that was the way Romans and Byzantines made dams: float barges full of rocks into position, and then scuttle them. It worked back then, I can't believe it wouldn't work today.
(sorry I didn't reply on the thread on which you posted this - it is locked)
In order to do that, you must first find a barge, or float one in. The CoE is bringing in barges from upriver, but those must proceed slowly. Katrina scattered all the local barges to hell and gone.
my Liege...
i see today they were at least talking about filling shipping containers and using them to fill the voids but i haven't heard anything else.