OMAHA, Neb. — Much-above average runoff in the upper Missouri River basin (above Sioux City, Iowa) extended into June following widespread and heavy rainfall in South Dakota and Nebraska.
Additionally, widespread and heavy rainfall in the lower basin, particularly in Kansas, has resulted in high tributary and Missouri River flows downstream of the six main stem reservoirs on the Missouri River.
June runoff in the upper basin was 8.7 million acre feet (MAF), which is 159 percent of average. The average June runoff is 5.4 MAF. Runoff remained particularly high in the Fort Randall to Gavins Point and Gavins Point to Sioux City reaches, which were three and four times average, respectively.
The 2019 upper basin runoff forecast is 49.9 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. Upper basin runoff in 2018 was 42.1 MAF, which is currently third highest.
“System releases from Gavins Point Dam are currently 70,000 cfs, which is more than 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 U.S. Army Corps of Engineers Missouri River Basin Water Management Division.
The System was storing 68.0 MAF as of July 1, occupying 11.9 MAF of the 16.3 MAF flood control zone. System storage normally peaks in early July. Fort Peck and Garrison are currently in 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.
The Corps has been coordinating with the U.S. Bureau of Reclamation (USBR) regarding the USBR projects in Montana and Wyoming with designated flood control storage. Releases from several of the USBR projects are being adjusted, and flood control storage is being used. This measure provides additional ability to manage the pools at all the mainstem reservoirs during July.
Missouri Basin observations, forecasts and updates from the U.S. Army Corps of Engineers, the National Weather Service, and other partner agencies are available through the Missouri Basin web app. The app provides links to the most up-to-date information on the Missouri Basin from the official information providers.
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. As of June 30, less than 1 percent of this year’s peak remains in both reaches. View the mountain snowpack graphic here: http://www.nwd-mr.usace.army.mil/rcc/reports/snow.pdf.
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.
AREA Reservoir Forecasts
• Gavins Point Dam
Average releases past month — 74,400 cfs
Current release rate — 70,000 cfs
Forecast release rate — 70,000 cfs
End-of-May reservoir level — 1206.3 feet
Forecast end-of-July reservoir level — 1206.0 feet
• Fort Randall Dam
Average releases past month — 65,000 cfs
End-of-June reservoir level — 1363.0 feet (down 7.2 feet from May)
Forecast end-of-July reservoir level — 1356.6 feet
Notes: Releases will be adjusted as necessary to maintain the desired reservoir elevation at Gavins Point.
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 1225 million kWh of electricity in June. Typical energy generation for June is 842 million kWh. The power plants are projected to generate 12.7 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.