Some observations on the effect of vertical density gradients on estuarine turbulent transport processes

Abstract

Measurements of the turbulent fluctuations of the vertical and horizontal components of velocity, salinity and suspended solids concentration have been made near to the limit of salinity intrusion in a moderately high tidal range estuary. Velocity and salinity were monitored at four points up to 3 m above the bed and suspended solids concentration was monitored at 0·5 m above the bed. The data show that the vertical gradients created by solutes and particulate matter affect the velocity turbulence field and hence modify the turbulent mean velocity field. Turbulent fluctuations can be generated either internally or at the bed. The velocity turbulence field is shown to be dependent on relative depth, local gradient Richardson number and acceleration effects. The scalar turbulence fields are shown to depend on at least relative depth, the vertical component of the turbulent velocity fluctuations and the relevant scalar gradient. The mixing length functions used to quantify the turbulent transport processes are shown to depend on the local gradient Richardson number.