Feb 13, 2017

The government was warned that the Oroville Dam emergency spillway was unsafe. It didn’t listen.

Oroville, CA
USA
by
Kristine Aguerra
,
Washington Post

In 2005, three environmental groups warned state and federal officials about what they believed was a problem with the Oroville Dam’s emergency spillway — the same one that was at risk of collapsing this week, after storms caused the adjacent reservoir to swell.

...

Federal officials, however, determined that nothing was wrong and the emergency spillway, which can handle 350,000 cubic feet of water per second, “would perform as designed” and sediment resulting from erosion would be insignificant, according to a July 2006 memo from John Onderdonk, then a senior civil engineer for the Federal Energy Regulatory Commission.

...

“The emergency spillway meets FERC’s engineering guidelines for an emergency spillway,” Onderdonk wrote. “The guidelines specify that during a rare flood event, it is acceptable for the emergency spillway to sustain significant damage.”

Fast-forward 11 years. The erosion of the emergency spillway became severe, with only up to 12,000 cubic feet of water per second, according to the Oroville Mercury Register. That’s a little more than 3 percent of what officials said the spillway can handle.

The water level in massive Lake Oroville rose significantly after potentially record-setting rain surged through the state following a long drought. The Oroville Dam, the tallest in the country, at 770 feet, remains stable, officials said as the water level fell several feet, to a point at which water was no longer spilling over.

But the structure of the spillways, which are designed to release water from the reservoir in a controlled fashion, have crumbled.