Veeder-Root Manual (EN)

Flood Modelling Guidance for Responsible Authorities Version 1.1

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1 Executive Summary

1 Executive Summary Developing our knowledge of flooding and how we can effectively assess potential impacts on our communities is essential in implementing effective and sustainable flood risk management plans. Flooding is a complex natural process arising from a range of sources (e.g. rivers, sea, surface water/pluvial) and from a range of mechanisms. Using information on the characteristics of floods we are able to assess the potential impact of floods using computer simulations.

Computer flood models are key tools in assessing, testing and informing the delivery of flood risk management actions; while there will remain inherent uncertainty in representing natural systems, quality models enable the production of flood maps and data that support communication with the public and enable key policy and investment decisions. Utilising a consistent framework to guide model development will support a common understanding and effective communication of flood study needs within and between organisations. Ensuring a clear description of model needs enables models to be developed appropriately to deliver study objectives.

Thus, with an improved knowledge base, common language and improved communication, model quality can be raised to improve confidence in information that empowers decision-makers to act in support of flood risk management. This modelling guidance document is therefore intended to provide a common technical basis to support Responsible Authorities in the planning, development and use of flood models to inform flood risk management decisions. As flood modelling science is constantly evolving, this guidance will be revised as our understanding improves.

SEPA’s strategic flood risk team ( strategic.floodrisk@sepa.org.uk) welcome any questions, comments or suggestions for improvement regarding this guidance. Flood Modelling Guidance for Responsible Authorities v1.1 1

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1 Executive Summary

Contents 1 Executive Summary ....................................................................................................... 1 2 Introduction .................................................................................................................... 6 2.1 Purpose of the Flood Modelling Guidance ............................................................. 6 2.2 How to use this guidance ....................................................................................... 8 2.3 SEPA input into modelling studies .........................................................................

9 3 Scoping ........................................................................................................................ 10 3.1 Introduction .......................................................................................................... 10 3.2 Define Modelling Objective .................................................................................. 10 3.3 Developing a Conceptual Model .......................................................................... 10 3.4 Spatial Extent ......................................................................................................

12 3.5 Joint Studies ........................................................................................................ 14 3.6 Level of Assessment............................................................................................ 17 3.7 Modelling Approach ............................................................................................. 17 3.7.1 Selection of Modelling Software ..................................................................... 20 4 Commissioning a study ................................................................................................

22 4.1 Introduction .......................................................................................................... 22 4.2 Statement of Requirements (SoR) ....................................................................... 22 4.3 Quality Control ..................................................................................................... 22 4.4 Resources ........................................................................................................... 22 4.5 Timescale/Milestones ..........................................................................................

23 4.6 Risk Register ....................................................................................................... 23 4.7 Meetings and Progress Reports .......................................................................... 23 4.8 Intellectual Property Rights .................................................................................. 23 5 Data ............................................................................................................................. 24 5.1 Introduction ..........................................................................................................

24 5.2 General Considerations ....................................................................................... 24 5.3 Data collection ..................................................................................................... 24 5.3.1 Data registers ................................................................................................ 24 5.3.2 Licensing ....................................................................................................... 25 5.4 Historic Flooding Information ...............................................................................

25 5.4.1 Use of data .................................................................................................... 25 5.4.2 Available Datasets ......................................................................................... 25 5.5 Topographic and Bathymetric Data ...................................................................... 27 5.5.1 Reuse of existing data ................................................................................... 27 5.5.2 Commissioning a New Survey ....................................................................... 28 5.5.3 Data Format ...................................................................................................

28 5.5.4 Channel Survey ............................................................................................. 28 5.5.4.1 Commissioning a New Channel Survey ................................................... 28 5.5.4.2 Cross-Sections ......................................................................................... 29 5.5.4.3 Hydraulic Structures ................................................................................. 30 5.5.4.4 Flood Defence Survey .............................................................................. 30 5.5.5 Digital Elevation Models (DEMs) ....................................................................

