“We moved more than 29 million cubic yards of sand, weighing as much as 92 Empire State Buildings,” says Bob Anderson, a USACE public affairs officer.

Speeding up permanent removal of rock pinnacles in the channel at Thebes, Ill., added 2 ft. to the channel’s depth, says Mike Petersen, another USACE spokesman.

“That’s a more long-term solution that will ease those choke points unless we hit new record lows,” Petersen says.

The situation was also aided by heavy rains associated with tropical storm Sandy and a long-term Corps effort to build “river training structures” that focus the force of the river’s flow to scour sediment from the channel – “like the effect of putting your thumb over the tip of your garden hose,” Petersen explains.

Still, there were repeated reports that the river might close in December and January. That uncertainty by itself created problems. “If you’re loading a barge in Houston to move North, the trip will take 10-14 days under a worst-case scenario,” says McCulloch. “If you don’t know whether you’ll have 9 ft. of water in two weeks, you have to make other plans.

“That’s why the Corps’ confidence about river levels through spring is so important. It helps give a degree of certainty.”

It’s been “a nail-biter of a winter,” says Petersen. “We’ve not had a single grounding on the mid-Mississippi navigation channel. That’s a testament not just to dredging, but also to the engineering of the past 20 years.”

The Corps plans to work more on the middle Mississippi, which can deliver a “huge return on investment,” Petersen says. “We could completely re-engineer the middle Mississippi for the cost of replacing one lock.”