Improvements at Garrison Dam

RIVERDALE Workers have been busy this summer on improvements to the Garrison Dam spillway and release gates. The gates and spillway below them were subjected to powerful flows during high water in Lake Sakakawea in 2011.

Garrison Dam was completed in 1953. The gates were opened and the spillway subjected to resulting flows for the first time in the dam’s history. The flows hit a record of 150,600 cubic feet per second in the middle of June 2011.

Following the initial release of water through the gates in 2011 a closure was ordered due to a problem with the spillway. After emergency repairs to concrete were made, the gates were opened to allow high water to be released from Lake Sakakawea.

“These are post-flood repairs,” said Todd Lindquist, U.S. Army Corps of Engineers. “We are hydromilling concrete and making a permanent fix on the spillway slab. We’re also making repairs to part of our pressure release system under the slab.”

The pressure release system is designed to combat water pressure building up beneath the spillway. Remote cameras discovered a broken pipe in the pressure releases system following the flood year of 2011. The fix will allow water pressure building up underneath the spillway slab to drain into the river below.

“All of the slab work is expected to be done this year,” said Lindquist.

Work is also being done on the dam’s massive flood control gates, all 28 of them. The gates have the capacity to release 660,000 cfs at maximum operating pool of 1,854 feet. A record level of 1,854.8 feet occurred in 1975. Lake Sakakawea reached 1,854.6 feet on July 1, 2011.

“The gates had never been used prior to 2011,” noted Lindquist. “We’re conducting testing to insure the welds and structural integrity of the gates. We’ll be painting them and replacing seals. Meanwhile, everything remains operational.”

Work on the gates is expected to last into 2015. Crews working on gate improvements will not work on the facility during the winter months, nor during the early part of the spring until the amount of water entering the reservoir can be determined.

“We want the gates to be available in the spring,” said Lindquist.

In additional to spillway gate improvements, a similar project is under way at the three flood tunnels adjacent to the Garrison Dam powerhouse. Those tunnels were used extensively in 2011 and were subject to high capacity flows for an extended period of time.

The five large turbines at the Garrison Dam power plant were recently upgraded. The improvement increased efficiency of the turbines, allowing for 5.3 percent more power generation at peak capacity.

“It all depend on where the turbine is operating. There are gates all the way around the circumference of the turbine,” explained Dale Evenson, power plant manager.

A new electrical switchyard remains under construction near the power plant. When finished, the new switchyard will be capable of handling up to 230,000 volts of electricity. That compares to an approximate maximum of 115,00 volts today.

“Construction coincides with oil development in western North Dakota and the need for increased transmission,” said Lindquist.

No estimated completion date has been announced for the new switchyard. It has been under construction for two years.