The Hell Hole Dam Core Raise Project was a key infrastructure upgrade undertaken by the Placer County Water Agency (PCWA) to increase seasonal water storage and improve dam safety at the Hell Hole Reservoir, located in Placer County’s high Sierra Nevada range. The project raised the dam’s impervious clay core by 10 feet, enhancing its ability to store an additional 8,000 acre-feet of water without increasing the dam’s overall height. The work included the installation of filter and drain zones, upstream and downstream rockfill placement, and in-reservoir excavation and preparation under challenging mountain conditions.
Completed in 2022 by Kiewit Infrastructure West Co., the $42 million project was recognized with ENR California’s Best Project Award in the Water/Environment category. The project earned accolades for excellence in construction execution, environmental compliance, and safety performance. This core raise increases the resiliency of the Middle Fork American River Project, one of PCWA’s most vital hydroelectric and water supply systems, by adapting the reservoir to store additional runoff during wetter winters for use in drier years—supporting both water supply and renewable energy production.
The project was designed to increase water security, improve hydroelectric reliability, and extend the life and utility of existing infrastructure without requiring the construction of new dams. PCWA’s vision integrates long-term sustainability, operational flexibility, and climate resilience by capturing more water when it’s available and reducing the risk of future shortages. The Hell Hole Dam Core Raise aligns with broader regional goals of water conservation, environmental stewardship, and energy efficiency.
- 10-foot vertical clay core raise
- Installation of filter, drain, and transition zones
- Rockfill placement upstream and downstream
- Cofferdam and in-reservoir construction under remote alpine conditions
- Logistics coordination for material and equipment delivery at elevation
Hell Hole Dam is located on the Rubicon River, a tributary of the Middle Fork of the American River in Placer County. The project site lies at high elevation in remote mountain terrain, requiring logistical precision for hauling, staging, and construction. The dam is part of PCWA’s Middle Fork Project, which provides water supply, hydroelectric generation, and recreational opportunities. Its strategic role in Northern California’s water infrastructure makes this upgrade crucial to future water reliability.
- 2020 – Design Finalization
- Summer 2020 – Construction Start
- Fall 2022 – Project Competition
The project maximized the capacity of existing infrastructure while minimizing environmental disruption. By implementing a core raise and structural upgrades to the existing dam, PCWA avoided new dam construction, limited habitat disturbance, and achieved long-term storage gains. The project also supports improved downstream flow management for environmental purposes.
The increased storage capacity ensures more reliable water supply during dry seasons, supports regional agriculture and municipal needs, and enhances renewable hydroelectric generation from the Middle Fork Project. Additionally, the dam improvements reduce flood risk and provide climate resilience for decades to come. The recognition from ENR California underscores the project’s contribution to both regional infrastructure and construction excellence.
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