Abstract: Dense buildings in modern city usually have a great influence on urban flood propagation, and the use of high resolution meshes to distinguish the buildings based on their actual size and elevation in large-scale urban flood simulation is often limited by the computational time. It is important to efficiently simulate the effect of buildings on flood propagation in the risk assessment of urban flood. In this paper, a two-dimensional numerical model of urban flood is established by introducing the Building Density Coefficient (BDC) in the shallow water equation to reflect the influence of buildings on the urban flood propagation. In the model, a central-upwind scheme is used to calculate the flux across the interface of computational mesh and the linear reconstruction of flow variables is adopted to achieve the second-order accuracy in space. A central difference method is used to discretize the bed slope source term to maintain the well-balanced property. The friction source term and local head loss term are calculated using a semi-implicit method to ensure the stability of model. The model can guarantee the positivity of water depth when the Courant number meets certain condition, which means there is no need to treat negative water depth problem. The simulated result shows that the established numerical model with BDC can deal with the building area as a whole zone and is not restricted by the grid size, which greatly shortens the computational time to 1/50 of that using high resolution method with good accuracy.

Key words: flood routing, urban buildings, building density coefficient, finite volume method, numerical simulation