Omaha, Neb. — The U.S. Army Corps of Engineers (Corps) Missouri River Basin Water Management Division reports April runoff in the Missouri River basin above Sioux City, Iowa was 2.8 million acre feet (MAF), 96 percent of normal.  The 2014 runoff forecast in the Missouri River basin above Sioux City, Iowa has decreased slightly from 32 MAF last month to 31.7 MAF, 125 percent of normal.  Average annual runoff is 25.2 MAF. 

“April inflows were less than previously forecasted, and the reservoirs continue to be well positioned to capture the expected above-normal runoff,” said Jody Farhat, chief of the U.S. Army Corps of Engineers Missouri River Basin Water Management Division.  “The total volume of water stored in the reservoir system on May 1 was 54.3 MAF.  System storage remains below the base of the annual flood control and multiple use zone of 56.1 MAF.” 

According to information from the Natural Resources Conservation Service, the mountain snowpack accumulation appears to have peaked in both the reach above Fort Peck Dam and the reach between Fort Peck and Garrison Dams.  Mountain snowpack typically peaks in mid-April. “This year’s mountain snowpack was tracking the levels recorded in 2011 through early April, but has since dropped off the pace, and is now declining,” said Farhat.  Mountain snowpack in the reach above Fort Peck Dam peaked on April 7 at 132 percent of the normal peak; as of May 6, it was 112 percent of the normal peak.  In the reach between Fort Peck and Garrison Dams, the mountain snowpack peaked on April 17 at 140 percent of the normal peak; as of May 6 it was 116 percent.  Runoff from the melting mountain snowpack enters the reservoir system from May through July.  The latest National Weather Service flood outlook shows the potential for minor to moderate flooding along tributaries in the headwaters areas of Montana and Wyoming as a result of the snowmelt. However, the reservoir system has sufficient storage to capture the runoff, and release it through the remainder of the season at rates that are well within the channel. 

View mountain snowpack graphic here:  http://www.nwd-mr.usace.army.mil/rcc/reports/snow.pdf. 

The potential also exists for minor to moderate flooding in the lower Missouri River and its tributaries due to normal thunderstorm activity.  The Corps will utilize the available flood control space in the reservoirs, if necessary, to limit downstream river levels.  “Typical summer thunderstorms can cause localized flooding downstream of the reservoir system.  Reducing releases from Gavins Point in response to downstream rainfall is part of our normal flood risk reduction measures, and the reservoir system has storage space available for these operations in the event of flooding downstream,” said Farhat.  

The Corps will continue to monitor the 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.  

Reservoir Forecasts 

Gavins Point Dam releases averaged 27,400 cubic feet per second (cfs) during April.  Releases, which are currently at 26,000 cfs, are expected to reach 30,000 cfs around mid-May to prevent endangered least terns and threatened piping plovers from nesting on low sandbars. These sandbars would be flooded later in the summer when higher releases are needed to meet downstream navigation flow targets.  The nesting season runs from May to late August.  The reservoir behind Gavins Point Dam ended April at elevation 1206.4 feet. The reservoir will remain near elevation 1206 feet during May. 

Fort Randall Dam releases averaged 25,600 cfs during April.  Fort Randall releases are currently at 24,000 cfs, and will be adjusted, as necessary, to maintain the desired pool elevation at Gavins Point. The reservoir ended April at elevation 1354.2 feet, up 2.7 feet during the month.  The pool is expected to rise until reaching 1355 feet and will remain near that elevation through the end of May. 

Big Bend Dam releases averaged 26,500 cfs during April.  They are expected to average 26,700 cfs this month. The reservoir will remain near its normal elevation of 1420 feet in May.  

Oahe Dam releases averaged 27,800 cfs during April.  Releases are expected to average 26,100 cfs this month.  The reservoir ended April at elevation 1605.8 feet, up 0.6 feet during the month. The reservoir is expected to rise less than 2 feet during May. 

Garrison Dam releases were increased from 16,000 cfs to 24,000 cfs during April, averaging 22,100 cfs during the month.  Releases will be gradually increased to 30,000 cfs by mid-May.  Garrison ended April at elevation 1837.3 feet, up 1.5 feet from the previous month.  It is expected to rise more than 1 foot during May. 

Fort Peck Dam releases were increased from 7,000 cfs to 8,000 cfs around mid-April.  Releases were increased to 9,000 cfs in early May.  The reservoir ended April at elevation 2225.8 feet, up 1.2 feet from the previous month.  The reservoir is forecast to rise 3 feet during May. 

The forecast reservoir releases and elevations discussed above are not definitive.  Additional precipitation, lack of precipitation, or other circumstances could cause adjustments to the reservoir release rates. 

The six mainstem power plants generated 828 million kilowatt hours (kWh) of electricity in April.  Typical energy generation for April is 684 million kWh. The power plants are projected to generate 9.7 billion kWh of electricity this year, compared to the normal 10 billion kWh.  

To view the detailed three-week release forecast for the mainstem dams, go to: http://www.nwd-mr.usace.army.mil/rcc/reports/twregfcast.pdf. 

MISSOURI RIVER MAINSTEM RESERVOIR DATA  

 WATER RELEASES AND ENERGY GENERATION FOR APRIL

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