Estimating bottom stress in tidal boundary layer from Acoustic Doppler Velocimeter data

Bed stresses in the bottom boundary layer of the York River estuary, Va., w ere estimated from 3D near-bottom velocities measured by Acoustic Doppler V elocimeters (ADVs) and also by a profiling array of electromagnetic current meters. By assuming the measurements were made in a constant stress layer, four methods of stress estimation were evaluated using ADVs: (1) direct co variance (COV) measurement; (2) turbulent kinetic energy; (3) inertial diss ipation utilizing the Kolmogorov spectrum; and (4) log profile. The four me thods yielded similar estimates of frictional velocity U-* based on ADV out put from both 14 and 44 cm above bed. All eight estimates of average U-* we re consistent with the overall mean of 1.10 cm/s to within the 95% confiden ce interval for individual burst estimates. The COV method worked slightly better nearer the bed, possibly because of the sensitivity of COV to the up per Limit of the constant stress layer. The inertial dissipation method per formed marginally well at 14 cm above bed, likely due to sediment induced s tratification and insufficient separation of turbulent production and dissi pation scales. The log profile method was the most variable and appeared mo st sensitive to stratification and to the thickness of the constant stress layer. The turbulent kinetic energy method was the most consistent at both heights and appears most promising for further development. Results encoura ge future use of the ADV in estuarine environments but also favor the simul taneous use of several methods to estimate bottom stress.