Structure of Turbulent Flow in a Shallow Tidal Estuary

Abstract

A high-resolution current profiler (HRCP), which belongs to a pulse-to-pulse coherent Doppler sonar, has been used to measure vertical profiles of turbulence parameters, such as the Reynolds stresses, eddy viscosity, production and dissipation rates, etc., and to test the parametrization of dissipation rate and eddy viscosity. The HRCP and automatic ascending/descending CTD are deployed during the autumn of 2001 for 24 h in a tidal estuary. Reliable velocities along the beams with HRCP are collected with 3 s intervals and a vertical resolution as fine as 0.03 m in the range 0.02–0.98 m above the bottom. Density profiles with the CTD are taken nominally every 30 sec. The turbulent velocity variables depend largely on the tidal phase; the variables during the ebb deviate from those in neutral equilibrium boundary layer. This deviation during the ebb presumably arises from the “inactive motion.” The stability function SM in the Mellor–Yamada (M–Y) model is smaller than 0.39 even when the stratification is negligible during the flood. The constant of proportionality B1 in the dissipation model is larger than 16.6 used in M–Y model. There is room for improving some of the mixing parametrizations in estuarine tidal flows.