OMAHA -- Releases from Gavins Point Dam will remain at more than twice above normal levels for the foreseeable future until near-record runoff from heavy spring rainfall has been evacuated from Missouri River reservoirs.
The U.S. Army Corps of Engineers hiked releases from the dam near Yankton, South Dakota, to 75,000 cubic feet per second on Saturday. The normal level is 30,000 cfs.
"We will maintain Gavins Point releases at this rate to continue evacuating water from (upriver reservoirs at) Oahe and Fort Randall, which have used much of their respective flood storage," John Remus, chief of the corps' Missouri River Water Management Division in Omaha, said Wednesday in a news release.
Widespread and heavy rainfall in Nebraska and South Dakota led to the second-highest runoff in the upper Missouri River basin above Sioux City in 121 years of record keeping. May runoff was 8.9 million acre-feet, second only to 9.2 MAF in 2011. Average May runoff is 3.3 MAF.
The corps has raised its 2019 runoff forecast to 50 MAF, which would be second only to 61 MAF in 2011. Runoff in 2018 was 42.1 MAF, currently the third-highest total.
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Remus said water levels at Oahe and Fort Randall, both located in South Dakota, have entered their exclusive flood control zones. Fort Peck reservoir in Montana and Garrison reservoir in North Dakota both are expected to enter exclusive flood control zones in June as runoff from melting snow in the Rocky Mountains continues to make its way to the Missouri River.
"Fort Peck and Garrison reservoir levels are positioned to ensure that there is adequate flood control space to capture and manage the mountain snowmelt runoff," Remus said.
As of Wednesday, the amount of water stored in the Missouri River's six reservoirs was at 67.7 MAF, occupying 11.6 MAF of the 16.3 MAF of the system's flood storage capacity.
The increased Gavins Point releases and runoff into rivers downstream of the dam have contributed to minor flooding in South Sioux City and heavier flooding in southwest Iowa and southeast Nebraska. Interstate 29 in Iowa is closed north and south of Council Bluffs because of water over the highway, and Interstate 680 east from Omaha to Iowa also is closed due to the high water.