E: Like don't get me wrong, internal waterways is a geographic blessing for US, but it also always required enormous/expensive (army) engineering efforts to keep it viable for modern operations (larger barges etc). It's one of those case where terraforming/technology has outstripped natural capacity, but it's possible to augment geography to facilitate more technology, but right now augmentation efforts are not sufficient, not just to improve through put, but to maintain it, because geography can decline.
The point is with the Jones Act there isn't much value in barges. So other uses of the water are prioritised. Adding water doesn't have an ROI commensurate with alternative uses.
""" It requires that all goods transported by water between U.S. ports be carried on ships that have been constructed in the United States and that fly the U.S. flag, are owned by U.S. citizens, and are crewed by U.S. citizens and U.S. permanent residents """
Our barge use is crippled by the Jones Act, not water levels. Make it lucrative to ship by barge and the incentives will get the levels back up.