Sakakawea enters slow decline

Kim Fundingsland/MDN This view from water level of the Garrison Dam release gates shows that Lake Sakakawea was within a foot of spilling over the gates this past Sunday. The massive reservoir has since begun a very slow decline.

RIVERDALE – Close. Very close.

Extensive runoff from a combination of melting mountain snowpack and rainfall over the Missouri River drainage caused a rush of water to enter Lake Sakakawea the past several weeks. The surge pushed the level of Lake Sakakawea to less than a foot from spilling.

The water level of massive reservoir reached a peak of 1,853.16 feet on the Fourth of July. Full capacity is 1,854 feet. Now though, Lake Sakakawea has begun a very slow decline as outflow exceeds inflow.

On Wednesday the reservoir level was 1,852.92 feet, a drop of .04 feet from the previous day. According to the U.S. Army Corps of Engineers three-week forecast, Lake Sakakawea should continue to decline ever so slightly in the coming days with a level of 1,852.4 feet expected by July 26.

Inflow Wednesday, primarily from water being released from Fort Peck reservoir in Montana and the Yellowstone River flowing out of Montana, was 56,000 cubic feet per second. Releases Wednesday through the turbines at Garrison Dam and the adjacent regulating tunnels was 60,100 cfs. The Corps’ forecast is for inflow to drop to 42,900 cfs by July 26 while maintaining a 60,000 cfs release.

The apparent peak of 1,853.16 feet last week, which was 94.5 percent of the reservoir’s capacity, is the fourth-highest level ever recorded for Lake Sakakawea. The reservoir reached 1,854.6 feet in 2011 which prompted the first-ever opening of the release gates at Garrison Dam.

Barring any changes in inflow caused by rainfall over the drainage, the Corps expects Lake Sakakawea to end the month of July at 1,852.0 feet. The projection for the end of August is 1,847.8 feet with an end of year level of 1,839.1 feet.