In this paper the rapidly varied unsteady flow caused by the failure of a dam in a rectangular dry bed horizontal channel has been studied both theoretically and experimentally. Experiments with dam-break flows in smooth and rough channel have been carried out. Comparisons have been made between measured depth hydrographs at different stations along the channel and analytical solution of Ritter and Dressier in this respect. It is Concluded that the forward zone of flow is highly sensitive to hydraulic resistance, consequently the measured forward wave velocities are markedly lower than those of theoretical one given by Ritter's solution. The roughness elements in the model, simulating the forest trees in prototype valley at downstream of the dam, tends to decrease the flow velocities and to increase flow depths. Finally the comparison showed that the experimental data of rough channel agreed closely with Dressler's solution. Thus, this latest theory may provide more satisfactory results for hydraulic prototypes previsions.
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