Santiago Creek Dam Improvement Project

The Santiago Creek Dam Improvement Project, managed by the Irvine Ranch Water District, involves a comprehensive rehabilitation and replacement of the dam's outlet tower and spillway facilities to enhance long-term water resource benefits. Located at the northwest end of Irvine Lake in unincorporated Orange County, California, the project scope includes the construction of new inlet and outlet works, such as an inclined structure, intake riser pipelines, a bifurcation valve vault, and emergency outlet systems. The existing spillway will be replaced with a new side-channel spillway and raised by six feet to an elevation of approximately 797.9 feet. This elevation increase is designed to allow for year-round water impoundment, providing an additional storage capacity of approximately 1,600 acre-feet. Additional infrastructure improvements include the modification of the dam embankment through the installation of a filter drain system, widening and raising the dam crest by up to one foot, and the relocation and upsizing of a portion of the Irvine Lake pipeline to a below-ground position beneath the new spillway. Ancillary site developments will feature a new dam control building, a spillway bridge, an inlet/outlet access roadway, and emergency access walkways and stairs. The project received formal approval on November 10, 2025, following the preparation of an Environmental Impact Report, with the Notice of Determination filed with the Orange County Clerk-Recorder on November 12, 2025.