RIVERDALE, N.D. — More and more shoreline is being exposed all along Lake Sakakawea as the U.S. Army Corps of Engineers, the agency charged with managing the reservoirs on the Missouri River Basin, continues to prepare the reservoir for runoff next spring.
Releases through the power plant and operating tunnels at Garrison Dam have been 48,000 cubic feet per second for several days and are slated to continue at that rate into November. Lake Sakakawea stood at 1,843.82 feet Tuesday, Oct. 22. According to the Corps, outflow from Garrison Dam, which backs up Lake Sakakawea, was 48,300 cfs Tuesday with inflow measured at 29,000 cfs. Lake Sakakawea has been dropping approximately one-tenth of a foot per day.
Given the current conditions, Sakakawea is expected to drop to 1,842.6 feet by Oct. 31. The annual goal for the reservoir is to be at 1,837.5 at the end of each February. Corps' projections have Lake Sakakawea dropping to 1,839.5 feet by the end of November with the expectation of reaching the February mark.
All three upper Missouri River reservoirs have seen very high amounts of water pass through them this year. Runoff for the entire system, spring snowmelt and rainfall this summer and fall, has been calculated at 61.0 million acre feet. If realized, that would equal the highest runoff in the history of the system.
Fort Peck reservoir in Montana, Lake Sakakawea and Lake Oahe which originates in South Dakota, are all below what is considered their exclusive flood control zones and are approximately at the midway point of their annual flood control and multiple use zones. All three reservoirs continue to discharge more water than they are taking in.
On Monday, Oct. 21, Fort Peck was a 2,241.5 feet with a Feb. 29 goal of reaching 2,234.0 feet. Fort Peck was discharging 15,000 cfs with an inflow of 9,300 cfs. Lake Oahe was at 1,613.3 feet Monday with outflow of 62,000 cfs and inflow of 51,700 cfs. The February operating goal for that reservoir is 1,607.5 feet.
A very wet fall has spurred concerns about the effect abundant soil moisture conditions will have on the snowmelt next spring. The amount of runoff next spring will be dependent on a variety of factors, including soil moisture conditions, the amount of snow that falls throughout the basin this winter, the speed of the melt and rainfall throughout the drainage in early 2020.