Lopez and Whale Rock dams are among more than 50 dams statewide considered highly hazardous that may have a design flaw and are being required to undergo an assessment of their concrete spillways “as soon as possible.”
The state Division of Safety of Dams is ordering comprehensive assessments of spillways and structures that are similar to Oroville Dam — whose spillway crumbled four months ago, forcing downstream evacuations of thousands of people.
A letter received by the San Luis Obispo County Flood control District on Monday says that the state agency completed an assessment of the Lopez Dam and noted that the spillway “may have potential geologic, structural, or performance issues that could jeopardize its ability to safely pass a flood event.”
The operator of Whale Rock received a similar letter last week.
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The Division of Safety of Dams, which confirmed that more than 50 letters have been sent, oversees and performs annual inspections on more than 100 high-hazard dams in California, including Oroville, Lopez and Whale Rock.
We question their (the dams’) ability to work as designed or intended.
Daniel Meyersohn, project engineer with the Division of Safety of Dams
High-hazard dams are categorized this way because of their height, the volume of water stored behind the dams, and the risk posed to those living downstream.
“Many of these dams are quite old,” said Daniel Meyersohn, a project engineer with the Division of Safety of Dams, in a phone interview. “Because they’re not designed or built to current design standards, we question their ability to work as designed or intended.”
Dam operators have been anxious to learn lessons from what happened at Oroville so that they can make any needed improvements.
While Lopez and Whale Rock dams hold back much less water than Oroville, the cement spillways designed to safely release water and protect downstream communities from flood were built in the same decade as Oroville: The 1960s.
“Infrastructure has a lifespan that needs to be maintained and it needs capital improvement on occasion,” said Noah Evans, supervisor of Whale Rock Reservoir. “Most of us that stare at a dam every day, we could thank everyone at Oroville for finding an opportunity to make everyone a little safer.”
Mark Hutchinson, deputy director of San Luis Obispo County Public Works, has been reviewing old design documents for Lopez Dam and old inspection reports. He agreed that this is a good opportunity to reassess the facilities comprehensively, but he is frustrated with a lack of information coming from the Department of Water Resources.
They’re the same ones, the same agency that inspected Oroville... Should we have been trusting them that much?
Mark Hutchinson, deputy director with SLO County Public Works
A full report detailing the cause of the spillway collapse at Oroville has not been released, and the letter provided little clarity about what dam operators should be looking for.
“We’re just very disappointed. You put a lot of faith in these inspectors every year. They’re the same ones, the same agency that inspected Oroville. ... Should we have been trusting them that much?” Hutchinson said.
“I want more information, more details. What are we looking for, exactly?”