Turbulence characteristics in the bottom layer of a shallow tidal channel

Abstract

Observation of a shallow tidal channel was executed to examine turbulent evolution in ideal condition of weak, stratified flow for a complete cycle of semi-diurnal tide. Duration of this study allows a maximum velocity variation and therefore gives comprehensive interpretation of the relevant processes such as momentum and heat transfer, turbulent kinetic energy (TKE) production and dissipation rates. Under weak stratification condition dominant through the observation period testing the parameterization of dissipation rate in the Mellor–Yamada type models revealed that close to the bed perhaps due to boundary effects experimental dissipation closure constant values were remarkably larger than commonly used value of 16.6. Also, the effect of extending critical Richardson number Ri_cr to infinity on parameterization of stability functions, eddy viscosity, and turbulent Prandtl number in Kantha–Carniel model was also examined. It was found that despite Kantha–Carniel model reconstructed bottom boundary layer (BBL) turbulence characteristics well during the flooding tide, it underestimates those parameters during the ebbing tide partially due to underestimation of turbulence macroscale.

Keywords:

• turbulence
• bottom boundary layer
• estuary
• tidal currents
• acoustic Doppler velocimetry
• Mellor–Yamada model
• Kantha–Carniel model