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