Field Measurements of Mean Velocity and Boundary Shear Stress with an Acoustic Doppler Current Profiler

The boat-mounted Acoustic Doppler Current Profiler (ADCP) is a powerful tool for measuring the three-dimensional flow field in rivers. Velocity data can be obtained using either fixed-(FV) or Moving-Vessel (MV) procedures. The reduced field effort involved in the collection of MV data has prompted investigators to seek MV procedures that provide equivalent results to FV measurements. This study compares mean velocity and boundary shear stress calculated with data from both survey procedures. Mean velocity values from MV data are computed using a spatial average and the boundary shear stress is found using the logarithmic law of the wall. The results indicate that MV data provides reasonable estimates of depth-averaged velocity characteristics; however, agreement for velocity profiles and shear stress, in particular, were found to be poor. Further work is needed to assess the role of MV survey procedures including the number of measurements collected and the duration of measurements.