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Sakakawea Snow pack 104 percent of average Corps News Release

by Friends of Lake Sakakawea

The full flood control capacity of the Missouri River mainstem reservoir system is available for the 2017 runoff season, according to the U.S Army Corps of Engineers (Corps) Missouri River Water Management Division. All 2016 stored flood water was evacuated from the reservoir system as of December 18, when the total volume stored in the Mainstem Reservoir System reached 56.1 million acre-feet (MAF).

“Due to the complete evacuation of the reservoir system, Gavins Point releases were reduced from 18,000 cubic feet per second (cfs) to the normal winter rate of 17,000 cfs on January 5. Basin conditions will continue to be monitored and reservoir releases adjusted as needed throughout the winter in preparation for the 2017 runoff season”, said Jody Farhat, Chief of the Missouri River Water Management Division.

“The entire flood control capacity of the Mainstem Reservoir System stands ready to capture spring runoff, reducing flood risk while providing support to other authorized project purposes.”Runoff in the Missouri River Basin above Sioux City, Iowa, was 0.9 MAF during December, 114 percent of average. December’s runoff resulted in a 2016 calendar year runoff total of 24.2 MAF, 96 percent of average, according to the Corps. Average annual runoff is 25.3 MAF.

The upper plains, particularly in North Dakota and northern South Dakota, experienced heavy snowfall during December. Some areas in central North Dakota are reporting as much as 3-4 inches of water content from current snowpack. The surrounding areas of eastern Montana and western and northern South Dakota have accumulated 1-3 inches of water content in the plains snowpack, while the remainder of the upper plains and the lower basin have little plains snow accumulation. The Corps is cooperating with other agencies to acquire plains snow measurements in the upper basin.

As of Jan. 9, the mountain snowpack was 78 percent of average in the reach above Fort Peck and 104 percent of average in the reach from Fort Peck to Garrison. Normally 44% of the total mountain snowpack accumulation has occurred by Jan. 1. Mountain snowpack will continue to accumulate overthe next few months and normally peaks in mid-April.

View mountain snowpack graphic here:

Based on the current soil moisture and mountain and plains snowpack conditions, 2017 runoff in the Missouri River Basin above Sioux City, Iowa, is forecast to be 25.4 MAF, 100 percent of average. Timing and distribution of the forecasted runoff, however, varies widely based on the snowpack data discussed above.

Winter releases from Gavins Point will be at least 17,000 cfs based on the September 1 system storage check, but will be adjusted if needed in response to basin conditions. Flow support for Missouri River navigation will likely be at full service levels for the first half of the 2017 season, which begins on April 1 at the mouth. The actual service level will be based on the total volume of water stored in the reservoir system on March 15, in accordance with guidelines in the Master Manual. Flow support for the second half of the navigation season, as well as the navigation season length, will be based on the actual July 1 system storage.

With increased chances of below average temperatures in the upper basin for the remainder of winter, ice conditions and river stages will be closely monitored throughout the basin. The Corps will make reservoir release adjustments as necessary to lessen the impact of river ice formation based on conditions below Garrison, Oahe and Gavins Point dams. Releases from Garrison are forecast to remain at 16,000 cfs during January to reduce the risk of ice-induced flooding in the Bismarck area and to help balance storage in the upper three reservoirs. Minimum releases will be specified at Oahe during extreme cold periods to reduce the risk of ice-induced flooding in the Pierre area.