History will be made today when for the first time ever the U.S. Army Corps of Engineers raises Garrison Dam spillway gates to help relieve a massive amount of water in Lake Sakakawea behind the dam.
The lake level is less than 1 foot from overtopping the spillway and the corps will raise about half the 28 gates to control the flow and equalize output between the regulatory tunnels on the west side of the dam and the spillway on the east side, said Lake Sakakawea manager Linda Phelps.
The corps planned to raise the gates at 8 a.m., about 1 foot. It will release about 15,000 cubic feet per second down the massive spillway apron, into the spillway pond far below and through an outlet channel out to the Missouri River.
Because the corps doesn't know exactly where the spillway water will flow, or how high it will get before the channel kicks into full running capacity, some precautionary measures are being taken to protect the public, Phelps said.
"It will back up until it opens the pilot channel," she said. "We don't think it will go into the campground, but we're not exactly sure where the water will go."
The corps closed its downstream campground Tuesday.
In addition, the west tailrace access road is closed, along with the road to the campground and to the spillway pond recreation area.
The public can still use the east and west diagonal roads on the downstream side of the dam, but there will be no access to points farther downstream from there for the duration, Phelps said.
She said the corps wants to accommodate a huge public interest in seeing the dam, itself a manmade engineering wonder and the focal point as the corps releases record amounts of water out of Lake Sakakawea into the Missouri River, causing massive downstream flooding.
Phelps said safety is first, however, and access will be restored once the outcome of the spillway release is better defined.
She said people have been walking around road closed signs and have been down on the rocks at the tailrace, where 85,000 cfs of water is pounding past. Some rocks have slipped there and it's imperative the public stay clear, she said. Tickets will be issued to people ignoring road closed signs.
The corps had to close a pullout on the east end of the dam Sunday because cars were pulled in four to five deep, she said.
The spillway gates will gradually be raised to increase the flow, until it reaches about 65,000 cfs. That will be in addition to the 85,000 cfs from the power house and regulatory tunnels.
By mid-June, the two release systems will be sending 150,000 cfs into the Missouri River, and will remain at that level well into July, or longer.