Selection of Interface Plane in the Assessment of Discharge in Two Stage Meandering and Straight Compound Channels

Abstract

An investigation concerning the distribution of shear stress in the main channel and floodplain of meandering and straight compound channels are presented. Discharge in meandering compound channels is strongly dependant on the interaction between flow in the main channel and that in the floodplain. The usual practice in one dimensional analysis is to separate a compound section into subsections using ‘divided channel method’ through the assumed interface planes running from the main channel–floodplain junctions. Discharge for each subsections are calculated using Manning’s equation and added up to get the total discharge of the compound section. If the assumed interface is wrong the resultant discharge becomes erroneous. The apparent shear force at the assumed interface plane gives an insight into the magnitude of flow interaction between the main channel and the adjacent floodplains basing on which the merits of the selection of the interface plains for discharge estimation are decided. Alternative uses of the traditional vertical interface plane for separation of compound channels are proposed. A set of smooth and rough sections is studied with aspect ratio varying between 2 to 5. The discharge results are compared with the results of variable-inclined interface method.