OMAHA -- March runoff into the Missouri River basin above Sioux City reached record levels and has led to a significant readjustment of the 2019 runoff forecast.
Runoff for the month was 11 million acre-feet, surpassing the previous high since record-keeping began of 7.3 MAF in 1952. The March average is 2.9 MAF.
The U.S. Army Corps of Engineers raised its 2019 runoff forecast to 38.2 MAF, 151 percent of normal. A month ago, the corps was predicting runoff of 28.4 MAF.
"The March runoff was nearly four times the average. Runoff in the Fort Randall Dam to Gavins Point Dam reach was nearly twice the record highest March runoff. March runoff in the Gavins Point to Sioux City reach was more than that reach typically sees during a year," John Remus, chief of the corps' Missouri River Water Management Division in Omaha, said in a news release.
The corps attributed the record runoff to 2-4 inches of rain that fell across the region on heavy plains snowpack, causing the snow to rapidly melt on frozen, saturated soils. The rapid runoff led to significant flooding along several Missouri River tributaries and along the Missouri River in southwest Iowa and southeast Nebraska.
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As a result of the March melting and rainfall, plus ongoing snowmelt in the Dakotas, the amount of water stored in the Missouri River's six reservoirs is at 63.2 MAF, occupying 7.1 MAF of the 16.3 MAF of flood storage capacity.
To clear space for spring rainfall and the continuing melting of snow in the plains, releases from Gavins Point Dam near Yankton, South Dakota, are scheduled to be raised from 39,000 cubic feet per second to 55,000 cfs by early next week. Gavins Point releases will remain above average for the next several months, possibly as late as November, the corps said.
Remus said runoff has begun to fill the Fort Peck, Garrison, Oahe and Fort Randall reservoirs upriver of Gavins Point, and levels at those reservoirs must be reduced in coming weeks to make room for mountain snowmelt, which typically begins in May.
As of Monday, mountain snowpack was at 93-97 percent of average, the corps reported. Snowpack typically peaks in mid April.
Corps representatives will be in Sioux City next week to discuss runoff, water releases and 2019 plans for reservoir operations. The meeting is scheduled for 4 p.m. April 10 at the Lewis & Clark Interpretive Center, 900 Larsen Park Road.