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Near-Record Runoff Continues In Missouri Basin

Runoff into the upper Missouri River basin in April was 7.8 million acre feet (maf.), the third highest April runoff in the 121 years of record-keeping, the Corps of Engineers reported. The average April runoff is 2.9 maf.

In the reach between Gavins Point Dam and Sioux City, Iowa, runoff was 2.3 maf., the second-highest April runoff for this reach.

The total March-April runoff for the upper basin was 18.7 maf., which is the highest March-April runoff since record-keeping began in 1898, exceeding the previous record of 15.9 maf., which occurred in 1952.

The near-record April runoff, which was nearly three times average, increased the 2019 upper basin runoff forecast to 42.3 maf. If realized, this runoff total will be the third highest runoff in 121 years of record-keeping, only surpassed by 1997 (49.0 maf.) and 2011 (61.0 maf.). Runoff in 2018 was 42.1 maf., which is currently third highest.

The Corps expects that releases from all dams in the system of large upstream reservoirs will be above average for the next several months, and possibly as late as November.

“Gavins Point releases are currently 55,000 cubic feet per second (cfs.), which is about 25,000 cfs. above average for this time of the year,” said John Remus, chief of the Corps’ Missouri River Basin Water Management Division. “We will maintain Gavins Point releases at this rate to continue evacuating water from Oahe and Fort Randall, which are using much of their respective flood storage. We want to reduce the pool levels in Oahe and Fort Randall a few feet to provide flexibility should we need to reduce Gavins Point releases for short periods over the remainder of the spring and summer.”

The mountain snowpack has begun melting in the reaches upstream from Fort Peck and Garrison Dams at near-average levels. The mountain snowpack peaked on April 18 in the Fort Peck reach at 105 percent of average and on April 17 in the Fort Peck to Garrison reach at 104 percent of average. Normally the mountain snowpack peaks in mid-April.

“Fort Peck and Garrison reservoirs have adequate flood control space to capture and manage the mountain snowmelt runoff,” Remus said..

Based on the Corps’ March 15 system storage check, flow support for the first half of the navigation season is full service. However, due to above average runoff in the upper basin, releases from Gavins Point have been above full service levels to reduce the occupied flood storage at Oahe and Fort Randall. Based on the May 1 service level check, the service level was increased another 5,000 cfs. to 20,000 cfs. above full-service levels.

The six mainstem power plants generated 794 million kilowatt hours (kwh.) of electricity in April. Typical energy generation for April is 693 million kwh. The power plants are projected to generate 12.3 billion kwh of electricity this year, compared to the long-term average of 9.4 billion kwh.

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