the period of the inundation the flood will produce danger to some, danger to most and danger to all, as defined by EA guidance see below. 5.7 In areas where land values are high behind defences or where development pressures mean that existing development needs to be maintained, or new development behind defences is necessary, the analysis of breach scenarios can guide the location of new development, or essential infrastructure, to areas at least risk even if the defences fail. The breach analysis also allows meaningful evacuation strategies to be formulated. Ref: 7293A/21/CW/06-07/1778 Page 29

34 5.8 In North Norfolk although breach scenarios might show the extent of the spread of inundation behind a defence to be less than the EA maps, it does not mean that the risk is less. All defended areas are special in that they can be inundated very quickly, to a significant depth, although the probability of occurrence is small. In North Norfolk it is unlikely that development pressure by itself will be sufficiently severe to necessitate planning decisions to be made on the basis of breach scenarios. The breach scenarios should be used to inform the preparation of Evacuation Plans and the planning of the emergency services. In these areas land use planning decisions can still be meaningfully made on the basis of the EA without defences flood maps. 5.9 Site specific FRAs prepared by developers should include a breach analysis, if a site behind existing defences is being considered The overtopping and breach scenarios at Sea Palling, Morston and Wells-Next-The-Sea were created by applying two-dimensional unsteady hydrodynamic modelling using the TUFLOW software The TUFLOW software was specifically developed to simulate flow patterns of twodimensional nature as can be observed on floodplains, coastal waters and estuaries. In TUFLOW models the study area is represented as a 2-D domain, whose properties, such as elevation or surface roughness, is assigned by a series of GIS layers The topography of the TUFLOW 2-D domains was based on LiDAR data surveyed between 1999 and 2001 and supplemented by ground survey data of existing flood defence structures Manning s roughness over the study area was assigned using land-use information supplied by the Environment Agency (see Table 5.1 below). Ref: 7293A/21/CW/06-07/1778 Page 30

35 Table 5.1: Manning s Roughness based on Land-Use Manning s n Land-Use Category 0.02 Commercial Industrial Playing Fields Theme Parks Town City 0.03 Intensive Pasture 0.03 Village 0.03 Beach (sand and shingle) Other Extensive Pasture Arable Horticulture 0.07 Forest, Scrub 0.45 Formal Parks 5.14 The boundary conditions for the TUFLOW models are based on a 1 in 200 year tidal event, with an allowance for future climate change appropriate to the next 100 years, with the addition of a three day storm surge to the design event, as indicated in Table 5.2. Sea Palling Table 5.2: Tide Hydrographs for SFRA Breach Models Peak Flood Level (200 year) Allowance for the effects of climate change (According to table B1 of PPS25) Total 3.790m AOD m AOD m AOD Wells-Next-the-Sea Peak Flood Level (200 year) Allowance for the effects of climate change (According to table B1 of PPS25) Total m AOD m AOD m AOD Morston (Blakeney) Peak Flood Level (200 year) Allowance for the effects of climate change (According to table B1 of PPS25) Total m AOD m AOD m AOD Ref: 7293A/21/CW/06-07/1778 Page 31

36 5.15 For defences with crest levels less than the flood level of the design event, the breach is assumed to occur at the point in the surge event where the defence first reaches maximum loading (ie at point of overtopping). Where the height of defences is greater than the design event the breach is assumed to occur such that the highest surge peaks are included within the breach period. The breach width (in hard defences) is assumed to be 50m wide and to be repaired 36 hours after the initial breach All boundary conditions are in accordance with EA national guidance and flood defence levels were agreed beforehand with the Environment Agency Local drains and watercourses have not been considered in these broad scale breach scenarios The mapping shows the maximum extent of inundation together with the maximum depth of the floodwater at any point experienced during the whole period of the breach event. Breach Model Setups 5.19 The Model setup for Sea Palling was as follows: The study area was modelled with a 2-D domain grid size of 25 m x 25 m Sea defences were modelled with a height of 5.65 m AOD at the breach location (50 m) and 200 m either side ie dunes removed for a length of 450 m The depth of the breach extended down to the landward toe of the sea defence at 3.3 m AOD The breach opening was assumed to occur at the third peak at 28 h (3.5 m AOD) until the sixth peak at 64 h (3.5 m AOD). See Figure 5.1 below: Ref: 7293A/21/CW/06-07/1778 Page 32

37 Water Level (m AOD) Time (hours) W ith Surge W ithout Surge Defence Level Timing of Breach Figure 5.1: Model Setup for Sea Palling Breach 5.20 The Model setup for Morston was as follows: The study area was modelled with a grid cell size of 25 m Sea defences were modelled with a height of 4.8 m AOD (Morston West Bank), 5.4 m AOD (East Bank) and 4.2 m AOD (Blakeney West and East Bank) The depth of the breach was at the landward toe of the sea defence at 2.3 m AOD The breach opening was assumed to occur from the time of overtopping of the sea defence at 38 h for 36 hours. See Figure 5.2 below: Ref: 7293A/21/CW/06-07/1778 Page 33

38 Water Level (m AOD) Time (hours) W ith Surge Without Surge West Bank East Bank Blakeney Timing of Breach Figure 5.2: Model Setup for Morston Breach 5.21 The Model setup for Wells-Next-The-Sea was as follows: Study area modelled with a grid of 15x15 m resolution Sea defences were modelled with a height of: m AOD (Wells West Bank to Holkham Gap), 5.0 m AOD (Freeman Street, The Quay), and 6.5 m AOD (Wells East Bank) The depth of the breach was set to the level at the landward toe of the sea defence (0.5 m AOD). The breach opening was assumed to occur from the fifth peak at 52 h (6.26 m AOD) until 88 h (2.39 m AOD). See Figure 5.3 below: Ref: 7293A/21/CW/06-07/1778 Page 34

39 Water Level (m AOD) Time (hours) with surge without surge West Bank Freeman Street East Bank Timing of Breach Figure 5.3: Model Setup for Wells-Next-the-Sea Breach 5.22 It should be noted that in the case of Sea Palling there is no overtopping associated with the breach scenario. In the case of Morston however there is overtopping associated with the breach. Similarly in the case of Wells-Next-The-Sea there is overtopping associated with the breach, and an additional overtopping only scenario has been modelled for this location Table 5.3 summarises the breach modelling parameters for the three locations. Ref: 7293A/21/CW/06-07/1778 Page 35

40 Table 5.3: Summary of Breach and Overtopping Model Setup Parameters Model Parameter Sea Palling Morston Wells Grid Size 25m x 25m 25m x 25m 15m x 15m Defence Crest Levels 5.65m AOD 4.8m AOD 5.3m 6.3m AOD (Wells (Morston West Bank), West Bank to Holkham Gap), 5.0m AOD (Freeman Street, 5.4m AOD The Quay), and 6.5m AOD (East Bank) (Wells East Bank) and 4.2m AOD (Blakeney West and East Bank) Peak Surge Tide Level (1 in 200 year event 4.81m AOD 6.01m AOD 6.26m AOD plus climate change allowance plus storm surge) Width of Breach 50m (and dunes 50m 50m removed for 200m each side of Breach) Base of Breach Level 3.3m AOD at 2.3m AOD 0.5m AOD breach and dunes removed down to 5.65m AOD 200m either side Period of Breach Repaired after Repaired Repaired after 36hrs 36hrs after 36hrs 5.24 In addition to maps and GIS outputs this study has also produced animations of the breach modelling. These show the flood direction and speed, together with depth, across the Ref: 7293A/21/CW/06-07/1778 Page 36

41 hinterland behind the breach, in 15-minute steps. evacuation routes, time of escape and the location of evacuation centres. These are useful for the analysis of Breach in Coastal Defences (200 year event with Climate Change) Residual Risk Hazard to People Mapping 5.25 The Hazard to People rating was modelled in accordance with the guidelines set out in the DEFRA/EA Document Flood Risks to People, Phase 2, R&D Technical Report FD2321 TR1. The hazard rating is a function of flood depth and velocity and is defined as: HR = (( v + 0.5) D) + DF where HR = hazard rating (dimensionless), v = velocity (metres per sec), D = depth (metres), DF = debris factor (set to 1) Other guidance relating to Flood Risks to People is given in Flood Risks to People, Phase 2, R&D Technical Report FD2321 TR2, and Flood Risk Assessment Guidance for New Development, Phase 2, R&D Technical Report FD2320/TR1 and TR The groups of people considered within the Hazard to People Rating are categorised as follows: Danger for Some includes children, the elderly and the infirm Danger for Most includes the general public Danger for All includes emergency services 5.28 The hazard modelling results were categorised into four degrees of flood hazard i.e. low, moderate, significant and extreme, based on the assessment set out in the R&D paper, in accordance with the Table 5.4 below. The hazard mapping was carried out using the TUFLOW Software. Ref: 7293A/21/CW/06-07/1778 Page 37

42 Table 5.4: Hazard to People as a Function of Flood Velocity and Depth (source: table3.2, p.8 DEFRA/EA R&D Flood Risk to People Phase 2 FD2321 TR1) Hazard Rating Degree of Flood Hazard Description <0.75 Low Caution Flood zone with shallow flowing water or deep standing water Moderate Dangerous for some (i.e. children) Danger: Flood zone with deep or fast flowing water Significant Dangerous for most people Danger: flood zone with deep fast flowing water >2.5 Extreme Dangerous for all Extreme danger: flood zone with deep fast flowing water 5.29 The Hazard Maps show the maximum degree of flood hazard experienced at the particular location during the entire period of the breach. Ref: 7293A/21/CW/06-07/1778 Page 38

43 6.0 SUSTAINABLE DRAINAGE SYSTEMS (SUDS) Introduction 6.1 Built development is likely to reduce the permeability of at least part of the site resulting in a change to natural drainage patterns and an increase in peak rates and total quantities of surface water runoff. Traditionally, developed areas have disposed of excess surface water via below ground piped networks, discharging at uncontrolled rates into local watercourses. In areas where both foul water and surface water was transported through the same sewer (ie combined sewers), additional strain was added to sewage treatment works due to the additional volumes of water and during heavy rainfall events these sewers often overflowed causing pollution incidents across neighbouring areas. However, over the past 50 years these systems have been constructed separately thus markedly reducing the number of pollution incidents to the local environment. This has not necessarily solved the issues associated with pollutant runoff from urban areas, which in turn drains into the surface water sewer network and subsequently into local watercourses. With this arrangement and no controls at the outfall locations, the volume and peak runoff rates of the surface water from development areas will increase, resulting in a potential change in the receiving watercourse regime and leading to a potential increase in flood risk to others upstream and downstream. 6.2 Sustainable drainage systems (SuDS) have therefore been developed to tackle these issues by minimising the impacts from the development on the quantity and quality of the runoff and to maximise biodiversity. The main objectives of sustainable drainage include the reduction of runoff rates and volumes, increased natural recharge of the underlying soils and aquifers, reduction of pollution concentrations in storm water and the enhancement of biodiversity. Figure 6.1 illustrates some of the matters that require consideration during the SuDS design process. Ref: 7293A/21/CW/06-07/1778 Page 39

44 Figure 6.1: SuDS design and planning: issues for consideration (taken from Figure 2.2 of CIRIA C697) 6.3 In order to mimic natural catchment processes as closely as possible, a management train can be adopted, using drainage techniques in series to incrementally reduce pollution, flow rates and volumes. A typical hierarchy for the management train is as follows: Prevention good site design and site housekeeping measures to prevent runoff and pollution (eg sweeping to remove surface dust and detritus from car parks), and rainwater reuse/harvesting. Prevention policies should generally be included within the site management plan. Source control control of runoff at or very near its source (eg soakaways, other infiltration methods, green roofs, pervious pavements). Site control management of water in a local area or site (eg routing water from building roofs and car parks to a large soakaway, infiltration or detention basin). Ref: 7293A/21/CW/06-07/1778 Page 40

