Hebgen Dam – Cellular Cofferdam

Design-build emergency deep intake structure to stabilize failed intake structure in the environmentally sensitive headwaters of the Madison River at the Hebgen Reservoir. Involved construction of closed cell cofferdam and tensioned rock anchors. 36-in diameter shafts installed 20-ft into bedrock at a water depth up to 35-ft. Concrete tremie seal utilized to stabilize rock between existing intake. 1,350 cubic yard tremie concrete poured in water depths up to 60-ft. Circular cells spaced 58-ft in diameter 70-ft centers using sheet pile between 80 and 85-ft.