Gavins Point Dam releases reduced to winter release rate

Julie Davis
Nebraska City News-Press

The U.S. Army Corps of Engineers began reducing the Gavins Point releases to the winter release rate on Nov. 24, marking the end of flow support for the 2020 Missouri River navigation season.

“Releases from Gavins Point Dam were reduced from 34,000 cubic feet per second to 17,000 cfs,” said John Remus, Chief of the Missouri River Water Management Division. “Releases from Gavins Point will be adjusted this winter as needed to lessen the impacts of river ice formation on water intakes in the lower river.” Based on the Sept. 1 System storage, Gavins Point Dam winter releases will be at least 17,000 cfs.

As the colder, winter temperatures enter the basin, USACE will closely monitor Missouri River ice conditions between the System reservoirs and downstream of Gavins Point Dam for potential ice jams that could impact river stages and water intakes.

Runoff in the upper Missouri River Basin above Sioux City, Iowa, was 1.2 million acre-feet during November, 116% of average. The 2020 calendar year runoff forecast is 30.6 MAF, 119% of average. Average annual runoff is 25.8 MAF. The total volume of water stored in the Missouri River mainstem reservoirs is currently 56.3 million acre-feet, occupying 0.2 MAF of the 16.3 MAF combined flood control storage zones. System storage is forecast to reach the base of the combined flood control storage zone in mid- to late-December.

Releases from Fort Peck Dam were increased to 10,500 cfs on Dec. 3 and will be increased to 11,500 cfs in January and February. Releases from Garrison Dam were increased to 16,000 cfs on Dec. 2. Releases from Garrison Dam are typically set near 16,000 cfs prior to the river freeze-in to reduce the risk of ice-induced flooding in the Bismarck, N.D., area. Releases will remain at that rate in December, and conditions permitting, will be gradually increased to 20,500 cfs following the formation of a stable river ice cover at Bismarck. Releases at Fort Peck and Garrison dams are being adjusted as part of balancing storage in the upper reservoirs.

Mountain and Plains Snowpack

Mountain snowpack in the upper Missouri River Basin is accumulating at near average levels. About 25% of the mountain snowpack typically accumulates by Dec. 1, and normally peaks near April 15. The mountain snowpack graphics can be viewed at  http://go.usa.gov/xE6wT. Currently, plains snowpack in the upper Missouri River Basin is sparse.

2020-2021 Annual Operating Plan

The comment period for the 2020-2021 Annual Operating Plan ended Nov. 20. The final AOP is scheduled for publication by the end of 2020 and will be posted on the Water Management website: https://www.nwd.usace.army.mil/MRWM/Public-Meetings/.

Reservoir Forecasts

Gavins Point Dam

Average releases past month – 31,300 cfs

Current release rate – 17,000 cfs

Forecast release rate – 17,000 cfs

End-of-November reservoir level – 1206.5 feet

Forecast end-of-December reservoir level – 1207.5 feet

Notes: Releases were reduced to 17,000 cfs on Nov. 29. The winter release rate will be at least 17,000 cfs based on the Sept. 1 System storage check and may be adjusted to lessen the impacts of winter ice formation.

Fort Randall Dam

Average releases past month – 26,300 cfs

End-of-November reservoir level – 1337.8 feet (down 7.4 feet from October)

Forecast end-of-December reservoir level – 1339.5 feet

Notes: Releases will be adjusted as necessary to maintain the desired reservoir elevation at Gavins Point. 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 reservoir will refill to the base of the flood control pool from December to February.

Big Bend Dam

Average releases past month – 19,800 cfs

Forecast average release rate – 17,500 cfs

Forecast reservoir level – 1420.5 feet

Oahe Dam

Average releases past month – 19,800 cfs

Forecast average release rate – 17,400 cfs

End-of-November reservoir level – 1606.8 feet (down 1.5 feet during November)

Forecast end-of-December reservoir level – 1606.3 feet

Garrison Dam

Average releases past month – 13,300 cfs

Current release rate – 16,000 cfs

Forecast average release rate – 16,000 cfs

End-of-November reservoir level – 1838.9 feet

Forecast end-of-December reservoir level – 1838.2 feet

Notes – Releases were set at 16,000 cfs prior to the river freeze-in at Bismarck, North Dakota. Current forecasts show this occurring in late December. Once an ice cover is established, releases will be gradually increased to 20,500 cfs.

Fort Peck Dam

Average releases past month – 6,300 cfs

Current release rate – 10,500 cfs

Forecast average release rate – 10,500 cfs

End-of-November reservoir level – 2237.2 feet

Forecast end-of-December reservoir level – 2235.8 feet

Notes: Releases will remain at 10,500 cfs in December. Releases will be increased to 11,500 cfs in January.

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.