Using ADV for cohesive sediment settling velocity measurements

Abstract

Using an Acoustic Doppler Velocimeter (ADV) to simultaneously measure the turbulent diffusivities and Suspended Sediment Concentrations (SSC) at one point in the water column provides an in-situ approach to measure the settling velocity of cohesive sediments. This approach does not alter the ambient turbulence, SSC, salinity and biological constituents that are the major factors affecting floc density and size, and thus, the settling velocity. The settling velocity measured using this technique is much higher than that obtained from the traditional Owen Tube method, which eliminates the effects of ambient turbulence. Using the settling velocities measured from this new approach and the erosion rates from in-situ measurements in a numerical study of the dynamics of turbidity maximum in the York River, the simulated results were quite reasonable. This is encouraging because it was the first time that a modeling study used in-situ measured settling velocities and erosion rates together and correctly predicted the formation of turbidity maximum. Although this is a promising approach, there are improvements that should be included to establish the procedures of using an ADV for measuring the settling velocity of cohesive sediments.