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¯ 0 5 10 15 20 2.5 Km Index Grid King's Lynn and West Norfolk Boundary KL_11 KL_03 KL_04 KL_71 KL_74 KL_76 KL_02 KL_06 KL_70 KL_72 KL_75 KL_05 KL_73 KL_07 KL_09 KL_10 KL_22 KL_25 KL_27 KL_28 KL_42 KL_45 KL_47 KL_48 KL_51 KL_54 KL_56 KL_57 KL_59 KL_62 KL_65 KL_68 KL_78 KL_81 KL_83 KL_91 KL_93 KL_08 KL_12 KL_21 KL_23 KL_26 KL_30 KL_41 KL_43 KL_46 KL_01 KL_52 KL_55 KL_58 KL_60 KL_63 KL_64 KL_66 KL_69 KL_77 KL_79 KL_82 KL_92 KL_24 KL_29 KL_44 KL_49 KL_53 KL_61 KL_67 KL_80 KL_90 KL_15 KL_17 KL_18 KL_32 KL_35 KL_37 KL_38 KL_84 KL_87 KL_89 KL_13 KL_16 KL_20 KL_31 KL_33 KL_36 KL_40 KL_85 KL_88 KL_14 KL_19 KL_34 KL_39 KL_86 KL_50 Legend ¯ Contains Ordnance Survey data © Crown copyright and database right 2018 © Crown copyright and database rights 2018 Ordnance Survey 100019340. Use of this data is subject to terms and conditions. This document is the property of Jeremy Benn Associates Ltd. It shall not be reproduced in whole or in part, nor disclosed to a third party, without the permission of Jeremy Benn Associates Ltd. This map forms part of a series of interactive maps that show all sources of flooding in King's Lynn and West Norfolk, as well as other supporting map layers. Clicking on a grid square in this map will open a separate interactive PDF map. Layers of interest can be made visible by clicking the boxes next to items in the legend. Note: the default setting has all layers switched off. Further information on the source and background of the information contained within the interactive PDF can be found in the Strategic Flood Risk Assessment and by clicking on the ‘Mapping Supporting Information' box in this map and the interactive PDFs. HOW TO USE THIS MAP Mapping Supporting Information

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  • ¯

    0 5 10 15 202.5 Km

    Index GridKing's Lynn and West Norfolk Boundary

    KL_11

    KL_03 KL_04

    KL_71 KL_74 KL_76

    KL_02 KL_06

    KL_70 KL_72 KL_75

    KL_05

    KL_73

    KL_07 KL_09 KL_10

    KL_22 KL_25 KL_27 KL_28

    KL_42 KL_45 KL_47 KL_48

    KL_51 KL_54 KL_56 KL_57

    KL_59 KL_62

    KL_65 KL_68

    KL_78 KL_81 KL_83

    KL_91 KL_93

    KL_08 KL_12

    KL_21 KL_23 KL_26 KL_30

    KL_41 KL_43 KL_46

    KL_01

    KL_52 KL_55

    KL_58 KL_60 KL_63

    KL_64 KL_66 KL_69

    KL_77 KL_79 KL_82

    KL_92

    KL_24 KL_29

    KL_44 KL_49

    KL_53

    KL_61

    KL_67

    KL_80

    KL_90

    KL_15 KL_17 KL_18

    KL_32 KL_35 KL_37 KL_38

    KL_84 KL_87 KL_89

    KL_13 KL_16 KL_20

    KL_31 KL_33 KL_36 KL_40

    KL_85 KL_88

    KL_14 KL_19

    KL_34 KL_39

    KL_86

    KL_50

    Legend

    ¯

    Contains Ordnance Survey data © Crown copyright and database right 2018© Crown copyright and database rights 2018 Ordnance Survey 100019340. Use of this data is subject to terms and conditions.

    This document is the property of Jeremy Benn Associates Ltd. Itshall not be reproduced in whole or in part, nor disclosed to a thirdparty, without the permission of Jeremy Benn Associates Ltd.

