A two-dimensional model is introduced for simulation of wave propagation of flood flows. The model has implicit finite difference scheme for integration of conservative form of equations of depthaveraged two-dimensional flow. Artificial viscosity is suggested as dissipative interface device and it can control nonlinear instability of two-dimensional model. Advantages of using smaller ratio of tail water to upstream head have been illustrated by examples. The propagation of flood waves in flood

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... lain, which comes from steep channel, has been simulated and the change of flow condition has been illustrated.