California

Four Months After Oroville Crisis, Spillway Inspections Ordered at 70 Aging California Dams

The inspections follow the failure of spillways at Oroville Dam during February downpours in Northern California

California is ordering immediate spillway inspections at about 70 aging dams that it believes might not be sound enough to protect downstream communities in a flood.

Supervising engineer Daniel Meyersohn at California's dam-safety division said Wednesday that a state records review is identifying large, aging dams that have people downstream for on-site spillway reviews. Meyersohn said the state is sending letters to dozens of those dam owners ordering them to carry out extra design reviews and site inspections.

The orders are part of stepped-up state reviews after this winter's failures of both spillways at the Oroville Dam, the nation's tallest. That crisis forced the evacuation of newly 200,000 people in February.

A full report on the spillway failure hasn't been completed, but a consultant's report delivered to the state's water resources department indicated a "high velocity flow" of water that went under the slab and caused it to lift, eventually leading to cracks.

Construction crews have been working on the damaged spillway at Oroville Dam for the past four months. This week, workers cleared concrete left behind after controlled blasts on what remains along part of the spillway chute.  The top 1,000 feet of the upper chute are expected to be replaced next year. 

Meyersohn said some of the dams targeted for extra inspections date back to California's 19th-century Gold Rush.

One of the worst civil engineering disasters in U.S. history occurred in Southern California in 1928. More than 450 people were killed when a dam in San Francisquito Canyon, about 40 miles northwest of, collapsed on March 12, 1928. More than 12 billion gallons of water swept across the region on a deadly five-hour march to the ocean near Oxnard, collecting mud, debris, bridges, buildings utility poles and anything else in its path. 

When it comes to single disasters in California, only the 1906 San Francisco earthquake and fires accounted for more fatalities.

Copyright AP - Associated Press
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