    This map forms part of a series of interactivemaps that show all sources of flooding inKing's Lynn and West Norfolk, as well as othersupporting map layers.Clicking on a grid square in this map willopen a separate interactive PDF map. Layersof interest can be made visible by clicking theboxes next to items in the legend. Note: thedefault setting has all layers switched off.Further information on the source andbackground of the information contained withinthe interactive PDF can be found in theStrategic Flood Risk Assessment and byclicking on the ‘Mapping SupportingInformation' box in this map and the interactivePDFs.

    HOW TO USE THIS MAP

    Mapping SupportingInformation

    https://www.west-norfolk.gov.uk/site/custom_scripts/static_content/strategic_flood_risk_assessment/FinalPDFs/2017s5962%20_Appendix_A__KL_01.pdfhttps://www.west-norfolk.gov.uk/site/custom_scripts/static_content/strategic_flood_risk_assessment/SupportingInformation/Appendix%20D.2%20Mapping%20Supporting%20Information%20August%202018.pdfhttps://www.west-norfolk.gov.uk/site/custom_scripts/static_content/strategic_flood_risk_assessment/FinalPDFs/2017s5962%20_Appendix_A__KL_02.pdfhttps://www.west-norfolk.gov.uk/site/custom_scripts/static_content/strategic_flood_risk_assessment/FinalPDFs/2017s5962%20_Appendix_A__KL_03.pdfhttps://www.west-norfolk.gov.uk/site/custom_scripts/static_content/strategic_flood_risk_assessment/FinalPDFs/2017s5962%20_Appendix_A__KL_04.pdfhttps://www.west-norfolk.gov.uk/site/custom_scripts/static_content/strategic_flood_risk_assessment/FinalPDFs/2017s5962%20_Appendix_A__KL_05.pdfhttps://www.west-norfolk.gov.uk/site/custom_scripts/static_content/strategic_flood_risk_assessment/FinalPDFs/2017s5962%20_Appendix_A__KL_06.pdfhttps://www.west-norfolk.gov.uk/site/custom_scripts/static_content/strategic_flood_risk_assessment/FinalPDFs/2017s5962%20_Appendix_A__KL_07.pdfhttps://www.west-norfolk.gov.uk/site/custom_scripts/static_content/strategic_flood_risk_assessment/FinalPDFs/2017s5962%20_Appendix_A__KL_08.pdfhttps://www.west-norfolk.gov.uk/site/custom_scripts/static_content/strategic_flood_risk_assessment/FinalPDFs/2017s5962%20_Appendix_A__KL_09.pdfhttps://www.west-norfolk.gov.uk/site/custom_scripts/static_content/strategic_flood_risk_assessment/FinalPDFs/2017s5962%20_Appendix_A__KL_10.pdfhttps://www.west-norfolk.gov.uk/site/custom_scripts/static_content/strategic_flood_risk_assessment/FinalPDFs/2017s5962%20_Appendix_A__KL_11.pdfhttps://www.west-norfolk.gov.uk/site/custom_scripts/static_content/strategic_flood_risk_assessment/FinalPDFs/2017s5962%20_Appendix_A__KL_12.pdfhttps://www.west-norfolk.gov.uk/site/custom_scripts/static_content/strategic_flood_risk_assessment/FinalPDFs/2017s5962%20_Appendix_A__KL_13.pdfhttps://www.west-norfolk.gov.uk/site/custom_scripts/static_content/strategic_flood_risk_assessment/FinalPDFs/2017s5962%20_Appendix_A__KL_14.pdfhttps://www.west-norfolk.gov.uk/site/custom_scripts/static_content/strategic_flood_risk_assessment/FinalPDFs/2017s5962%20_Appendix_A__KL_15.pdfhttps://www.west-norfolk.gov.uk/site/custom_scripts/static_content/strategic_flood_risk_assessment/FinalPDFs/2017s5962%20_Appendix_A__KL_16.pdfhttps://www.west-norfolk.gov.uk/site/custom_scripts/static_content/strategic_flood_risk_assessment/FinalPDFs/2017s5962%20_Appendix_A__KL_17.pdfhttps://www.west-norfolk.gov.uk/site/custom_scripts/static_content/strategic_flood_risk_assessment/FinalPDFs/2017s5962%20_Appendix_A__KL_18.pdfhttps://www.west-norfolk.gov.uk/site/custom_scripts/static_content/strategic_flood_risk_assessment/FinalPDFs/2017s5962%20_Appendix_A__KL_19.pdfhttps://www.west-norfolk.gov.uk/site/custom_scripts/static_content/strategic_flood_risk_assessment/FinalPDFs/2017s5962%20_Appendix_A__KL_20.pdfhttps://www.west-norfolk.gov.uk/site/custom_scripts/static_content/strategic_flood_risk_assessment/FinalPDFs/2017s5962%20_Appendix_A__KL_21.pdfhttps://www.west-norfolk.gov.uk/site/custom_scripts/static_content/strategic_flood_risk_assessment/FinalPDFs/2017s5962%20_Appendix_A__KL_22.pdfhttps://www.west-norfolk.gov.uk/site/custom_scripts/static_content/strategic_flood_risk_assessment/FinalPDFs/2017s5962%20_Appendix_A__KL_23.pdfhttps://www.west-norfolk.gov.uk/site/custom_scripts/static_content/strategic_flood_risk_assessment/FinalPDFs/2017s5962%20_Appendix_A__KL_24.pdfhttps://www.west-norfolk.gov.uk/site/custom_scripts/static_content/strategic_flood_risk_assessment/FinalPDFs/2017s5962%20_Appendix_A__KL_25.pdfhttps://www.west-norfolk.gov.uk/site/custom_scripts/static_content/strategic_flood_risk_assessment/FinalPDFs/2017s5962%20_Appendix_A__KL_26.pdfhttps://www.west-norfolk.gov.uk/site/custom_scripts/static_content/strategic_flood_risk_assessment/FinalPDFs/2017s5962%20_Appendix_A__KL_27.pdfhttps://www.west-norfolk.gov.uk/site/custom_scripts/static_content/strategic_flood_risk_assessment/FinalPDFs/2017s5962%20_Appendix_A__KL_28.pdfhttps://www.west-norfolk.gov.uk/site/custom_scripts/static_content/strategic_flood_risk_assessment/FinalPDFs/2017s5962%20_Appendix_A__KL_29.pdfhttps://www.west-norfolk.gov.uk/site/custom_scripts/static_content/strategic_flood_risk_assessment/FinalPDFs/2017s5962%20_Appendix_A__KL_30.pdfhttps://www.west-norfolk.gov.uk/site/custom_scripts/static_content/strategic_flood_risk_assessment/FinalPDFs/2017s5962%20_Appendix_A__KL_31.pdfhttps://www.west-norfolk.gov.uk/site/custom_scripts/static_content/strategic_flood_risk_assessment/FinalPDFs/2017s5962%20_Appendix_A__KL_32.pdfhttps://www.west-norfolk.gov.uk/site/custom_scripts/static_content/strategic_flood_risk_assessment/FinalPDFs/2017s5962%20_Appendix_A__KL_33.pdfhttps://www.west-norfolk.gov.uk/site/custom_scripts/static_content/strategic_flood_risk_a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  • Appendix D.2 Mapping Supporting Information August 2018.docx I

