Isabella Dam construction project lauded by national award

The United States Army Corps of Engineers received a national award for safety, innovation and resourcefulness for its design and execution of the reconstruction of the Isabella Dam complex, according to a press release from the Army Corps.

The $650-million project that succeeded in taking Isabella Dam off the Army Corps’ list as one of the nation’s “highest-risk dams,” received the National Academy of Construction’s 2024 Recognition of Special Achievement Award.

The award considers planning, engineering and solving design challenges among international practitioners in the engineering, design and construction industries, according to the release.

Isabella Dam had been considered at significant risk for failure or overtopping prior to the safety modification project, which raised the main and auxiliary dams 16 feet and created a new emergency spillway with an iconic “labyrinth weir.” The project, according to the release, greatly lowered flood risk for the more than 400,000 people living downstream of the dam, which was originally built in 1953.

“From conception through completion, the project delivery team displayed the USACE ethos, developing creative and innovative solutions to solve significant challenges without sacrificing project schedule, budget, and, most importantly, safety,” Chief of Engineers and Army Corps Commanding General Lt. Gen. Scott Spellmon was quoted in the release.

The labyrinth weir alone was a unique solution, increasing the amount of water that could be safely released from a relatively narrow space using a three-story tall zig-zagging configuration built in a roughly 1,300-foot opening. If straightened out, the weir would be about 3,000 feet long.

To construct the new spillway, contractors had to blast out three million cubic yards of rock that was then crushed onsite for use in the two dams, saving time, money and emissions.

Even with 2.6 million working hours, the project didn’t incur any significant accidents or injuries, according to the release.

The project was completed in October 2022, just a few months before California’s epic 2023 winter brought hundreds of thousand of acre feet of water rushing out of the mountains filling Lake Isabella to the brim for the first time in years.