1. WP1.2: Inundation modelling to support uncertainty analysis Jeff Neal 1, Ignacio Villanueva 2, Nigel Wright 3, Thomas Willis 3, Timothy Fewtrell 4, Paul Bates 1, Caroline Keef 5, Keith Beven 6 and David Leedal 6 1 School of Geographical Sciences, University of Bristol, Bristol. BS8 1SS. UK, 2 Ofiteco Ltd., Avenida de Portugal, 81. 28071, Madrid. Spain. 3 School of Civil Engineering, University of Leeds, Leeds. LS2 9JT. UK 4 Willis Research Network, Willis Re, Willis Building, 51 Lime Street, London. EC3M 7DQ. UK 5 JBA Consulting, South Barn, Broughton Hall, Skipton, N Yorkshire, BD23 3AE, UK. 6 Lancaster Environment Centre, Lancaster University, Lancaster, LA1 4YQ, UK.

2. Why develop and benchmark models to support uncertainty analysis? Two-dimensional models of floodplain hydraulics require a lot of computation time. Increasing resolution requires increased computation. Monte Carlo… also increases computation Simple models: Require less computation per time-step than a shallow water models. Force modellers to think about the minimum process representation necessary to predict particular quantities. Are generally not as widely applicable as shallow water models – thus we need to understand their limits. Some may require shorter time-steps to remain stable especially at 1-10 m resolutions (Hunter et al., 2005).

3. LISFLOOD-FP (ACC) formulation Continuity Equation Continuity equation relating flow fluxes and change in cell depth Momentum Equation Flow between two cells is calculated using: Time stepping ij h flow i j Representation of flow between cells in LISFLOOD-FP

4. EA 2D model benchmarking EA testDescriptionTested here 1Flooding a disconnected water body.Yes 2Filling of floodplain depressions.Yes 3Momentum conservation over a small (0.25m) obstruction.Yes 4Speed of flood propagation over an extended floodplain.Yes 5Valley flooding.Yes + finer resolution 6a&bDam break. a) Flume scale, b) Field scale.Yes, b only 7River to floodplain linking.No 8a&bUrban flood. a) Rainfall, b) Rainfall and sewer surcharge.No Taken from Environment Agency 2D model benchmarking project Simulation results from commercial codes available ISIS2D, TUFLOW, SOBEK, MIKE FLOOD, InfoWorks2D FlowRoute, JFLOW-GPU, Dynamic RFSM

5. Results – Valley filling following dam failure

6. The frequently of velocity output had as much impact on hazards assessment as model physical complexity.

7. Carlisle: Probabilistic flood risk mapping. www.lancs.ac.uk/staff/leedald/Carlisle/visualisation.html