    1 Appendix D.2: Mapping Supporting Information

    1.1 Introduction

    This document provides supporting information to Appendix A: mapping of all sources of flood risk across the SFRA study area. Appendix A is presented as interactive GeoPDFs. The information in this document lists the mapping layers contained in Appendix A and the approaches used to derive the mapping layers.

    An accompanying User Guide is provided with the GeoPDFs in Appendix D.3. This provides step-by step instructions on how to navigate to data and how to use the interactive GeoPDFs.

    1.2 Appendix A mapping layers

    1.2.1 Administrative Area

    The local authority admistrative area boundary.

    1.2.2 Study Area

    This shows the boundary of the combined study area and covers a consortium of Norfolk Local Planning Authorities adminstrative boundaries including Broadland District Council, Great Yarmouth Borough Council, the Borough Council of King’s Lynn and West Norfolk, North Norfolk District Council, Norwich City Council, South Norfolk Council and the Broads Authority. These authorities comissioned this 2017 SFRA.

    1.2.3 River networks

    Main Rivers are based on the Environment Agency's Statutory Main River layer.

    Ordinary Watercourses are based on the Lead Local Flood Authority's Detailed River Network (DRN) layer.

    1.3 The Broads

    The Broads Authority Executive Area for which they are the Local Planning Authority.

    1.4 Flood Zones

    Flood Zones 2, 3a and 3b shown in Appendix A has been compiled for the study area as part of the 2017 SFRA.

    Important: The 2018 SFRA has been developed using the best available information at the time of preparation, taking into account the latest flood risk data and the current state of national planning policy. This relates both to the current risk of flooding from fluvial, tidal, pluvial, groundwater, sewers and reservoirs as well as the potential impacts of future climate change.

    At the time of preparing the 2018 SFRA, there were several on-going flood modelling studies being undertaken by or on behalf of the Environment Agency. In a number of cases, the flood modelling studies involve updating existing hydrology and hydraulic models and re-running the models for a suite of return periods. The Environment Agency regularly reviews their hydrology, hydraulic modelling and flood risk mapping, and it is important that they are approached to determine whether updated (more accurate) information is available prior to commencing a site-specific Flood Risk Assessment.

    Once a layer is selected in the interactive GeoPDFs, the associated data will display. If no data is shown in the area / grid-tile being viewed, this does not necesserily mean that there is no risk in the areas and could simply mean that there is no data available. Developers are advised to refer to Appendix D and Section 5 of the main SFRA reports which provides an overview of the approaches used and the key limitations.

  • Appendix D.2 Mapping Supporting Information August 2018.docx II

    1.4.1 Flood Zone 3b

    Flood Zone 3b comprises land where water has to flow or be stored in times of flood (the functional floodplain). Flood Zone 3b was mapped for areas covered by existing detailed hydraulic models which were available and supplied by the Environment Agency for use in the assessments.

    The mapping in the SFRA identifies this Flood Zone as land which would flood with a 5% chance in each and every year (a 1 in 20-year annual exceedance probability [AEP]), where modelling exists for both river and sea flooding. Where the 5% AEP model outputs are not available, the 4% AEP (a 1 in 25-year AEP) results were used as an alternative. The presence of defences is considered when mapping Flood Zone 3b.

    Appendix D.1 provides a full list of detailed models used in the 2018 SFRA and where the 1 in 20-year or the 1 in 25-year results have been used to prepare Flood Zone 3b.

    1.4.2 Indicative extent of Flood Zone 3b

    In the absence of detailed hydraulic model information, a precautionary approach has been adopted with the assumption that the extent of Flood Zone 3b would be equal to Flood Zone 3a (i.e. termed ‘indicative extent of Flood Zone 3b’). For example, the BESL model is due to be updated in 2019 and therefore the precautionary approach has been adopted to represent Flood Zone 3b.

    If a proposed development is shown to be in indicative Flood Zone 3b, further investigation should be undertaken as part of a detailed site-specific Flood Risk Assessment to define and confirm the extent of Flood Zone 3b. This may require detailed hydraulic modelling.

    1.4.3 Flood Zones 2 and 3a

    Flood Zone 2 comprises land assessed as having between a 1 in 100 and 1 in 1,000 annual probability of river flooding (1% - 0.1%) or between 1 in 200 and 1 in 1,000 annual probability of sea flooding (0.5% – 0.1%) in any year.

    Flood Zone 3a comprises land assessed as having a greater than 1 in 100 annual probability of river flooding (>1%) or a greater than 1 in 200 annual probability of flooding from the sea (>0.5%) in any year. Developers and the local authorities should seek to reduce the overall level of flood risk, relocating development sequentially to areas of lower flood risk and attempting to restore the floodplain and make open space available for flood storage.

