- Location: Lakeside, California
- Owner: San Diego County Water Authority
- Engineer(s): MWH Americas, Inc.
- Contract Type: Fixed Unit Price (competitive bid)
- Status: Completed
To double the holding capacity of the San Vicente Dam by adding height, the San Diego County Water Authority launched a multi-phase project, beginning with its Foundation Preparatory Work Project. Before the existing 220-foot-tall dam could be raised 117 feet over the next several years the dam had to be prepared. One of SDCWA's main challenges was construction of a 13-foot-diameter tunnel through the existing dam to allow for installation of large-diameter steel pipe for the future Low Level Outlet Works without lowering the reservoir pool elevation. This required installation of a 111-foot-tall semicircular cofferdam on the dam's upstream face to facilitate the tunnel through the dam.
Installation of this steel structure presented many technical and logistical challenges. Thorough planning and exceptional communication by all stakeholders at all levels allowed this work to be accomplished with very few issues. By utilizing a lifting structure on the dam crest with hydraulic strand-jacks to hold and lift the cofferdam as it was constructed, the amount of work performed in the wet was minimized. Once fully erected, the jacking system was able to tilt the cofferdam to match the dam's upstream batter and move it into place for final connection and sealing by the dive team.