FLUME SIMULATION OF RECIRCULATING FLOW AND SEDIMENTATION

Experiments were conducted in a 4-m-wide flume to simulate recirculating flow and sedimentation in a lateral eddy within a channel expansion. The percentage of main stem sediment that was captured by the eddy decreased from 37% (when the eddy was empty) to 24% (when sand filled approximately 32% of the eddy volume). The reattachment bar within the eddy grew in an upstream direction, and the finest size sediment was deposited in the lee of the obstruction; both observations are consistent with field observations. Measurements of reattachment length during sediment transport (0.5-1.0 kg/s) at constant discharge (0.60 m3/s) show that reattachment length depends not only on characteristics of the expanding jet, but also on the topography of the channel bed downstream; reattachment length decreased when part of the channel expansion was filled by an aggrading midchannel bar. Comparison of these results with measurements in the Colorado River in Grand Canyon suggests that downstream channel irregularities play a large role in controlling the length of eddies in natural rivers.