September precipitation was well-below normal in the Missouri River Basin.  As a result, September runoff in the upper Missouri River Basin above Sioux City, Iowa was 69% of average. 

Since January 1, precipitation in the upper Basin is well-below normal.  The National Weather Service’s Climate Prediction Center is forecasting that below-normal precipitation will continue in October.  The 2020 calendar year runoff forecast for the upper Basin, updated on Oct. 1, is 30.2 million acre-feet (MAF), 117% of average. Average annual runoff for the upper Basin is 25.8 MAF.

“Upper basin runoff was below average in September. We expect runoff to be below average during the remainder of the calendar year. Lower basin runoff has been below average as well,” said John Remus, chief of the U.S. Army Corps of Engineers’ Missouri River Basin Water Management Division.  “Releases from Gavins Point Dam are being made to meet full service Missouri River navigation flow targets”, Remus added. 

The navigation flow support season ends on December 1 at the mouth of the Missouri River. 

As of Oct. 5, the total volume of water stored in the System was 58.6 MAF, occupying 2.5 MAF of the System’s 16.3-MAF flood control zone. System storage peaked at 61.8 MAF on July 16 and will decline during the fall. All 16.3 MAF of flood control storage is expected to be available prior to the start of the 2021 runoff season. If fall and winter runoff continues to be below average as forecasted, System storage will be about 0.8 MAF below the base of the annual flood control zone by the start of the 2021 runoff season.

According to the National Drought Mitigation Center (NDMC), drought conditions continue to worsen across much of the upper Basin. Wide-spread areas of drought classified as Extreme are evident in Colorado and Wyoming.  Moderate to Severe drought conditions are present in large areas of Montana, North Dakota, South Dakota, Nebraska and Iowa.

Navigation

The July 1 System storage check indicated flow support for the second half of the navigation season would be at least at the full service level for a full-length 8-month flow support season. Full service flow support is designed to work in tandem with the Missouri River Bank Stabilization and Navigation Project to provide a 9-feet deep by 300-foot wide navigation channel from Sioux City, Iowa to the mouth of the river near St. Louis, Missouri. Gavins Point releases will be reduced to winter levels beginning around Nov. 22.

Winter Release Rate

The winter release rate is determined based on the Sept. 1 System storage. Per the Sept. 1 System storage, winter releases from Gavins Point Dam will be at least 17,000 cfs.

Fall Public Meetings

Two public meetings will be conducted by webinar on Nov. 2. The purpose of these meetings is to update the region on current hydrologic conditions and the planned operation of the mainstem reservoir system during the remaining fall months as well as present the draft plans for operating the System during 2021. Meeting times and webinar information will be at the following link when it becomes available: https://www.nwd.usace.army.mil/MRWM/Public-Meetings/.

Reservoir Forecasts:

• Gavins Point Dam
  • Average releases past month – 32,200 cfs
  • Current release rate – 32,500 cfs (as of October 1)
  • Forecast release rate – 33,000 cfs (month of October)
  • End-of-September reservoir level – 1207.5 feet
  • Forecast end-of-October reservoir level – 1207.5 feet
  • Note: Releases will be adjusted as necessary to meet all downstream navigation targets.
     
• Fort Randall Dam
  • Average releases past month – 30,500 cfs
  • End-of-September reservoir level – 1353.5 feet
  • Forecast end-of-October reservoir level – 1344.6 feet
  • Note: Releases will be adjusted as necessary to maintain the desired reservoir elevation at Gavins Point. The Fort Randall pool is normally drawn down to 1337.5 feet in the fall to provide space for winter hydropower generation at Oahe and Big Bend. The annual drawdown will continue in October and November.
     
• Big Bend Dam
  • Average releases past month – 28,500 cfs
  • Forecast average release rate – 20,200 cfs
  • Forecast reservoir level – 1420.7 feet
     
• Oahe Dam
  • Average releases past month – 28,900 cfs
  • Forecast average release rate – 20,300 cfs
  • End-of-September reservoir level – 1610.4 feet
  • Forecast end-of-October reservoir level – 1608.5 feet
  • Notes: Oahe will undergo a full powerplant outage during the day on October 13 to conduct scheduled maintenance.  Zero releases, though not unusual from Oahe, will be scheduled during the daylight hours so that the work crew can complete maintenance in the tailrace area. 
     
• Garrison Dam
  • Average releases past month – 17,900 cfs
  • Current release rate – 14,000 cfs
  • Forecast average release rate – reduce to 13,000 cfs on 8 October
  • End-of-September reservoir level – 1839.7 feet
  • Forecast end-of-October reservoir level – 1839.3 feet
     
• Fort Peck Dam
  • Average releases past month – 8,400 cfs
  • Current release rate – 6,000 cfs
  • Forecast average release rate – 6,000 cfs
  • End-of-September reservoir level – 2237.7 feet
  • Forecast end-of-October reservoir level – 2237.1 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.

Hydropower:

The six mainstem power plants generated 875 million kWh of electricity in September. Typical energy generation for September is 905 million kWh. The power plants are projected to generate 10.1 billion kWh of electricity this year, compared to the long-term average of 9.4 billion kWh.

To view the detailed three-week release forecast for the mainstem dams, go to http://go.usa.gov/xVgWr.