Interaction of Flow in Meandering and Straight Channel with Floodplains

Abstract

Reliable estimates of discharge capacity are essential for the design, operation, and maintenance of open channels, more importantly for the prediction of flood, water level management, and flood protection measures. During floods, the river water overtops its banks and spreads to the adjoining floodplains. For such compound channels, the flow structure becomes complex due to the transfer of momentum between the deep main channel and the adjoining floodplains. Discharge in meandering compound channels is strongly dependant on the interaction between flow in the main channel and that in the floodplain. Laboratory test results are presented concerning the boundary shear stress, shear force, and discharge characteristics of compound meandering river sections composed of a rectangular main channel and floodplains disposed off to its sides. Dimensionless parameters are used to form equations representing the total shear force percentage carried by floodplains. A curved interface is proposed understanding the important flow interaction for which apparent shear force is calculated as zero. Equations are presented to predict the section discharge carried by the meandering and straight channels. The equations agree well with experimental discharge data. Using the proposed area method, the error between the measured and calculated discharges for the meandering compound sections is found to be the minimum when compared with that using other interfaces.