Innovations & dam safety | USACE tackles ageing dams
The US Army Corps of Engineers is pushing the envelope to address the vulnerabilities of its ageing fleet of dams
Right: Engineers from the Omaha District of the US Army Corps of Engineers, provide a tour to contractors attending an industry day for the Garrison Dam spillway modification project in North Dakota during October 2023 (US Army photo by Delanie Stafford)
Below: Chad Vensel, a hydraulic engineer with the US Army Corps of Engineers, Omaha District, briefs contractors (US Army photo by Delanie Stafford)
Bottom: The multi-year Garrison Dam spillway modification project is considered to be the largest dam safety modification project in US Army Corps of Engineers’ history (US Army photo by Delanie Stafford)
CONTRACTORS FROM TEN CONSTRUCTION and engineering firms attended an industry day at the Garrison Dam in North Dakota at the end of 2023. The industry day was part of early planning efforts for a US Army Corps of Engineers’ multi-year project, considered to be the largest dam safety modification project in USACE history. The project will modernise the dam and reduce risks associated with the spillway’s performance when used to reduce flooding and balance river flows in the Upper Missouri River basin during significant storms or snowmelt.
“The dam, built in the 1950s, was not originally designed for the reservoir elevations and spillway releases that would be expected under today’s conditions,” says Andrew Barry, Chief of the USACE Omaha District’s Dam Safety Production Centre. “Modifying the spillway and other structural work will help ensure the dam and spillway can be operated at the full range of potential flows and continue to reduce the impact of flooding on people and property downstream of the dam.” Concerns with the spillway were identified during dam safety inspections following record runoff into the Upper Missouri River Basin and Lake Sakakawea in 2011. High water levels in Lake Sakakawea required the opening of the dam’s spillway gates for flood risk management purposes for the first time since the dam became operational in 1955. The peak flow of about 60,000 cubic feet per second of water released through the spillway created a high pressurisation of the spillway’s subdrainage system, damaging the system and concrete within the spillway chute. Barry explains that the modifications primarily focus on critical spillway components, including the spillway’s Tainter gates, abutments, areas behind the spillway chute walls, drainage pipes, chute slab and stilling basin. They also include new seepage drains on the embankment near the dam’s powerhouse. “Flooding can still occur, even when a dam performs as it was designed,” he says, adding that while these modifications will improve conditions at the dam, no dam is risk-free and no dam can eliminate flooding.
20 | March 2024 |
www.waterpowermagazine.com
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