Low Runoff Predicted On Missouri River

Runoff in the Missouri River Basin above Sioux City, Iowa, was 134 percent of average in January, but that’s not necessarily good news for those looking for an end to the basin’s drought, the Corps of Engineers reports. That’s because warmer-than-normal temperatures in the upper basin resulted in some snowmelt runoff that ordinarily would have come later in the spring.

Precipitation in January was below normal for most of the upper basin except for southern South Dakota, which saw above-normal precipitation.

“Despite January’s runoff being above average, we expect 2023 runoff to remain below average,” said John Remus, chief of the Corps’ Missouri River Basin Water Management Division. “Drought conditions currently exist across most of the basin.”

The Corps’ 2023 calendar year runoff forecast above Sioux City is 21.1 million acre-feet (maf.), which would be 82 percent of average. The runoff forecast is based on current soil moisture conditions, plains snowpack, mountain snowpack and long-term precipitation and temperature outlooks.

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At the start of the 2023 runoff season, which typically begins around March 1, the total volume of water stored in the Missouri River mainstem reservoir system is expected to be 46 maf., 10.1 maf. below the top of the carryover multiple use zone.

To conserve water in the system, the Corps is making minimum releases from Gavins Point Dam this winter, while considering the needs of the municipal, industrial and powerplant water intakes along the lower river.

“While the winter target release from Gavins Point Dam is 12,000 cfs., releases were increased to 14,000 cfs. in late January and early February to mitigate some of the effects of the much colder temperatures across the lower basin,” Remus said. Releases were reduced back to 12,000 cfs. on February 7.

Navigation flow support for the Missouri River is forecast to be at minimum service for the first half of the 2023 season, which begins April 1 at the mouth of the river near St. Louis, Mo. The actual service level will be based on the total volume of water stored within the system on March 15, in accordance with the guidelines in the Master Manual. Flow support for the second half of the navigation season, as well as navigation season length, will be based on the storage in the system on July 1.