SECONDARY CURRENTS AND BED SHEAR STRESS IN COMPOUND OPEN-CHANNEL FLOWS WITH SHALLOW FLOOD PLAIN

摘要

The pattern of the secondary currents in compound open-channel flows is affected strongly by the water depth ratio between the flood plane and main channel. The bed shear stress is also affected strongly by the pattern of the secondary currents. However, almost researchers have estimated the bed shear stress by the log-law without detailed verification whether this law is valid or not. In this study, the turbulence measurements of compound open-channel flows over smooth bed were conducted by making use of a laser Doppler anemometer(LDA) with high accuracy. The friction velocity was evaluated firstly by a linear formula in the viscous sublayer in compound open-channel flows. It was found that the effect of the spanwise Reynolds stress on the bed shear stress is greater than that of the mean secondary currents in shallower compound open-channel flows.