Ag Weather Forum

Benign Early Flood Outlook

Bryce Anderson
By  Bryce Anderson , Ag Meteorologist Emeritus
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Snow water amounts in the Upper Missouri Basin are running below average and well-below amounts that helped to set off extensive flooding in 2011. (USACE graphic)

It may be the middle of winter, but many thoughts are focused on the upcoming spring. A news release from the Army Corps of Engineers Missouri River Basin office indicates an optimistic outlook regarding flood potential this year. (That's optimism in terms of low risk of flooding in the Missouri River valley.)

The following are excerpts from the news release.

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The full flood control capacity of the Missouri River Mainstem Reservoir System is available for the 2021 runoff season.

"All 2020 flood water stored in the annual flood control zone has been evacuated as of Dec. 21," said John Remus, chief of the U.S Army Corps of Engineers, Missouri River Basin Water Management Division.

"The entire flood control capacity of the Mainstem System is available to capture and manage 2021 runoff ..."

Gavins Point releases will be maintained at the winter release rate of 17,000 cubic feet per second (cfs) but will be adjusted if needed in response to ice formation on the Missouri River below Gavins Point Dam.

December 2020 runoff in the Missouri River Basin above Sioux City, Iowa, was 1.2 million acre-feet (MAF), 148% of average. The 2020 calendar year runoff above Sioux City was 31.1 MAF, 121% of average. Average annual runoff is 25.8 MAF.

The 2021 calendar year runoff forecast for the upper Missouri Basin above Sioux City is 23.1 MAF, 90% of average. The runoff forecast is based on significantly drier-than-normal soil moisture conditions, low plains snowpack, and below-average mountain snowpack.

"Runoff forecasts are developed using the best information as it exists today. As mountain snowpack continues to accumulate, our forecasts will be updated to reflect those changes," added Remus.

ICE CONDITIONS:

River ice conditions below all System projects will be closely monitored throughout the winter season. Garrison releases will be maintained at 16,000 cfs until the river freezes near Bismarck, North Dakota. Releases are typically set at 16,000 cfs prior to the freeze-in to reduce the risk of ice-induced flooding. Releases will be gradually increased to 23,000 cfs following the formation of a stable river ice cover at Bismarck.

Basin and river conditions continue to be monitored, including plains and mountain snow accumulation, and will adjust System regulation based on the most up-to-date information ...

MOUNTAIN AND PLAINS SNOWPACK:

Mountain snowpack in the upper Missouri River Basin is accumulating at a below-average rate. The Jan. 3 mountain snowpack in the Fort Peck reach was 81% of average, while the mountain snowpack in the Fort Peck to Garrison reach was 82% of average. More than half of the mountain snowfall typically occurs from Jan. 1 to mid-April, and it normally peaks near April 15.

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The full USACE report is available at this link: https://go.usa.gov/…

Bryce Anderson can be reached at bryce.anderson@dtn.com

Follow him on Twitter @BAndersonDTN

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