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Posted 9/6/2018

Release no. 18-052

Eileen Williamson

OMAHA, NE – Higher-than-average releases from all Missouri River Mainstem System dams, including Gavins Point, will continue through the fall, the U.S. Army Corps of Engineers announced today.

“Due to this year’s high runoff and the water currently being stored in the reservoirs, Gavins Point releases will remain near 58,000 [cubic feet per second] for the remainder of the navigation season to ensure evacuation of all stored flood waters prior to the 2019 runoff season,” said John Remus, chief of the Missouri River Basin Water Management Division.

The 2018 runoff forecast in the Missouri River Basin above Sioux City, Iowa, is 39.8 million acre feet, 157 percent of average. August runoff was 1.8 MAF, 138 percent of normal.

The Missouri River Mainstem Reservoir System storage was 64.7 MAF as of Sept. 1, occupying 8.6 MAF of the 16.3 MAF flood control zone. “System storage declined 2.7 MAF in August and will continue to gradually decline in September,” said Remus. System storage peaked on July 8 at 68.4 MAF. 

“Reservoir releases will be adjusted as necessary to provide downstream flood risk reduction and continue evacuation of stored flood water,” said Remus. 

It is important to note that the ability to significantly reduce flood risk along the lower Missouri River diminishes at locations further downstream due to the large uncontrolled drainage area and the travel time from Gavins Point Dam, Remus noted.

Based on the Sept. 1 reservoir system storage, winter releases from Gavins Point will be at least 17,000 cfs. Based on the latest reservoir studies, there will be a 10-day extension to navigation flow support and a Gavins Point winter release of 20,000 cfs. Navigation flow support at the mouth of the Missouri River will end on Dec. 11. 

Weekly updates on basin conditions, reservoir levels and other topics of interest can be viewed at http://www.nwd-mr.usace.army.mil/rcc/reports/pdfs/weeklyupdate.pdf.

The Corps will continue to monitor basin and river conditions and will adjust System regulation based on the most up-to-date information.

In late September, the Corps will issue the 2018-2019 draft Annual Operating Plan for the Missouri River Mainstem System. It will be available at: http://www.nwd.usace.army.mil/MRWM/Public-Meetings/. The agency also will present a synopsis of its 2018 operations and plans for regulating the reservoir system in 2019 at public meetings in six cities throughout the basin in early November. Meeting times and locations will be announced when additional details become available.

Reservoir Forecasts

  • Gavins Point Dam releases averaged 57,300 cfs during August. Releases will remain near 58,000 cfs during September - downstream conditions permitting. The Gavins Point reservoir ended August at elevation 1207.1 feet. The reservoir will end September near 1207.5 feet.
  • Fort Randall Dam releases averaged 54,100 cfs in August. Releases will be adjusted as necessary to maintain the desired reservoir elevation at Gavins Point. Releases are being made from both the powerhouse and outlet tunnels. The reservoir ended August at elevation 1357.1 feet, falling 1 foot during the month. The reservoir will gradually fall to near 1351 feet during September. The reservoir is normally drawn down to 1337.5 feet in the fall to provide space for winter hydropower generation at Oahe and Big Bend. The annual drawdown will continue in October and November. 
  • Big Bend Dam releases averaged 48,400 cfs in August. Releases are expected to average 47,000 cfs during September. The reservoir will remain near its normal elevation of 1420 feet during September.
  • Oahe Dam releases averaged 53,200 cfs during August. Releases are expected to average 47,000 cfs in September. Beginning Sept. 10, releases will be made from the powerhouse and the regulating tunnels. Releases from the regulating tunnels are required due to scheduled maintenance on the hydropower units and the need to continue evacuating stored runoff. The reservoir ended August at elevation 1615.9 feet, decreasing 1.3 feet during the month. Levels will continue to decline during September with a projected end-of-month elevation near 1614.2 feet. 
  • Garrison Dam releases were stepped down from 53,000 to 46,000 cfs during August averaging 47,100 cfs during the month. Releases will be stepped down to 43,000 cfs in early September, and then gradually reduced to 31,000 cfs by about mid-month. Releases are currently being made from the powerhouse and the regulating tunnels. The reservoir ended August at 1846.5 feet, down more than 4 feet during the month. The reservoir is expected to continue falling ending September near 1844.0 feet. Recent inspections on the regulating tunnels showed some cavitation but no areas of concern.
  • Fort Peck Dam releases averaged 16,000 cfs during August. Releases will be reduced to 12,000 cfs around mid-September. Releases are currently greater than the maximum powerhouse capacity, so releases are being made from the powerhouse and spillway. The reservoir ended August at elevation 2243.5 feet, down 2.6 feet during the month. The reservoir is expected to continue falling ending September at 2241.3 feet.
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 power plants generated 1,426 million kWh of electricity in August. Typical energy generation for August is 995 million kWh. The power plants are projected to generate 13.0 billion kWh of electricity this year, compared to the long-term average of 9.3 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.