Quantifying and understanding turbulent fluxes of salinity, temperature and momentum is a fundamental problem in estuarine/coastal oceanography. Regional ocean models such as POM (Princeton Ocean Model) and ROMS (Regional Ocean Modeling Systems) cannot resolve small-scale turbulent processes and rely on turbulence closure models to parameterize the unresolved processes. However, these parameterization schemes often fail to properly represent important turbulent mixing processes. For example, Mellor-Yamada model is known to produce too little mixing in stratified fluids. We are using Large Eddy Simulation (LES) model to investigate stratified shear flows in shallow-water estuaries. Our goal is to develop improved mixing parameterization schemes. 

The following figure shows an example of LES results for an unstratified tidal channel. The tidal current has a semi-diurnal frequency and a maximum speed of 0.5 m/s. The water depth is 10 m and the bottom roughness length is 3 mm. During flood tides, turbulence is actively generated from the bottom boundary layer and penetrates through most of the water column. In contrast, turbulence during slack tides has the characteristics of decaying remnant eddies.  

 

Flood tide	Slack tide