The U.S. Army Corps of Engineers reduced releases from Gavins Point Dam in late November, marking the end of flow support for Missouri River navigation for the 2015 season.

“Starting on Nov. 21, Gavins Point releases were stepped down over a 5-day period from 28,500 cubic feet per second to the normal winter release rate of 17,000 cfs,” said Jody Farhat, chief of the Missouri River Water Management Division. Gavins Point winter releases are set based on the total volume of water stored in the Mainstem Reservoir System on Sept. 1.

The Corps will closely monitor conditions throughout the basin during the winter and make reservoir regulation adjustments to lessen the impact of river ice formation. 

“Gavins Point releases may be increased above 17,000 cfs for short periods during extremely cold conditions to offset water lost to ice formation,” said Farhat. “Ice conditions will also be monitored below Garrison and Oahe dams, and releases will be adjusted if necessary.” 

Releases from Garrison Dam will be scheduled at 15,000 cfs during December, which is below the rate typically set during the river freeze-in, reducing the risk of ice-induced flooding.

Runoff in the Missouri River Basin above Sioux City, Iowa, for the month of November was 1.0 million acre feet, 100 percent of average. The 2015 runoff forecast is 25.3 MAF, also 100 percent of average. 

“While overall runoff was average during November, runoff into Fort Peck and Garrison dams was below normal, while runoff in the reaches from Oahe Dam down to Sioux City was above normal,” said Farhat.

The total volume of water stored in the Mainstem Reservoir System is currently 57.2 MAF, which includes 1.1 MAF of the 16.3 MAF allocated for flood storage. 

“System storage declined 0.8 MAF during November,” said Farhat. “Our plan is to evacuate all water stored in the flood zones of the reservoirs prior to the start of next year’s runoff season, which typically begins around March 1.”

The comment period for the 2015-2016 Annual Operating Plan ended Nov. 20. The final AOP is expected to be completed in late December and will be posted on the Missouri River Water Management website at https://www.nwd-mr.usace.army.mil/rcc.

The Corps will continue to monitor basin conditions, mountain snow and plains snow accumulation, and fine tune the regulation of the reservoir system based on the most up-to-date information.

Reservoir Forecasts

Gavins Point Dam releases averaged 21,200 cfs in November. Releases will be maintained near 17,000 cfs during December. The reservoir behind Gavins Point Dam ended November at elevation 1207.5 feet. It will remain near its normal seasonal pool elevation of 1207.5 feet in December.

Fort Randall Dam releases averaged 22,700 cfs in November. Releases were stepped down approximately one day prior to Gavins Point and reached 14,000 cfs on Nov. 24. Releases will range from 14,000 cfs to 16,000 cfs during December as necessary to maintain the elevation at Gavins Point. The reservoir ended November at elevation 1339.4 feet, down 5.4 feet during the month. The reservoir is expected to remain nearly steady during December. The reservoir is normally drawn down in the fall to provide space for winter hydropower generation at Oahe and Big Bend.

Big Bend Dam releases averaged 16,000 cfs during the month of November. Releases are expected to average 15,900 cfs this month. The reservoir will remain near its normal elevation of 1420.0 feet during December.

Oahe Dam releases averaged 16,900 cfs during the month of November. Releases are expected to average 15,500 cfs this month. The reservoir ended November at elevation 1609.6 feet, down 0.7 feet during the month. The reservoir is expected to drop less than 1 foot during the month of December.

Garrison Dam releases averaged 12,900 cfs in November. Releases were increased to 15,000 cfs on Dec. 5.  Garrison ended November at elevation 1840.7 feet, down 0.5 feet from the end of October. The reservoir is expected to drop about 1 foot during December.

Fort Peck Dam releases averaged 4,800 cfs in November. Releases will be increased to 6,000 cfs on Dec. 12.  The reservoir dropped slightly during November, ending the month at elevation 2234.5 feet. The reservoir is forecast to drop less than a foot during December.

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 571 million kilowatt hours of electricity in November. Typical energy generation for the month of November is 724 million kWh. The power plants are projected to generate 8.5 billion kWh of electricity this year, compared to the normal of 10 billion kWh.

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

Missouri River mainstem reservoir data

.

Water releases and energy generation for November