45 Regional control management of runoff from a site or several sites, typically in a balancing pond or wetland. 6.4 The management train is summarised in Figure 6.2. Wherever possible, stormwater should be managed in small, cost-effective landscape features located within small subcatchments rather than being conveyed to and managed in large systems at the bottom of drainage areas (end of pipe solutions). The techniques that are higher in the hierarchy are preferred to those further down so that prevention and control of water at source should always be considered before site or regional controls. However, where upstream control opportunities are restricted, a number of lower hierarchy options should be used in series. Water should be conveyed elsewhere only if it cannot be dealt with on site. Figure 6.2: SuDS Management Train (taken from Figure 1.5 of CIRIA C697) 6.4 Annex F of PPS25 recommends the maximum practical use of Sustainable Drainage Systems (SuDS) within proposals for new sites. PPS25 requires that SuDS be installed where appropriate, in order to limit the amount of surface water runoff entering drainage systems and to return surface water into the ground to follow its natural drainage path. Ref: 7293A/21/CW/06-07/1778 Page 41

46 Typical SuDS Components 6.5 The following descriptions of the various types of SuDS techniques demonstrate how particular SuDS components are suited for providing a particular drainage function. For example, ponds, lagoons and basins are generally used for attenuation of flows and volumes prior to discharge into the watercourse whereas soakaways and infiltration trenches are generally used to dispose of surface water directly below ground thus recharging aquifers. The development layout and site characteristics together with the sub-surface soil types will influence which types of SuDS component are suitable. Filter Strips 6.6 These are wide vegetated strips of gently sloping land, which accept and treat runoff by filtering particulate material from adjacent paved areas. They require high land take, which may restrict their use in high density areas, however they provide a positive amenity value. Swales 6.7 Swales are broad, shallow depressions covered by grass or other vegetation. They receive storm water runoff from adjacent paved areas and convey this water to a pipe or other structure. Infiltration can occur across the length of the swale if the soils permit and some level of treatment can be facilitated with appropriate floral species. They are useful for conveying surface water during small events, however are less effective for higher return period events. They also require suitably sized verge areas, which may not be available in high density developments. Infiltration Basins 6.8 These comprise of dry depressions with a stripped or vegetated base. They are located across highly permeable soils thus deposing surface water through infiltration. The sensitivity of the underlying groundwater needs to be taken into consideration when proposing such measures. Although land take can be significant, they can be located within open space areas and as a single entity rather than several systems across the whole development. Ref: 7293A/21/CW/06-07/1778 Page 42

47 Pervious Surfaces 6.9 Pervious surfaces are frequently used for car parking areas or pedestrianised areas. They allow surface water to infiltrate through gaps between blocks (ie permeable) or through the block surfaces themselves (ie porous). The sub-base is suitably constructed in order to promote infiltration or to attenuate surface water depending on the soil types. Pervious surfaces act not only as an effective way to store or dispose of surface water but have also been shown to act as a filter and retainer for pollutants, in particular oil. Infiltration Devices 6.10 These devices allow rainwater to be temporarily stored and to percolate into the ground. Soakaways are infiltration devices commonly used to drain surface water from roofs. They comprise of below ground concrete perforated rings with a granular surround although plastic geocellular units are available. Soakaways are very useful for reducing the volume of runoff from a development, however in order to be effective they require suitably permeable soils. The soakaways should be a minimum distance of 5m from any structure with foundations and located within the back garden. Runoff rates from a roof into a soakaway is generally higher than the natural runoff across a greenfield surface and infiltration into the ground surface. Therefore, soakaways have a propensity to reduce the volume of surface water which is lost to runoff and evaporation (especially in summer) on the ground surface by returning it directly into the sub-soils of the site. This is also useful when natural recharge is limited due to periods of frost and snow cover in winter or when evaporation rates in the summer are limiting the recharge of the underlying water bearing strata Infiltration trenches are based on similar principles but are linear and tend to be shallower. Green Roofs 6.12 These are multi-layer systems that cover the roof of a building with vegetation. Below this system is an appropriately designed drainage layer, together with other layers which provide protection and waterproofing. Green roofs are effective in providing attenuation and a reduction in runoff: however there is a disadvantage in that surface water drainage from the Ref: 7293A/21/CW/06-07/1778 Page 43

48 roof area can carry an increased sediment load to soakaways or piped networks. There are also maintenance and aesthetic implications associated with this SuDS component. Rainwater Harvesting 6.13 Rainwater from roofs and hardstanding can be stored and used across the development area. This re-use of rainwater (eg for flushing toilets or washing machines) can reduce the demand and dependence from mains supply and can also reduce the volumes and rates of runoff from the site. The water is typically stored within an external storage tank and piped to appropriate areas of the building Water butts are connected to rainwater down pipes and provide temporary attenuation during rainfall events. They typically hold approximately 0.5 cu m of rainwater and can be used as part of the rainwater harvesting regime of the building or used to provide attenuation prior to discharge into a soakaway. As long as they are regularly emptied, they have the potential to reduce runoff volumes from small events although they have no ecological benefits. Wet Ponds 6.15 Wet Ponds are permanently wet basins providing both attenuation of runoff rates and treatment of the received storm water. Side slopes of the ponds should be shallow for health and safety reasons and the base and sides of the ponds are normally lined and vegetated. Some volume reduction is achieved through evaporation and transpiration and runoff rates into neighbouring watercourses can be controlled through suitably sized outlet structures. Ponds provide good ecological benefits if appropriately designed and maintained, however they require significant land take if other SuDS measures such as soakaways are not incorporated across the remainder of the site Wetlands are very similar to wet ponds; however they are more complex, requiring shallower zones to enhance the biodiversity of the area. The focus of these areas is storm water treatment and therefore wetland areas are dependant on controlled water levels and other design criteria, which in turn can result in significant land take. Ref: 7293A/21/CW/06-07/1778 Page 44

49 Dry Ponds (Detention Basins) 6.17 These normally consist of dry depressions, which provide attenuation of runoff rates and volumes from the development and to provide some treatment to the storm water (although this is not as effective as ponds). Detention basins require less land take than ponds as greater attenuation depths and runoff losses can be achieved Table 6.1 shows a multi-criteria selection matrix for these SuDS components, which can be used to assist with the decision-making process. Ref: 7293A/21/CW/06-07/1778 Page 45

50 Table 6.1: Selection matrix for SuDS components (adapted from Table 5.2, 5.4 and 5.9 of CIRIA C697) SuDS Technique Soils Available Low Residential Local Commercial Brownfield Contaminated Maintenance Community Cost Habitat Space? Density Roads Land acceptability creation potential Impermeable Permeable Low High Filter Strips Y Y N Y Y Y Y Y Y Y H H M H Swales Y Y N Y Y Y Y Y Y Y L M L M Infiltration Basins N Y N Y Y Y Y Y Y Y L M L M Pervious Surfaces Y Y Y Y Y Y N Y Y Y M M M L Infiltration devices N Y Y Y Y Y Y Y Y Y L M M L Green Roofs Y Y Y Y Y Y N Y Y Y H H H H Rainwater Harvesting Y Y Y Y Y Y N Y Y Y H M H L Ponds/Wetlands Y Y N Y Y Y Y Y Y Y H H H H Detention Basins Y Y N Y Y Y Y Y Y Y L H L M Y = Yes N = No H = High M = Medium L = Low Ref: 7293A/21/CW/06-07/1778 Page 46

51 SuDS Suitability Across the Study Area 6.19 The suitability of the various SuDS techniques across the study area can be related to the soil types and geology. The permeability of the underlying soils across development areas is a key factor when determining the practical use of the various SuDS components. Other factors such as water table and contaminated land also determine SuDS suitability and will vary on a site by site basis. These factors have not been taken into account in this study The superficial deposits (or Quaternary drift deposits) which comprise the upper layers of the soil types are likely to be the most relevant when considering SuDS applications. These deposits include; Alluvium; Glacial Sands and Gravels; Boulder Clay and Contoured Drift, Norwich Brickearth and Loams. The infiltration capacity and percolation ability of the soils can vary markedly from one soil type to another across the study area. For example, Boulder Clay is likely to be relatively impermeable and therefore not particularly suited to infiltration devices; however Glacial Sands and Gravels are likely to posses a sufficient volume of voids to effectively allow surface water to percolate through the soil horizon. Table 6.2 sets out the soil types which exist across the study area. Ref: 7293A/21/CW/06-07/1778 Page 47

52 Table 6.2: Expected soil types and characteristics across the study area Geological Succession (Drift) Alluvium River Gravels Glacial Sands and Gravels Boulder Clay Contoured Drift, Norwich Brickearth and Loams Geological Succession (Solid) London Clay Norwich Crag Upper Cretaceous Chalk Soil Characteristics These deposits consist of the latest material transported by streams and form areas of flat land. They comprise silty deposits of sandy clay or peaty marl with occasional gravels. Gravel deposits associated with material transported by streams. Sand and gravel deposits associated with meltwater close to an ice front. A chalky glacial till deposit with occasional fine interbedded sands. Mainly unbedded clays and loamy sands. Consists of blue-grey impermeable clays. Consists mainly of interbedded sands and gravels with shelly sands and lenticular clays. A soft, white fine-grained limestone. SuDS Suitability Across the North Norfolk District Council Area 6.21 There are four main soil types expected to be encountered across the North Norfolk area: Alluvium; Glacial Sands and Gravels, Boulder Clay and Contoured Drift, Norwich Brickearth and Loam. Some London Clay deposits are also likely to be encountered especially around the main river valleys. Table 6.3 describes where these deposits exist and indicates their suitability to the SuDS techniques as detailed earlier. Ref: 7293A/21/CW/06-07/1778 Page 48

53 Table 6.3: General applications of SuDS in relation to soil types across the North Norfolk District area Soil Type Locations Infiltration Capacity Alluvium These soils are restricted mainly to the River networks within Average dependant this area (ie Thurne, Ant and Bure) and do not generally on the proportions of occupy higher ground where settlements are typically located each soil type (apart from at Hoveton). encountered. Glacial Sands and Gravels These deposits are concentrated towards the north of the Good district area (ie at Holt, Fakenham, Felbrigg, North Walsham and Knapton). Boulder Clay These deposits are located mainly to the west of the district Poor area covering settlements including Great Snoring, Briston and Langham. Contoured Drift, Norwich Brickearth and Loams. These soil types cover much of the central and north east of the district encompassing settlements which include Aldborough, Poor Swanton Abbott, Lessingham, Hickling, Happisburgh, Sheringham, Cromer and Sea Palling. London Clay These are located generally around the main River networks Poor and adjacent to the alluvial deposits. Settlements such as Homing, Sutton, Potter Heigham and Ludham are all located within these areas. Appropriate SuDS components Filter Strips, Swales, Infiltration Basins (depending on depth to water table), Pervious Surfaces, Infiltration devices (dependant on depth to water table and proportion of soil types), Green Roofs, Water butts, Ponds/Wetlands and Detention Basins. Filter Strips, Swales, Infiltration Basins (depending on depth to water table), Pervious Surfaces, Infiltration devices (dependant on depth to water table), Green Roofs, Water butts, Ponds/Wetlands and Detention Basins. Filter Strips, Swales, Pervious Surfaces, Green Roofs, Water butts, Ponds/Wetlands and Detention Basins. Filter Strips, Swales, Pervious Surfaces, Green Roofs, Water butts, Ponds/Wetlands and Detention Basins. Filter Strips, Swales, Pervious Surfaces, Green Roofs, Water butts, Ponds/Wetlands and Detention Basins. Ref: 7293A/21/CW/06-07/1778 Page 49

