Kachess Dam Safety of Dams Modification Project Environmental Assessment
Project Overview
Aerial photograph of Kachess Dam and Reservoir taken by Reclamation.
Project Overview
Kachess Dam, located about 14 miles northwest of Cle Elum, Wash., was constructed from 1910 to 1912. It was one of the first dams constructed by the U.S. Reclamation Service and increased the storage capacity of a large natural lake. The 115-foot-high, earth-filled Kachess Dam created a reservoir with an actively managed capacity of 239,000 acre-feet.
Reclamation has identified seepage and internal erosion issues through the dam embankment along the outlet works conduit, which conveys water from the reservoir to the Kachess River downstream. In other words, water seeping through the dam embankment and the soils surrounding the conduit is carrying soil materials with it and leaving behind voids. This “internal erosion” creates a risk of potential dam failure. Reclamation is proposing this project to filter and monitor the seepage so as to prevent eroded soils from exiting the dam.
Purpose and Need
The purpose and need of the proposed project include:
1) Implement cost effective measures to reduce risks per Reclamation’s Public Protection Guidelines.
2) Maintain water deliveries to irrigation districts, Tribes, and others throughout the Yakima Basin.
3) Minimize impacts to the environment.
4) Maintain water flows for endangered species.
Reclamation is committed to ensuring its dams do not present unacceptable risk levels to people, property, and the environment as part of its Safety of Dams program mission. These requirements result in a need for Reclamation to implement corrective action to bring static and hydrologic risks at Kachess Dam below public protection guidelines while minimizing impacts to the environment.
Project Overview Map
Proposed Action
Reclamation proposes to reduce the risk by performing the following improvements:
construct an access road, prepare the site, develop staging areas to support construction and long-term maintenance
extend and line the conduit, install filter and stabilization berm.
Reservoir level restrictions are not anticipated to occur, and construction of the extension and lining of the outlet works would be timed to avoid major issues with water deliveries.
Reclamation conducted extensive field surveys to identify any sensitive cultural resources, wildlife habitat, and wetlands located in the proposed project area. The results of these surveys will inform the project designs to avoid, minimize, or mitigate resource impacts.
For further information
For more information on the Kachess Dam Safety of Dams modification project environmental assessment, please contact Candace McKinley, supervisory environmental protection specialist at BOR-SHA-KSODNEPA@usbr.gov.
To be added or removed from the mailing list, please contact Alli Yamnitsky at alli.yamnitsky@empsi.com.
Information also is available on Reclamation’s Kachess Dam Safety of Dams modification project environmental assessment website.