Representation of a Built-up Area in the Numerical Simulation of Urban Flash Flooding

The paper concerns numerical simulation of rapidly varied water flow resulting from flash flood propagation in a built-up floodplain. As the mathematical model of free surface unsteady water flow, the shallow water equations are assumed. In order to solve the equations, a numerical scheme of finite volume method is applied. For approximation of mass and momentum fluxes, the Roe method is used. Two methods of built-up area representation in a numerical model are presented in the paper - exclusion of the buildings from the numerical mesh of flow area and substitution of the buildings with high friction zones. In order to assess the quality of the numerical results obtained using both methods, the flow in the model city area with the building group representing a simplified town configuration was simulated. The numerical results were examined against the experimental data available due to laboratory depth measurements. The experiment of model city flooding was carried out in the hydraulic laboratory of Gdańsk University of Technology. Finally, the influence of the type of the boundary conditions imposed on building walls on simulation results is studied.