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There are more than 87,000 dams in America and, like most infrastructure, they go largely unnoticed — until something goes wrong.
That was the case in and around South Carolina's capital this week, when at least 20 dams collapsed during catastrophic floods.
The number of dam breaches was rare. But to experts who monitor dam safety in America, it wasn't entirely surprising. In its most recent Report Card for America's Infrastructure, the American Society of Civil Engineers gave the state of America's dams a "D," in part because about 4,000 dams in the country are in need of repairs — and about half of those deficient dams could cost lives if they were to fail.
That's in large part because of their age. Several of the dams that breached this week in South Carolina were more than 100 years old — and they are far from exceptional. Nearly 3,000 dams across the U.S. predate the 20th century:
And when it comes to dam integrity, age matters. Inside of many of America's dams, metal pipes and other structural components are degrading. The process is accelerated by chemical runoff in the waterways, particularly in areas that have become more populated in recent decades.
Outdated technology is another issue.
"[Older dams] were built with the best construction and engineering standards available at that time, but we've learned a lot since then about things like earthquakes and floods," says John France, with the international engineering consulting firm AECOM.
"South Carolina is an example of what can happen," he says, "and, unfortunately, we're seeing those kinds of floods every few years now."
Government officials are well aware of the problem — even more so in recent years, as dam inspections have increased.
But dams are expensive to fix. According to the Association of State Dam Safety Officials, it would cost about $54 billion to rehabilitate all of the dams in the country in need of repairs. The money would need to come from myriad local, state and federal coffers — as well as thousands of private owners.
Federal dams are both inspected and financed by the agencies that own them, many of which only have enough money in any given year to tackle the most potentially dangerous defects. The U.S. Army Corps of Engineers, for example, estimates that at current funding levels, it would take them about 50 years to work through their backlog, according to the ASCE report.
Meanwhile, many more dams — locally owned, state-owned or privately owned — are monitored by state authorities, which presents its own set of problems.
First, the amount each state spends on dam oversight varies widely. The South Carolina Dams and Reservoirs Safety Program, for example, regulates 2,499 dams and spends $260,000 a year doing so. That comes to about 380 dams per dam safety employee.
While that's significantly less funding than the national average, it is much more than some states spend. Alabama doesn't even have a dam safety program.
Second, while states might pay or contribute to the repairs of those dams that are publicly-owned, most dams in the country are privately owned, which puts the onus on private parties and associations.
When private owners' dams require repairs and the owner is slow to make them, state enforcement mechanisms can be weak and slow, often bogged down in litigation or paperwork, says Mark Ogden of the Association of State Dam Safety Officials.
In most states, governments do have the ability to step in if lives or property are in imminent danger. But, he said, "It is not good policy to have to wait until emergency situations to have to deal with a lot of these issues."
Still, in many cases, that's exactly what happens. The only source of federal funding for dam repair — for dams that aren't owned and regulated by the feds — comes through FEMA, and that money only becomes available after a dam fails.
Which might create a rare opportunity in South Carolina to use public money to build stronger, more modern dams.
At least 20 of them.