Source: Paul Rogers | progers@bayareanewsgroup.com | Bay Area News Group
PUBLISHED: January 6, 2021 at 6:00 a.m link to article
The Santa Clara Valley Water District has proposed building a 319-foot tall dam on Pacheco Creek in Southern Santa Clara County near Highway 152 and Henry Coe State Park, a location shown here in August, 2019. But the project’s chances of success have suffered a major setback. (Photo: Santa Clara Valley Water District)
The project calls for a 319-foot-high dam to be built along the South Fork of Pacheco Creek. The existing San Luis reservoir was built on the North Fork of Pacheco Creek in 1939. It holds only 5,500 acre-feet of water behind an aging 100-foot-high earthen dam, while the new reservoir would hold more than 23 times as much.
The district hopes to take water it now stores in nearby San Luis Reservoir and pipe it into the new Pacheco reservoir, filling it during wet years.
But studies by a contractor earlier this year found the area has unstable rock. About 130 test borings found that crews would have to dig down at least 30 feet deeper to hit bedrock than previously thought. That will add three years to construction — from five to eight years — and increase project costs from $1.3 billion to $2.5 billion.
“You want to put your foundation on bedrock, solid granite,” said Chris Hakes, the water district’s deputy operating officer for dam safety and capital delivery. “There are historic slides in the area, loose material that is subject to movement. You don’t want to put your foundation on that obviously because if there is any sort of seismic event, or even heavy rains or mudslides, it could undermine the foundation.”
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