    Flood Zones 2 and 3a are taken from the Environment Agency’s Flood Maps for Planning. Where new 2017 and 2018 model results are available:

    • the undefended 100-year fluvial results have been spliced into Flood Zone 3a and the undefended 1,000-year fluvial results have been spliced into Flood Zone 2.

    • the combined maximum extent of the undefended and defended 200-year tidal results have been spliced into Flood Zone 3a and the combined maximum extent of the undefended and defended 1000-year tidal results have been spliced into Flood Zone 2

    Where new models have been included to update Flood Zone 2 and Flood Zone 3, there may be some minor discrepancies with the Environment Agency's Flood Map for Planning (Rivers and Sea). In these instances the developer should contact the Environment Agency for further clarification.

    Appendix D.1 provides a full list of detailed hydraulic models used in the 2017 and 2018 SFRAs and which 2017 and 2018 model results were used to update Flood Zones 3a and 2.

  • Appendix D.2 Mapping Supporting Information August 2018.docx III

    1.5 Surface Water

    Mapping of surface water flood risk has been taken from the Flood Map for Surface Water (RoFfSW) published online by the Environment Agency. The RoFfSW is derived primarily from identifying topographical flow paths of existing watercourses or dry valleys that contain some isolated ponding locations in low lying areas. They provide a map which displays different levels of surface water flood risk depending on the annual probability of the land in question being inundated by surface water. The different levels of flood risk are shown in the below table.

    Category Definition

    High Flooding occurring as a result of rainfall with a greater than 1 in 30 chances in any given year (annual probability of flooding 3.3%)

    Medium Flooding occurring as a result of rainfall of between 1 in 100 (1%) and 1 in 30 (3.3%) chance in any given year.

    Low Flooding occurring as a result of rainfall of between 1 in 1,000 (0.1%) and 1 in 100 (1%) chance in any given year.

    Very Low Flooding occurring as a result of rainfall with less than 1 in 1,000 (0.1%) chance in any given year.

    Although the RoFfSW offers improvement on previously available datasets, the results should not be used to understand flood risk for individual properties. The results should be used for high level assessments such as SFRAs for local authorities. If a particular site is indicated in the Environment Agency mapping to be at risk from surface water flooding, a more detailed assessment should be considered to more accurately illustrate the flood risk at a site-specific scale. Such an assessment will use the RoFfSW in partnership with other sources of local flooding information to confirm the presence of a surface water risk at that particular location.

    1.6 Climate change

    1.6.1 Fluvial climate change

    Climate change is expected to increase the frequency, extent and impact of flooding, reflected in peak river flows. Wetter winters and more intense rainfall may increase fluvial flooding and surface water runoff and there may be increased storm intensity in summer. Increased river levels may also increase flood risk.

    Fluvial climate change mapping provides a strategic assessment of climate change risk. Developers should undertake detailed modelling of climate change allowances as part of a site-specific FRA, following the guidance set out in the SFRA and Environment Agency guidance.

    In the 2018 SFRA, climate change modelling for the watercourses in the combined study area was undertaken using the new climate change guidance (see Section 4 and 5 of the main SFRA report). Where appropriate existing Environment Agency hydraulic models were run for the following allowances:

    • 25% (Central) climate change allowance for the 0.1% AEP defended scenario

    • 35% (Higher Central) and 65% (Upper End) climate change allowance for the 1% AEP defended scenario

    When defining the scope of this commission, the Environment Agency recommended that the above allowances were used in this assessment, to assist with forward planning across the combined

    Notes on Flood Zone mapping:

    The Flood Zones, whilst generally accurate on a large scale, are not provided for land where the catchment of the watercourse falls below 3km2. There are a number of small watercourse and field drains which may pose a risk to development (e.g. some ordinary watercourses and / or drains managed by Internal Drainage Boards). Therefore, whilst these smaller watercourses may not be shown as having flood risk on the flood risk mapping, it does not necessarily mean that there is no flood risk. As part of a site-specific FRA the potential flood risk and extent of flood zones should be determined for these smaller watercourses.

