re: -

In the shape of a wedge, because apparenty salt water has a greater specific gravity than fresh water or it's denser or some shite I forget from Chemistry class.

A few years back, like maybe 15 or 20, we had unusually low water. The salt water wedge was way up the river, I want to say approaching Belle Chasse. The USACE dredged sediment and built a berm across the river. It was deep enough to not impede shipping, but high enough of the bottom to stop the wedge before it reached the water intakes. I thought that was pretty cool.