Coupling surface and subsurface flows in a depth averaged flood wave model

Abstract

In this paper, vertically averaged free-surface and subsurface flows are linked and solved simultaneously in a two-dimensional numerical model for predicting flood flows. A TVD-MacCormack scheme is used to solve the shallow water equations for free surface flows, while the standard MacCormack scheme is employed to solve the transient Boussinesq equations for unconfined groundwater flows. The dynamic linking of the surface/subsurface models enables the interactions between the surface water flow and the neighbouring groundwater flow in the horizontal plane to be studied. The developed model is firstly verified against the analytical solutions and experimental measurements. The model is then used to investigate the influence of buildings on flood flows, where the buildings are modelled as porous media. This approach of modelling buildings is compared with two other commonly used methods: the first being to represent the buildings by solid blocks, and the second is to include the buildings by increasing the local roughness. It has been found that the combined surface/subsurface model provides a high degree of flexibility in representing the buildings in a flood flow simulation.