Measurements of the relationship between turbulence and sediment in suspension over mobile sand dunes in a laboratory flume

Abstract

The relationship between fluid and particle motions over a mobile dune bed was investigated using a laboratory flume with mobile sand dunes. Fluid turbulence data from a laser Doppler velocimeter (LDV) and suspended‐sediment data from an acoustic backscatter system (BSS) were collected from the same sampling volume at a constant position relative to passing sand dunes in a laboratory channel by using a motion control system to follow bed forms through the test section. A second BSS continually traversed the test section to map the bed profile. The data from the LDV and the two BSS units were correlated in order to link turbulence data with variations in suspended sediment concentration and position on bed forms. Local values of suspended sediment concentration were poorly correlated with quadrant classification, indicating a weak relationship between local turbulence and sediment in suspension. Reynolds stress values were not strongly affected by dune size over the scales covered in the experiments. Sweeps (quadrant 4 events) were the most numerous, but bursts (quadrant 2 events) generally had higher relative magnitudes. Bursts were best correlated with changes in suspended sediment concentration and with cumulative sediment suspension.