Corps decreases runoff forecast due to lower than normal mountain snowpack

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For Immediate Release: April 6, 2015

Contact: Michael Coffey or Serena Baker, U.S. Army Corps of Engineers, Northwestern Division

Phone: 503-808-3722                                     E-mail:      michael.a.coffey@usace.army.mil

       503-808-3710                                              serena.baker@usace.army.mil

Corps decreases runoff forecast due to lower than normal mountain snowpack

Omaha, Neb. — The U.S. Army Corps of Engineers (Corps) Missouri River Basin Water Management Division is decreasing the annual runoff forecast for the Missouri River Basin above Sioux City, Iowa, to 20.3 million acre feet (MAF), which is 80 percent of normal and 4.9 MAF less than average. The decreased forecast is due to below normal mountain snowpack and the lack of plains snow in the basin.

“While below normal runoff is expected, the reservoirs are well positioned to meet all of the authorized purposes this year,” says Jody Farhat, chief of the Missouri River Basin Water Management Division. “The Missouri River Mainstem Reservoir System is designed and operated to provide the Corps with the necessary flexibility to adjust for varying conditions.” The total volume of water stored in the reservoir system is 57.6 MAF, 1.5 MAF into the 16.3-MAF annual flood control and multiple use zone.

Above normal temperatures coupled with below normal precipitation patterns have stalled mountain snowpack accumulation and melted the plains snow. As of April 1, mountain snowpack was 68 percent of normal in the reach above Fort Peck Dam and 74 percent of normal in the reach between Fort Peck and Garrison dams.  Mountain snowpack appears to have peaked nearly a month earlier than normal this year in the reaches above the Fort Peck and Garrison dams.  The mountain snowpack typically peaks in mid-April, and runoff from the melting snow enters the reservoir system from May through July.  View mountain snowpack graphic here:  http://www.nwd-mr.usace.army.mil/rcc/reports/snow.pdf.

In mid-March, Gavins Point Dam releases were increased from 17,000 cubic feet per second (cfs) to approximately 28,000 cfs in support of the navigation season, which began April 1 near St. Louis, Mo.  “Flow support for the first half of the navigation season will be full service,” said Farhat.  Full service navigation flow support is generally sufficient to provide a 9-foot-deep by 300-foot-wide channel.  Flow support for the second half of the navigation season as well as the season length will be determined following the system storage check on July 1. 

Steady-to-rising reservoir levels during the forage fish spawn at the three, large upper reservoirs (Fort Peck, Garrison and Oahe) are preferred but may be difficult to accomplish without significant rainfall in the Missouri River Basin during the coming weeks.  If the runoff distribution allows, the Corps will set releases to result in steady to rising pools at Fort Peck and Oahe dams.  The forage fish spawn generally occurs from early April through mid-June. The Corps will continue to monitor the plains and mountain snowpack, basin soil conditions and rainfall events to fine tune the regulation of the reservoir system based on the most up-to-date information.

Read the entire press release here http://www.nwd.usace.army.mil/Media/NewsReleases/tabid/1989/Article/583650/corps-decreases-runoff-forecast-due-to-lower-than-normal-mountain-snowpack.aspx.

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