Dedicated in 1956, the Chief Joseph Dam stretches over one mile in length, possesses a 980-foot spillway, and is the second largest hydropower producing dam in the United States. Traylor Bros., Inc. was awarded the project to build gas abatement spillway deflectors along the entirety of the dam’s spillway. Due to the fact that the work must be executed as far as 50 feet below the water’s surface, a floating, mobile, cofferdam was employed to allow workers the necessary access in a dry environment.
The work included positioning the floating cofferdam at one of the dam’s existing concrete monoliths, dewatering the cofferdam cell, demolition of a portion of concrete, 39,000 linear feet of percussion drilling, constructing concrete forms, and pouring concrete for the spillway deflector. When work was completed at a monolith, the cofferdam was re-immersed and moved to another monolith. This process was carried out at all nineteen monoliths along the entirety of the dam’s spillway.