Measuring velocity and shear stress over dunes with acoustic Doppler profiler

This study evaluates the use of an acoustic Doppler profiler (ADP) for measurement of velocity profiles over dunes in an estuary. The ADP can be deployed from a moving launch and provides three-dimensional velocity profiles that can be used to describe flow structure and to provide rough estimates of shear stress. Quadratic stress models are recommended for shear stress because they estimate skin friction and form stress whereas the law of the wall only reliably estimates total stress over dunes. The most serious limitation of the ADP is a beam geometry that results in a large sampling, diameter close to the bed that does not adequately measure velocity in dune troughs.