RIVERDALE, ND – Releases from Garrison Dam have been reduced to a rate of 54,000 cfs and will drop to 50,000 cfs this Thursday. After a month at 60,000 cfs, releases were reduced to 57,000 cfs on July 24.
The reduced releases have already translated to a lowered river stage at Bismarck, which is now 12.35 feet about 6 inches lower than last week.
The gage at Bismarck peaked at a stage of 13.4 feet on June 29, which is approximately 1 foot below flood stage. Rapid mountain snowmelt in June coupled with heavy rains in Montana and northern Wyoming, would have caused much higher stages in Bismarck without Garrison Dam capturing that runoff. Instead of a peak of 13.4 feet on June 29, the river rise would have begun in late March hovering above flood stage through late June with a peak stage of 19.2 feet.
“This has been a high runoff year,” said John Remus, Chief of the Missouri River Basin Water Management Division. “For the month of June, more than 6 million acre feet of water flowed into Lake Sakakawea and more than 5 million acre feet of that came from tributaries such as the Yellowstone River. That’s nearly twice what we see on average.”
July 12 marked the last day pool elevations on Lake Sakakawea at Garrison Dam in North Dakota rose. Since then, the reservoir has been gradually declining by a little more than an inch a day. The pool elevation peaked on July 7 at 1853.16 feet, still more than 1 ½ feet below the peak elevation in 2011.
The project intends to transition flows from the regulating tunnels to the spillway early next month. Flows through the spillway will be less than 10,000 cfs. In preparation, crews are removing logs and debris from the approach channel and off the embankment.
“Right now, we’re clearing debris to avoid project damages and to keep it from making its way downstream. Using the spillway will allow us to inspect the regulating tunnels and gates as well as test repairs we made following the flooding in 2011,” said Todd Lindquist, Operations Project Manager at Garrison Dam.
A date for the transition to spillway flows will be announced soon.
“Once we pin down the date, we will invite the public to view the opening of the spillway gates. I think it’s an opportunity for people to understand how we operate the dam and that spillway flows don’t necessarily equate to flooding or require an emergency,” said Lindquist.
“We still have to lower the pool elevation about 14 feet before the lake and river ices in. We release water year round, but by December, our releases are restricted by the capacity of the iced over river channel and are rarely more than 20,000 cfs,” he added.