Simulation of gradually varied flow in compound channels

Great difference of flow depth and Manning's roughness coefficients in main channels and floodplains, generate a strong gradient of lateral velocity and hence, a lateral shear stress in the interface of the main channel and floodplain. This phenomenon increases the head loss in river system. Mathematical models which are currently used for water surface profile computations in rivers, e.g. HEC-RAS and MIKE11, neglect this mechanism. For taking into account this mechanism, the energy slope and energy correction factor should be modified in gradually varied flow computations. In this paper, using exchange discharge method, the current procedure of gradually varied flow computations were modified for compound channels. Comparison of this method and HEC-RAS results in an experimental flume with heterogeneous compound section in case of drawdown profile, M2, showed that the accuracy of these methods are 95 and 84.5%, respectively.