The U.S. Army Corps of Engineers reports March runoff in the upper Missouri River Basin was 151 percent above normal.
Pool levels in the four System projects that have significant flood control storage – Fort Peck, Garrison, Oahe and Fort Randall – have all increased significantly to capture much of the runoff.
Chief of the Missouri River Basin Water Management Division John Remus says they need to reduce pool levels in Oahe and Fort Randall over the next several weeks so those reservoirs are in position to reduce flood risk during the spring and summer. He says the Fort Peck and Garrison reservoirs are well positioned to receive the runoff from the mountain snowmelt, which typically begins in May.
The Oahe Dam reservoir rose 7.9 feet in March to a level of 1614.7 feet. The Corps expects Oahe to go up about another foot and a half– to 1616 feet– by the end of April. Oahe averaged releases last month (March) of 9,500 cfs. The forecast average release rate is 31,400 cfs.
Incidentally, the Corps will hold a meeting Wednesday (April 10) at 10am CDT at the Casey Tibbs Rodeo Center in Fort Pierre. Officials will give an update on current conditions and will discuss the planned operation of the mainstem reservoir system during the coming months.
Find updated Missouri River reservoir levels on the Corps website: http://www.nwd-mr.usace.army.mil/rcc/reports/pdfs/MRBWM_River_Daily.pdf
However, the Corps says the forecast reservoir releases and elevations may be altered by additional precipitation, lack of precipitation or other circumstances that could cause adjustments to the reservoir release rates.
The record high runoff in March was caused by 2-4 inches of rain falling on heavy plains snowpack causing the snowpack to rapidly melt on frozen, saturated soils.
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 into the Oahe and Fort Randall reservoirs, releases from Gavins Point have been above full service levels to lessen the time that those projects have water stored in their exclusive flood control zones. Flow support for the second half of the navigation season, as well as navigation season length, will be based on the actual July 1 System storage. Flow support is generally sufficient to provide a 9-foot-deep by 300-foot-wide channel.
The Corps plans to increase Gavins Point releases to 55,000 cubic feet per second by early next week. Gavins Point releases will be above average for the next several months, and possibly as late as November.
As of April 1, the mountain snowpack was 97 percent of average in the reach above Fort Peck and 93 percent of average in the reach from Fort Peck to Garrison. Normally the mountain snowpack peaks in mid-April. View the mountain snowpack graphic here: http://www.nwd-mr.usace.army.mil/rcc/reports/snow.pdf.
Much of the plains snowpack in central North Dakota and eastern South Dakota has melted. The heaviest snowpack remains in isolated areas of north central South Dakota and south central North Dakota where the snowpack’s liquid content, or snow water equivalency (SWE), ranges from 1 to 5 inches. Frost depth is still deep in much of the upper basin, including the areas with the remaining snowpack. The Corps is cooperating with other agencies to acquire plains snow measurements in the upper basin.
Weekly 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.
The Corps will host six public meetings April 9-11 to discuss the Missouri River Mainstem System, its runoff and reservoir operations. Meeting information is detailed in a separate news release: https://go.usa.gov/xmqSp.
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.