54 SuDS Suitability Across the LDF Preferred Sites 6.22 Table 6.4 below sets out the results of a site specific assessment of the suitability of particular SuDS elements, for each of the preferred development sites identified in the NNDC September 2006 Site Specific Proposals Preferred Options Consultation Paper. The analysis is made from an assessment of soils data, taken largely from the current BGS Geological Maps, together with some borehole data where available. Anglian Water 6.23 The analysis below also includes where possible relevant information from Anglian Water relating to the available use and capacity of sewer assets if SuDS components cannot be utilised. The AWS data is not exhaustive and is in many cases inconclusive. The AWS company view has been stated to us as follows: In general we would try to push for surface water from new development to go to soakaway or direct connection to existing watercourse, where possible. If these are not possible and a surface water sewer exists we would seek to limit the discharge rate as much as possible to protect sewer and watercourse capacity. For brownfield sites we would look to limit flows to existing or preferably less and for greenfield sites the restriction would be as much as is reasonably practicable. If we have made specific reference to surface water sewer capacity being an issue then we would look for a delay in development to enable time to plan, design and construct improvements. Nevertheless AWS has certain statutory obligations under the 1989 Water Act relating to the provision, adoption and maintenance of surface water drainage infrastructure for new developments and the company view stated above does not affect these obligations. Typical Attenuation Storage Areas 6.24 Table 6.4 also includes an assessment of the approximate size for a typical attenuation storage area appropriate to the particular settlement. The typical attenuation storage area has been calculated using Figure A3.2 of the HR Wallingford document Use of SUDS in High Density Developments Guidance Manual (2005) - reproduced at Fig 6.3 below. Appendix Ref: 7293A/21/CW/06-07/1778 Page 50

55 3 of that document describes the methodology. The calculations are based upon a 1 in 100 year return period storm event. The various parameters contributing to Fig 6.3 below are: the assumed percentage impermeable area (PIMP) which is generally assumed to be 70%; a climate change factor of 10%; specific hydrological zones for the region; an assumed 100% runoff from paved areas; Standard Annual Average Rainfall (SAAR) for the location; the Winter Rainfall Acceptance Potential (WRAP) for the soil type. For example, to find the attenuation volume and storage area for an allocation in Cromer, the SAAR value is extracted from the data within the Flood Estimation Handbook (FEH) CD- ROM. The settlement is located on the WRAP map contained within the Flood Studies Report (FSR) 1977, and this determines the WRAP category appropriate to the settlement (categories range from 1-5 depending on the soil composition). The SAAR value and WRAP category are then used to define the corresponding attenuation volume in cubic metres per site hectare. For Cromer, the SAAR value of 649mm and the WRAP category of 1 results in an attenuation volume of approximately 510 m 3 /ha. Assuming that the attenuation feature (e.g. a dry pond) would be 1m in depth for health and safety purposes, the area of the feature would equate to approximately 510 m 2 /ha. Ref: 7293A/21/CW/06-07/1778 Page 51

56 Fig 6.3: Attenuation Storage Volume for South and East England - for Developments with Percentage Impermeable Area (PIMP) = 70%. Taken from Fig A3.2 in Appendix 3 of The Use of SuDS in High Density Developments Guidance Manual: HR Wallingford, In Table 6.4 the preferred development sites are considered by settlement, in the following order: Cromer, Fakenham, Holt, Hoveton, North Walsham, Sheringham, Stalham, Wells, Aldborough, Blakeney, Briston and Melton Constable, Catfield, Corpusty and Saxthorpe, Horning, Little Snoring, Little Walsingham, Ludham, Roughton, Sculthorpe, Southrepps, Tattersett, Mundesley, Weybourne, Overstrand, Happisburgh and Bacton. Ref: 7293A/21/CW/06-07/1778 Page 52

57 Table 6.4: APPLICABILITY OF SUDS AT NORTH NORFOLK SETTLEMENTS SETTLEMENT SOIL TYPES INFILTRATION APPROPRIATE SUDS TYPICAL ANGLIAN WATER AS DEFINED IN CAPACITY COMPONENTS ATTENUATION CAPACITY AND LDF STORAGE SCHEDULE FOR AREA* IMPROVEMENT Cromer Gravelly Head is beneath Average Filter Strips, Swales, Infiltration Basins 510m 2 /ha with No spare capacity sites C11, ROSS2 and (depending upon depth to water table), discharge into local CP1. Pervious Surfaces, Infiltration devices watercourses. (depending upon depth to water table and Head, which is mainly Average proportion of soil types) Green Roofs, stony, sandy clay and Water Butts, Ponds/Wetlands and clayey sand is beneath sites Detention Basins CO2, CO3. Head is also predominant Average beneath sites CO5 and CO6 although undifferentiated contorted clay, silts, sands and gravel are to be found in eastern areas. Ref: 7293A/21/CW/06-07/1778 Page 53

58 SETTLEMENT SOIL TYPES INFILTRATION APPROPRIATE SUDS TYPICAL ANGLIAN WATER AS DEFINED IN CAPACITY COMPONENTS ATTENUATION CAPACITY AND LDF STORAGE SCHEDULE FOR AREA* IMPROVEMENT Undifferentiated contorted Average clay, silts sands and gravels exist beneath sites CO1, ROSS 3, ROSS 4, C12 and ROSS1. The greatest extent of site Average CO4 is over undifferentiated contorted clay, silts sands and gravels although the eastern area covers Briton s Lane Sand and Gravel Member. Briton s Lane Sand and Good Filter Strips, Swales, Infiltration Basins, Gravel Member is to be Pervious Surfaces, Infiltration devices, found beneath sites C17, Green Roofs, Water Butts, CO8, C15, C16, C22, HC1, Ponds/Wetlands and Detention Basins. CO9, C18, C19 and HC2. Ref: 7293A/21/CW/06-07/1778 Page 54

59 SETTLEMENT SOIL TYPES INFILTRATION APPROPRIATE SUDS TYPICAL ANGLIAN WATER AS DEFINED IN CAPACITY COMPONENTS ATTENUATION CAPACITY AND LDF STORAGE SCHEDULE FOR AREA* IMPROVEMENT Sites C10 and C13 overlay Average Filter Strips, Swales, Infiltration Basins a mix of gravelly Head and (depending upon depth to water table), undifferentiated contorted Pervious Surfaces, Infiltration devices clay, silts, sands and (depending upon depth to water table and gravels. proportion of soil types) Green Roofs, Water Butts, Ponds/Wetlands and Detention Basins CO7 is over a mix of Good for Briton s Across Sand and Gravel where infiltration Briton s Lane Sand and Lane Sand and capacity is good, Filter Strips, Swales, Gravel Member and Gravel Deposits Infiltration Basins, Pervious Surfaces, gravelly Head. Infiltration devices, Green Roofs, Water Butts, Ponds/Wetlands and Detention Basins. Average gravelly Head for Filter Strips, Swales, Infiltration Basins (depending upon depth to water table), Pervious Surfaces, Infiltration devices (depending upon depth to water table and proportion of soil types) Green Roofs, Water Butts, Ponds/Wetlands and Detention Basins Ref: 7293A/21/CW/06-07/1778 Page 55

60 SETTLEMENT SOIL TYPES INFILTRATION APPROPRIATE SUDS TYPICAL ANGLIAN WATER AS DEFINED IN CAPACITY COMPONENTS ATTENUATION CAPACITY AND LDF STORAGE SCHEDULE FOR AREA* IMPROVEMENT The eastern area of C14 is Good in the east Across Sand and Gravel where infiltration over Briton s Lane Sand capacity is good, Filter Strips, Swales, and Gravel Member. The Infiltration Basins, Pervious Surfaces, southern site is over Head Infiltration devices, Green Roofs, Water and the western site is a Butts, Ponds/Wetlands and Detention mix of Head and Basins. undifferentiated contorted clay, silts, sand and gravel. Average Filter Strips, Swales, Infiltration Basins elsewhere (depending upon depth to water table), Pervious Surfaces, Infiltration devices (depending upon depth to water table and proportion of soil types) Green Roofs, Water Butts, Ponds/Wetlands and Detention Basins Ref: 7293A/21/CW/06-07/1778 Page 56

61 SETTLEMENT SOIL TYPES INFILTRATION APPROPRIATE SUDS TYPICAL ANGLIAN WATER AS DEFINED IN CAPACITY COMPONENTS ATTENUATION CAPACITY AND LDF STORAGE SCHEDULE FOR AREA* IMPROVEMENT Fakenham Till comprising chalky, Average for Filter Strips, Swales, Infiltration Basins 410m 2 /ha with No spare capacity pebbly clay is beneath all Chalky Pebbly (depending upon depth to water table), discharge into IDB of F05, F06 and F09. Also Clay Pervious Surfaces, Infiltration devices drainage ditches or covers the vast majority of (depending upon depth to water table and the River Wensum. F01 except for a small proportion of soil types) Green Roofs, pocket at the eastern Water Butts, Ponds/Wetlands and boundary, and F07 except Detention Basins for an area adjacent to the southern boundary. Areas of site not over Till, overlays sand and gravel. Good for Sand and Gravel Across Sand and Gravel where infiltration capacity is good, Filter Strips, Swales, Infiltration Basins, Pervious Surfaces, Infiltration devices, Green Roofs, Water Butts, Ponds/Wetlands and Detention Basins. Ref: 7293A/21/CW/06-07/1778 Page 57

62 SETTLEMENT SOIL TYPES INFILTRATION APPROPRIATE SUDS TYPICAL ANGLIAN WATER AS DEFINED IN CAPACITY COMPONENTS ATTENUATION CAPACITY AND LDF STORAGE SCHEDULE FOR AREA* IMPROVEMENT F02, F03, and ROSS 7, are Good Across Sand and Gravel where infiltration over sand and gravel. capacity is good, Filter Strips, Swales, Infiltration Basins, Pervious Surfaces, Infiltration devices, Green Roofs, Water Butts, Ponds/Wetlands and Detention Basins. F04 and F08 are above Poor Filter Strips, Swales, Pervious Surfaces, Alluvium comprising silt Green Roofs, Water Butts, Ponds/ and clay, with subordinate Wetlands and Detention Basins peat. The north of ROSS 6 is Good in north Across Sand and Gravel where infiltration over sand and gravel with capacity is good Filter Strips, Swales, the southern part of the site Infiltration Basins, Pervious Surfaces, over Alluvium of silt and Infiltration devices, Green Roofs, Water clay with subordinate peat. Butts, Ponds/Wetlands and Detention Basins. Ref: 7293A/21/CW/06-07/1778 Page 58

