September 21: The Safety of the Garrison Dam
The Garrison Dam, which went into operation in 1955, is the fifth-largest earthen dam in the world. Its construction created Lake Sakakawea. The lake is a popular recreation destination for fishing, boating, camping, and hiking with three state parks and an Audubon National Wildlife Refuge located along its shoreline.
Lake Sakakawea covers 307,000 acres. At 178 miles long, it is the second-largest manmade lake in the United States. The deepest point is 180 feet with an average depth of 42 feet. The surface area of the lake is over 350,000 acres. Garrison Dam holds back trillions of gallons of water.
Concerns about the safety of the dam have surfaced over the years. A failure of the dam would be catastrophic. According to Jeff Greenwald, project manager for a dam safety study, North Dakota cities, including the capitol of Bismarck, would see significant damage. Bridges and roads would be washed away and twelve states would be impacted.
On this date in 1962, Lieutenant Colonel Thomas Barry of the Army Corps of Engineers addressed rumors of a leak at the dam. He reassured downstream residents that the dam was safe. He said the rumors of a leak were prompted by some minor work being done on the spillway.
Concerns resurfaced in 2011 when a Missouri River flood exposed weaknesses in the spillway. Flows more than twice the previous record were reached as 150,000 cubic feet per second passed through the spillway. An inspection of the dam following the flood revealed a potential risk. The rushing water had peeled away one of twenty-eight manhole covers, allowing water to enter a drainage system designed to collect seepage and prevent frost damage. It was not designed to handle rushing flood water.
In a response to the 2011 flood, the Army Corps of Engineers initiated a study to identify potential problems in the dam and devise solutions. The study identified improvements that could be made in the spillway to avoid problems posed by severe storms. Jeff Greenwald, the lead planner on the project, said that when it comes to managing risk at an Army Corps of Engineers dam, “Public safety really is the number one priority, and we take that very seriously.”
Dakota Datebook by Carole Butcher
- Bismarck Historical Society. “It Happened in Bismarck.” http://www.bismarckhistory.org/ithappenedinbismarck/september/ Accessed 8/6/2023.
- World Atlas. “Lake Sakakawea.” https://www.worldatlas.com/lakes/lake-sakakawea.html Accessed 8/6/2023.
- Friends of Lake Sakakawea. “Study finds flaw in Garrison Dam spillway.” https://lakesakakawea.com/study-finds-flaw-in-garrison-dam-spillway-corps-evaluating-repair-options-assures-flaw-poses-low-risk-to-downstream-cities/ Accessed 8/6/2023.
- A-Z Animals. “Lake Sakakawea.” https://a-z-animals.com/blog/lake-sakakawea-fishing-size-depth-and-more/ Accessed 8/6/2023.
- KFYR-TV. “Army Corps of Engineers study looking at possible Garrison Dam updates.” https://www.kfyrtv.com/2022/06/03/army-corps-engineers-study-looking-possible-garrison-dam-updates/ Accessed 8/6/2023.
- Bismarck Tribune. “US Army Corps of Engineers chooses plan for updating Garrison Dam spillway.” https://bismarcktribune.com/news/state-and-regional/corps-of-engineers-chooses-plan-for-updating-garrison-dam-spillway/article_89ac8e68-b920-11ed-a863-6351e4f6e6e5.html Accessed 8/6/2023.
- Dickinson Press. “Flaw in Garrison Dam spillway poses low chance of failure that could threaten North Dakota cities.” https://www.thedickinsonpress.com/news/flaw-in-garrison-dam-spillway-poses-low-chance-of-failure-that-could-threaten-north-dakota-cities#:~:text=In%20all%2C%2012%20states%20including%20North%20Dakota%2C%20South,and%20significant%20travel%20and%20commerce%20delays%2C%E2%80%9D%20Greenwald%20said. Accessed 8/6/2023.