El Dorado Irrigation District Forebay Dam Modification

Pollock Pines, CA

The Forebay Dam and Reservoir is an off-stream reservoir located on the westward side of the Sierra Nevada’s that regulates water for drinking and hydroelectric power purposes. Operated by El Dorado Irrigation District the dam was originally constructed in 1923 and is a key part of the El Dorado Hydroelectric Project 184. The El Dorado Dam Modification Project brought this centenarian dam up to current dam safety standards. The primary improvements were the construction of an earthen stability buttress on the downstream face that both strengthened the dam and increases its water storage capacity. It consisted 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 phase, work consisted of constructing the lower portion of the earthen stability buttress. Other work completed during that phase included repairing the unstable reservoir inlet and installing water control gates at the power and water supply intake structures as well as repair of the existing penstock and abandonment of the other penstock.

 

The third phase, which occurred in 2019, included the final construction of the buttress, raising the dam crest by 10 feet, and improving the emergency spillway to prevent erosion and compensating for the new dam crest elevation. Additional benefits include improved reliability and availability of water supply, safety, accessibility enhancements, and improvements of roadways and trails.

 

MCK provided Project Controls, Cost Estimating, Office Administration, Inspection, Cost Estimating and Scheduling services. The $20M project was completed in 2020.