Columbia-Pacific Northwest Region

Conconully Safety of Dams Modification Project Environmental Assessment

Aerial View of Conconully Dam, Okanogan Project, Washington

As part of its Safety of Dams program mission, Reclamation is committed to ensuring its dams do not present unacceptable risk levels to people, property, and the environment. Conconully Dam was constructed between 1907 and 1910 using hydraulic fill methods and is performing as designed; however, the resulting puddled-core embankment is currently known to be susceptible to liquefaction and increased risk of failure in the event of significant seismic activity. To comply with Reclamation's Safety of Dams requirements and bring static and hydrologic risks at Conconully Dam below Public Protection Guidelines, Reclamation needs to improve control of water flows through the outlet works and increase the reliability and longevity of the dam and water conveyance system. The purpose of the Conconully Safety of Dams Modification project is to reduce the seismic risks of dam failure, provide water deliveries and flows for irrigators and endangered species, and maintain additional benefits for recreation and fish and wildlife habitat.

Reclamation proposes to reduce the risk of dam failure by constructing a stability berm on a foundation of deep soil mix reinforcement columns on the downstream face of the dam. To provide improved operational functionality and compatibility with the proposed stability berm, Reclamation also proposes to upgrade the outlet works by extending, lining, and reinforcing water conveyance components and installing contemporary water control systems and facilities (e.g., multiple state-of-the-art valves and valve house). The proposed modifications address issues important to public safety and the long-term functionality of the facilities.

The proposed project will implement cost-effective measures to reduce long-term performance risks per Reclamation’s Public Protection Guidelines; maintain water deliveries and flows for irrigators and endangered species; and continue to provide recreational benefits and fish and wildlife habitat.

Documents

08/2024

Conconully Safety of Dams Modification project News ReleaseHTML