A New Flood Inundation Modelling Gareth Pender School of Built Environment Heriot Watt University

Introduction to rapid flood spreading modelling- prediction of flood depth and flood extent. A new conceptual model for maximum velocity prediction. IIIustration of application to an artificial digital elevation model. IIIustration of application to case studies. Contents

RFSMs Heriot Watt University Martin Krupka and Yang Liu. HR Wallingford Julien Lhomme et al. (1) Krupka M., Wallis S., Pender S., Neélz S., 2007, Some practical aspects of flood inundation modelling, Transport phenomena in hydraulics, Publications of the Institute of Geophysics, Polish Academy of Sciences, E-7 (401), (2) Lhomme J., Sayers P., Gouldby B., Samuels P., Wills M., Mulet-Marti J., 2008, Recent development and application of a rapid flood spreading model, River Flow 2008, September. (3) Liu Y, Pender G (2010) “A new rapid flood inundation model”, the first IAHR European Congress, Edinburgh, UK. Halcrow ISIS Fast. 1.1 Existing RFSMs

Short time to run (Typically < 5s) A good overall agreement of the final water depth and flood extent predictions between SWEM and RFSM. A good overall agreement of the maximum velocity prediction over a flood cell between SWEM and RFSM. useful for application to catchment scale flood modelling and probabilistic flood risk analysis (e.g. Bayesian Analysis). 1.2: Requirements for an RFSM

Pre-calculation An array of flood storage cells is constructed from DEM Inundation A specified volume of flood water is distributed across the storage cells. An example of constant extra head (source: Krupka et al. 2007) An example of pre-calculation process Minimum Depth (Dmin) Minimum Cell Plan area (Amin) Water level (m) Volume (cubm) 1.3 Basic RFSM algorithm DTM grid cells RFSM flood cells Real Floodplain

Next active grid Current active grid (a) (b) One-directional RFSMMulti-directional RFSM 1.4 Two different spreading algorithms

Rules to provide accurate prediction: (1) Water will spread from high location to lower locations (one directional or multiple directional spilling algorithms) with merging process. (2) Dynamic Driving head based on inflow hydrograph (3) Floodplain area with a high roughness uses a high driving head t discharge Area 1 = Area2 1.5 Our improved RFSM Fig. Inflow Hydrograph

(1) (2) (3) 1.6 Model parameters and evaluation functions

3D plot Inflow hydrograph Inflow 1.7 Application example

Flood extent using ISIS2D after 10 hours Flood extent using MD-RFSMFlood extent using OD-RFSM Water depth of cross section comparison using ISIS2D and RFSMs 1.8 Compare RFSMs with ISIS2D

1.9 ISIS2D simulation 10 m grid resolution ISIS2D model will take about 1 hour to run.

1.10 One directional RFSM spilling process RFSM will take about 1 second to run.

Area of a big flood cell Volume = vol Inflow at time outflow at time 2.1 Maximum Velocity prediction using a new conceptual model

Maximum velocity using ISIS2D Average Maximum velocity for 17 regions using ISIS2D Average Maximum velocity predictions for 17 regions using our proposed model The conceptual model parameter C was calibrated using one ISIS2D simulation with peak inflow value= 150cubm/s for inflow hydrograph. 2.2 Performance Comparison of the conceptual model and ISIS2D

2.3 Performance statistics

2.4 Application to Thamesmead, London Thamesmead 2m resolution grid digital elevation data and inflow hydrograph.

(a): Final water depth after 1hour using RFSM (b) : Final water depth after 1hour using TUFLOW (c): Region average maximum velocity prediction using the new conceptual model(d): Region average maximum velocity prediction using TUFLOW 2.5 Performance Comparison of the conceptual model and TUFLOW

2.6 Current work about 2005 Carlisle flood event

Fig1. Flood extent and water depth after hours using ISIS2D. (15m grid resolution model will take more than 1 hour to run) Fig.2. Flood extent and water depth at hours using RFSM. ( 5m grid resolution model will take 2 seconds to run) 2.7 Flood extent predictions Using ISIS2D and RFSM

2.8 Performance statistics

(1) Test more locations. (2) Fast Rapid flood spreading Modelling using Cellular Automata. Future work Thank you!