Santiago Creek Dam Improvement Project

Santiago Creek Dam Improvement Project

Santiago Creek Dam was originally constructed in 1933 to store water in Irvine Lake for the benefit of the surrounding communities. The Project proposes to rehabilitate and replace the Santiago Creek Dam outlet tower and spillway facilities and to modify the embankment to permit operation of the facilities for a long-term water resource benefit. The Project includes construction of a new inlet/outlet works, including an inclined inlet/outlet structure, intake riser pipelines and platforms, bifurcation valve vault, emergency outlet pipeline, and emergency outlet valve vault. The existing spillway would be replaced with a new side-channel spillway, and a portion of the Irvine Lake pipeline would be upsized and relocated to belowground beneath the proposed spillway structure. The Project includes improvements to the dam crest, removing the dam face, installing a filter drain system within new embankment shell material, widening the dam crest, raising the elevation of the dam crest by up to one foot, and installing protective railings. Ancillary site improvements are also proposed for the Project, including a new inlet/outlet access roadway, spillway bridge, dam control building, and emergency access walkway and stairs. The Project also includes raising the spillway by six feet to approximately 797.9 feet, which is two feet higher than the existing maximum water storage elevation with the flashboards installed. Raising the spillway would allow the dam to Impound water up to the 797.9-foot elevation contour year-round, which would allow for storage of an additional approximately 1,600 acre-feet of water. Construction work is anticipated to occur over a four-year period of time, assuming downtime associated with weather restrictions, beginning in approximately fall 2027 (exact dates subject to change).

Irvine, Unincorporated area

Orange

Unincorporated

California Air Resources Board (ARB), California Department of Conservation (DOC), California Department of Fish and Wildlife, South Coast Region 5 (CDFW), California Department of Forestry and Fire Protection (CAL FIRE), California Department of Parks and Recreation, California Department of Toxic Substances Control (DTSC), California Department of Transportation, District 12 (DOT), California Department of Water Resources (DWR), California Fish and Game Commission (CDFGC), California Governor's Office of Emergency Services (OES), California Highway Patrol (CHP), California Native American Heritage Commission (NAHC), California Natural Resources Agency, California Regional Water Quality Control Board, Lahontan Victorville Region 6 (RWQCB), California State Lands Commission (SLC), Office of Historic Preservation, San Gabriel and Lower Los Angeles Rivers and Mountains Conservancy (RMC), State Water Resources Control Board, Division of Drinking Water, State Water Resources Control Board, Division of Drinking Water, District 8, State Water Resources Control Board, Division of Water Quality, State Water Resources Control Board, Division of Water Rights, State Water Resources Control Board, Divison of Financial Assistance, University of California Natural Reserve System (UCNRS)

Water Facilities (Dam improvements)(Type Dam & reservoir, MGD 22.3)

Project approval

Aesthetics, Agriculture and Forestry Resources, Air Quality, Biological Resources, Cultural Resources, Cumulative Effects, Drainage/Absorption, Energy, Flood Plain/Flooding, Geology/Soils, Greenhouse Gas Emissions, Growth Inducement, Hazards & Hazardous Materials, Hydrology/Water Quality, Land Use/Planning, Mandatory Findings of Significance, Mineral Resources, Noise, Population/Housing, Public Services, Recreation, Schools/Universities, Septic System, Sewer Capacity, Solid Waste, Transportation, Tribal Cultural Resources, Utilities/Service Systems, Vegetation, Wetland/Riparian, Wildfire