Spillway gates opened at Garrison Dam
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RIVERDALE - Flow through the regulating tunnels at Garrison Dam ended yesterday as the U.S. Army Corps of Engineers opted to use the spillway gates to regulate releases into the Missouri River.
The action allowed the Corps to test repairs made to spillway gates following the high water year of 2011. It was then, for the first time since Garrison Dam was completed in 1955, that the gates were opened to allow excess water to be released into the Missouri.
Total flow through the powerhouse and the operating tunnels reached 60,000 cubic feet per second earlier this summer, 41,000 cfs through the turbines at the powerhouse and 19,000 cfs through the adjacent regulating tunnels. Lake Sakakawea was within one foot of overflow for several weeks, a level which prompted the high releases.
The release rate is expected to be cut to 46,000 cfs on Wednesday and remain at that level through the end of the month. Lake Sakakawea was at 1,850.01 feet Monday with an inflow of 28,000 cfs. Projections show the reservoir should end August at about 1,847 feet.
Yesterday's switch from allowing excess releases through the regulating tunnels to the spillway gates was also made to allow for post-release inspection of the large tunnels. According to the Corps, the test actions are aimed at ensuring they have the flexibility of all options for releasing water from Lake Sakakawea if necessary.