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Upper Missouri River reservoirs continue releasing high volume of water

Reservoir drawdowns on target

Kim Fundingsland/ MDN Water flows through release gates onto the spillway at Garrison Dam as part of an ongoing effort to lower the reservoir prior to next spring’s runoff.

RIVERDALE – The amount of water being released through Garrison Dam will continue at 48,000 cubic feet per second at least until late November. The release rate is approximately twice the long-term average for the facility due to one of the highest runoff seasons on record.

The November runoff projection for the Missouri River Basin, as issued by the U.S. Army Corps of Engineers, anticipates that 60.2 million acre feet of water will enter the system this year. One month ago the Corps placed that number at 61.0 maf, which would have equaled the all-time high runoff season of 2011.

While the latest projections provide some relief from the massive volume of water entering the system in 2019, it still provides a challenge for the lowering of water levels in impoundments on the Missouri prior to the target date of Feb. 1, 2020. As a result, releases from dams on the Missouri remain very high.

The amount of water being released from the upper three Missouri River reservoirs, Fort Peck in Montana, Lake Sakakawea and Lake Oahe in both South and North Dakota, exceeds the maximum release capacity through the electricity generating turbines at each facility. That means either release tunnels or spillway gates must be partially opened to allow adequate flow through the system.

At Garrison Dam the maximum amount of water that can be released through the power generating turbines is considered 40,000 cfs. The additional 8,000 cfs is being released through spillway gates. The last reservoir on the Missouri River system is Gavins Point, Nebraska, which has been releasing 80,000 cfs for several weeks and is scheduled to continue to do so until at least late this year if not beyond.

According to the Corps, runoff into the system this month and next will continue above the long-term average but not so much as to cause additional concerns. Based on current conditions it is expected that the upper three reservoirs on the system, if not all of them, will reach their Feb. 1 target levels.

The Feb. 1 target levels place the pools of all reservoirs on the Missouri at the base of their prescribed Flood Control Zones in preparation for annual spring runoff. Lake Sakakawea’s Flood Control Zone is 1,837.5 to 1,850 feet. The level from 1,850 to 1,854 feet, which is spillway level, is referred to as the Exclusive Flood Control Zone. Lake Sakakawea has been dropping for several weeks and, as of Tuesday, was at 1,841.7 feet.

According to the latest basin update supplied by the Corps, about 26% of the flood control storage in the entire Missouri River system remains to be evacuated “over the next five weeks and the winter.” The update added that the “entire Missouri River Basin is drought free” and that “soil conditions remain very wet across most of the basin.”

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