63 SETTLEMENT SOIL TYPES INFILTRATION APPROPRIATE SUDS TYPICAL ANGLIAN WATER AS DEFINED IN CAPACITY COMPONENTS ATTENUATION CAPACITY AND LDF STORAGE SCHEDULE FOR AREA* IMPROVEMENT Filter Strips, Swales, Pervious Surfaces, Poor in south Green Roofs, Water Butts, Ponds/ Wetlands and Detention Basins Holt All site specific proposals Good Filter Strips, Swales, Infiltration Basins, 510m 2 /ha with No spare capacity for Holt, H01, H02, H03, Pervious Surfaces, Infiltration devices, discharge into local H04, H05, H06, H07, H08, Green Roofs, Water Butts, Ponds/ watercourses. H09, H10, H11, H12 and Wetlands and Detention Basins. E2 are above Briton s Lane Sand and Gravel Member. Hoveton Sites HV01, HV02 and the Good Filter Strips, Swales, Infiltration Basins, 470m 2 /ha with Limited capacity at HV01 majority of HV03 are Pervious Surfaces, Infiltration devices, discharge into the otherwise no spare capacity above sand and gravel. Green Roofs, Water Butts, Ponds/ River Bure. Wetlands and Detention Basins. Ref: 7293A/21/CW/06-07/1778 Page 59

64 SETTLEMENT SOIL TYPES INFILTRATION APPROPRIATE SUDS TYPICAL ANGLIAN WATER AS DEFINED IN CAPACITY COMPONENTS ATTENUATION CAPACITY AND LDF STORAGE SCHEDULE FOR AREA* IMPROVEMENT E3 and HV04 are over Crag which is also present Average Filter Strips, Swales, Infiltration Basins (depending upon depth to water table), beneath the north east Pervious Surfaces, Infiltration devices corner of HV03. (depending upon depth to water table and proportion of soil types) Green Roofs, Water Butts, Ponds/Wetlands and Detention Basins North Walsham The majority of sites to the Good Filter Strips, Swales, Infiltration Basins, 510m 2 /ha with No spare capacity east of North Walsham Pervious Surfaces, Infiltration devices, discharge into the NW01, NW02, NW04, Green Roofs, Water Butts, North Walsham NW16, NW17, NW18, Ponds/Wetlands and Detention Basins. and Dilham Canal NW20, NW21, NW22, or local NW23, NW24, NW26, watercourses. NW27, NW33, NW34, NW35, NW36, E5, ROS8 overlay sands and gravels. Ref: 7293A/21/CW/06-07/1778 Page 60

65 SETTLEMENT SOIL TYPES INFILTRATION APPROPRIATE SUDS TYPICAL ANGLIAN WATER AS DEFINED IN CAPACITY COMPONENTS ATTENUATION CAPACITY AND LDF STORAGE SCHEDULE FOR AREA* IMPROVEMENT NW19 is above Head Average Filter Strips, Swales, Infiltration Basins comprised mainly of stony, (depending upon depth to water table), sandy clays and clayey Pervious Surfaces, Infiltration devices sands. (depending upon depth to water table and proportion of soil types) Green Roofs, Water Butts, Ponds/Wetlands and Detention Basins Ref: 7293A/21/CW/06-07/1778 Page 61

66 SETTLEMENT SOIL TYPES INFILTRATION APPROPRIATE SUDS TYPICAL ANGLIAN WATER AS DEFINED IN CAPACITY COMPONENTS ATTENUATION CAPACITY AND LDF STORAGE SCHEDULE FOR AREA* IMPROVEMENT The British Geological Good Filter Strips, Swales, Infiltration Basins, Survey Map immediately Pervious Surfaces, Infiltration devices, to the west of North Green Roofs, Water Butts, Ponds/ Walsham is not published Wetlands and Detention Basins. at a scale of 1: 50,000. Reviewing the information shown it is highly likely that sands and gravels are to be found in this area as they are prevalent elsewhere to the east. This has been confirmed verbally with the British Geological Survey who consulted the 1: map of the area and spoke with the District Geologist. Sites to which this applies are listed as follows: Ref: 7293A/21/CW/06-07/1778 Page 62

67 SETTLEMENT SOIL TYPES INFILTRATION APPROPRIATE SUDS TYPICAL ANGLIAN WATER AS DEFINED IN CAPACITY COMPONENTS ATTENUATION CAPACITY AND LDF STORAGE SCHEDULE FOR AREA* IMPROVEMENT NW03, NW05, NW06, NW07, NW08, NW09, NW10, NW11, NW14, NW15, NW25, NW28, NW29, NW30, NW31, NW32, ED1 Sheringham Sites SH01, SH08 and Average Filter Strips, Swales, Infiltration Basins 510m 2 /ha with No spare capacity SH07 are over (depending upon depth to water table), discharge into local undifferentiated contorted Pervious Surfaces, Infiltration devices watercourses. clay, silts, sand and gravel. (depending upon depth to water table and proportion of soil types) Green Roofs, Water Butts, Ponds/Wetlands and Detention Basins Gravelly Head is to be Average found beneath sites ROS5 and SH02. Ref: 7293A/21/CW/06-07/1778 Page 63

68 SETTLEMENT SOIL TYPES INFILTRATION APPROPRIATE SUDS TYPICAL ANGLIAN WATER AS DEFINED IN CAPACITY COMPONENTS ATTENUATION CAPACITY AND LDF STORAGE SCHEDULE FOR AREA* IMPROVEMENT Gravelly Head and Average undifferentiated contorted clay, silts, sand and gravel are to be found beneath sites SH04, SH05, SH09 and SH10. Sites SH11 and SH06 have Average areas above undifferentiated contorted clay, silts, sand and gravel as well as Britons Land Sand and Gravel Member. POS 3 is above Briton s Good Across Sand and Gravel where infiltration Lane Sand and Gravel capacity is good, Filter Strips, Swales, Member. Infiltration Basins, Pervious Surfaces, Infiltration devices, Green Roofs, Water Butts, Ponds/Wetlands and Detention Basins. Ref: 7293A/21/CW/06-07/1778 Page 64

69 SETTLEMENT SOIL TYPES INFILTRATION APPROPRIATE SUDS TYPICAL ANGLIAN WATER AS DEFINED IN CAPACITY COMPONENTS ATTENUATION CAPACITY AND LDF STORAGE SCHEDULE FOR AREA* IMPROVEMENT Stalham Sites ST04, ST05, ST07, Poor Areas of allocation sites over Diamicton 470m 2 /ha with Limited capacity at ST01 and ST08, ST09, ST14 are and glacio-lacustrine silts with poor discharge into ST02 otherwise no spare above Diamicton and infiltration capacity: Filter Strips, Swales, Stalham Staithe. capacity glacio-lacustrine silts. Pervious Surfaces, Green Roofs, Water Butts, Ponds/Wetlands and Detention Basins Sites ST02, ST10, ST11, Good Over Sand and Gravel Areas with good ST12, ST13 and a great infiltration capacity: Filter Strips, Swales, proportion of E4 and ST15 Infiltration Basins, Pervious Surfaces, overlay sand and gravel. Infiltration devices, Green Roofs, Water Butts, Ponds/Wetlands and Detention Basins. The northern half of ST06 Poor (North) Filter Strips, Swales, Pervious Surfaces, is over Diamicton and Green Roofs, Water Butts, glacio-lacustrine silts. Ponds/Wetlands and Detention Basins Ref: 7293A/21/CW/06-07/1778 Page 65

70 SETTLEMENT SOIL TYPES INFILTRATION APPROPRIATE SUDS TYPICAL ANGLIAN WATER AS DEFINED IN CAPACITY COMPONENTS ATTENUATION CAPACITY AND LDF STORAGE SCHEDULE FOR AREA* IMPROVEMENT Over Sand and Gravel Areas with good The south is above sand Good (South) infiltration capacity: Filter Strips, Swales, and gravel. Infiltration Basins, Pervious Surfaces, Infiltration devices, Green Roofs, Water Butts, Ponds/Wetlands and Detention Basins. The west of site ST01 is Good (West) Over Sand and Gravel Areas with good above sand and gravel with infiltration capacity: Filter Strips, Swales, the remainder of the site Infiltration Basins, Pervious Surfaces, above Diamicton and Infiltration devices, Green Roofs, Water glacio-lacustrine silts. Butts, Ponds/Wetlands and Detention Basins. Poor elsewhere Filter Strips, Swales, Pervious Surfaces, Green Roofs, Water Butts, Ponds/ Wetlands and Detention Basins Ref: 7293A/21/CW/06-07/1778 Page 66

71 SETTLEMENT SOIL TYPES INFILTRATION APPROPRIATE SUDS TYPICAL ANGLIAN WATER AS DEFINED IN CAPACITY COMPONENTS ATTENUATION CAPACITY AND LDF STORAGE SCHEDULE FOR AREA* IMPROVEMENT The north of site ST03 is Good (North) Over Sand and Gravel Areas with good above sand and gravel with infiltration capacity: Filter Strips, Swales, the south above Diamicton Infiltration Basins, Pervious Surfaces, and glacio-lacustrine silts. Infiltration devices, Green Roofs, Water Butts, Ponds/Wetlands and Detention Basins. Poor (South) Filter Strips, Swales, Pervious Surfaces, Green Roofs, Water Butts, Ponds/Wetlands and Detention Basins Wells The British Geological Poor Filter Strips, Swales, Pervious Surfaces, 510m 2 /ha with Limited capacity at W01 and Survey 1: 50,000 scale Green Roofs, Water Butts, Ponds/ discharge into the W02 otherwise no spare capacity maps are yet to be Wetlands and Detention Basins IDB drainage published for the area. ditches or Wells Liaison with the British Salt Marshes. Geological Survey has established that the superficial geology in the vicinity of W01 is comprised of glacio-fluvial sand and gravel with some Diamicton to the south-east Ref: 7293A/21/CW/06-07/1778 Page 67

72 SETTLEMENT SOIL TYPES INFILTRATION APPROPRIATE SUDS TYPICAL ANGLIAN WATER AS DEFINED IN CAPACITY COMPONENTS ATTENUATION CAPACITY AND LDF STORAGE SCHEDULE FOR AREA* IMPROVEMENT and head to the north and south of the site. Borehole logs 700m from the allocation site indicate sandy/silty clay overlain by made ground. It is considered prudent to base the assessment on the least favourable geology for all sites, W01, W02, W03, W04 and CP2 due to the lack of information and the presence of silty clay and Diamicton. Aldborough The surface geology Average Filter Strips, Swales, Infiltration Basins 510m 2 /ha with No Data beneath site ALD02 is (depending upon depth to water table), discharge into local identified as Hanworth Till Pervious Surfaces, Infiltration devices watercourses or Member: sandy, pebbly, (depending upon depth to water table and IDB drainage clayey, silt. proportion of soil types) Green Roofs, ditches. Water Butts, Ponds/Wetlands and Detention Basins Ref: 7293A/21/CW/06-07/1778 Page 68

73 SETTLEMENT SOIL TYPES INFILTRATION APPROPRIATE SUDS TYPICAL ANGLIAN WATER AS DEFINED IN CAPACITY COMPONENTS ATTENUATION CAPACITY AND LDF STORAGE SCHEDULE FOR AREA* IMPROVEMENT ALD01 is above Head: Average mainly stony, sandy clay and clayey sand. Alluvium: mainly clay, silt Average and sand are beneath ALD 03. ALD04 is likely to overly Average Head, Till and Alluvium referred to above. Blakeney BLA01 is predominantly Good Over Sand and Gravel Areas with good 510m 2 /ha with No Data over Briton s Lane Sand infiltration capacity: Filter Strips, Swales, discharge into Agar and Gravel Member and Infiltration Basins, Pervious Surfaces, Creek. Esker is also shown in Infiltration devices, Green Roofs, Water close proximity west of the Butts, Ponds/Wetlands and Detention site on the British Basins. Geological Survey map. Briston and Following correspondence Poor Filter Strips, Swales, Pervious Surfaces, 510m 2 /ha with No Data Melton Constable with the British Geological Green Roofs, Water Butts, Ponds/ discharge into the Ref: 7293A/21/CW/06-07/1778 Page 69

