ARI SHAPIRO, HOST:
There are more than 90,000 dams in the U.S. Most are more than half a century old. Many are in poor condition, and civil engineers are warning that they're at risk of catastrophically failing just like a century-old dam did in Michigan two months ago. NPR's David Schaper reports.
DAVID SCHAPER, BYLINE: In the afternoon of May 19, after some five inches of rain fell onto already saturated ground, word spread quickly around Midland County, Mich., that the Edenville Dam on the Tittabawassee River could fail at any time. Local resident Lynn Coleman was at the dam when a huge portion of it collapsed.
(SOUNDBITE OF ARCHIVED RECORDING)
LYNN COLEMAN: There it goes.
UNIDENTIFIED PERSON: There it is.
COLEMAN: There it goes.
SCHAPER: His smartphone video shows a huge chunk of the grass-covered earthen part sliding down, followed by a surging flow of mud and then a pause before brown water gushes through the breach.
(SOUNDBITE OF ARCHIVED RECORDING)
COLEMAN: There we go. There's the rush.
SCHAPER: A short time later, that torrent of rushing water overtopped another dam seven miles downstream. Ten thousand people were evacuated in towns like Edenville and Sanford. And the city of Midland was soon under more than nine feet of water.
LORI SPRAGENS: It was devastating, I mean, to see that.
SCHAPER: Lori Spragens heads the Association of State Dam Safety Officials and watched the video of the dam collapsing that night online.
SPRAGENS: I was not surprised - not at all. Unfortunately, we've seen some high-profile dams in the last three years fail.
SCHAPER: And Spragens says there are thousands more dams all around the country that could also catastrophically fail, risking people's lives and huge property losses. In its latest infrastructure report card, the American Society of Civil Engineers gives the nation's dams an overall grade of D.
DARREN OLSON: Generally, they're all pretty old.
SCHAPER: Chicago-based civil engineer Darren Olson is on the committee that grades dams and says their average age is 57 years old.
OLSON: This infrastructure that's out there, whether it's, you know, steel or concrete or even earth, it just deteriorates over time. Just like anything - your car, your house - it needs a lot of maintenance and rehabilitation.
SCHAPER: And Olson says it's not just the age of the dam but what's changed since they were built. Upstream development increases the amount of runoff, while development downstream has put more people at risk if a dam fails.
OLSON: The other thing, too, is that these dams that were built so long ago - the rainfall patterns that we're seeing now - these dams that were built that long ago just aren't built to withstand the sort of rain events that we're seeing today.
SCHAPER: The most recent national climate assessment finds that extreme rainfall events have increased more than 50% in the Midwest since 1950. And other parts of the country are seeing greater rainfall amounts, too, as the climate heats up. Bill McCormick, chief of dam safety for the state of Colorado, says warmer air simply holds more water.
BILL MCCORMICK: For us in Colorado, based on the results of our study, we implemented a new rule that says we have to add 7% additional rainfall onto our design storms when we design dams going forward.
SCHAPER: But not all states are factoring climate change in to dam standards. And rehabbing or rebuilding older dams and spillways to meet today's higher water amounts is a huge challenge. Unlike fixing up highways and bridges, there's little public funding for dam infrastructure, in part because most are privately owned. They were built by loggers and paper mills, by utilities for hydroelectric power or drinking water and by farmers, among others. Again, Lori Spragens.
SPRAGENS: Owners don't tend to have this amount of funding available to do these big upgrades.
SCHAPER: And while some dams are federally regulated, about 70% of them are only regulated by the state. And Spragens says resources for adequate safety oversight just aren't there.
SPRAGENS: It's mind-boggling. It is absurd. It really is.
SCHAPER: As a result, she and other experts fear that it won't be long before another dam catastrophically fails.
David Schaper, NPR News.
(SOUNDBITE OF AKIRA KOSEMURA'S "DNA") Transcript provided by NPR, Copyright NPR.