Sediment eddy diffusivities in the nearshore zone, from multifrequency acoustic backscatter

Acoustic backscatter measurements made on the seaward face of a submerged nearshore bar are used to determine the vertical eddy diffusivity profile for sand in suspension. Suspended sand size and concentration estimates, obtained from the multifrequency backscatter inverse, permit the sediment eddy diffusivity to be determined by assuming a balance between settling and vertical diffusion after correcting for the vertical wave flux. The resulting diffusivity profiles exhibit a nearbed linear region scaling approximately with the mean maximum friction velocity. Above this region, the data do not collapse to a universal form using a single vertical length scale.