I work in the canals right now which are under tidal influence. The water levels thus are stable and change as the tide Floods and Ebbs.

The Corps of Engineers will normally dredge a narrower bit of the channel at a chokepoint and thus the water depth can be maintained if only for one way traffic. This tactic will also increase the current speed through the chokepoint which means a fast passage for downstream vessels and a slower passage for upstream vessels which are fighting that faster current.

Rivers such as the Quachita River in Louisiana and Arkansas have been so low this past summer that only one barge at a time can be pushed upstream to a grain elevator (2 days travel), lightly loaded (6-8ft deep), and then brought down to a fleet staging area (2days travel. This means that a lightly loaded grain cargo leaves the elevator every 5-6 days. That is why the elevators are still full and most have corn or other grains heaped upon tarps and covered by tarps. Some of those outside piles have measured 300ft long x 100ft wide x 3 stories in height.

Lack of water is also reducing tow sizes from 42 barges for a 10,500hp tow down to 25 barges for a 5,000-6,500hp tow. So the barges are loaded lighter, the tows are smaller, and grain is still waiting out in the weather, waiting to go to market. Higher food prices are already reflecting the transportation problems being encountered.