Simplified hydraulic models for urban inundation modelling

Based on research by: Paul D. Bates1, Timothy J. Fewtrell1, Jeffrey C. Neal1, Mark A. Trigg1, Guy J-P. Schumann1 and Matthew S. Horritt2

1 School of Geographical Sciences, University of Bristol, Bristol, BS8 1SS, UK2 Halcrow Ltd., Burderop Park, Swindon, Wiltshire SN4 0QD, UK

Reduced complexity models of flooding

• Storage cell models originally created using irregular floodplain units (Zanobetti et al., 1970)

• Increased resolution of topographic data proliferated the development of regular grid versions in 2 dimensions

• Models either solve uniform flow formulae (e.g. Manning’s eqn) or finite difference approximation of diffusion wave (e.g. Bradbrook et al., 2004)

• Hunter et al. (2004) noted a number of problems with storage cell model type approach• If the time step was too large, “chequerboard” oscillations will

develop• Hunter et al. (2005) proposed a solution to these problems

by a von Neumann stability analysis of the diffusion wave equation

• However, as a result of the stability condition, computation time increases quadratically with increasing grid resolution

Computationally intractable for high resolution grids required for urban flood modelling

Testing: Planar surface

Model RMSE (m)

Volume Error (%)

Minimum Tstep (s)

Computation Time (s)

Speed up

Diffusive

0.06 1.27 0.15 0.33

Inertial 0.03 -1.27 7.25 0.02 17x

Testing: Wetting and drying

Testing: Model efficiency

Over 600x increase in time step → 1000x increase in computational speed

Model development: OpenMP

Application: Dead Run, Baltimore, US (July ‘04)

Application: Uncertain loss estimates

Application: Tewkesbury, UK (Summer ‘07)