A mathematical model is presented for the prediction of flood wave resulting from the instantaneous and complete failure of a dam and subsequent emptying of the reservoir into a prismatic dry channel having a parabolic cross section of arbitrary degree. It consists of the numerical integration of the characteristic equations over the irregular grid of characteristic lines using a predictor-corrector scheme. The solution is advanced towards the wave front by a gradual refinement of the characteristics net. Over a very short region comprising the wave tip, the solution is extended to the wave front, characterized by zero depth, using a simplified form of the momentum equation resulting from physical considerations in the tip region. Computed results are compared with experimental data obtained by others. Corroboration by the experimental results is considered adequate. Dimensionless graphs of practically important flood characteristics were prepared for a wide range of channel shape, size, slope and roughness, and dam height.