74 SETTLEMENT SOIL TYPES INFILTRATION APPROPRIATE SUDS TYPICAL ANGLIAN WATER AS DEFINED IN CAPACITY COMPONENTS ATTENUATION CAPACITY AND LDF STORAGE SCHEDULE FOR AREA* IMPROVEMENT Survey the area in the Wetlands and Detention Basins. River Bure at vicinity of BRI01 is shown Briston and local as having surface geology watercourses and comprised of Diamicton. IDB drainage A borehole within 190m ditches at Melton indicates the presence of Constable. sand and clay. Catfield Site CAT01 lies above Poor Filter Strips, Swales, Pervious Surfaces, 470m 2 /ha with no No Data Diamicton and glacio- Green Roofs, Water Butts, obvious outfall. lacustrine silts. Ponds/Wetlands and Detention Basins Corpusty and Following correspondence Poor Filter Strips, Swales, Pervious Surfaces, 510m 2 /ha with No Data Saxthorpe with the British Geological Green Roofs, Water Butts, discharge into the Survey the area in the Ponds/Wetlands and Detention Basins. River Bure and vicinity of COR1 is shown IDB drainage as having surface geology ditches. comprised of Diamicton and Head. A borehole approximately half a kilometre east of COR1 does record the presence of sand and Ref: 7293A/21/CW/06-07/1778 Page 70

75 SETTLEMENT SOIL TYPES INFILTRATION APPROPRIATE SUDS TYPICAL ANGLIAN WATER AS DEFINED IN CAPACITY COMPONENTS ATTENUATION CAPACITY AND LDF STORAGE SCHEDULE FOR AREA* IMPROVEMENT gravel which could indicate that the site may have better infiltration characteristics. Until such time as more detailed, site specific information is made available then the recommendation is to base the infiltration capacity upon the worst case surface geology scenario. Horning The north east of site Poor Filter Strips, Swales, Pervious Surfaces, 470m 2 /ha with No Data HOR01 overlays Green Roofs, Water Butts, discharge into the Diamicton and glacio- Ponds/Wetlands and Detention Basins River Bure. lacustrine silts. The remainder of the Average Filter Strips, Swales, Infiltration Basins allocation is above Crag. (depending upon depth to water table), Pervious Surfaces, Infiltration devices (depending upon depth to water table and proportion of soil types) Green Roofs, Water Butts, Ponds/Wetlands and Ref: 7293A/21/CW/06-07/1778 Page 71

76 SETTLEMENT SOIL TYPES INFILTRATION APPROPRIATE SUDS TYPICAL ANGLIAN WATER AS DEFINED IN CAPACITY COMPONENTS ATTENUATION CAPACITY AND LDF STORAGE SCHEDULE FOR AREA* IMPROVEMENT Detention Basins Little Snoring SNO1 is within an area Average across Filter Strips, Swales, Infiltration Basins 460m 2 /ha with No Data shown to comprise clay, Sheringham Cliff (depending upon depth to water table), discharge into IDB silt, sand and gravel Formation areas Pervious Surfaces, Infiltration devices drainage ditches. (Sheringham Cliff (depending upon depth to water table and Formation). Sand and proportion of soil types) Green Roofs, gravel and Diamicton Water Butts, Ponds/Wetlands and deposits are also present. Detention Basins Good across Sand Over Sand and Gravel Areas with good and Gravel areas infiltration capacity: Filter Strips, Swales, Infiltration Basins, Pervious Surfaces, Infiltration devices, Green Roofs, Water Butts, Ponds/Wetlands and Detention Basins. Poor across Filter Strips, Swales, Pervious Surfaces, Diamicton Green Roofs, Water Butts, deposits areas Ponds/Wetlands and Detention Basins. Ref: 7293A/21/CW/06-07/1778 Page 72

77 SETTLEMENT SOIL TYPES INFILTRATION APPROPRIATE SUDS TYPICAL ANGLIAN WATER AS DEFINED IN CAPACITY COMPONENTS ATTENUATION CAPACITY AND LDF STORAGE SCHEDULE FOR AREA* IMPROVEMENT Walsingham WAL01 is in an area Average Filter Strips, Swales, Infiltration Basins 510m 2 /ha with No Data shown to comprise clay, (depending upon depth to water table), discharge into the silt, sand and gravel Pervious Surfaces, Infiltration devices River Stiffkey. (Sheringham Cliff (depending upon depth to water table and Formation) as well as proportion of soil types) Green Roofs, Diamicton, according to Water Butts, Ponds/Wetlands and the correspondence Detention Basins received from the British Geological Survey. Poor across Filter Strips, Swales, Pervious Surfaces, Diamicton Green Roofs, Water Butts, Ponds/ deposits areas Wetlands and Detention Basins Ludham Sites LUD01 and LUD03 Average Filter Strips, Swales, Infiltration Basins 510m 2 /ha with No Data are above Crag. The (depending upon depth to water table), discharge into majority of LUD02 is also Pervious Surfaces, Infiltration devices Womack Water. above Crag although Head (depending upon depth to water table and deposits are also shown proportion of soil types) Green Roofs, entering the site from the Water Butts, Ponds/Wetlands and west. Detention Basins Ref: 7293A/21/CW/06-07/1778 Page 73

78 SETTLEMENT SOIL TYPES INFILTRATION APPROPRIATE SUDS TYPICAL ANGLIAN WATER AS DEFINED IN CAPACITY COMPONENTS ATTENUATION CAPACITY AND LDF STORAGE SCHEDULE FOR AREA* IMPROVEMENT The majority of LUD04 is Average across Filter Strips, Swales, Infiltration Basins above Crag with Crag areas (depending upon depth to water table), Diamicton and glacio- Pervious Surfaces, Infiltration devices lacustrine silts in evidence (depending upon depth to water table and to the east. proportion of soil types) Green Roofs, Water Butts, Ponds/Wetlands and Detention Basins Poor across Silt Filter Strips, Swales, Pervious Surfaces, areas Green Roofs, Water Butts, Ponds/ Wetlands and Detention Basins Roughton Sites ROU5, ROU6 and Average Filter Strips, Swales, Infiltration Basins 510m 2 /ha with No Data ROU7 lie above Crag. (depending upon depth to water table), discharge into Pervious Surfaces, Infiltration devices Hagon Beck. (depending upon depth to water table and proportion of soil types) Green Roofs, Water Butts, Ponds/Wetlands and Detention Basins Ref: 7293A/21/CW/06-07/1778 Page 74

79 SETTLEMENT SOIL TYPES INFILTRATION APPROPRIATE SUDS TYPICAL ANGLIAN WATER AS DEFINED IN CAPACITY COMPONENTS ATTENUATION CAPACITY AND LDF STORAGE SCHEDULE FOR AREA* IMPROVEMENT Sites ROU3 is Average predominantly above Head comprised mainly of stony, sandy clays and clayey sands ROU2 and ROU4 have Average areas above Crag with Head in other locations. Site ROU1 is above both Average Head and Alluvium: mainly clay, silt and sand. Sculthorpe Sand and gravel is beneath Good Over Sand and Gravel Areas with good 510m 2 /ha with No Data site WG02. infiltration capacity: Filter Strips, discharge into IDB Swales, Infiltration Basins, Pervious drainage ditches or Surfaces, Infiltration devices, Green River Wensum. Roofs, Water Butts, Ponds/Wetlands and Detention Basins. Ref: 7293A/21/CW/06-07/1778 Page 75

80 SETTLEMENT SOIL TYPES INFILTRATION APPROPRIATE SUDS TYPICAL ANGLIAN WATER AS DEFINED IN CAPACITY COMPONENTS ATTENUATION CAPACITY AND LDF STORAGE SCHEDULE FOR AREA* IMPROVEMENT The major part of site Predominantly Over Sand and Gravel Areas with good WG01 is above sand and Good infiltration capacity: Filter Strips, gravel although Till Swales, Infiltration Basins, Pervious comprising chalky, pebbly Surfaces, Infiltration devices, Green clay may be encountered at Roofs, Water Butts, Ponds/Wetlands and the very north of the site. Detention Basins Average at the very north Filter Strips, Swales, Infiltration Basins (depending upon depth to water table), Pervious Surfaces, Infiltration devices (depending upon depth to water table and proportion of soil types) Green Roofs, Water Butts, Ponds/Wetlands and Detention Basins Southrepps Crag is prevalent beneath Average Filter Strips, Swales, Infiltration Basins 510m 2 /ha with no No Data all the Southrepps sites, (depending upon depth to water table), obvious outfall. SOU1, SOU2, SOU3, Pervious Surfaces, Infiltration devices SOU4, SOU5 and SOU6. (depending upon depth to water table and Head will also be found proportion of soil types) Green Roofs, beneath SOU5. Water Butts, Ponds/Wetlands and Detention Basins Ref: 7293A/21/CW/06-07/1778 Page 76

81 SETTLEMENT SOIL TYPES INFILTRATION APPROPRIATE SUDS TYPICAL ANGLIAN WATER AS DEFINED IN CAPACITY COMPONENTS ATTENUATION CAPACITY AND LDF STORAGE SCHEDULE FOR AREA* IMPROVEMENT Tattersett Sands and gravel as well as Good Over Sand and Gravel Areas with good 510m 2 /ha with No data Chalk are to be found infiltration capacity: Filter Strips, discharge into the beneath site E7. Swales, Infiltration Basins, Pervious River Tat. Surfaces, Infiltration devices, Green Roofs, Water Butts, Ponds/Wetlands and Detention Mundesley Crag is the dominant Average Filter Strips, Swales, Infiltration Basins 510m 2 /ha with No Data geological stratum in the (depending upon depth to water table), discharge into area. Pervious Surfaces, Infiltration devices Mundesley Beck. (depending upon depth to water table and proportion of soil types) Green Roofs, Water Butts, Ponds/Wetlands and Detention Basins Weybourne Till is prevalent with seams Poor for Till Filter Strips, Swales, Pervious Surfaces, 510m 2 /ha with No Data of Head Green Roofs, Water Butts, discharge into Ponds/Wetlands and Detention Basins Spring Beck. Average for Head Filter Strips, Swales, Infiltration Basins (depending upon depth to water table), Ref: 7293A/21/CW/06-07/1778 Page 77

82 SETTLEMENT SOIL TYPES INFILTRATION APPROPRIATE SUDS TYPICAL ANGLIAN WATER AS DEFINED IN CAPACITY COMPONENTS ATTENUATION CAPACITY AND LDF STORAGE SCHEDULE FOR AREA* IMPROVEMENT Pervious Surfaces, Infiltration devices (depending upon depth to water table and proportion of soil types) Green Roofs, Water Butts, Ponds/Wetlands and Detention Basins Overstrand The major part of town Predominantly Filter Strips, Swales, Infiltration Basins 510 m 2 /ha with no No Data overlays Gravelly Head. Average (depending upon depth to water table), obvious outfall. Undifferentiated contorted Pervious Surfaces, Infiltration devices clay, silts sand and gravel (depending upon depth to water table and is found in the south, proportion of soil types) Green Roofs, north-west, south-west and Water Butts, Ponds/Wetlands and east of the town. Detention Basins Briton s lane Sand and Good at the Over Sand and Gravel Areas with good Gravel Member is outskirts of town. infiltration capacity: Filter Strips, prevalent at the outskirts of Swales, Infiltration Basins, Pervious the town with seams of Surfaces, Infiltration devices, Green Gravelly Head. Roofs, Water Butts, Ponds/Wetlands and Detention Ref: 7293A/21/CW/06-07/1778 Page 78

