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Natural Flood Storage and Extreme Flood Events Final Report

JBA Consulting
Environment Group Research Report 2005/1

ISBN 0-7559-3935-2

This document is also available in pdf format (2.3mb)

Contents

ABBREVIATIONS
EXECUTIVE SUMMARY
1 CONTEXT
1.1 Background
1.2 Definitions
1.3 Aims and Objectives
1.4 Datasets and information gathering
1.5 Digital elevation model (DEM)
2 ROLE OF FLOODPLAIN ATTENUATION IN SUSTAINABLE FLOOD MANAGEMENT
2.1 Schemes designed to encourage better floodplain utilisation for flood storage
2.2 Floodplain schemes in Scotland
2.3 Opportunities for biodiversity improvements through natural floodplain storage
2.4 Washland flooding requirements to enhance biodiversity
2.5 Flood Duration and Seasonality
2.6 Examples of schemes that provide flood attenuation and biodiversity gains
3 MODELLING AND GIS ANALYSIS
3.1 Natural storage and attenuation
3.2 Flood events
3.3 Event modelling
3.4 Model development
3.5 Scope for utilising the natural floodplain
4 ENVIRONMENTAL AND ECONOMIC ASSESSMENTS
4.1 Ecosystems and historical assessments
4.2 Rural land management
4.3 Built-up areas
4.4 Floodplain assets
4.5 Development and flood management plans
5 CASE STUDY 1 - WHITE CART WATER
5.1 Background
5.2 Modelling
5.3 Environmental assessment
5.4 Agricultural economic assessment
6 CASE STUDY 2 - SOUTH ESK (ANGUS)
6.1 Background
6.2 Modelling
6.3 Environmental assessment
6.4 Agricultural economic assessment
7 CASE STUDY 3 - TAY
7.1 Background
7.2 Modelling
7.3 Environmental assessment
7.4 Agricultural economic assessment
8 CASE STUDY 4 - RIVER CLYDE
8.1 Background
8.2 Flood volume and outline
8.3 Environmental assessments
8.4 Agricultural economic assessment
9 GENERIC ASSESSMENT OF NATURAL FLOODPLAIN STORAGE
9.1 Introduction
9.2 Main steps
9.3 Modelling methodology
9.4 Environmental and historical assessments
9.5 Floodplain assets
10 CONCLUSIONS
10.1 'Natural' flood storage
10.2 Further steps
10.3 Potential for use of 'natural' storage
11 RECOMMENDATIONS
12 REFERENCES
LIST OF FIGURES
Figure 1-1: Case study river catchments
Figure 3-1: Simple hydrograph volume analysis
Figure 4-1: Proportion of built-up area with distance upstream
Figure 5-1: White Cart Water routing model
Figure 5-2: White Cart Water - Distance-area curves for natural flood extents
Figure 5-3: White Cart Water - Distance-depth curves for natural flood extents
Figure 5-4: White Cart Water - SSSIs and Scheduled Ancient Monuments
Figure 5-5: White Cart Water - Electricity assets
Figure 5-6: White Cart Water - Distance-cost curve for the 200 year natural flood extent
Figure 6-1: South Esk routing model schematic
Figure 6-2: South Esk - Distance-area curves for natural flood extents
Figure 6-3: South Esk - Distance-depth curves for natural flood extents
Figure 6-4: South Esk - SSSIs and Scheduled Ancient Monuments
Figure 6-5: South Esk - Distance-cost curve for the 200 year natural flood extent
Figure 7-1: Tay routing model
Figure 7-2: Tay -Distance-area curves for natural flood extents
Figure 7-3: Tay - Distance-depth curves for natural flood extents
Figure 7-4: Tay - SSSIs and Scheduled Ancient Monuments
Figure 7-5: Tay - Distance-cost curve for the 200 year natural flood extent
Figure 8-1: Clyde catchment
Figure 8-2: Clyde - Distance-area curves for natural flood extents
Figure 8-3: Clyde - Distance-depth curves for natural flood extents
Figure 8-4: Clyde - SSSIs and Scheduled Ancient Monuments
Figure 8-5: Clyde - Electricity assets
Figure 9-1: Outline generic assessment method
Figure 9-2: BSEIM outline flowchart
Figure 10-1: Washlands on the River Rother
LIST OF TABLES
Table 1-1: Land cover in case study catchments
Table 2-1: Take up of the Rural Stewardship Scheme Flood Plain option
Table 2-2: Classification of washlands by flood and soil water regimes and related habitat types
Table 4-1: Agricultural land cover in case study floodplains
Table 5-1: White Cart Water - Flood flows and return periods
Table 5-2: White Cart Water-Storage volumes derived from hydrograph analysis
Table 5-3: White Cart Water - Notional average depth of natural flooding
Table 5-4: White Cart Water - Economic cost of flooding on agricultural land, based on MDSF
Table 5-5: White Cart Water - Annual compensation costs, based on single payment
Table 6-1: South Esk - Flood flows and return periods
Table 6-2: South Esk - Storage volumes derived from hydrograph analysis
Table 6-3: South Esk - Notional average depth of natural flooding
Table 6-4: South Esk - Economic cost of flooding on agricultural land, based on MDSF
Table 6-5: South Esk - Annual compensation costs, based on single payment
Table 7-1: Tay -Flood flows and return periods
Table 7-2: Tay - Storage volumes derived from hydrograph analysis
Table 7-3: Tay - Notional average depth of natural flooding
Table 7-4: Tay - Economic cost of flooding on agricultural land, based on MDSF
Table 7-5: Tay - Annual compensation costs, based on single payment
Table 8-1: Clyde - Economic cost of flooding on agricultural land, based on MDSF
Table 8-2: Clyde - Potential annual compensation costs, based on single value

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