Distribution of Sediment Transport and Shear Stress in a Meander Bend

Abstract

In a 1-m wide, meandering flume with movable sand bed, uniform flow was established at discharges of 20, 35, and 50 1/sec. Bed shear stresses, bed geometry, the distribution of sediment in transport, and the strength of secondary flow were determined at each discharge. The zones of maximum bed shear stress, \tau, and maximum sediment discharge per unit width, $$q_{s}'$$, coincide. They are on the point bar in the upstream part of the bend, cross the channel centerline in the middle or downstream part of the bend, and follow the concave or down-valley bank to the next point bar downstream. With increasing discharge, secondary currents increase in strength. Consequently, the zone of maximum \tau and $$q_{s}$$ remains closer to the inside bank across the point bar, and crosses the channel centerline somewhat lower in the bend. It appears that bed geometry is adjusted to provide, at each point on the bed, precisely the shear stress necessary to transport the sediment load supplied. For example, the gradual decrease in depth along the down-valley side of the channel from the deep in one bend to the point bar in the next results in a continual acceleration of the flow, and hence in shear stresses here which are higher than average for the channel.