The US Army Corps of Engineers says May runoff in the upper Missouri River basin (above Sioux City, Iowa) was 8.9 million acre feet– 267% of average (5.6 MAF).
May runoff was the second highest on record, only surpassed by 2011’s 9.2 MAF. Runoff in the Fort Randall Dam to Gavins Point Dam reach was 1.4 MAF, which is more than the average yearly runoff for that reach.
The high May runoff increased the 2019 upper basin runoff forecast to 50 MAF. If realized, the 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 MAF observed in 1997. Runoff in 2018 was 42.1 MAF, which is currently third highest.
Chief of the U.S. Army Corps of Engineers Missouri River Basin Water Management Division John Remus says the Oahe and Fort Randall Dam reservoirs are currently in their respective exclusive flood control zones. Fort Peck and Garrison are expected to enter their exclusive flood control zones this month as the remaining mountain snowpack melts. As a result of the high reservoir levels, the Corps expects releases from all System projects will be above average for the next several months.
Because of the above average runoff in the upper basin, releases from Gavins Point Dam at Yankton have been above full service levels to reduce the occupied flood storage at Oahe and Fort Randall. Remus says additional precipitation, lack of precipitation or other circumstances could cause adjustments to the reservoir release rates.
Reservoir Forecasts
◾Gavins Point Dam ◦Average releases past month – 57,400 cfs
◦Current release rate – 75,000 cfs
◦Forecast release rate – 75,000 cfs
◦End-of-May reservoir level – 1207.6 feet
◦Forecast end-of-June reservoir level – 1206.0 feet
◾Fort Randall Dam ◦Average releases past month – 47,800 cfs
◦End-of-May reservoir level – 1370.2 feet (up 6.7 feet from April)
◦Forecast end-of-May reservoir level – 1370.2 feet
◦Notes: Releases will be adjusted as necessary to maintain the desired reservoir elevation at Gavins Point.
◾Big Bend Dam ◦Average releases past month – 41,300 cfs
◦Forecast average release rate – 47,600 cfs
◦Forecast reservoir level – 1420.0 feet
◾Oahe Dam ◦Average releases past month – 35,900 cfs
◦Forecast average release rate – 47,000 cfs
◦End-of-May reservoir level – 1618.8 feet (rising 2.4 feet during May)
◦Forecast end-of-June reservoir level – 1617.0 feet
◾Garrison Dam ◦Average releases past month – 23,500 cfs
◦Current release rate – 15,000 cfs
◦Forecast average release rate – 46,000 cfs (late June)
◦End-of-May reservoir level – 1847.8 feet (rising 1.4 feet during May)
◦Forecast end-of-June reservoir level – 1851.8 feet
◦Notes: Releases will be stepped up from 15,000 cfs to 46,000 cfs during June.
◾Fort Peck Dam ◦Average releases past month – 8,200 cfs
◦Current release rate – 9,000 cfs
◦Forecast average release rate – 15,000 cfs (late June)
◦End-of-May reservoir level – 2243.8 feet (up 3.2 feet from April)
◦Forecast end-of-June reservoir level – 2247.4 feet
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.
Missouri River Basin daily update:
http://www.nwd-mr.usace.army.mil/rcc/reports/pdfs/weeklyupdate.pdf
All US Army Corps managed dams–reservoir levels, inflows and releases:
http://www.nwd-mr.usace.army.mil/rcc/reports/pdfs/MRBWM_River_Daily.pdf