Effects of silt loading on turbulence and sand transport
Abstract The transport of bed material and fluid turbulence are affected by many factors, including the fine sediment load being carried in a channel. Current research has focused on sand-sized particles introduced to gravel beds, while the effect of silt load on sand transport has received less attention. Experiments on the effects of silt load, in concentrations 0-26,900 mg l −1 , on sand transport were performed with a recirculating laboratory flume using three different sand bed configurations: ripples ( Fr =0.24), dunes ( Fr =0.34), and dunes ( Fr =0.48). Three Acoustic Doppler Velocimeters were arranged to measure flow and turbulence quantities simultaneously in one vertical. Sand transport did not change in a consistent manner with increasing silt load, increasing up to 4,000 mg l −1 for dunes ( Fr =0.48) and up to 2,000 mg l −1 for dunes ( Fr =0.34) and then declining to near the clear water case with increasing silt concentrations. Silt addition for the ripple case caused a relatively small change in sand transport, decreasing with added silt up to approximately 2,000 mg l −1 and then increasing as silt went up to approximately 10,000 mg l −1 . Dunes ( Fr =0.48) decreased in length and height as silt increased, while dunes ( Fr =0.34) did not show a consistent trend. A clear trend of decreasing Reynolds stress with increasing silt concentration was observed in the ripple case, with a 33% reduction in near-bed Reynolds stress caused by an 8,900 mg l −1 concentration of silt.