This week, the U.S. Army Corps of Engineers will reduce water releases from Lake Oahe into the power plant that houses seven turbines turning the water power into electrical power on a alternating schedule of maintenance that will last nearly until Christmas.
But the total release from the dam north of Pierre and Fort Pierre won’t change, it will just be adjusted to include releases from the other, or west, end of the dam into the “regulating tunnels,” that feed into the stilling basin, according to Eileen Williamson, spokeswoman for the Army Corps in its Upper Missouri River Basin office in Omaha.
“Right now, the releases are set to be 57,000 cfs (cubic feet per second) through Sept. 13,” Williamson said in email message to the Capital Journal on Thursday, Aug. 22.
The dam normally moves water from Lake Oahe through the power plant’s seven units, seen just below the east end of the dam, with the water intake coming from the large structure seen in the lake above the dam going to the east shore.
That water powers the seven turbines that pump out electricity.
During the maintenance schedule, in which one or two of the seven power plant units will be offline at different times between Monday, Aug. 26 and Dec. 20, water will be released into the regulating tunnels on the west end of the dam, according to Williamson.
That water comes out of the regulating tunnels into the stilling basin below the west end of the dam, so water will be seen flowing into the stilling basin beginning Monday, Williamson said.
The water shortly joins the Lake Oahe water coming down from the power plant at the southern tip of the Oahe Downstream State Recreation Area.
“There is no change to the overall release amount, it is just a change to where the water will be released,” Williamson said.
A similar diversion was used for a short time in April for a different reason: a blizzard downed some large electrical distribution lines near Oahe Dam.
That meant there was no way to transmit all the power coming from the seven turbines.
So some of the turbines were shut down while the commensurate amount of water was released through the regulating tunnels on the west end of the dam into the stilling basin, Williamson said.
As of Wednesday, Aug. 22, Lake Oahe was at 1,616.4 feet above sea level, which is down 0.3 feet from the previous week and 0.6 feet below the “exclusive flood control zone,” at the top of the reservoir which extends from 1,617 to 1,620 feet above sea level.
All the big reservoirs in the Upper Missouri are now below the exclusive flood control zone, showing the ongoing drop in what has been a season of the second-highest runoff in recorded history.
The highest runoff was in 2011 when big floods devastated the Upper Basin, including Pierre and Fort Pierre.
Releases from Gavins Point Dam, the “bottom” dam in the Upper Basin and sort of the “plug” to the whole system of stored water behind six mainstem dams, will remain at 70,000 cfs into September to keep lowering the water levels in the system, Corps officials said Thursday in their weekly briefing.