Missouri River Dam System storage has peaked; Releases expected to remain high

Widespread and heavy rainfall in the upper Missouri River basin (above Sioux City) resulted in another month of above average runoff. Areas of Montana, Wyoming, South Dakota, and Nebraska received two to three times normal precipitation during July.

July runoff in the upper basin was 7.0 million acre feet (MAF), which is 213% of average. The average July runoff is 3.3 MAF. Runoff remained particularly high in the reaches from Garrison Dam in North Dakota to Sioux City, Iowa, which ranged between three to seven times average.

The 2019 upper basin runoff forecast is 52.9 MAF. If realized, this runoff total will be the second highest runoff in 121 years of record-keeping, only surpassed by 2011 (61.0 MAF) and exceeding 49.0 MAF observed in 1997. Total upper basin runoff through July 31 was 45.3 MAF, exceeding the total upper basin runoff in 2018 of 42.1 MAF.

System releases from Gavins Point Dam are currently 70,000 cubic feet per second (CFS), which is nearly twice the average release for this time of the year.

“We will maintain Gavins Point releases at this rate to continue evacuating water from the Missouri River mainstem reservoir system (System),” said John Remus, chief of the Corps’ Missouri River Basin Water Management Division.

System storage was 68.0 MAF as of August 1, occupying 11.9 MAF of the 16.3 MAF flood control zone. System storage, which normally peaks in early July, peaked at 68.5 MAF on July 20. Garrison is currently in its exclusive flood control zone while Fort Peck and Oahe are slightly below their respective exclusive flood control zones. As a result of the high reservoir levels and the forecast above-average runoff during the summer and fall, releases from all System projects will be above average for the next several months, and possibly as late as November, to ensure evacuation of all stored flood waters.

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
- Average releases past month – 70,000 cfs
- Current release rate – 70,000 cfs
- Forecast release rate – 70,000 cfs
- End-of-July reservoir level – 1206.6 feet
- Forecast end-of-August reservoir level – 1206.6 feet
Fort Randall Dam
- Average releases past month – 63,500 cfs
- End-of-July reservoir level – 1361.3 feet (down 1.7 feet from June)
- Forecast end-of-August reservoir level – 1356.1 feet
- Notes: Releases will be adjusted as necessary to maintain the desired reservoir elevation at Gavins Point.
Big Bend Dam
- Average releases past month – 51,900 cfs
- Forecast average release rate – 56,300 cfs
- Forecast reservoir level – 1420.0 feet
Oahe Dam
- Average releases past month – 55,500 cfs
- Forecast average release rate – 56,500 cfs
- End-of-July reservoir level – 1617.0 feet (rising 0.3 foot during July)
- Forecast end-of-August reservoir level – 1615.3 feet
Garrison Dam
- Average releases past month – 46,400 cfs
- Current release rate – 46,000 cfs
- Forecast average release rate – 46,000 cfs
- End-of-July reservoir level – 1851.7 feet (falling 0.2 foot during July)
- Forecast end-of-August reservoir level – 1848.0 feet
Fort Peck Dam
- Average releases past month – 12,900 cfs
- Current release rate – 15,000 cfs
- Forecast average release rate – 15,000 cfs
- End-of-July reservoir level – 2246.2 feet (down 0.2 foot from June)
- Forecast end-of-August reservoir level – 2244.0 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 mainstem power plants generated 1490 million kWh of electricity in July. Typical energy generation for July is 951 million kWh. The power plants are projected to generate 13.1 billion kWh of electricity this year, compared to the long-term average of 9.4 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.

Missouri River Dam System storage has peaked; Releases expected to remain high

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