-
¯
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_assessment/FinalPDFs/2017s5962%20_Appendix_A__KL_34.pdfhttps://www.west-norfolk.gov.uk/site/custom_scripts/static_content/strategic_flood_risk_assessment/FinalPDFs/2017s5962%20_Appendix_A__KL_35.pdfhttps://www.west-norfolk.gov.uk/site/custom_scripts/static_content/strategic_flood_risk_assessment/FinalPDFs/2017s5962%20_Appendix_A__KL_36.pdfhttps://www.west-norfolk.gov.uk/site/custom_scripts/static_content/strategic_flood_risk_assessment/FinalPDFs/2017s5962%20_Appendix_A__KL_37.pdfhttps://www.west-norfolk.gov.uk/site/custom_scripts/static_content/strategic_flood_risk_assessment/FinalPDFs/2017s5962%20_Appendix_A__KL_38.pdfhttps://www.west-norfolk.gov.uk/site/custom_scripts/static_content/strategic_flood_risk_assessment/FinalPDFs/2017s5962%20_Appendix_A__KL_39.pdfhttps://www.west-norfolk.gov.uk/site/custom_scripts/static_content/strategic_flood_risk_assessment/FinalPDFs/2017s5962%20_Appendix_A__KL_40.pdfhttps://www.west-norfolk.gov.uk/site/custom_scripts/static_content/strategic_flood_risk_assessment/FinalPDFs/2017s5962%20_Appendix_A__KL_41.pdfhttps://www.west-norfolk.gov.uk/site/custom_scripts/static_content/strategic_flood_risk_assessment/FinalPDFs/2017s5962%20_Appendix_A__KL_42.pdfhttps://www.west-norfolk.gov.uk/site/custom_scripts/static_content/strategic_flood_risk_assessment/FinalPDFs/2017s5962%20_Appendix_A__KL_43.pdfhttps://www.west-norfolk.gov.uk/site/custom_scripts/static_content/strategic_flood_risk_assessment/FinalPDFs/2017s5962%20_Appendix_A__KL_44.pdfhttps://www.west-norfolk.gov.uk/site/custom_scripts/static_content/strategic_flood_risk_assessment/FinalPDFs/2017s5962%20_Appendix_A__KL_45.pdfhttps://www.west-norfolk.gov.uk/site/custom_scripts/static_content/strategic_flood_risk_assessment/FinalPDFs/2017s5962%20_Appendix_A__KL_46.pdfhttps://www.west-norfolk.gov.uk/site/custom_scripts/static_content/strategic_flood_risk_assessment/FinalPDFs/2017s5962%20_Appendix_A__KL_47.pdfhttps://www.west-norfolk.gov.uk/site/custom_scripts/static_content/strategic_flood_risk_assessment/FinalPDFs/2017s5962%20_Appendix_A__KL_48.pdfhttps://www.west-norfolk.gov.uk/site/custom_scripts/static_content/strategic_flood_risk_assessment/FinalPDFs/2017s5962%20_Appendix_A__KL_49.pdfhttps://www.west-norfolk.gov.uk/site/custom_scripts/static_content/strategic_flood_risk_assessment/FinalPDFs/2017s5962%20_Appendix_A__KL_50.pdfhttps://www.west-norfolk.gov.uk/site/custom_scripts/static_content/strategic_flood_risk_assessment/FinalPDFs/2017s5962%20_Appendix_A__KL_51.pdfhttps://www.west-norfolk.gov.uk/site/custom_scripts/static_content/strategic_flood_risk_assessment/FinalPDFs/2017s5962%20_Appendix_A__KL_52.pdfhttps://www.west-norfolk.gov.uk/site/custom_scripts/static_content/strategic_flood_risk_assessment/FinalPDFs/2017s5962%20_Appendix_A__KL_53.pdfhttps://www.west-norfolk.gov.uk/site/custom_scripts/static_content/strategic_flood_risk_assessment/FinalPDFs/2017s5962%20_Appendix_A__KL_54.pdfhttps://www.west-norfolk.gov.uk/site/custom_scripts/static_content/strategic_flood_risk_assessment/FinalPDFs/2017s5962%20_Appendix_A__KL_55.pdfhttps://www.west-norfolk.gov.uk/site/custom_scripts/static_content/strategic_flood_risk_assessment/FinalPDFs/2017s5962%20_Appendix_A__KL_56.pdfhttps://www.west-norfolk.gov.uk/site/custom_scripts/static_content/strategic_flood_risk_assessment/FinalPDFs/2017s5962%20_Appendix_A__KL_57.pdfhttps://www.west-norfolk.gov.uk/site/custom_scripts/static_content/strategic_flood_risk_assessment/FinalPDFs/2017s5962%20_Appendix_A__KL_58.pdfhttps://www.west-norfolk.gov.uk/site/custom_scripts/static_content/strategic_flood_risk_assessment/FinalPDFs/2017s5962%20_Appendix_A__KL_59.pdfhttps://www.west-norfolk.gov.uk/site/custom_scripts/static_content/strategic_flood_risk_assessment/FinalPDFs/2017s5962%20_Appendix_A__KL_60.pdfhttps://www.west-norfolk.gov.uk/site/custom_scripts/static_content/strategic_flood_risk_assessment/FinalPDFs/2017s5962%20_Appendix_A__KL_61.pdfhttps://www.west-norfolk.gov.uk/site/custom_scripts/static_content/strategic_flood_risk_assessment/FinalPDFs/2017s5962%20_Appendix_A__KL_62.pdfhttps://www.west-norfolk.gov.uk/site/custom_scripts/static_content/strategic_flood_risk_assessment/FinalPDFs/2017s5962%20_Appendix_A__KL_63.pdfhttps://www.west-norfolk.gov.uk/site/custom_