83 SETTLEMENT SOIL TYPES INFILTRATION APPROPRIATE SUDS TYPICAL ANGLIAN WATER AS DEFINED IN CAPACITY COMPONENTS ATTENUATION CAPACITY AND LDF STORAGE SCHEDULE FOR AREA* IMPROVEMENT Happisburgh Most of Happisburgh is Poor for Silts Filter Strips, Swales, Pervious Surfaces, 510 m 2 /ha with no No Data above Diamicton and Green Roofs, Water Butts, obvious outfall. Glacio Lacustrine Silts. Ponds/Wetlands and Detention Basins Sand and Gravel is found Good for Sand Over Sand and Gravel Areas with good beneath the western, and Gravel infiltration capacity: Filter Strips, eastern and southern parts Swales, Infiltration Basins, Pervious of the town. Surfaces, Infiltration devices, Green Roofs, Water Butts, Ponds/Wetlands and Detention Happisburgh Most of Happisburgh is Poor for Silts Filter Strips, Swales, Pervious Surfaces, 510 m 2 /ha with No data above Diamicton and Green Roofs, Water Butts, discharge into a Glacio Lacustrine Silts. Ponds/Wetlands and Detention Basins local watercourse. Sand and Gravel is found Good for Sand Over Sand and Gravel Areas with good beneath the north-western, and Gravel infiltration capacity: Filter Strips, south-eastern and far- Swales, Infiltration Basins, Pervious eastern parts of Surfaces, Infiltration devices, Green Happisburgh. Roofs, Water Butts, Ponds/Wetlands and Detention Ref: 7293A/21/CW/06-07/1778 Page 79

84 SETTLEMENT SOIL TYPES INFILTRATION APPROPRIATE SUDS TYPICAL ANGLIAN WATER AS DEFINED IN CAPACITY COMPONENTS ATTENUATION CAPACITY AND LDF STORAGE SCHEDULE FOR AREA* IMPROVEMENT Bacton Sand and Gravel is Predominantly Over Sand and Gravel Areas with good 510 m 2 /ha with no No data prevalent beneath the entire Good infiltration capacity: Filter Strips, obvious outfall. area. Swales, Infiltration Basins, Pervious Surfaces, Infiltration devices, Green Roofs, Water Butts, Ponds/Wetlands and Detention Gravelly Alluvium and Average in the Filter Strips, Swales, Infiltration Basins Head consisting of mainly south (depending upon depth to water table), stony, sandy clays and Pervious Surfaces, Infiltration devices clayey sands are also (depending upon depth to water table and present in the south. proportion of soil types) Green Roofs, Water Butts, Ponds/Wetlands and Detention Basins * Based on Figure A3.2 of HR Wallingford document entitled Use of SuDS in High Density Developments. Assumes 70% impermeable area and a 1 in 100 year return period (plus 10% climate change) storm event. Area is based on a 1m deep attenuation feature. Ref: 7293A/21/CW/06-07/1778 Page 80

85 7.0 RECOMMENDATIONS 7.1 Development proposals in North Norfolk should be tested against the flood probability maps in this SFRA, which indicate flood probability associated with river systems, together with the sustainable drainage suitability maps and tables, and the Environment Agency maps indicating risk of coastal flooding. Coastal flooding and flooding associated with defence failure are likely to produce the most significant consequences and greatest hazard because of the speed of onset of the flood, the high water velocities and the deep water. Decisions associated with development proposals for coastal areas should be influenced by and linked to the funding status and the implementation programme for associated flood defence maintenance and improvement. Flooding from tidally influenced systems, typically in the eastern and central areas of North Norfolk, is likely to be less hazardous, because of the slower onset. Fluvial flooding associated with upstream areas of individual catchments can arise rapidly, but in the North Norfolk terrain the catchments are not normally flashy and the hazard from these floods, excepting unusual meteorological conditions, is least onerous. 7.2 Consideration of the flood risk at a particular location should take account of the climate change enhanced flood outlines in this SFRA in accordance with PPS Any development encroaching within any of the plotted flood zones will increase flood risk to adjacent areas, and the effect on flood risk of a number of small encroachments is cumulative. If the requirements of PPS25 are met in full then additional development will not increase flood risk elsewhere. Ref: 7293A/21/CW/06-07/1778 Page 81

86 8.0 SITE SPECIFIC FLOOD RISK ASSESSMENTS 8.1 PPS25 Appendix E paragraphs E8, E9 and E10 set out the general circumstances in which a site specific flood risk assessment is required to be submitted by the proposer of new development: E8. At the planning application stage, an appropriate FRA will be required to demonstrate how flood risk from all sources of flooding to the development itself and flood risk to others will be managed now and taking climate change into account. Policies in LDDs should require FRAs to be submitted with planning applications in areas of flood risk identified in the plan. E9. Planning applications for development proposals of 1 hectare or greater in Flood Zone 1 and all proposals for new development located in Flood Zones 2 and 3 (see Table D.1, Annex D) should be accompanied by a FRA. This should identify and assess the risks of all forms of flooding to and from the development and demonstrate how these flood risks will be managed, taking climate change into account. For major developments in Flood Zone 1, the FRA should identify opportunities to reduce the probability and consequences of flooding. A FRA will also be required where the proposed development or change of use to a more vulnerable class may be subject to other sources of flooding (see Annex C) or where the Environment Agency, Internal Drainage Board and/or other bodies have indicated that there may be drainage problems. E10. The FRA should be prepared by the developer in consultation with the LPA. The FRA should form part of an Environmental Statement when one is required by the Town and Country Planning (Environmental Impact Assessment) (England and Wales) Regulations 1999 as amended. 8.2 PPS25 Appendix E paragraphs E1 to E3 set out the general principles involved and the requirements for the scope of a site specific FRA: Ref: 7293A/21/CW/06-07/1778 Page 82

87 The Assessment of Flood Risk General Principles E1. Properly prepared assessments of flood risk will inform the decision-making process at all stages of development planning. There should be iteration between the different levels of flood risk assessment. E2. Any organisation or person proposing a development must consider whether that development will not add to and should where practicable reduce flood risk. The future users of the development must not be placed in danger from flood hazards and should remain safe throughout the lifetime of the plan or proposed development and land use. E3. At all stages of the planning process, the minimum requirements for flood risk assessments are that they should: be proportionate to the risk and appropriate to the scale, nature and location of the development; consider the risk of flooding arising from the development in addition to the risk of flooding to the development; take the impacts of climate change into account (see Annex B); be undertaken by competent people, as early as possible in the particular planning process, to avoid misplaced effort and raising landowner expectations where land is unsuitable for development; consider both the potential adverse and beneficial effects of flood risk management infrastructure including raised defences, flow channels, flood storage areas and other artificial features together with the consequences of their failure; Ref: 7293A/21/CW/06-07/1778 Page 83

88 consider the vulnerability of those that could occupy and use the development, taking account of the Sequential and Exception Tests and the vulnerability classification (see Annex D), including arrangements for safe access; consider and quantify the different types of flooding (whether from natural and human sources and including joint and cumulative effects) and identify flood risk reduction measures, so that assessments are fit for the purpose of the decisions being made; consider the effects of a range of flooding events including extreme events on people, property, the natural and historic environment and river and coastal processes; include the assessment of the remaining (known as residual ) risk (see Annex G) after risk reduction measures have been taken into account and demonstrate that this is acceptable for the particular development or land use; consider how the ability of water to soak into the ground may change with development, along with how the proposed layout of development may affect drainage systems; and be supported by appropriate data and information, including historical information on previous events. 8.3 The PPS25 Practice Guide considers that FRA s can be classified into three levels of detail, as shown in Table 8.1 below: Table 8.1: Levels of Site Specific Flood Risk Assessment (taken from the PPS 25 Practice Guide Table 2.3) FRA Level Level 1 Description Screening study to identify whether there are any flooding or surface water management issues related to a development site that may warrant further consideration. This should be based on readily available existing information, including the SFRA, Environment Agency Flood Map and Standing Advice. The Ref: 7293A/21/CW/06-07/1778 Page 84

89 screening study will ascertain whether a FRA is required. Level 2 Scoping study to be undertaken if the Level 1 FRA indicates that the site may lie within an area that is at risk of flooding or that the site may increase flood risk due to increased run-off. This study should confirm the sources of flooding which may affect the site. The study should include the following: an appraisal of the availability and adequacy of existing information a qualitative appraisal of the flood risk posed to the site, and potential impact of the development on flood risk elsewhere an appraisal of the scope of possible measures to reduce the flood risk to acceptable levels. The scoping study may identify that sufficient quantitative information is already available to complete a FRA appropriate to the scale and nature of the development. Level 3 Detailed study to be undertaken if the Level 2 FRA concludes that further quantitative analysis is required to assess flood risk issues related to the development site. The study should include: quantitative appraisal of the potential flood risk to the development quantitative appraisal of the potential impact of development site on flood risk elsewhere quantitative demonstration of the effectiveness of any proposed mitigation measures. 8.4 The Practice Guide also identifies sources of information appropriate to each level of FRA, as shown in Table 8.2 below: Ref: 7293A/21/CW/06-07/1778 Page 85

90 Table 8.2: Typical Sources of Information for FRA s (taken from the PPS25 Practice Guide Table 2.4) FRA Typical Sources of Information Level 1 Environment Agency Flood Map Environment Agency Standing Advice PPS25 table D.1 SFRA 2 Regional or local policy statements or guidance (eg Regional Spatial Strategies, Local Development Documents) Regional Flood Risk Appraisals (RFRAs) Strategic Flood Risk Assessments (SFRAs) Catchment Flood Management Plans (CFMPs)/Shoreline Management Plans SMPs) Surface Water Management Plans Consultation with the LPA/Environment Agency or other flood risk consultees to identify, in broad terms, what issues, related to flood risk, need to be considered including other sources of flooding Historic maps Local libraries and newspaper reports Interviews with local people Walkover survey to assess: Potential sources of flooding Likely routes for flood waters The site s key features, including flood defences, and their condition Site survey to determine: General ground levels across the site Levels of any formal or informal flood defences relevant to the site All other documents listed in Appendix B of this Guide. 3 As above, plus Detailed topographical survey Ref: 7293A/21/CW/06-07/1778 Page 86

91 Detailed hydrographic survey Site-specific hydrological and hydraulic modelling studies Monitoring to assist with model calibration/verification Continued consultation with the LPA, Environment Agency and other flood risk consultees. Content of a Site Specific FRA 8.5 The PPS25 Practice Guide gives the following guidance on the contents of a site specific FRA: The content of a FRA should always be appropriate to the scale and nature of the development. A FRA may include some, but seldom all, of the following outputs. The detailed scope of the FRA should be agreed in advance with the LPA in consultation with the Environment Agency and any other relevant flood risk consultees. A typical Level 2 or Level 3 FRA might cover the following: 1. Development description and location What type of development is proposed and where it will be located? What is its Vulnerability Classification? Is the proposed development consistent with the Local Development Documents? Evidence that the Sequential Test or Exception Test has been applied in the selection of this site for the development type proposed. 2. Definition of the flood hazard What sources of flooding could affect the site? Ref: 7293A/21/CW/06-07/1778 Page 87

