Widespread and heavy rainfall in the Missouri River basin above Sioux City, IA (upper basin) resulted in another month of much above average runoff. Precipitation during September was more than 200 percent of normal in eastern Montana, much of North Dakota, portions of South Dakota and northern Nebraska. As a result, September runoff into the upper basin above Sioux City, was nearly twice the record runoff, which was recorded in 1986.

Runoff in the Gavins Point to Sioux City reach was more than 16 times the long-term average and more than twice the previous record. Runoff in the Fort Randall to Gavins Point reach was over 4 times average and almost twice the previous record. Runoff between Oahe and Fort Randall was over 12 times average and set a new record. Runoff between Garrison and Oahe was over 4 times average. Finally, runoff between Fort Peck and Garrison was over 2 times average and is the second highest runoff of record, and Fort Peck was 1.5 times average.

The 2019 upper basin runoff forecast is 61.0 million acre-feet (MAF). If realized, this runoff total would equal the highest runoff in 121 years of record-keeping, 2011 (61.0 MAF). The January-September observed runoff (53.6 MAF) has already exceeded the second highest runoff in 121 years of record-keeping, 49.0 MAF observed in 1997, with three months still remaining.

“In response to the increased upstream runoff, releases from Gavins Point Dam have been increased to 80,000 cfs. This release rate is more than 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).

The Missouri River mainstem reservoir system (System) storage was 64.0 MAF as of October 1, occupying 7.9 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 forecast above-average runoff for the remainder of the fall, releases from all System projects will be much above average through November, to evacuate all stored flood waters prior to the start of the 2020 runoff season.  “We are monitoring the situation very closely and will make any necessary adjustments. Failure to evacuate the stored flood water will lead to increased risk of flooding in 2020, said Remus.”

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 are available at the following link: https://www.nwd.usace.army.mil/MRWM/Public-Meetings/

Updates on basin conditions, reservoir levels and other topics of interest can be viewed here: https://www.nwd.usace.army.mil/MRWM/MRWMApp/.

Monthly Water Management Conference Calls

Water management calls include an update 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 next call is Thursday, Oct. 10 at 3 p.m., 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 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 – 72,100 cfs
  • Current release rate – 80,000 cfs
  • Forecast release rate – 80,000 cfs
  • End-of-September reservoir level – 1206.2 feet
  • Forecast end-of-October reservoir level – 1207.5 feet
     
• Fort Randall Dam
  • Average releases past month – 63,800 cfs
  • End-of-September reservoir level – 1359.1 feet (down 0.8 foot from August)
  • Forecast end-of-October reservoir level – 1351.8 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 November.
     
• Big Bend Dam
  • Average releases past month – 53,900 cfs
  • Forecast average release rate – 60,900 cfs
  • Forecast reservoir level – 1420.5 feet
     
• Oahe Dam
  • Average releases past month – 55,600 cfs
  • Forecast average release rate – 61,000 cfs
  • End-of-September reservoir level – 1615.1 feet (falling 0.6 foot during September)
  • Forecast end-of-October reservoir level – 1612.9 feet
     
• Garrison Dam
  • Average releases past month – 45,900 cfs
  • Current release rate – 46,000 cfs
  • Forecast average release rate – 46,000 cfs
  • End-of-September reservoir level – 1845.7 feet (falling 2.2 feet during September)
  • Forecast end-of-October reservoir level – 1842.2 feet
     
• Fort Peck Dam
  • Average releases past month – 15,000 cfs
  • Current release rate – 15,000 cfs
  • Forecast average release rate – 15,000 cfs
  • End-of-September reservoir level – 2242.8 feet (down 1.3 feet from August)
  • Forecast end-of-October reservoir level – 2240.9 feet
  • Notes: Spillway releases will be adjusted 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 1393 million kWh of electricity in August. Typical energy generation for September is 895 million kWh. The power plants are projected to generate 13.3 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.