The U.S. Army Corps of Engineers (Corps) began reducing Gavins Point releases to the winter release rate on December 2. The releases will be stepped down at a rate of 3,000 cubic feet per second (CFS) per day until they reach 20,000 cfs on Dec. 11. Releases are expected to remain at or near 20,000 cfs for the remainder of the winter. Gavins Point Dam winter releases normally range between 12,000 and 17,000 cfs. 

“The higher-than-average winter releases from the Missouri River Mainstem System (System) projects, including Gavins Point, will continue the evacuation of the stored flood waters from the 2018 runoff season,” said John Remus, Chief of the Corps’ Missouri River Basin Water Management Division. “The higher-than-average winter releases will provide additional hydropower generation during the winter, which is one of the peak power demand periods. In addition, they will benefit municipal and industrial water intakes below Gavins Point Dam, which can be impacted by low water levels during periods of ice formation”, added Remus.

The November runoff above Sioux City was 1.2 MAF, 118 percent of average. The 2018 runoff forecast in the Missouri River Basin above Sioux City, Iowa is 41.3 million acre feet (MAF), 163 percent of average. If this forecast is realized, the 41.3 MAF of runoff will be third highest runoff in 120 years of record-keeping (1898-2017), exceeded only in 1997 and 2011.

The Missouri River Mainstem reservoir system storage was 57.1 million acre feet (MAF) as of Dec. 1, occupying 1.0 MAF of the 16.3 MAF flood control zone. The remaining stored flood waters will be evacuated over the winter and all flood control storage will be available by the start of the 2019 runoff season. System storage peaked on July 8 at 68.4 MAF, occupying 12.3 MAF of the designated 16.3 MAF of flood control storage.

Flows to support navigation will end on December 11 at the mouth of the Missouri River. The navigation season was extended 10 days this year to provide additional time to evacuate stored flood waters.

River ice conditions below all System projects will be closely monitored throughout the winter season. The Corps will also continue to monitor basin and river conditions, including plains and mountain snow accumulation, and will adjust System regulation based on the most up-to-date information. The mountain snowpack accumulation period is underway. The mountain snowpack normally peaks near April 15. The mountain snowpack graphics can be viewed here: http://www.nwd-mr.usace.army.mil/rcc/reports/snow.pdf.

The comment period for the 2018-2019 Annual Operating Plan (AOP) ended Nov. 23. The final AOP, which is to be completed in late December, will be posted on the Water Management website:https://www.nwd.usace.army.mil/MRWM/Public-Meetings/.

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

Reservoir Forecasts

Gavins Point Dam releases averaged 56,700 cfs during November. Releases are currently being reduced by 3,000 cfs per day until the winter release rate of 20,000 cfs is reached around December 11. The Gavins Point reservoir ended November at elevation 1206.8 feet and will be near 1207.5 feet during the winter months. Fort Randall Dam releases averaged 53,000 cfs in November. Releases will be adjusted as necessary to maintain the desired reservoir elevation at Gavins Point. The outlet tunnel is scheduled to be closed on December 6 and all releases will be made through the powerhouse. The reservoir level was at 1337.4 feet at the end of November, falling 9.0 feet during the month. The reservoir will gradually be refilled during the winter to increase winter hydropower generation at Oahe and Big Bend. Big Bend Dam releases averaged 42,100 cfs in November. Releases are expected to average 24,500 cfs and the reservoir will remain near is normal elevation of 1420.0 feet during December. Oahe Dam releases averaged 45,600 cfs during November. Releases are expected to average 24,400 cfs in December. The outlet tunnels were shut down on November 29 and all releases are currently being made through the powerhouse. The reservoir ended November at elevation 1607.2 feet, falling 3.5 feet during the month. The reservoir level is expected to decline approximately another 0.9 foot during December. Garrison Dam releases averaged 28,000 in November. Releases are currently 21,000 cfs and will be reduced to 16,000 cfs near mid to late-month to prepare for possible river freeze-in at Bismarck. Once an ice cover is established, releases will be gradually increased to 24,500 cfs. The reservoir level was 1840.2 feet at the end of November, a reduction of 1.5 feet from the end of October. The reservoir level is expected to continue declining through December and be near elevation 1839.5 feet at the end of the month. Fort Peck Dam releases averaged 11,700 cfs during November. Releases were increased from 12,000 cfs to 12,500 cfs in early December and will remain at that rate during the month. The spillway was closed on November 8 and all releases are now being made through the powerhouse. The reservoir level was 2238.6 feet at the end of November, declining 1.4 feet during the month. The reservoir level is expected to continue declining through December and be near elevation 2236.8 feet at the end of the month.

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 1,108 million kWh of electricity in November. Typical energy generation for November is 738 million kWh. The power plants are projected to generate 12.4 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.