92 For each identified source, describe how flooding would occur, with reference to any historic records wherever these are available. What are the existing surface water drainage arrangements for the site? 3. Probability Which flood zone is the site within? If there is a Strategic Flood Risk Assessment (SFRA) covering this site, what does it show? What is the probability of the site flooding taking account of the contents of the SFRA and of any further site-specific assessment? What are the existing rates and volumes of run-off generated by the site? 4. Climate change How is flood risk at the site likely to be affected by climate change? 5. Detailed development proposals Details of the development layout, referring to the relevant drawings. Where appropriate, demonstrate how land-uses most sensitive to flood damage have been placed in areas within the site that are at least risk of flooding. 6. Flood risk management measures How will the site be protected from flooding, including the potential impacts of climate change, over the development s lifetime? Ref: 7293A/21/CW/06-07/1778 Page 88

93 7. Off site impacts How will you ensure that the measures to protect your site from flooding will not increase flood risk elsewhere? How will you prevent run-off from the completed development causing an impact elsewhere? 8. Residual risks What flood-related risks will remain after you have implemented the measures to protect the site from flooding? How, and by whom, will these risks be managed over the lifetime of the development? 8.6 The PPS25 Practice Guide includes a draft Site Specific FRA pro-forma, with Guidance Notes, which can be issued to a developer by the LPA, for submission with the developer s planning application. This pro-forma is included in Appendix C. 8.7 The PPS25 Practice Guide also includes some other guidance relating to site specific FRA s: Use of modelling software The modelling software chosen for detailed assessments should be capable of producing the required output. It will generally be appropriate to choose commercial hydraulic/river modelling software that is in widespread use. In certain circumstances, for example where the applicability of a model to a specific situation has not been previously demonstrated, it will be necessary for those conducting the FRA to have independent benchmarking tests carried out to demonstrate model performance using standard data. Examples of how this may be achieved under a range of scenarios are provided in the Defra/Environment Agency R&D Report Benchmarking of hydraulic river modelling software packages (WS-105). Ref: 7293A/21/CW/06-07/1778 Page 89

94 This is available on the Joint Defra/Environment Agency Flood and Coastal Erosion Risk Management R & D Programme web site. In reporting on any hydraulic modelling carried out as part of the FRA, a technical description of the model should be provided. This should include the name and version of the software used. Where non-standard software has been used, evidence should be provided to demonstrate the applicability of the model(s) to the situation in question. Allowing for uncertainty Flood risk assessments may require complex analyses and the use of specialist techniques and software, particularly in the design of measures to protect vulnerable properties from flooding. Hydrologists and hydraulic modellers seldom have all the data they require in order to accurately determine the flows and flood levels associated with events with annual probabilities as low as 1 per cent. LPAs should liaise with the Environment Agency to ensure that, where such studies are undertaken, the approach adopted has taken adequate account of the need to: calibrate and verify numerical models using all relevant information reasonably available allow for uncertainties in the input parameters consider the sensitivity of modelling results to errors in the input parameters and adopt a precautionary approach, particularly where errors could have serious consequences. Compensatory Flood Storage/Conveyance Undefended areas Where development is proposed in undefended areas of floodplain, which lie outside of the functional floodplain, the implications of ground raising operations for flood risk elsewhere needs to be carefully considered. There are few circumstances where provision of compensatory flood storage or conveyance will not be required for undefended fluvial Ref: 7293A/21/CW/06-07/1778 Page 90

95 floodplain areas. This is because, whilst single developments may have a minimal impact, the cumulative impact of many such developments can be significant. In undefended tidal areas, raising the ground is unlikely to impact on maximum tidal levels and provision of compensatory storage should not be necessary. Defended areas When proposing new development behind flood defences, the impact on residual flood risk to other properties should be considered. New development behind flood defences can increase the residual flood risk, should these defences breach or overtop, by disrupting conveyance routes (flow paths) and/or by displacing flood water. If conveyance routes that allow flood water to pass back into a river or the sea following failure of a flood defence are blocked, this will potentially increase flood risk to existing properties. If there is a finite volume of water able to pass into a defended area following a failure of the defences, then a new development, by displacing some of the flood water, will increase the risk to existing properties. It is recommended that, should any land allocation be proposed in a defended flood area, the potential cumulative impact of loss of storage at the allocation sites on flood risk elsewhere within the flood cell should be considered. Such assessment should be appropriate to the scale and nature of the proposed development and flood risk. If the potential impact is unacceptable, mitigation should be provided. Run-off Rates and Volumes from New Development The policies in Annex F of PPS25 state that both the rates and volumes of run-off from new developments should be no greater than the rates prior to the proposed development, unless specific off-site arrangements are made which result in the same net effect. This may have significant implications for new developments, which developers will need to factor into the earliest stages of their site assessments. Ref: 7293A/21/CW/06-07/1778 Page 91

96 9.0 CONCLUSIONS 9.1 This SFRA is compiled in accordance with the recommendations of PPS25. It will allow appropriate strategic land use planning decisions to be made in areas which may be at risk of flooding and will provide the basis from which to apply the Sequential Test and Exception Test in the development allocation and development control process. 9.2 The information in this SFRA, particularly the flood probability maps and the sustainable drainage schedules and maps, will allow development to be allocated to areas which are not at risk of flooding, and to areas which are most able to accommodate sustainable drainage. 9.3 As well as being relevant to planning decisions, the hazard maps and animations associated with the coastal defence breach scenarios are intended as guidance for evacuation strategies in the specific settlements covered. 9.4 Climate change predictions are likely to be revised from time to time with ongoing research, and planning policy will change, so it would be prudent to review the basis of this SFRA periodically, possibly every four or five years. Ref: 7293A/21/CW/06-07/1778 Page 92

97 10.0 REFERENCES i. Communities and Local Government Planning Policy Statement 25: Development and Flood Risk. HMSO. ii. Communities and Local Government February Development and Flood Risk: A Practice Guide Companion to PPS25 Living Draft A Consultation Paper (Web-only publication). iii. DEFRA/EA Flood Risk Assessment Guidance for New Development, Phase 2, Flood and Coastal Defence R&D Programme, R&D Technical Report FD2320/TR2.. Water Research Council. iv. DEFRA/EA 2005a. Flood Risks to People, Phase 2, R&D Technical Report FD2321/TR2, Flood and Coastal Defence R&D Programme. Water Research Council. v. DEFRA/EA 2005b. Flood Warning for Vulnerable Groups: A review of the literature, Flood and Coastal Defence R&D Programme. Environment Agency. vi. DEFRA/EA 2005c. Preliminary rainfall runoff management for developments, Flood and Coastal Defence R&D Programme, R&D Technical Report W5-074/A/TR/1, Revision C. Water Research Council. vii. DEFRA/MAFF Flood and Coastal Defence Project Appraisal Guidance. viii. Environment Agency Guidance Note 3, Planning Policy Statement 25: Development and Flood Risk Assessments Development in Flood Zones 3 and 2. ix. Halcrow/HR Wallingford ISIS [CD-ROM]. Version x. Hulme, M., Jenkins, G.J., Lu, X., Turnpenny, J.R., Mitchell, T.D., Jones, R.G., Lowe, J., Murphy, J.M., Hassell, D., Boorman, P., Mcdonald, R. and Hill, S Climate Change Scenarios for the United Kingdom: The UKCIP02 Scientific Ref: 7293A/21/CW/06-07/1778 Page 93

98 Report, Tyndall Centre for Climate Change Research, School of Environmental Sciences, University of East Anglia, Norwich, UK. 120pp xi. Marshall, D.C.W. and Bayliss, A.C Flood Estimation for Small Catchments, IH Report 124. Institute of Hydrology. xii. NERC Flood Estimation Handbook [CD-ROM]. Institute of Hydrology. xiii. NERC Flood Studies Report (FSR). Institute of Hydrology. xiv. Newman, A.P Protecting groundwater with oil-retaining pervious pavements: historical perspectives, limitations and recent developments. Quarterly Journal of Engineering Geology and Hydrogeology, 37, pp xv. ODPM Preparing for Floods. London: ODPM. xvi. Reed, R., Faulkner, D. and Bayliss, A Flood Estimation Handbook (FEH), 5 Volumes. Institute of Hydrology. xvii. WinDes Micro Drainage. Version xviii. Woods-Ballard., et al The SUDS Manual, Report C697. London: CIRIA. xix. Bettess, R Infiltration drainage Manual of good practice, Report C156. London: CIRIA. xx. ADAS MAFF Report 5, Pipe size design for field drainage. xxi. BRE Digest 365. Soakaway Design. xxii. British Geological Survey Solid Geology Map, UK South Sheet, 1:625,000. Coventry: Clifford Press Ltd. Ref: 7293A/21/CW/06-07/1778 Page 94

99 xxiii. Chatwin, C. P British Regional Geology: East Anglia and Adjoining Areas. Fourth Edition, London: HMSO. xxiv. DOE The Wallingford Procedure: Design and Analysis of Urban Storm Drainage. HR Wallingford. xxv. DOE Modified Rational Method: The Wallingford Procedure. HR Wallingford. xxvi. Institute of Geological Sciences Anglia, 1:125,000. London: Cook, Hammond and Kell Ltd. Hydrogeological map of Northern East xxvii. Institute of Geological Sciences Quaternary Map of the United Kingdom, 1:625,000. Ordnance Survey. xxviii. Martin, P. et al Sustainable urban drainage systems best practice guide, Report C523. London: CIRIA. xxix. Martin, P. et al Sustainable urban drainage systems - Design manual for England and Wales, Report C522. London: CIRIA. xxx. National SuDS Working Group Interim Code of Practice for Sustainable Drainage Systems. xxxi. Pratt, C., Wilson, S., and Cooper, P Source control using constructed pervious surfaces; hydraulic, structural and water quality performance issues, Report C582. London: CIRIA. xxxii. Water UK Sewers for Adoption 6 th Edition, A design and construction guide for developers. Water Research Council. xxxiii. Wavin Stormwater Management, Design and Installation Manual. Ref: 7293A/21/CW/06-07/1778 Page 95

100 xxxiv. Wilson, S., Bray, R. and Cooper, P Sustainable Drainage Systems; hydraulic, structural and water quality advice, Report C609. London: CIRIA. Ref: 7293A/21/CW/06-07/1778 Page 96

101 11.0 GLOSSARY Actual Risk The qualitative assessment of risk taking into account the performance of any flood defences. Breach A failure of flood defences. Catchment The area of land contributing to the flow in a watercourse. Coastal Pertaining to the coast, or open sea. Coastal flooding can occur when beaches, cliffs or defences are overtopped, or where coastal erosion occurs. cu m/sec Unit of volume rate of fluid flow; cubic metres per second, sometimes written cumecs, or cu m/s DCLG Department for Communities and Local Government. DEFRA Department for Environment, Food and Rural Affairs. DEM Digital Elevation Model; a digital representation, or map, of topography. Design Flood Event Flood event of given probability of occurrence which is used for design purposes or for flood probability mapping. DPD Development Plan Document (see under LDF below). DTM Digital Terrain Model; a digital representation, or map, of topography, usually more accurate than a DEM, which may have certain features filtered out. EA Environment Agency Ref: 7293A/21/CW/06-07/1778 Page 97

