Study on Conveyance Coefficient Influenced by Momentum Exchange Under Steady and Unsteady Flows in Compound Open Channels

Many natural compound channels with differential stages play a vital role during high flow events in real-time. When a flood occurs, and water flows into floodplains, the flow structure becomes more complex because of the momentum transfer between sub-segments of the compound channel, caused by the large difference of velocities in different sub-segments. The conventional methods of discharge calculation based on conveyance coefficients of a single channel do not consider momentum transfer, resulting in inaccurate prediction for compound channels. This paper uses a new method of determining conveyance coefficient in compound channels to be incorporated in the two-dimensional analytical solution of the Reynolds averaged Navier–stokes equations for stage-discharge and hydrographs prediction. The proposed conveyance model for flood routing is obtained by solving 1D unsteady flow equations. The flow calculation considers the interaction between sub-segments of compound channels using the momentum equation for shallow water. The proposed model was evaluated to show that incorporating the momentum flux improves the predicted maximum discharge and flow depth in the output hydrographs of the unsteady flow. This result suggests that the proposed method can effectively determine the conveyance coefficient of the compound channel in steady and unsteady flow prediction.