  • Appendix D.2 Mapping Supporting Information August 2018.docx IV

    study area. The climate change allowances reflect the allowances most commonly used by developers i.e. for residential development, classified as ‘More Vulnerable’ under Table 2 of the NPPG. The epoch selected i.e. the total potential change anticipated for the ‘2080s’ (2070 to 2115), generally reflects the anticipated lifetime for residential development (i.e. 100 years), as stated in Paragraph 026 of the NPPG.

    1.6.2 Tidal climate change

    Environment Agency climate change modelling of parts of the Norfolk coastline was supplied for use in this study. The Norfolk coastal climate change modelling was undertaken in line with the revised climate change guidance and was agreed as part of a separate commission to the 2018 SFRA. The Norfolk coastal climate change modelling followed the guidance relating to sea level increases. In the wave models, a 5% allowance for increases in wind speed for the 2050s epoch and a 10% allowance for increases in wave height for the 2115 epoch, were used.

    1.6.3 Alternative mapping approaches

    Alternative mapping approaches have only been applied in instances where advances in 1D mapping techniques have created inconstancies with the Environment Agency's Flood Zones.

    In instances where standard mapping techniques have produced inconsistencies with the Environment Agency Flood Zones, the level and flow data of the 100-year plus 65% climate change (Upper End) results were compared to the existing 1,000-year results provided by the Environment Agency. In all cases, the levels and flows found during the 1,000-year event were suitably similar to provide an indication of the extent of flooding which would occur in the 100-year plus 65% climate change (Upper End) scenario. For these models, no data is provided for the 100-year plus 35% (Higher Central) and 1,000-year plus 25% (Central) scenarios.

    Details of where this alternative mapping approach has been applied can be found in Appendix D.1.

    1.6.4 Surface Water Climate Change

    Climate change modelling for surface water was undertaken based on the new climate change guidance. The Risk of Flooding from Surface Water model was rerun for the 1% AEP event plus a 40% increase for climate change. When defining the scope of this commission, the LLFA advised that a 40% (Upper End) allowance was to be used in the climate change assessment for surface water.

    1.6.5 Using climate change allowances

    To help decide which allowances to use to inform the selection of flood levels for flood risk management measures at a development or development plan allocation, the following should be considered:

    • likely depth, speed and extent of flooding for each allowance of climate change over time considering the allowances for the relevant epoch (2020s, 2050s and 2080s)

    • vulnerability of the proposed development types or land use allocations to flooding

    Additional notes on fluvial and tidal climate change mapping:

    Within King's Lynn borough, the fluvial hydraulic models were not available to be re-run, and consequently no fluvial climate change modelling was undertaken. At such locations developers should undertake further investigations as part of a site-specific Flood Risk Assessment to ensure that fluvial climate change allowances are adequately considered.

    In coastal areas, there will be no fluvial climate change extents shown in the Appendix A interactive GeoPDFs where the hydraulic models represent the tidal flood risk. In such instances, climate change extents will be shown under the tidal climate change layers, rather than the fluvial climate change layers, where detailed models exist, and the outputs were supplied and available at the time of preparing the SFRAs.

    Where the Tidal Hazard Mapping (Tidal Great Ouse Modelling) model is used please note that the 2015 was a combined sensitivity test on the variables that affect the breach extent and a breach model that expanded the coverage of the model. The flood map for planning was not updated as part of this project.

    https://www.gov.uk/guidance/flood-risk-and-coastal-change#Table-2-Flood-Risk-Vulnerability-Classification

    https://www.gov.uk/guidance/flood-risk-and-coastal-change#Table-2-Flood-Risk-Vulnerability-Classification

    https://www.gov.uk/guidance/flood-risk-and-coastal-change

  • Appendix D.2 Mapping Supporting Information August 2018.docx V

    • ‘built in’ resilience measures used, for example, raised floor levels

    • capacity or space in the development to include additional resilience measures in the future, using a ‘managed adaptive’ approach