scripts/static_content/strategic_flood_risk_assessment/FinalPDFs/2017s5962%20_Appendix_A__KL_64.pdfhttps://www.west-norfolk.gov.uk/site/custom_scripts/static_content/strategic_flood_risk_assessment/FinalPDFs/2017s5962%20_Appendix_A__KL_65.pdfhttps://www.west-norfolk.gov.uk/site/custom_scripts/static_content/strategic_flood_risk_assessment/FinalPDFs/2017s5962%20_Appendix_A__KL_66.pdfhttps://www.west-norfolk.gov.uk/site/custom_scripts/static_content/strategic_flood_risk_assessment/FinalPDFs/2017s5962%20_Appendix_A__KL_67.pdfhttps://www.west-norfolk.gov.uk/site/custom_scripts/static_content/strategic_flood_risk_assessment/FinalPDFs/2017s5962%20_Appendix_A__KL_68.pdfhttps://www.west-norfolk.gov.uk/site/custom_scripts/static_content/strategic_flood_risk_assessment/FinalPDFs/2017s5962%20_Appendix_A__KL_69.pdfhttps://www.west-norfolk.gov.uk/site/custom_scripts/static_content/strategic_flood_risk_assessment/FinalPDFs/2017s5962%20_Appendix_A__KL_70.pdfhttps://www.west-norfolk.gov.uk/site/custom_scripts/static_content/strategic_flood_risk_assessment/FinalPDFs/2017s5962%20_Appendix_A__KL_71.pdfhttps://www.west-norfolk.gov.uk/site/custom_scripts/static_content/strategic_flood_risk_assessment/FinalPDFs/2017s5962%20_Appendix_A__KL_72.pdfhttps://www.west-norfolk.gov.uk/site/custom_scripts/static_content/strategic_flood_risk_assessment/FinalPDFs/2017s5962%20_Appendix_A__KL_73.pdfhttps://www.west-norfolk.gov.uk/site/custom_scripts/static_content/strategic_flood_risk_assessment/FinalPDFs/2017s5962%20_Appendix_A__KL_74.pdfhttps://www.west-norfolk.gov.uk/site/custom_scripts/static_content/strategic_flood_risk_assessment/FinalPDFs/2017s5962%20_Appendix_A__KL_75.pdfhttps://www.west-norfolk.gov.uk/site/custom_scripts/static_content/strategic_flood_risk_assessment/FinalPDFs/2017s5962%20_Appendix_A__KL_76.pdfhttps://www.west-norfolk.gov.uk/site/custom_scripts/static_content/strategic_flood_risk_assessment/FinalPDFs/2017s5962%20_Appendix_A__KL_77.pdfhttps://www.west-norfolk.gov.uk/site/custom_scripts/static_content/strategic_flood_risk_assessment/FinalPDFs/2017s5962%20_Appendix_A__KL_78.pdfhttps://www.west-norfolk.gov.uk/site/custom_scripts/static_content/strategic_flood_risk_assessment/FinalPDFs/2017s5962%20_Appendix_A__KL_79.pdfhttps://www.west-norfolk.gov.uk/site/custom_scripts/static_content/strategic_flood_risk_assessment/FinalPDFs/2017s5962%20_Appendix_A__KL_80.pdfhttps://www.west-norfolk.gov.uk/site/custom_scripts/static_content/strategic_flood_risk_assessment/FinalPDFs/2017s5962%20_Appendix_A__KL_81.pdfhttps://www.west-norfolk.gov.uk/site/custom_scripts/static_content/strategic_flood_risk_assessment/FinalPDFs/2017s5962%20_Appendix_A__KL_82.pdfhttps://www.west-norfolk.gov.uk/site/custom_scripts/static_content/strategic_flood_risk_assessment/FinalPDFs/2017s5962%20_Appendix_A__KL_83.pdfhttps://www.west-norfolk.gov.uk/site/custom_scripts/static_content/strategic_flood_risk_assessment/FinalPDFs/2017s5962%20_Appendix_A__KL_84.pdfhttps://www.west-norfolk.gov.uk/site/custom_scripts/static_content/strategic_flood_risk_assessment/FinalPDFs/2017s5962%20_Appendix_A__KL_85.pdfhttps://www.west-norfolk.gov.uk/site/custom_scripts/static_content/strategic_flood_risk_assessment/FinalPDFs/2017s5962%20_Appendix_A__KL_86.pdfhttps://www.west-norfolk.gov.uk/site/custom_scripts/static_content/strategic_flood_risk_assessment/FinalPDFs/2017s5962%20_Appendix_A__KL_87.pdfhttps://www.west-norfolk.gov.uk/site/custom_scripts/static_content/strategic_flood_risk_assessment/FinalPDFs/2017s5962%20_Appendix_A__KL_88.pdfhttps://www.west-norfolk.gov.uk/site/custom_scripts/static_content/strategic_flood_risk_assessment/FinalPDFs/2017s5962%20_Appendix_A__KL_89.pdfhttps://www.west-norfolk.gov.uk/site/custom_scripts/static_content/strategic_flood_risk_assessment/FinalPDFs/2017s5962%20_Appendix_A__KL_90.pdfhttps://www.west-norfolk.gov.uk/site/custom_scripts/static_content/strategic_flood_risk_assessment/FinalPDFs/2017s5962%20_Appendix_A__KL_91.pdfhttps://www.west-norfolk.gov.uk/site/custom_scripts/static_content/strategic_flood_risk_assessment/FinalPDFs/2017s5962%20_Appendix_A__KL_92.pdfhttps://www.west-norfolk.gov.uk/site/custom_scripts/static_content/strategic_flood_risk_assessment/FinalPDFs/2017s5962%20_Appendix_A__KL_93.pdf
-
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”.