The U.S. Army Corps of Engineers recently informed state officials that they have determined the Snake Creek embankment — an earthen dam that's over 2 miles long — separating Lake Sakakawea and Lake Audubon could fail during times of severe drought in the Missouri River basin.
Lake Audubon, located 8 miles northeast of Riverdale, N.D., is a potential source of Missouri River water for the Red River Valley Water Supply Project, which would make supplemental water available to central and eastern North Dakota.
The safety problem could arise when the level of Lake Sakakawea, the reservoir of Garrison Dam, is significantly lower than the level of adjacent Lake Audubon, the water source for the McClusky Canal, a feature of the now-defunct Garrison Diversion project, which was designed to use Missouri River water to irrigate farmland in eastern North Dakota.
The Garrison Diversion Conservancy District, which manages the Red River Water Supply Project, is considering using Lake Audubon water, which is the most cost-effective way to deliver water to the east for drought relief.
Duane DeKrey, general manager of the Garrison Diversion Conservancy District, said the embankment concerns and the implications for the water supply project raise "quite a few questions for us."
The long embankment dividing Lake Sakakawea and Lake Audubon is topped by U.S. Highway 83, which connects Bismarck and Minot, as well as railroad tracks and a power line.
To prevent a dangerous difference in the lake levels — when Audubon is 43 feet or more higher than Sakakawea — the corps would pump water from Lake Audubon into Lake Sakakawea.
"Our primary focus is always going to be in preserving the embankment," said Matt Nelson, a hydraulic engineer for the corps in Omaha, Neb.
But North Dakota officials worry that could draw down Lake Audubon so far that it would be unable to provide water for irrigation and for the McClusky Canal, which would connect with a pipeline to take the water to eastern North Dakota.
It's possible that a severe drought in the Missouri River basin could coincide with a severe drought in the Red River basin, when the water supply project would be needed, DeKrey said.
Garrison Diversion has hired a consulting engineer to determine how much water Lake Audubon must hold to ensure water delivery to the Red River Valley Water Supply Project.
If the embankment were to fail, Lake Audubon would no longer exist, and would be unable to supply water or serve any of its other authorized uses, including provide water for fish and wildlife, recreation and irrigation, Nelson said.
"We want to be able to continue to provide those authorized purposes for many years beyond the drought," he said.
The corps will hold public meetings Tuesday, June 27, in Garrison and Wednesday, June 28, in Bismarck to discuss the Snake Creek embankment failure risk, its plan to preserve the embankment, and to invite public comment.
The embankment vulnerability was discovered during an extended Missouri River drought from 2000 to 2009. During 2005, Lake Sakakawea was 41 feet lower than Lake Audubon.
Engineers with the corps have determined that serious seepage problems could result when Lake Audubon is 43 feet higher than Lake Sakakawea. The concern is that, under certain conditions, the seepage could result in erosion that could cause the embankment to collapse.
That would pose a risk to anyone on the embankment, including motorists traveling on Highway 83, said Ross Cullin, a dam safety engineer for the corps.
"There's certainly life safety risks when you're talking about any dam failure," he said.
Using Lake Audubon water and the McClusky Canal would require permission from the U.S. Bureau of Reclamation, and Garrison Diversion officials have been in discussion with the bureau.
Other options for providing Missouri River water for the Red River Water Supply Project include building pumps near Washburn, N.D. Building the pumps or collector wells would add $171 million to the cost of the project, estimated to cost $1 billion, DeKrey said.
Drawing water near Washburn also would add significantly to operating costs, he said, because pumps would have to push water more than 300 feet uphill.
DeKrey said the corps should fix the Snake Creek embankment. Crude estimates of the cost of fixing the embankment range up to about $100 million, but the corps has not yet determined if any of those options should be pursued, Nelson said.
Ryan Bernstein, chief of staff for Sen. John Hoeven, R-N.D., said the corps should "consider all impacts if they do anything to the embankment," including the Red River Water Supply Project, while also continuing all of Lake Audubon's authorized uses.
Lt. Gov. Brent Sanford said the complications posed by the Snake Creek embankment present the latest obstacle in North Dakota's decades-long quest to transfer Missouri River water to the east.
The Garrison Diversion project, authorized by Congress and an outgrowth of the 1944 Pick-Sloan Flood Control Act, was scrapped after decades of controversy over environmental and economic objections to the project.
The former Garrison Diversion project ultimately evolved into the Red River Water Supply Project. The North Dakota Legislature has appropriated $30 million for the project, including design studies and money to allow construction to start.
Sanford is "very optimistic" that a solution will be found to the Snake Creek embankment problem. He cited Trump administration officials' eagerness to eliminate burdensome regulations and to move approved projects to completion.
"Maybe we can have a productive conversation with the federal government," he said.
If you go
What: Public meetings to discuss interim measures to reduce dam safety risks at the Snake Creek embankment, which runs under U.S. Highway 83 and impounds Lake Audubon, located 8 miles northeast of Riverdale, N.D. The U.S. Army Corps of Engineers is conducting the meetings.
When and where:
— 6 to 8 p.m. Tuesday, June 27, City Auditorium, 32 S. Main St., Garrison, N.D.
— 6 to 8 p.m. Wednesday, June 28, Ramkota Hotel and Conference Center, 800 S. Third St., Bismarck, N.D.
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