Missouri Releases About To Slow As Low Water Plagues Mississippi
Low water and shoaling have slowed cargo movements on the middle Mississippi River, below the confluence with the Missouri River at St. Louis, Mo., just as the Corps prepares to slow Missouri River navigation releases for the season at the end of November. During times of low water, Missouri River flows can supply up to two-thirds of total flows on the middle Mississippi River.
In two virtual public meetings held November 2, the Corps of Engineers’ Missouri River Water Management Division presented current hydrologic conditions and its planned operation of the Missouri River mainstem reservoir system for the remainder of 2020. The meetings included draft plans for operating the system during 2021.
“We will continue to make releases from Gavins Point Dam to meet full-service Missouri River navigation flow targets through the end of the navigation flow support season,” said John Remus, chief of the Missouri River Water Management Division.
Gavins Point release reductions are scheduled to begin around November 22. Releases will be stepped down by approximately 3,000 cubic feet per second (cfs.) each day until reaching the winter release rate of 17,000 cfs.
The navigation flow support season normally ends on December 1 at the mouth of the Missouri River. Gavins Point Dam winter releases normally range from 12,000 – 17,000 cfs. But this has not been a normal navigation season. The historic floods of 2019 left huge silt deposits that have caused shoaling, light-loading and delays on both the lower Missouri River and parts of the Mississippi River. The Corps and its contractors have been working overtime to clear them, but without enough resources. A letter to the Corps from members of Congress representing districts along the Missouri River estimated that the area needs 10 times the resources available.
Despite cold, snowy weather in October, precipitation for the month was well below normal in much of the upper Missouri River basin, the Corps said. The 2020 calendar year runoff forecast for the upper basin, updated on November 2, is 30.2 million acre-feet (maf.), 117 percent of average. Average annual runoff for the upper basin is 25.8 maf.
As of November 5, the total volume of water stored in the system was 57.1 maf., occupying 1.0 maf. of the system’s 16.3-maf. flood control zone. System storage peaked at 61.8 maf. on July 16 and is expected to continue to decline in the late fall and winter. All 16.3 maf. of flood control storage is expected to be available prior to the start of the 2021 runoff season.
Most of the Missouri River basin is experiencing some form of drought. The latest National Drought Mitigation Center drought monitor shows drought degradation over large areas of Montana and North Dakota. The basin continues to have large areas of extreme drought in Colorado, Wyoming and western Nebraska, with severe to moderate drought in large areas of Montana, North Dakota, South Dakota, Nebraska and Iowa.
Navigation
The July 1 system storage check indicated that flow support for the second half of the navigation season would be at least at the full-service level for a full-length eight-month flow support season. Full-service flow support is designed to work in tandem with the Missouri Riverbank Stabilization and Navigation Project to provide a 9-foot-deep by 300-foot-wide navigation channel from Sioux City, Iowa, to the mouth of the river near St. Louis.
