The Corps of Engineers began increased releases from 517.8-MW Garrison Dam Aug. 23 to better balance the effects of drought among the Missouri River’s three largest mainstem reservoirs.
The Corps said it waited until endangered piping plover and least tern chicks became mature enough to fly before releasing water through their downstream nesting areas.
The Corps’ Water Management Office in Omaha said it increased releases at the North Dakota dam to 24,000 cubic feet per second from 21,000 cfs.
The releases primarily will benefit the next reservoir downstream, at the 786-MW Oahe project in South Dakota. They will continue until mid-September, when they will be cut to 15,000 cfs. The additional releases from Garrison are expected to slow the decline of Oahe’s water level until Oahe’s releases can be reduced after Sept. 5.
On Sept. 5, annual drawdown begins in the reservoir farther downstream at 320-MW Fort Randall Dam in South Dakota. Fort Randall’s reservoir is lowered each year about 15 feet to provide storage for winter hydropower releases and to prevent ice-related damage along the reservoir.
Drought hits Oahe reservoir hardest
The government said extreme drought across much of the upper Missouri River Basin affected large reservoirs of Garrison and the 185.3-MW Fort Peck project in Montana, but especially at Oahe. The Corps said Oahe’s reservoir level stood at 1,571.3 feet above sea level, dropping below the previous low level of 1,572 feet set Aug. 11.
Oahe’s reservoir now is 36.2 feet below the top of the conservation pool and is setting record lows nearly every day, the Corps said. The previous record low was set in August 2004. The higher releases from Garrison Dam over the three weeks will add about 0.6 feet to Oahe, and drop the reservoir behind Garrison by the same amount.
The reservoirs behind Garrison and Fort Peck dams have not dipped below their record low levels. As of Aug. 22, Garrison’s reservoir stood at 1,813.4 feet, 24.1 feet below the top of the conservation pool but 7.6 feet above its record low of 1,805.8 feet, set in May 2005. The Corps reported the reservoir at Fort Peck Dam was at 2,204 feet, 30 feet below the conservation pool but 5.7 feet above its record low of 2,198.3, set in January 2005.
The Corps did not state how increasing releases from the Garrison Dam might affect hydropower generation at the various powerhouses. However, Corps spokesman Paul Johnston said the government expects to generate 40 percent less hydropower this year from Missouri River projects (6 billion kilowatt-hours vs. 10 billion kWh) because of reduced releases from dams and lower reservoir levels.
In July, the Western Area Power Administration, which markets the power from the mainstem dams, spent $2.7 million to purchase electricity to make up for lost generation, Johnston said.