While crews scramble to perform emergency repairs to California’s Oroville Dam as forecasts for more rain looms, the crisis that caused nearly 200,000 downstream residents to evacuate has brought the safety of many of the state’s other dams into question.
As HydroWorld.com reported Feb. 8, flows had already been temporarily suspended over Oroville Dam’s main spillway after massive concrete erosion near its bottom was being evaluated.
High flows into Lake Oroville — the state’s largest reservoir — caused the California Department of Water Resources to reopen the main spillway, in addition to an auxiliary spillway that had not been used since the dam was finished in 1968.
Subsequent erosion under the concrete retaining wall at the top of the auxiliary spillway caused officials to fear that it could collapse, sending an uncontrollable wave careening toward communities downstream on the Feather River. The threat forced evacuations in Butte, Sutter and Yuba counties.
Officials feared a similar scenario could present itself at the L.L. Anderson Dam in California’s Santa Clara County, which has, since 2006, impounded a reservoir limited to 68% of its capacity due to fears that a catastrophic flood or earthquake could cause the structure to fail.
The reservoir’s level is now nearing 99% full, officials said earlier today, testing a spillway and infrastructure that — like many at dams throughout California — has been largely unused during the state’s prolonged drought.
Though plans to rehabilitate Anderson Dam have long been in the works, Anderson is one of many within the state that could pose a significant threat along the seismically unpredictable Pacific coast.
According to data from the Association of State Dam Safety Officials, more than half of California’s 1,250 dams — including Anderson — qualify as “high hazard” due to the impact a failure could have.
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