Forebay Dam Project

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Background

The El Dorado Forebay Dam and Reservoir (Forebay), constructed in 1923, is a key part of the El Dorado Hydroelectric Project 184. Forebay is an off-stream reservoir that regulates water for drinking water and hydroelectric power purposes.

Water is delivered into Forebay from the South Fork American River and from four upper watershed reservoirs, Caples and Silver Lakes located along Highway 88, and Echo Lake and Lake Aloha near Highway 50. Water is diverted from the South Fork American River at the El Dorado Diversion Dam in Kyburz and conveyed through the 22-mile-long El Dorado Canal. The canal is made up of a series of man-made structures mostly consisting of concrete-lined earthen canal, interspersed with wooden and concrete flumes, tunnels and steel pipe sections. Forebay’s water is utilized for both hydroelectric power generation and water supply. The water supply portion is released from Forebay into EID’s Main Ditch and conveyed about 3 miles to Reservoir 1 where it is treated and distributed to the District’s drinking water system. Water is also conveyed via the penstock to El Dorado Powerhouse and, after flowing through two turbines that can produce up to 21 megawatts of power, returns to the South Fork American River.

Project Description

The El Dorado Forebay Dam Modification Project (Project) will bring the near century-old facility up to current dam safety standards. The primary improvements will be to construct an earthen stability buttress on the downstream face that will both strengthen the dam and increase its water storage capacity. The District has recently completed the design, environmental review, permit and construction bid process. On August 14, 2017, the EID Board of Directors awarded the construction contract to Shimmick Construction.

We anticipate three construction seasons. The first is scheduled to begin mid-September and continue through mid-November 2017. This first season will consist of harvesting timber downstream of the dam, at the reservoir inlet, and in the soil borrow area on EID property located adjacent to Forebay. During the second construction season, scheduled to begin in summer 2018, work will consist of constructing the lower portion of the earthen stability buttress. Other work planned during the 2018 construction season includes repairing the unstable reservoir inlet and installing water control gates at the power and water supply intake structures. This work will require the reservoir to be dewatered October through mid-December of 2018. The third season, scheduled for 2019, will include the final placement of soil for the buttress, raising the dam by 10 feet, and improving the lining of the emergency spillway to prevent erosion. We anticipate the project will be completed in 2019.

Why is the Project Required

Forebay Dam has been well maintained and has performed reliably over its 94-year operating history. While Forebay Dam’s condition still meets the standards applicable at the time of its construction in 1923, dam safety standards have changed and it is necessary for the dam to undergo design and construction improvements. Since 2003, EID has worked with the California Department of Water Resources - Division of Safety of Dams (DSOD) and the Federal Energy Regulatory Commission (FERC) to assess the dam’s condition compared to modern standards, evaluate alternatives for accomplishing the necessary improvements, and develop the detailed plans and specifications to support the required improvements. Extensive environmental reviews and permitting efforts have brought us to this stage to begin this important project.

Community Benefits

Raising the dam not only meets the needed regulatory improvements but will recover lost reservoir storage capacity from 94 years of sediment deposition. Since 1923, Forebay has lost about one third of its original volume capacity. Storage recovered by raising the dam will prevent summer-long draining of the Forebay when water supply demands and the need to have standby water supply for fire suppression are highest. 

Benefits also include:

  • Improved availability and reliability of water supply from Forebay
  • A safer dam that meets all modern safety standards
  • Grading, paving and accessibility improvements to the Forebay day use area
  • Realignment and improvement to the walking trail along the north side of Forebay Reservoir near Forebay Road
  • Potential revenue to local businesses by workers utilizing food, lodging and other services during project construction

Frequently Asked Questions

What will the reservoir level be during the construction? The reservoir level is expected to be near normal levels throughout the construction period except for a three month period, during the fall of 2018, when the reservoir must be completely drawn-down to perform work within the reservoir bed.

What will the reservoir level be after construction? After construction and the stabilization is complete, the current water level restriction will be lifted. The dam will safely store and operate with an additional 10 feet of water. Water levels will, as they have in the past, fluctuate according to drinking water needs and hydropower generation.

What parts of the reservoir will be closed-off during the construction? The entire site will be closed for the duration of the construction period due to the level of construction activities that could make for unsafe conditions to the public. EID offers a variety of other recreational opportunities for the public which will not be affected by this Project. The nearest, and largest, is Sly Park Recreation Area (Jenkinson Lake), located approximately five miles south of the Project.

What recreational activities will be allowed after construction? The same opportunities that exist today will continue to be available after construction. The Project includes updating and enhancing the recreation areas along with the restrooms and parking. After construction activities are completed, visitors to Forebay will be able to resume passive recreation such as fishing and picnicking opportunities provided at the reservoir. The Project will not change the current restriction on swimming or boating, which is regulated by the California Department of Public Health because the reservoir serves public drinking water.

Why are there paint marks and colored flags on trees at the Project site? The paint marks and colored flags placed on trees are intended to assist field personnel in identifying area boundaries for various environmental surveys. Paint marks and colored flags are also being placed to identify areas where tree removal is necessary. These areas include, but are not limited to, the borrow area, below the dam, and within the new high water mark of the reservoir.

How will the park benches and trail between the main day use area and fishing access be affected by the new maximum water level? There are currently two park benches located near the shoreline and an informal trail that connects the day use areas near the dam and reservoir inlet that will be inundated at the new maximum water surface level. As a part of the Project, the District will install two new replacement benches and realign the trail to maintain access and recreational use between the two areas.

Will there be any changes to the day use areas? The new maximum water level will bring the shoreline closer to the day use areas. Following completion of construction activities, the day use areas will be reopened. In addition, the main day use area will be updated to meet current American with Disabilities Act (ADA) standards.

Is there any connection between the Project and the recreation property east of Forebay Road? There is no connection between the Forebay Dam Remediation Project and the recreation property located east of the Forebay Road now owned by El Dorado County.


Project Maps

  • E-News: Sign up for eNews and receive periodic updates on this project by e-mail.
  • Phone: Call EID's main line at (530) 622-4513 and ask to speak with a project representative.
  • E-mail: Send a message directly to the Forebay Project representatives at ForebayProject@eid.org.