    The Environment Agency has produced a guidance document called “Flood risk assessment: Climate Change allowances” which details the application of the allowances, local considerations in East Anglia and the local precautionary allowances for potential climate change impacts, that can be used in basic assessments in absence of the updated, detailed modelling (i.e. areas covered by the BESL model). This document is available to download from: These documents are available from: https://www.norfolk.gov.uk/rubbish-recycling-and-planning/flood-and-water-management/ information-for-developers

    1.7 Residual Risk (Breach)

    The breach extents have been extracted from a number of existing hydraulic models supplied by the Environment Agency when preparing this SFRA. Details of the models used to map the breach extents are contained in Appendix D.1. Due to the number of breach scenarios modelled and the number of models available, the extents from the individual breaches and models have been merged into:

    • One combined extent for the tidal 200-year with climate change (2115) scenario; and,

    • One combined extent for the fluvial 100-year with climate change scenario.

    Where breaches have not been supplied for the 100-year with climate change event the 100-year event breach has been included in the outline.

    1.8 Reservoir flooding

    Mapping indicating flooding from reservoir sources has been developed based on Environment Agency supplied National Inundation Reservoir Mapping dataset. Please note that the reservoir inundation outlines shown in the mapping are made up of reservoirs which are located outside the SFRA study area of interest. For further information please see the main SFRA report.

    1.9 Groundwater

    Mapping of groundwater flood risk has been based on the Areas Susceptible to Groundwater (AStGWf) dataset. The AStGWf dataset is a strategic-scale map showing groundwater flood areas on a 1km square grid. It shows the proportion of each 1km grid square, where geological and hydrogeological conditions indicate that groundwater might emerge. It does not show the likelihood of groundwater flooding occurring and does not take account of the chance of flooding from groundwater rebound. This dataset covers a large area of land, and only isolated locations within the overall susceptible area are actually likely to suffer the consequences of groundwater flooding.

    The AStGWf data should be used only in combination with other information, for example local data or historical data. It should not be used as sole evidence for any specific flood risk management, land use planning or other decisions at any scale. However, the data can help to identify areas for assessment at a local scale where finer resolution datasets exist.

    The AStGWf data should be used only in combination with other information, for example local data or historical data. It should not be used as sole evidence for any specific flood risk management, land use planning or other decisions at any scale. However, the data can help to identify areas for assessment at a local scale where finer resolution datasets exist.

    1.10 BESL Model

    The BESL hydraulic model outputs were not available at the time of preparing the 2018 SFRA. The 2008 BESL model extent is shown on the Appendix A mapping. The BESL model covers several Norfolk authority administrative areas and notably covers much of the Broads Authority Executive Area. The Environment Agency’s Flood Map for Planning (Rivers and Sea) and Flood Zones extents, may be subject to change in this area, following completion of the BESL hydraulic modelling. This further reinforces the importance of approaching the Environment Agency, to determine where updated (more accurate) information is available prior to commencing a site-specific FRA.

    https://www.norfolk.gov.uk/rubbish-recycling-and-planning/flood-and-water-management/%20information-for-developers

    https://www.norfolk.gov.uk/rubbish-recycling-and-planning/flood-and-water-management/%20information-for-developers

  • Appendix D.2 Mapping Supporting Information August 2018.docx VI

    1.11 Dry Islands

    Dry islands are areas which are identified as being in Flood Zone 1 but are completely surrounded by areas at a higher risk of flooding i.e. surrounding areas which fall within Flood Zones 2. Dry islands can present specific hazards, primarily the provision of safe access and egress during a flood event.

    The threshold used to determine the presence of dry islands is: land areas of 0.5 hectares or greater in size, identified as being in Flood Zone 1 and completely surrounded by land which falls within Flood Zones 2. The 0.5 hectares threshold was selected as this reflects one of the criteria used to define “major development”.