Santiago Creek Dam Outlet Tower and Spillway Improvements Project


SCH Number
Lead Agency
Irvine Ranch Water District
Document Title
Santiago Creek Dam Outlet Tower and Spillway Improvements Project
Document Type
NOP - Notice of Preparation of a Draft EIR
Present Land Use
The Project site has a General Plan designation of Open Space and has a consistent zoning designation of OS FP-2 (Open Space).
Document Description
The proposed Project is located at Santiago Creek Dam at the northwest end of Irvine Lake in unincorporated Orange County, California. Santiago Creek Dam impounds Irvine Lake. The proposed Project is located south of State Route (SR) 261 and east of SR-241 and Santiago Canyon Road. Existing structures include the dam, outlet tower in Irvine Lake, spillway channel, flashboard storage shed, control house/outlet works, energy dissipater structure, Irvine Lake pipeline (ILP), and dam access road. The Project proposes to construct a new inclined inlet/outlet structure located on the left abutment of the dam. Inlet/Outlet works would be configured to incorporate the new structure, including new valves and fittings. The ILP would be upsized and relocated underneath the proposed spillway structure. The existing spillway would be replaced with a new side-channel spillway at the left abutment. Ancillary site improvements are also proposed for the Project, including a new access road and ramp to provide vehicle access to the new inclined/outlet structure; a new control building to house the pneumatic actuation system for the submerged butterfly valves; widening of the existing dam crest with a retaining wall system; raising of the dam crest with a concrete parapet wall; a new emergency access walkway and stair system to reach the inclined inlet/outlet structure and dam crest from the adjacent landfill facility during a reservoir spill event; and a new prefabricated truss-type bridge structure across the proposed spillway. The Project also includes raising the spillway 6 feet to 797.9 feet, which is 2 feet higher than the existing maximum water storage elevation with the flashboards installed. Raising the spillway would allow the dam to impound water to be up to the 797.9-foot elevation contour year-round, which would allow storage of approximately an additional 1,600 acre-feet of water.

Contact Information

Andy Uk
Agency Name
Irvine Ranch Water District
Job Title
Environmental Compliance Analyst
Contact Types
Lead/Public Agency / Project Applicant


Unincorporated Area
Cross Streets
South of SR-261 and East of SR-241 and Santiago Canyon Road
Total Acres
State Highways
John Wayne Airport
Santiago Canyon Community College, Chapman Hills Elementary
Irvine Lake
4S, 5S
3, 4
Other Location Info
Section: 33, 34
Other Information
Base: Blackstar Canyon

Notice of Completion

State Review Period Start
State Review Period End
State Reviewing Agencies
California Air Resources Board (ARB), California Department of Conservation (DOC), California Department of Forestry and Fire Protection (CAL FIRE), California Department of Parks and Recreation, California Department of Transportation, District 12 (DOT), California Department of Transportation, Division of Aeronautics (DOT), California Department of Transportation, Division of Transportation Planning (DOT), California Department of Water Resources (DWR), California Governor's Office of Emergency Services (OES), California Highway Patrol (CHP), California Natural Resources Agency, California Regional Water Quality Control Board, Santa Ana Region 8 (RWQCB), California State Lands Commission (SLC), Department of Toxic Substances Control, Office of Historic Preservation, State Water Resources Control Board, Division of Drinking Water, 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, California Native American Heritage Commission (NAHC), California Department of Fish and Wildlife, South Coast Region 5 (CDFW)
State Reviewing Agency Comments
California Native American Heritage Commission (NAHC), California Department of Fish and Wildlife, South Coast Region 5 (CDFW)
Development Types
Water Facilities (Dam Outlet and Spillway Improvements)(Type Dam , MGD 0.000001)
Local Actions
Site Plan
Project Issues
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
Local Review Period Start
Local Review Period End


Notice of Completion [NOC] Transmittal form
State Comment Letters [Comments from state reviewing agencies]

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