34 5.5.5.1 Existing Data Sets .................................................................................... 34 5.5.5.2 New Data Collection ................................................................................. 35 5.5.6 Bathymetric Data ........................................................................................... 38 5.5.6.1 Commissioning New Bathymetric Surveys ............................................... 38 5.5.6.2 Coastal Defence Survey .......................................................................... 38 5.6 Operating Information ..........................................................................................

38 5.7 Existing Studies ................................................................................................... 39 5.8 Hydrometric Data ................................................................................................. 40 5.8.1 River Levels and Flows .................................................................................. 40 5.8.2 Rainfall Data .................................................................................................. 42 5.8.3 Soil Moisture and Evaporation Data ............................................................... 43 Flood Modelling Guidance for Responsible Authorities v1.1 2

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1 Executive Summary

5.8.4 Reservoir Data ............................................................................................... 43 5.8.5 Sea Level Data .............................................................................................. 43 5.8.5.1 Gauge Data.............................................................................................. 43 5.8.5.2 Tide Tables .............................................................................................. 44 5.8.5.3 Sea level boundary conditions ................................................................. 44 5.8.6 Wave Data .....................................................................................................

44 5.8.7 Wind data ...................................................................................................... 45 5.9 Other Data ........................................................................................................... 45 5.9.1 Sewer Network Data ...................................................................................... 45 5.9.2 National Coastal Change Assessment ........................................................... 45 5.9.3 Water Framework Directive Status/Pressures ................................................ 45 5.9.4 Mapping Data ................................................................................................

45 6 Boundary Conditions .................................................................................................... 47 6.1 Introduction .......................................................................................................... 47 6.2 Terminology ......................................................................................................... 47 6.3 Fluvial .................................................................................................................. 48 6.3.1 Review of Hydrometric Data ..........................................................................

50 6.3.2 Design Flows ................................................................................................. 50 6.3.2.1 Statistical Method (single site and pooled analysis).................................. 51 6.3.2.2 Design Event Method (Rainfall-Runoff Method) ....................................... 51 6.3.3 Hydrograph Shapes ....................................................................................... 52 6.3.4 Catchment Schematisation/Boundary Locations ............................................ 53 6.3.5 Flow Reconciliation ........................................................................................

53 6.3.6 Climate Change ............................................................................................. 54 6.4 Pluvial .................................................................................................................. 54 6.4.1 Rainfall Models .............................................................................................. 54 6.4.2 Losses ........................................................................................................... 55 6.4.3 Climate Change .............................................................................................

56 6.5 Coastal ................................................................................................................ 58 6.5.1 Still Water Boundary Conditions..................................................................... 59 6.5.2 Waves............................................................................................................ 62 6.5.2.1 Offshore design wave conditions .............................................................. 62 6.5.2.2 Joint probability of extreme still water levels and extreme wave conditions 63 6.5.2.3 Wave transformation modelling ................................................................

63 6.5.2.4 Wave Overtopping ................................................................................... 64 6.5.3 Climate Change ............................................................................................. 64 6.6 Joint Probability ................................................................................................... 64 6.6.1 Extreme Sea Level and Fluvial Flows ............................................................ 64 6.7 Groundwater ........................................................................................................

65 6.8 Uncertainty .......................................................................................................... 65 7 Model Schematisation .................................................................................................. 66 7.1 Introduction .......................................................................................................... 66 7.2 1D fluvial Models ................................................................................................. 66 7.2.1 Channel representation ..................................................................................

67 7.2.1.1 Cross Sections ......................................................................................... 67 7.2.1.2 Roughness ............................................................................................... 68 7.2.1.3 Hydraulic Structures ................................................................................. 68 7.2.2 Floodplain Representation ............................................................................. 70 7.2.3 Common Problems with 1D Models ............................................................... 72 7.3 2D models ...........................................................................................................

73 7.3.1 Model Resolution ........................................................................................... 74 7.3.2 DTM ............................................................................................................... 75 7.3.2.1 Building representation ............................................................................ 75 7.3.2.2 Hydraulic Structures and Linear Features ................................................ 76 Flood Modelling Guidance for Responsible Authorities v1.1 3

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