DAVID GREENE, HOST:
Let's turn now to a story we were covering this morning and will be covering throughout the day. In Northern California, there is a massive evacuation underway following damage to emergency infrastructure at the country's tallest dam. The evacuation order affects more than 180,000 people living in the lowlands near the Oroville Dam, about 80 miles north of Sacramento.
The winter heavy rain filled that dam. A few days ago, engineers released water into what's called a spillway, a flood-control measure. The release of water cratered the spillway, making a 200-foot hole, so they adjusted and let water overflow into a second emergency spillway.
JEFFREY MOUNT: And that's when things kind of went to pieces.
GREENE: This is Jeffrey Mount, a flood control expert with the Public Policy Institute of California at UC Davis. The second spillway also began to erode here, and that threatened to send a wall of water downstream. And that's when officials told nearby residents to evacuate. Butte County Sheriff Kory Honea spoke at a press conference last night.
(SOUNDBITE OF PRESS CONFERENCE)
KORY HONEA: The time frame that we were dealing with, at that point, was mere hours. And we couldn't risk the lives of thousands of people, so we took this rather significant step.
GREENE: It's a significant step that has caused traffic to back up for miles around Lake Oroville. The Oroville Dam was finished in the late 1960s, when Ronald Reagan was governor. And Jeffrey Mount says, in the decades since, the emergency spillway had never been tested.
MOUNT: Well, they're probably wishing they had tested it because the weaknesses were revealed immediately in the design, and it threatened to collapse.
GREENE: The problem, Mount says, is you can't exactly test the full capacity of emergency infrastructure until there is an emergency.
MOUNT: So you do the best job you can in designing it, and then nature discovers the errors in your design pretty quickly. And that's basically what happened.
GREENE: He says, it is too soon to tell what caused what he calls this cascade of failures, but it will be very expensive to fix.
MOUNT: And I can tell you that this event will cause us to do some soul-searching about the amount of money we're spending on infrastructure, maintenance particularly, here in California.
GREENE: That is the background. We'll be covering the news. Governor Jerry Brown has issued an emergency proclamation to help with these massive evacuations right now in Northern California. Transcript provided by NPR, Copyright NPR.
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