102 Exception Test In exceptional circumstances, and following the PPS25 Sequential Test, there may be a valid reason for a development type on a site which is not compatible with the level of flood risk. The Exception Test must be applied. There are three stringent requirements, roughly that a) the development provides wider sustainability benefits that outweigh flood risk, b) must be on previously developed land (or shown that there are no reasonable alternative sites on previously developed land, and c), a site specific FRA must demonstrate that the site will be safe, not increase flood risk elsewhere, and will reduce overall flood risk if possible. The exact requirements for the Exception Test are given in PPS25 Annex D paragraph D9. FEH Flood Estimation Handbook (1999); contains the current national guidance and methodology for rainfall and river flood flow estimation. The Handbook is accompanied by a CD-ROM of records and other data relating to all UK catchments and river and rainfall gauging stations. Flood Resilience Measures involved in preventing or limiting damage to property which otherwise might be damaged as a result of flooding. Can be associated with preventing floodwater entering the property, or the use of designs and constructions materials which will not be damaged if wet. Flood Zone Flood probability zone as defined by PPS25. Delineates areas at risk of fluvial, tidal or coastal flooding by mapped zones categorised as high, medium and low risk. The mapped zones are available on the EA website; the EA mapping takes no account of existing defences. Risk is defined as probability of occurrence of flooding. PPS25 defines a further category of functional floodplain for areas of land where water has to flow or be stored in times of flood. Certain restrictions and requirements covering built development are associated with each of the four flood zones. It is important to note that the Environment Agency Flood Maps (available on the EA website) ignore the presence of defences, whereas Ref: 7293A/21/CW/06-07/1778 Page 98

103 the Flood Probability Maps within this Strategic Flood Risk Assessment do take account of existing defences. Flood Zone 1 Flood Zone 1 (Low Probability) is defined in PPS25 as land assessed as having a less than 1 in 1,000 annual probability of river or sea flooding in any year (<0.1%). These areas are on higher ground than the areas defined by Zones 2, 3a and 3b. Flood Zone 2 Flood Zone 2 (Medium Probability) is defined in PPS25 as land assessed as having between a 1 in 100 and 1 in 1,000 annual probability of river flooding (1% 0.1%) or between a 1 in 200 and 1 in 1,000 annual probability of sea flooding (0.5% 0.1%) in any year. Flood Zone 3a Flood Zone 3a (High Probability) is defined in PPS25 as land assessed as having a 1 in 100 or greater annual probability of river flooding (>1%) or a 1 in 200 or greater annual probability of flooding from the sea (>0.5%) in any year. Flood Zone 3b Flood Zone 3b (Functional Floodplain) is defined in PPS25 as land where water has to flow or be stored in times of flood. SFRAs are required to identify this Flood Zone (land which would flood with an annual probability of 1 in 20 (5%) or greater in any year or is designed to flood in an extreme (0.1%) flood, or at another probability to be agreed between the LPA and the Environment Agency, including water conveyance routes). Fluvial Pertaining to fresh water, ie not seawater. Fluvial flooding occurs in inland catchments, where there is no tidal influence. FRA Flood Risk Assessment. Freeboard The difference between water level and the top of riverbank, sea wall, defence structure, etc. Often used to refer to the extra height provided on a flood defence or other structure to allow for uncertainties in water Ref: 7293A/21/CW/06-07/1778 Page 99

104 level prediction, the effects of future climate change, wave run-up, future settlement of foundations of the structure, etc. FSR Flood Studies Report (1975), used prior to the FEH for the purpose of estimating flood peaks. Functional Floodplain Functional Floodplain is defined in PPS25 as land where water has to flow or be stored in times of flood. Equivalent to Flood Zone 3b. SFRAs are required to identify this Flood Zone (land which would flood with an annual probability of 1 in 20 (5%) or greater in any year or is designed to flood in an extreme (0.1%) flood, or at another probability to be agreed between the LPA and the Environment Agency, including water conveyance routes). Hydrograph Diagram showing fluid flow rate varying with time. IDB Internal Drainage Board. A statutory public body operating under the 1976 Land Drainage Act to provide drainage service within its prescribed drainage district. It raises income through the direct rating of agricultural land and buildings in its drainage district and levies constituent district councils or unitary authorities an income in recognition of the benefit arising from its work to all non-agricultural land and property. An IDB owns and maintains drains, pumping plant and other assets and is the relevant operating authority for ordinary watercourses within its district. INFOWORKS RS Computer software, which allows the investigation, routing and mapping of river flows. ISIS Computer software used for the one-dimensional analysis of flow in channels. Used to create a river model for the predictive analysis of water levels etc. in river systems. Ref: 7293A/21/CW/06-07/1778 Page 100

105 LDF Local Development Framework. The planning system introduced by the Planning and Compulsory Purchase Act 2004 requires local planning authorities to compile an LDF comprising of local development documents (LDD s - statutory planning documents), and supplementary planning documents (providing greater detail). Usually includes a Core Strategy and Site Specific Allocations. LDF s are intended to be guided by Regional Spatial Strategies (RSS s) compiled by the appropriate regional body. For Norfolk the RSS is the East of England Plan produced by the East of England Regional Authority (EERA). LiDAR Light Detection and Ranging; a ground survey which is carried out from aircraft and used for the creation of a ground model or DTM. LPA Local Planning Authority. m metre. Main River Statutory category assigned to major watercourses (usually large rivers and streams but can include smaller watercourses of local significance). Marked on official Main River maps. The EA has permissive powers covering flood defence allowing works to be carried out by the EA. m AOD Metres Above Ordnance Datum; a measure of height, expressed relative to the particular zero datum used in the UK. All topographical ground levels, water levels and river bed levels are expressed in this form. As a very general guide, mean sea level is zero, ie Ordnance Datum is approximately mean sea level. Mitigation The management or reduction of flood risk by special measures or planned actions. mm millimetre. Ref: 7293A/21/CW/06-07/1778 Page 101

106 m/sec metres per second, a unit of velocity, sometimes written m/s. ODPM Office of the Deputy Prime Minister. Ordinary Watercourse A watercourse not classified as Main River or part of Main River. Usually the smaller watercourses where the local authority or IDB is the operating authority. Permissive powers for defence or other works on ordinary watercourses are usually retained by the local authority or IDB. Overtopping Flood water rises higher than the river bank, flood defence or sea defence crest level and flows over the defence, flooding the area behind the defence. PPG25 Planning Policy Note 25: Development and Flood Risk. Issued in 2001 and now superseded by PPS25. PPS25 Planning Policy Statement 25: Development and Flood Risk. Issued in December Requires flood risk to be taken into account at all stages of the planning process in order to avoid inappropriate development in areas at risk and to direct new development away from areas at highest risk. Requires that flood risk is appraised, managed and reduced as part of the development planning process. Classifies flood risk in terms of zones, defines functional floodplain, specifies which type of development is appropriate to each zone, and classifies the vulnerability of each type of development. Requires flood resilience and SuDS in new development. Requires the formulation of regional flood risk assessments, district wide strategic flood risk assessments and site specific flood risk assessments with development proposals. Probability A statistical concept expressing the likelihood of occurrence of a particular event within a certain time period or within a sample group of events. The probability of occurrence of a flood of a certain magnitude can be expressed either as a) a percentage likelihood of Ref: 7293A/21/CW/06-07/1778 Page 102

107 occurrence within (typically) one year, or as b) the average time period until the next flood of the same magnitude. For example, the flood of certain magnitude, which has a 1% probability of occurrence within any one year, is likely to occur on average once in a period of 100 years. This flood event has a 1% annual probability of occurrence or a return period of 100 years. Because this is a statistical concept used to define a flood of a particular magnitude, it is important to recognise that this flood can in fact occur tomorrow, or tomorrow and again next week. Rapid Inundation Zone Typically areas behind defences where, due to a defence failure or overtopping, inundation is likely to occur at a rapid pace. The area would then be subject to high water velocities and significant water depths, with significant risk to persons and property. Evacuation plans are essential in these areas. Computer modelling of overtopping and breach scenarios is necessary to quantify the risk, the degree of hazard to groups of persons, and in order to formulate evacuation strategies. A convenient definition of the rapid inundation zone is the area that would flood to a depth of 500mm within 30 minutes of a defence breach or overtopping. However a rigid definition is not always appropriate. Reach (of river) A certain length of river. Return Period The average time before the next occurrence of a flood of the specified (or greater) magnitude. Usually expressed in years. RFRA Regional Flood Risk Assessment. Run-off The flow of water from an area caused by rainfall. Sequential Test The method of treating development sites in order of preference such that those sites which are not at risk of flooding are considered most preferable and those most at risk are considered least preferable or not Ref: 7293A/21/CW/06-07/1778 Page 103

108 preferable at all. authorities. Defined in PPS25 Annex D. PPS25 requires this approach from planning SFRA Strategic Flood Risk Assessment. SMP Shoreline Management Plan; a coastal defence management document. The coastline is divided into particular cells to which are assigned defence policies based upon an assessment of technical, environmental, and socio-economic objectives. Defence policies for a particular stretch of coastline might be advance the (defence) line, hold the line, managed retreat or no active intervention, based on an assessment of all objectives. sq km A unit of area equivalent to a square of 1km side length. Sometimes written km2. SuDS Sustainable Drainage Systems. These are surface water drainage techniques which mimic natural drainage patterns and avoid or minimise the use of piped systems. Piped systems can, because of fixed or limited capacity, cause flooding or overflowing during high rainfall. Piped systems also speed up and accentuate the flow of drainage water to rivers, concentrating the flows into higher peaks, exacerbating flooding in the watercourse. SuDS techniques return the water to the ground rather than directing it to pipes, and slow down, attenuate or store any water flows which do have to be directed to watercourses. SuDS techniques are very useful in the reduction of flood risk especially in urban areas. PPS25 requires the use of SuDS. Tidal Affected by tides. Estuaries and the lower downstream lengths of rivers are affected by tidal influence from the open sea. Flooding in tidally influenced lengths of rivers can be caused either by fluvial flood flows originating in the inland catchment, or from tidal influence causing water to flow back up the estuary, or from a combination of both. Ref: 7293A/21/CW/06-07/1778 Page 104

109 TUFLOW Computer software which allows the two dimensional analysis of flood flow across floodplains. Vulnerability Classification PPS25 classifies the different types of development into classes according to how vulnerable the development type is to flooding, and to assess whether the development type will be appropriate in a particular flood risk zone. WINFAP-FEH A computer software package associated with the Flood Estimation Handbook. 1-D One dimensional. 2-D Two dimensional. 1 in 20 year return period flood event A measure of flood magnitude. The flood event that is of such magnitude that it is likely to occur (return) once within any 20-year period on average. It is equivalent to the flood event that has a 5% annual probability, ie it has a 5% probability of occurring in any one year. 1 in 100 year return period flood event A measure of flood magnitude. The flood event that is of such magnitude that it is likely to occur (return) once within any 100-year period on average. It is equivalent to the flood event that has a 1% annual probability, ie it has a 1% probability of occurring in any one year. 1 in 200 year return period flood event A measure of flood magnitude. The flood event that is of such magnitude that it is likely to occur (return) once within any 200-year period on average. It is equivalent to the flood event that has a 0.5% annual probability, ie it has a 0.5% probability of occurring in any one year. Ref: 7293A/21/CW/06-07/1778 Page 105

110 1 in 1,000 year return period flood event A measure of flood magnitude. The flood event that is of such magnitude that it is likely to occur (return) once within any 1,000-year period on average. It is equivalent to the flood event that has a 0.1% annual probability, ie it has a 0.1% probability of occurring in any one year. Ref: 7293A/21/CW/06-07/1778 Page 106

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