Silver L
ake is located just off Highway 88 at an elevation of about 7,250 feet in Amador County and is part of EID’s Federal Energy Regulatory Commission (FERC) licensed Project 184 hydroelectric project.
EID’s hydroelectric division was established in 1999 when PG&E transferred ownership of a 20-megawatt powerhouse to EID. Along with the transfer came 15,080 acre-feet of water rights from the South Fork American River and from water that is stored and released from four high-Sierra lakes and reservoirs, including Silver Lake.
Under the terms of EID’s 40-year license for Project 184, EID is required to meet conditions that dictate project operations, dam safety, resource monitoring, restoration measures, and recreation facility improvements and maintenance. In the spring of 2015, EID staff discovered a small sinkhole in the Silver Lake Dam. Repairing this facility is an important condition for long-term safety as well as a requirement under the license terms.
The small sinkhole brought the long-term reliability of the dam into question. In response, the California Division of Safety of Dams (DSOD) temporarily restricted the reservoir level, and EID crews quickly made repairs and initiated a geotechnical investigation.
Investigations indicate the likely cause of the sinkhole is voids inside the dam caused by rotting interior logs that were part of the original 1876 rock-and-soil-filled timber crib structure.
In addition, the upstream gunite face of Silver Lake Dam is at the end of its useful life and is no longer reliable. Gunite is a mixture of cement, sand, and water that is applied through a pressure hose.
The project will need to undergo a progression of design and environmental activities over the next several years. At FERC’s request, the District submitted a preliminary project schedule that estimates construction occurring in 2027. Contractors for the District recently completed drilling and seismic refraction surveys to better understand foundation conditions and support the next phases of design. In 2023, staff plans to complete reservoir sediment depth probing (to define the extent of sediment removal needed to dewater the dam during construction), reach 30 percent design status, initiate public outreach, and begin environmental reviews.
Replacing a dam, no matter the size, is a significant undertaking. The project will require compliance with the California Environmental Quality Act (CEQA) and the National Environmental Policy Act (NEPA), a FERC License Amendment, and will require various federal, state, and local permits.
The District plans to initiate proactive outreach efforts to engage agencies and interested stakeholders early in the design process. Costs for replacement have not been determined at this time and will be estimated and updated as design and environmental permitting progresses. The District will pursue grant funding for this required project and expects any balance will come from bond sales.
If you have questions regarding this project, email SilverLakeDam@EID.org.
