Set up some lock exchanges with varying salinity differences between the two sides of the lock. Time the seiche period of the tank with the different density differences and see how it scales with the density difference (approximately)
Set up an inverted sill in a long narrow tank that has a two layer fluid in it (salinity stratified) and tow the sill along the tank, observing the response of the stratified interface. Try a few different towing speeds and note how the response changes (or doesn’t).