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An automated routing methodology to enable direct rainfall in high resolution shallow water models

Authors


Christopher Sampson, School of Geographical Sciences, University of Bristol, Bristol, BS8 1SS, UK. E-mail: chris.sampson@bristol.ac.uk

Abstract

Recent high profile flood events have highlighted the need for hydraulic models capable of simulating pluvial flooding in urban areas. This paper presents a constant velocity rainfall routing scheme that provides this ability within the LISFLOOD-FP hydraulic modelling code. The scheme operates in place of the shallow water equations within cells where the water depth is below a user-defined threshold, enabling rainfall-derived water to be moved from elevated features such as buildings or curbstones without causing instabilities in the solution whilst also yielding a reduction in the overall computational cost of the simulation. Benchmarking against commercial modelling packages using a pluvial and point-source test case demonstrates that the scheme does not impede the ability of LISFLOOD-FP to match both predicted depths and velocities of full shallow water models. The stability of the scheme in conditions unsuitable for traditional two-dimensional hydraulic models is then demonstrated using a pluvial test case over a complex urban digital elevation model containing buildings. Deterministic single-parameter sensitivity analyses undertaken using this test case show limited sensitivity of predicted water depths to both the chosen routing speed within a physically plausible range and values of the depth threshold parameter below 10 mm. Local instabilities can occur in the solution if the depth threshold is >10 mm, but such values are not required even when simulating extreme rainfall rates. The scheme yields a reduction in model runtime of ~25% due to the reduced number of cells for which the hydrodynamic equations have to be solved. Copyright © 2012 John Wiley & Sons, Ltd.

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