INVESTIGATION ON SHEAR LAYER IN COMPOUND CHANNELS

Abstract

A compound channel is a special case of rivers high stage, when the flow spreads to the adjacent floodplains. The bed of the floodplain is generally higher and rougher than the bed of the main channel, so that during flood, the river section consists of a relatively deep main channel and one or two shallow floodplains. The interaction between the faster fluid velocities in the main channel and the slower moving flow on the floodplains causes shear stresses at their interface which significantly distort flow and boundary shear stress patterns. As a result of this, large gradient of depth averaged velocities and boundary shear stress are observed in a region adjacent to the main channel and flood plain interface, commonly known as shear layer region. Identification of this zone for straight compound channels under various hydraulic conditions is integral to research work presented in this paper. Smooth straight compound channel experimental data from FCF series(A) and the depth averaged velocity data from experiment conducted in the laboratory of NIT, Rourkela are analyzed and shear layer width under various geometric and hydraulic conditions are found out. The findings of the analysis are presented and discussed in the paper. Finally mathematical model is presented for computation of shear layer width in a compound channel