El Dorado Forebay Dam Modifications
El Dorado Forebay Dam is a 100-feet-high earthfill dam constructed in 1923 and owned and operated by the El Dorado Irrigation District (EID). The dam is under the regulatory authority of the California Department of Water Resources (DWR), Division of Safety of Dams (DSOD) and the Federal Energy Regulatory Commission (FERC).
The regulatory agencies required EID to review the stability of the dam. GEI assisted by performing a series of technical investigations and studies, which indicated that dam stability improvements were required to address safety concerns. The concerns related to seismic stability, seepage, and potential overtopping issues, all potential risks to downstream residents’ lives and properties in the event of an earthquake or major storm.
EID and GEI worked with DSOD and FERC to determine the engineering design and extent of the modifications needed to achieve the necessary stability requirements. Additionally, EID proposed raising the dam to increase the water storage capacity, improving the reservoir’s efficiency for local water supply and hydroelectric power generation.
The El Dorado Forebay Dam modifications benefited the community by enhancing safety, increasing water storage capacity, and improving environmental protection. By addressing seismic stability, seepage, and overtopping risks, the project significantly reduced the likelihood of dam failure and flooding, ensuring the safety of downstream communities.
In addition, the increased water storage provided more reliable access to water for households, agriculture, and hydroelectric power generation, supporting local economic stability and resource management. These improvements also safeguarded the environment from potential damage, while boosting the region’s resilience to droughts and natural disasters.
GEI provided analysis, design engineering, construction management, and engineering services for the construction phase of this project. The project included:
– an analysis to determine the dam’s stability
– supporting analysis to develop plans and specifications for a new downstream stability berm to enhance the structural integrity of the dam,
– modifications to the spillway to increase the storage
– raising the dam by 10 feet,
– improvements to the existing inlet canal
– a new seepage pump-back station
– relocation and upgrade of the irrigation canal inlet for domestic water supply
– abandoning two existing penstocks through the dam embankment
– refurbishing the existing penstock to EIDs power plant
– improvements to the existing emergency spillway, and
– harvesting and site clearing of approximately 54 acres of timber to create a borrow site providing for construction areas and site access.
