The Klamath River Renewal Project, the largest dam removal and river restoration project in US history, involved the removal of four hydroelectric dams along the Klamath River in Oregon and California to restore volitional fish passage to historic habitat and spawning grounds. Knight Piésold (KP), as the lead designer for the prime contractor Kiewit Infrastructure West Co. (Kiewit), developed innovative designs for safe dam decommissioning under a progressive design-build contract with the owner Klamath River Renewal Corporation (KRRC).

KP developed comprehensive solutions for safely decommissioning four aging hydroelectric dams: J.C. Boyle, Copco No. 1, Copco No. 2, and Iron Gate. The work included designing construction access routes, reservoir drawdown using new or refurbished low-level outlets, developing staged removal for dams and ancillary facilities, creating on-site material disposal strategies, and designing erosion protection for the restored river channel through the former dam sites.

KRRC, a nonprofit organization established under the amended Klamath Hydroelectric Settlement Agreement (KHSA), led the effort to re-establish the Klamath River’s natural vitality. Signatories of the KHSA included state and local governments, Tribal Nations, the former dam owner, irrigators, and conservation groups.

The project’s Environmental Impact Statement mandated removing all dams in the same year, with reservoirs drawn down during the preceding winter to minimize impacts on downstream aquatic species. For dam safety reasons, the two earthfill embankment dams (J.C. Boyle and Iron Gate) had to be removed during the low-flow summer season to minimize the risk of overtopping flows during removal.

The reservoir drawdowns were successfully executed in January 2024, the dams were removed in the summer of 2024, reconnecting over 400 stream-miles of salmon habitat, and salmon was observed migrating up the reopened river channel in the autumn of 2024.

KP designed a safe, effective way to drain the reservoirs during the winter season, using a combination of historic low-level conveyance structures, where feasible, or developing new low-level outlets, where needed. At Iron Gate, the historic diversion tunnel used during dam construction was retrofitted with energy dissipation and venting. For Copco No. 1, a new low-level outlet was designed through the concrete arch dam using progressive blasting and a “lake tap” technique.

With the oldest dam over 100 years old, the project faced unanticipated challenges due to unknown conditions of the aging facilities. KP was able to adapt the designs and provide timely guidance to address issues such as unconsolidated material beneath tunnel slabs, unexpected dam material composition, and fractured bedrock in access road areas.

A flexible dam removal staging plan was developed that considered seasonal hydrologic conditions. This plan was updated during the removal year based on actual conditions and coordination with upstream dam regulators, allowing for earlier and more efficient dam removal while ensuring safety and minimizing environmental impacts. This allowed the dam removals to begin earlier and be completed in advance of the start of the annual salmon run.

The Klamath River Renewal Project has successfully restored over 400 stream-miles of salmon habitat, with adult chinook salmon returning within weeks of dam removal. The project’s legacy lies in the restoration of a vital river system, benefiting local communities, including Native American tribes, and promoting the sustainability and resilience of both the hydroelectric industry and the ecosystems it impacts. The project provides a blueprint for future decommissioning efforts.