Diffiision wave based modeling of flood inundation based on sub-grid connectivity

We now routinely model flood inundation using reduced complexity models. Traditionally, these have involved both depth-averaging and width-averaging of the mass and momentum equations. Strictly, this assumption is only valid when the flow is shallow and the topographic forcing term is dominant and it still leaves the problem of discretisation and solution, given the strong sensitivity to topographic resolution. In this paper, we present and validate an alternative sub-grid formulation that introduces an explicit representation of finer resolution topographic. This approach uses high-resolution topographic data to develop explicit parameterization of sub-grid-scale topographic variability to represent both the volume of a grid cell that can be occupied by the flow and the effect of that variability upon the timing and direction of the lateral fluxes. This approach is found to give significantly better prediction of fluvial flood inundation in urban areas than traditional calibration of sub-grid-scale effects using Manning's n.