Mike Petersen of the corps' office in St. Louis said efforts have been under way for months to fight back against the drought. Dredging operations that normally begin in August started in July, with work going on around the clock to remove sediment from the river bottom.
The corps also plans to use explosives to blast away treacherous rock formations at the bottom of the river near two southern Illinois towns, Thebes and Grand Tower. If the river level gets too low, those formations could bring barge traffic to a standstill.
The project has passed environmental approval, but contracts must still be awarded. Work is expected to begin in early February.
But Petersen conceded the river could be closed if the drought persists. He said closure at St. Louis would become more likely if the river gauge gets to around minus-5 feet. It was at minus-1.2 feet Tuesday morning.
"The middle Mississippi is a tricky spot because we're depending on the upper Mississippi and the Missouri and what they give us," Petersen said. "For us, the reduced flow from the Missouri is a fact of life in how we operate the river."
Farmer said the corps must tend to eight congressionally authorized purposes on the Missouri River: hydropower, water supply, water quality control, fish and wildlife, recreation, irrigation, navigation and flood control.
Because of the drought, the Mississippi has received as much as 78 percent of its water from the Missouri this year, compared with 60 percent in a normal year, according to Nixon's office.