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This paper evaluates the results of benchmark testing a new inertial formulation of the de St. Venant equations, implemented within the LISFLOOD-FP hydraulic model, using different high resolution terrestrial LiDAR data (10 cm, 50 cm and 1 m) and roughness conditions (distributed and composite) in an urban area. To examine these effects, the model is applied to a hypothetical flooding scenario in Alcester, UK, which experienced surface water flooding during summer 2007. The sensitivities of simulated water depth, extent, arrival time and velocity to grid resolutions and different roughness conditions are analysed. The results indicate that increasing the terrain resolution from 1 m to 10 cm significantly affects modelled water depth, extent, arrival time and velocity. This is because hydraulically relevant small scale topography that is accurately captured by the terrestrial LIDAR system, such as road cambers and street kerbs, is better represented on the higher resolution DEM. It is shown that altering surface friction values within a wide range has only a limited effect and is not sufficient to recover the results of the 10 cm simulation at 1 m resolution. Alternating between a uniform composite surface friction value (n = 0.013) or a variable distributed value based on land use has a greater effect on flow velocities and arrival times than on water depths and inundation extent. We conclude that the use of extra detail inherent in terrestrial laser scanning data compared to airborne sensors will be advantageous for urban flood modelling related to surface water, risk analysis and planning for Sustainable Urban Drainage Systems (SUDS) to attenuate flow

In recent years, urban flood modelling studies have taken the form of either validation against observations of a single event or benchmarking models of varying complexity for a synthetic flood event. In this paper, the latter framework is undertaken for hypothetic flooding scenarios at Greenwich on the River Thames, UK. A simple diffusion wave storage cell model, LISFLOOD-FP, is compared to a fully 2D hydrodynamic model, SOBEK, at multiple resolutions for a 1-in-100 year return period event. The models yield consistent results at the highest resolution (5 m) with minor differences accounted for by inertial effects and model schematisation. Secondly, both models predict significant degradation in model results at coarse resolutions compared to the high resolution benchmark. Specifically, results at 25 and 50 m suggest different flow structures emerge as the representation of urban structures becomes more coarse. As a result of this finding, the models are setup using a digital terrain model (DTM) with the buildings removed to investigate these emergent flow structures.

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