Two-dimensional flood and debris flow simulation model in urban areas

We propose a two-dimensional simulation model for overland flood and debris flow in urban areas. Since there are many houses and office buildings in urban areas, this model includes two kinds of resistance terms in the momentum equations. One is due to the bottom shear stress and the other to drag forces on the houses and buildings. We apply the simulation model to the Fukuoka flood disaster in 1999 and compute the behavior of the overland flood flow from the rivers for the various values of the roughness coefficient n for Manning equation and drag coefficient CD for buildings and houses. It is found that the value of 0.043 is suitable for n and that of 2.05 for CD; the former value is previously proposed for roads and the latter for square cylinders. Using these values of the roughness and drag coefficient, we compute the behavior of the overland flow of the Shimabara debris-flow disaster in 1993. It is found that the computations agree with the simulation of the Shimabara debris-flow disaster.