Irvine Lake started draining this morning, kicking off a years-long overhaul of the 93-year-old dam that holds it back. Water levels at the reservoir were set to drop from roughly 738 feet to 720 feet starting Monday, Oct. 26, the first visible step in a project that will eventually leave the lake completely empty for construction.
The Santiago Creek Dam, which forms Irvine Lake, was built in 1933, according to the Irvine Ranch Water District. IRWD launched a comprehensive assessment of the then-84-year-old dam back in 2017 and found it was still operational but could be made safer. That review set the stage for the Santiago Creek Dam Improvement Project, which will rebuild the spillway and outlet tower, strengthen the structure to modern standards, and restore 3,700 acre-feet of storage capacity that had been lost over time.
About 300 acre-feet of water is expected to remain in the lake until next summer, when the reservoir will be fully drained for construction, according to the Orange County Register. From there, the newspaper reports construction is expected to take five years, with the lake sitting empty the entire time. CBS News reported the draining got underway this morning, part of what the station described as an upgrade to the 93-year-old reservoir.
Why Orange County Needs This Water Back
Irvine Lake isn’t just scenery off Santiago Canyon Road — it’s a working piece of the region’s water supply. IRWD states that Irvine Lake water, used for both drinking and irrigation, makes up about 5% of its overall supply…