Discharge Estimation in Compound Channels Having Narrowing and Enlarging Floodplains

Abstract

River floods are generally described as two stage compound open channels. The lateral variation in depth and roughness across the cross section of a compound channel causes momentum transfer at the interface. So, prediction of discharge primarily depends upon the proper quantification of momentum transfer at the junction. As overbank flows are commonly non-uniform along the stream-wise direction, therefore analysis and estimation of flow variables under non-uniform flow condition is a challenging task which can comfortably be used for prediction in natural rivers. In the present research, compound open channels with narrowing and enlarging floodplains are considered as the flow is generally non-uniform in these types of channels. Modified divided channel method is again extended to estimate the discharge in converging and diverging compound channels. These developed expressions are depending upon percentage of the boundary shear forces carried by non-prismatic floodplains. So, individual models of boundary shear force carried by floodplains for converging and diverging compound channels are taken from author’s previous work. It is seen that the proposed models give simple ways for the computation of discharge in non-prismatic channels. The predictions results are then compared with their observed values.