Corps cuts Missouri River dam releases as flooding looms

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Fort Peck Dam

An aerial view shows Fort Peck Dam and ice covering the lake in April 2018. The U.S. Army Corps of Engineers is already announcing cuts to dam releases as flooding looms downriver.

After a brutal and long flood season last year along the lower Missouri River, the U.S. Army Corps of Engineers is cutting dam releases as rivers begin to rise again.

Outflows from Gavins Point Dam, which is located on the South Dakota-Nebraska border, were cut from 38,000 cubic feet per second to 35,000 cfs as tributaries downstream began to rise due to the melting of the plains snowpack.

The Corps is also predicting that the potential for above average runoff in the upper Missouri Basin, “coupled with continued high river stages on many of the uncontrolled tributaries downstream of the reservoir system, increases the potential for flooding, particularly in the lower river.”

Current conditions, including soil moisture, plains and mountain snowpack, as well as long-term temperature and precipitation outlooks forecast runoff to be 36.9 million acre-feet, 143% of average, for the upper Missouri River basin above Sioux City, Iowa, for 2020. Average annual runoff for the upper basin is 25.8 MAF. 

As of March 3, the total volume of water stored in the system is 56.4 MAF, occupying 0.3 MAF of the 16.3 MAF combined flood control storage zones. System storage reached 56 MAF on Jan. 22, 0.1 MAF below the base of the combined flood control zone.

Mountain snowpack accumulation continues and is slightly above average — 104 to 105% above average — in the Fort Peck and Garrison Dam reaches. The mountain snowpack normally peaks near April 15. 

A public meeting will be held on April 6 in Fort Peck at 10:30 a.m. in the Fort Peck Interpretative Center to update the region on current hydrologic conditions and the planned operation of the mainstem reservoir system during the coming months. 

Water releases from Fort Peck Dam have been cut back from an average of 12,300 cfs to 10,000 cfs. That is expected to be curtailed even more, down to 7,500 cfs by March 7.

At the end of February the reservoir elevation was 2,234.9 feet (down 0.4 foot from January). The forecast end-of-March reservoir level is 2,235.9 feet.

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