Klamath River Renewal Project - Design of Dam Modification for Reservoir Drawdown, River Diversion and Dam Removal of the Copco No. 1 Dam
Authors: Benoit Otis1, Carlo Capucao1
Conference: CDA 2025 Annual Conference and Trade Show
Date: September 28 - October 1, 2025
1 Knight Piesold Ltd., Vancouver, BC, Canada
ABSTRACT
The Copco No. 1 Dam, a former dam on the Klamath River in California, was removed in 2024. The 38.4 m high concrete arch-gravity dam with a gated overflow spillway retained a 50 million m3 reservoir. Reservoir drawdown and temporary river diversion were required to evacuate the reservoir, release accumulated sediment and to allow removal of the concrete dam and foundation below the original river grade.
The pre drawdown activities required the construction of a new low-level outlet consisting of a 3.2 m D-shaped tunnel section with an outlet conduit and reopening of the existing diversion tunnel. The outlet works were sized to provide sufficient discharge capacity to evacuate the reservoir and divert the river in conditions up to the 5% probable monthly flood. The pre drawdown work was completed while the hydroelectric facility was in operation.
The design phase and construction of the project required evaluation of various reservoir outlet alternative layouts. The selection of the preferred arrangement was made based on reducing construction costs and schedule risks.
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