Widespread and heavy rainfall in the Missouri River basin above Sioux City, IA (upper basin) resulted in another month of above average runoff. Precipitation during August was more than 150 percent of normal in eastern Montana, portions of North Dakota, much of South Dakota and Nebraska. As a result, the Fort Randall and Gavins Point reaches experienced their wettest Augusts on record, while the Sioux City and Oahe reaches were second and third, respectively.

The 2019 upper basin runoff forecast is 54.6 million acre-feet (MAF). If realized, this runoff total would be the second highest runoff in 121 years of record-keeping, only surpassed by 2011 (61.0 MAF) and exceeding the 49.0 MAF observed in 1997. Accumulated runoff in the lower four reaches (Oahe, Fort Randall, Gavins Point, and Sioux City) was 27.3 MAF. In each of the lower four reaches, the observed runoff exceeded the maximum annual runoff with four months of the year remaining to accumulate additional runoff. By the end of 2019, the forecasted runoff in these four reaches is roughly 30.0 MAF, which exceeds the average annual runoff for the entire upper basin.

The Missouri River mainstem reservoir system (System) storage was 65.6 MAF as of September 1, occupying 9.5 MAF of the 16.3 MAF flood control zone. All three of the upper three reservoirs (Fort Peck, Garrison, and Oahe) have fallen out of their exclusive flood control zones but remain high. “As a result of the high reservoir levels and the forecasted above-average runoff for the remainder of the summer and fall, releases from all System projects will be much above average for the next several months, and possibly as late as November, to ensure evacuation of all stored flood waters prior to the start of the 2020 runoff season. System releases from Gavins Point Dam are currently 70,000 cfs, which is nearly twice the average release for this time of the year,” said John Remus, chief of the U.S. Army Corps of Engineers Missouri River Basin Water Management Division (MRBWMD).

Seven public meetings will be conducted throughout the basin October 22-25. 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 2020. Meeting times and locations will be announced when additional details become available.

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.

Monthly Water Management Conference Calls

Due to continued high water concerns, water management calls were reformatted and held weekly through the end of August. Calls include a briefing from the National Weather Service’s Missouri Basin River Forecast Center, an update on the Missouri River mainstem reservoir system operations, and updates on the ongoing and planned flood recovery efforts in both the Omaha and Kansas City Districts. The Thursday, September 5 is a webinar for Congressional delegations; Tribes; state, county and local government officials, levee and drainage districts; and the media. Calls for the remainder of 2019 will be held October 10, November 7, and December 5. Calls will be recorded in their entirety and made available to the public on the Defense Video and Imagery Distribution System at www.dvidshub.net/unit/usace-nwd.

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-August reservoir level – 1206.4 feet
  • Forecast end-of-September reservoir level – 1206.5 feet
     
• Fort Randall Dam
  • Average releases past month – 65,300 cfs
  • End-of-August reservoir level – 1359.9 feet (down 1.4 feet from July)
  • Forecast end-of-September reservoir level – 1354.3 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 annual drawdown will continue in October and November.
     
• Big Bend Dam
  • Average releases past month – 54,100 cfs
  • Forecast average release rate – 56,400 cfs
  • Forecast reservoir level – 1420.0 feet
     
• Oahe Dam
  • Average releases past month – 57,000 cfs
  • Forecast average release rate – 56,500 cfs
  • End-of-August reservoir level – 1615.7 feet (falling 1.7 feet during August)
  • Forecast end-of-September reservoir level – 1613.4 feet
     
• Garrison Dam
  • Average releases past month – 46,300 cfs
  • Current release rate – 46,000 cfs
  • Forecast average release rate – 42,000 cfs
  • End-of-August reservoir level – 1847.9 feet (falling 3.7 feet during August)
  • Forecast end-of-September reservoir level – 1844.9 feet
     
• Fort Peck Dam
  • Average releases past month – 15,100 cfs
  • Current release rate – 15,000 cfs
  • Forecast average release rate – 14,800 cfs
  • End-of-August reservoir level – 2244.1 feet (down 2.1 feet from July)
  • Forecast end-of-September reservoir level – 2242.2 feet
  • Notes: Spillway releases will be increased this month during scheduled maintenance at the powerhouse. Total releases will remain unchanged during the maintenance.

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 a record 1540 million kWh of electricity in August. Typical energy generation for August is 1003 million kWh. The power plants are projected to generate 13.4 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.