Klamath River Renewal Project - Optimization of the Iron Gate Dam Historic Diversion Tunnel Using CFD Analysis to Support Reservoir Drawdown
Authors: Carlo Capucao1, Katrina Wechselberger1
Conference: CDA 2025 Annual Conference and Trade Show
Date: September 29 - October 1, 2025
1 Knight Piesold Ltd., Vancouver, BC, Canada
ABSTRACT
The Iron Gate Dam was the most downstream of four hydroelectric facilities on the Klamath River that were decommissioned in 2023 and 2024. The 58,000 acre-ft (71.5 km2-m) reservoir was retained by a 173-foot (52.7-metre) high embankment dam with an ungated overflow spillway. A near complete drawdown of the reservoir through the historic diversion channel was required prior to embankment removal.
Design of pre-drawdown modifications in the diversion tunnel had the following primary objectives:
- Achieve adequate discharge capacity to facilitate the reservoir drawdown during the limited winter and spring months of the drawdown year, and
- Optimize the hydraulic performance and energy dissipating properties of the tunnel to safely operate under full reservoir head and maximum flows
Accurate representation of the irregular unlined rock geometry in lieu of typical cross sections with a generic roughness was fundamental to understanding the inherent in situ energy dissipating qualities of the tunnel and facilitated the decision to eliminate expensive design features such as a stilling basin, new full diameter gate and extensive new liner system. Additional design concepts aided by the CFD analysis included air ventilation, gate downpull forces and the discharge rating curve for a complex and variable tunnel geometry.
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