Sub-grid scale parameterisation of 2D hydrodynamic models of inundation in the urban area

This paper presents preliminary results from a study considering the parameterisation of coarse- grid 2D flood models to take into account sub- grid scale flow patterns occurring in the urban area. A simulation of a severe flood in an urbanized coastal floodplain is first run using a fine grid that can resolve the flow around and between buildings. Next, the same model is run again using the same underlying topography, although stripped from any buildings, and a set of 7 values of the roughness parameter ( Manning's n), all larger than ( or equal to) the value used in the original run. A further set of simulations is carried out using a five- fold increased grid cell size. It is found that while it may be possible to model the overall effects of the buildings using strongly increased roughness parameter values, using a coarse grid otherwise has implications related to the loss of information about the site topography that results in flood flow routes being incorrectly modelled.