California’s aging dams face new perils, 50 years after Sylmar quake crisis

Source(s)
Los Angeles Times

By Louis Sahagún

It was a harrowing vision of the vulnerability of aging California dams — crews laboring feverishly to sandbag and drain the lower San Fernando Reservoir, as billions of gallons of Los Angeles drinking water lapped at the edge of a crumbling, earthquake-damaged embankment that threatened catastrophe on the neighborhoods below.

Although the 1971 San Fernando earthquake and the near failure of the Lower Van Norman Dam have given rise to construction improvements — the much newer Los Angeles Dam survived an equivalent shaking in the 1994 Northridge quake — the overwhelming majority of California dams are decades past their design life span.

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Federal engineers have found that three major dams in Southern California — Whittier Narrows, Prado and Mojave River — are structurally unsafe and could collapse in a significant flood event and potentially inundate millions of people downstream.

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“Even if engineers had made risk assessments that were accurate at the time these structures were built, they aren’t accurate now, and won’t be anymore due to climate change,” said Daniel Swain, a UCLA climatologist.

These extreme weather events compound problems posed by earthquakes, which are inherently unpredictable and can cause safety problems that remain hidden or hard to identify.

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