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Near-Normal Runoff Forecast For Missouri River

The Corps is continuing to prepare the Missouri River Mainstem Reservoir System  for the upcoming runoff season, according to a January 9 conference call. Current Gavins Point Dam releases are 21,500 cubic feet per second (cfs.).

“Higher-than-average runoff during 2017 has allowed us to provide a slightly higher-than-average release during the winter months,” said John Remus, chief of the U.S. Army Corps of Engineers’ Missouri River Basin Water Management Division. “Higher winter releases provide additional hydropower generation during the winter, which is one of the peak power demand periods. It also benefits municipal and industrial water intakes below Gavins Point Dam, which can be impacted by low water levels during periods of ice formation. Once evacuation of water stored in the annual flood control pool is complete, releases will be reduced to near normal levels.” Gavins Point Dam winter releases normally range between 12,000 and 17,000 cfs.

The total volume of water stored in the system is currently 56.3 million acre-feet (maf.), occupying 0.2 maf. of the 16.3 maf. combined flood control storage zones. Based on current soil moisture conditions, plains and mountain snowpack, the 2018 calendar year runoff forecast is 26.6 maf. above Sioux City, Iowa, 105 percent of average. Average annual runoff is 25.3 maf.

Flow support for Missouri River navigation will likely be at full-service levels for the first half of the 2018 season, which begins on April 1 at the mouth. The actual service level will be based on the total volume of water stored in the system on March 15, in accordance with guidelines in the Master Manual. Flow support for the second half of the navigation season, as well as navigation season length, will be based on the actual July 1 system storage.

Releases from Fort Peck were increased to 10,500 cfs. in January and are expected to be increased to 11,000 cfs. during February. Releases from Garrison will be gradually increased from 16,000 cfs. to 25,000 cfs. and will remain near 25,000 cfs. during the winter months. River ice formation downstream of all the mainstem projects will be monitored and releases will be adjusted accordingly.

Annual Operating Plan Released

After reviewing comments received on the draft, the Missouri River Basin Water Management Division developed and released the Final Annual Operating Plan (AOP) for the Missouri River Basin for 2017–2018 in December.

The AOP presents pertinent information and plans for regulating the Missouri River Mainstem Reservoir System through December 2018 under widely varying water supply conditions. The plan can be viewed at www.nwd-mr.usace.army.mil/rcc/reports/pdfs/finalAOP2017-2018.pdf.

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

Reservoir Forecasts

Gavins Point Dam releases averaged 22,500 cfs. during December 2017. Releases are expected to be reduced to 18,000 cfs. once the system flood storage has been evacuated. Releases will be adjusted as necessary based on runoff and downstream river conditions. The Gavins Point reservoir ended December at elevation 1,204.6 feet and will be near 1207.5 feet during the remainder of the winter.

Fort Randall Dam releases averaged 20,800 cfs. in December. Releases will be adjusted as necessary to maintain the desired reservoir elevation at Gavins Point. The reservoir ended December at elevation 1,338.8 feet. The reservoir will be refilled during the winter to increase winter hydropower generation at Oahe and Big Bend.

Big Bend Dam releases averaged 19,800 cfs. in December. Releases are expected to average 26,100 cfs. this month. The reservoir will remain near its normal elevation of 1,420 feet during January.

Oahe Dam releases averaged 22,700 cfs. during December. Releases are expected to average 25,100 cfs. in January. The reservoir ended December at elevation 1,606.6 feet, falling 1.6 feet during the month. The reservoir level is expected to decline approximately another 0.3 feet during January.

Garrison Dam releases averaged 16,500 cfs. for the month. Releases were set at 16,000 cfs. in December to prepare for the river freeze-in, which occurred in late December. Releases are gradually being increased to the winter release rate of 25,000 cfs. and will remain at that rate through February, river conditions permitting. Garrison reservoir ended December at elevation 1,840.6 feet, declining 0.6 feet during the month. The reservoir level is expected to decline 2 feet during January, ending the month near elevation 1,838.6 feet.

Fort Peck Dam releases averaged 6,800 cfs. during December. Releases were increased to 10,500 cfs. in early January. The reservoir ended December at elevation 2,235.8 feet, declining 0.2 feet during the month. The reservoir is expected to fall approximately 1.2 feet during January ending the month near elevation 2,234.6 feet.

The Corps noted that 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 690 million kwh. of electricity in December. Typical energy generation for December is 682 million kwh. The power plants are projected to generate 10.1 billion kwh. of electricity this year, compared to the long-term average of 9.3 billion kwh.

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