Much above average runoff continues in the upper Missouri River basin. April runoff in the upper basin, the Missouri River above Sioux City, Iowa, was 7.8 million acre feet (MAF), the third highest April runoff in the 121 years of record. The average April runoff is 2.9 MAF. Runoff in the Gavins Point Dam to Sioux City reach was 2.3 MAF, the second highest April runoff for this reach. The total March-April runoff for the upper basin was 18.7 MAF, which is the highest March-April runoff since record-keeping began in 1898, exceeding the previous record of 15.9 MAF, which occurred in 1952.

The near-record April runoff, which was nearly 3 times average, increased the 2019 upper basin runoff forecast to 42.3 million acre-feet (MAF). If realized, this runoff total will be the third highest runoff in 121 years of record-keeping, only surpassed by 1997 (49.0 MAF) and 2011 (61.0 MAF). Runoff in 2018 was 42.1 MAF, which is currently third highest. 

“Gavins Point releases are currently 55,000 cfs, which is about 25,000 cfs above average for this time of the year. We will maintain Gavins Point releases at this rate to continue evacuating water from Oahe and Fort Randall, which are using much of their respective flood storage,” said John Remus, Chief of the U.S. Army Corps of Engineers (Corps) Missouri River Basin Water Management Division. “We want to reduce the pool levels in Oahe and Fort Randall a few feet to provide flexibility should we need to reduce Gavins Point releases for short periods over the remainder of the spring and summer.”

The Corps expects that releases from all System projects will be above average for the next several months, and possibly as late as November.

Big Bend will have a scheduled powerplant outage May 7-10 where all turbines will be offline for maintenance. During that time, releases will be made through the spillway.

The mountain snowpack has begun melting in the reaches upstream from Fort Peck and Garrison Dams at near-average levels. The mountain snowpack peaked in both reaches: on April 18 in the Fort Peck reach at 105 % of average and on April 17 in the Fort Peck to Garrison reach at 104 % of average. Normally the mountain snowpack peaks in mid-April. “Fort Peck and Garrison reservoirs have adequate flood control space to capture and manage the mountain snowmelt runoff,” added Remus. View the mountain snowpack graphic here: http://www.nwd-mr.usace.army.mil/rcc/reports/snow.pdf.

Based on the March 15 System storage check, flow support for the first half of the navigation season is full service. However, due to above average runoff in the upper basin, releases from Gavins Point have been above full service levels to reduce the occupied flood storage at Oahe and Fort Randall. Based on the May 1 service level check, the service level was increased another 5,000 cfs to 20,000 cfs above full service levels.

Beginning on May 7, updates on basin conditions, reservoir levels and other topics of interest will return to their original schedule to be updated each Tuesday. The updates are posted to Facebook and Twitter at NWDUSACE and can be viewed here: http://www.nwd-mr.usace.army.mil/rcc/reports/pdfs/weeklyupdate.pdf.

Monthly Water Management Conference Calls

The fourth monthly conference call of the 2019 runoff season will be held Tuesday, May 7 to inform basin stakeholders on current weather and runoff forecasts and the planned operation of the System. Presentation materials will be posted on the MRBWM website at: http://www.nwd.usace.army.mil/MRWM/. The call is intended for Congressional delegations; Tribes; state, county and local government officials; and the media. It will be recorded in its 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 – 52,500 cfs
  • Current release rate – 55,000 cfs
  • Forecast release rate – 55,000 cfs
  • End-of-April reservoir level – 1206.1 feet
  • Forecast end-of-May reservoir level – 1206.0 feet

• Fort Randall Dam
  • Average releases past month – 46,000 cfs
  • End-of-April reservoir level – 1363.4 feet (down 3.4 feet from March)
  • Forecast end-of-May reservoir level – 1360.0 feet
  • Notes: Releases will be adjusted as necessary to maintain the desired reservoir elevation at Gavins Point.

• Big Bend Dam
  • Average releases past month – 30,800 cfs
  • Forecast average release rate – 38,100 cfs
  • Forecast reservoir level – 1420.0 feet
  • Notes: Spillway releases will occur May 7-10 while maintenance is performed on all turbines.

• Oahe Dam
  • Average releases past month – 30,200 cfs
  • Forecast average release rate – 37,600 cfs
  • End-of-April reservoir level – 1616.4 feet (rising 1.7 feet during April)
  • Forecast end-of-April reservoir level – 1615.9 feet

• Garrison Dam
  • Average releases past month – 13,400 cfs
  • Current release rate – 21,000 cfs
  • Forecast average release rate – 30,000 cfs (end of May)
  • End-of-April reservoir level – 1846.4 feet (rising 3.8 feet during April)
  • Forecast end-of-May reservoir level – 1847.2 feet
  • Notes: Releases will be stepped up from 21,000 cfs to 30,000 cfs during May.

• Fort Peck Dam
  • Average releases past month – 6,600 cfs
  • Current release rate – 8,000 cfs
  • Forecast average release rate – 10,000 cfs (late May)
  • End-of-April reservoir level – 2240.6 feet (up 2.5 feet from March)
  • Forecast end-of-April reservoir level – 2242.8 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 794 million kWh of electricity in April. Typical energy generation for April is 693 million kWh. The power plants are projected to generate 12.3 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.