You can probably trust the U.S. Army Corps of Engineers on this one. The dam holding back Lake Lewisville probably isn't going to fail in the immediate future. The 180 billion or so gallons of water it holds back probably won't burst free and wash away the half-million people in its path. The recent appearance of a sand boil, which indicates that water has seeped under and potentially weakened the dam, and the portion of the barrier that sloughed off into the lake — a "slide," as they call it — are admittedly worrisome. It's not unreasonable to suspect that the Corps might be massaging the actual risk level to tamp down fears of catastrophe. But it also seems likely that the local and federal government learned something from Hurricane Katrina and would warn people of imminent cataclysm.
That's not to suggest that you should trust the government to effectively manage flood risk. Quite the opposite in fact. Our Jim Schutze has noted that much of the risk to life and property that would result from a breach of the Lewisville Dam is the result of decades of awful land-use planning. Maybe the government never should have let so much development happen in the path of devastating flooding, or else created a flood-insurance system that does a better job of reflecting flood risk. There weren't a half-million people in the path of an unleashed Lake Lewisville when the six-mile-long dam was built in 1955.
But that's just one of the big, system-wide failures embodied by the Lewisville Dam. Its troubles also reflect the country's chronic inability to adequately fund vital infrastructure.
The dam was completed in 1955, though it wasn't until two years later, when the Corps breached the upstream dam holding back comparatively tiny Lake Dallas, that the reservoir filled to something close to its modern volume. This was all happening in the context of what historians term the "big dam era," when the U.S., enamored with its technical prowess, set out to tame nature in service of human progress, the civil engineering version of Manifest Destiny. The initial impetus for Lake Lewisville and its sister projects Lake Lavon and Lake Grapevine was flood control, which The Dallas Morning News opined in a 1950 editorial was vital to both the protection of human life and property and future economic growth:
Already the Trinity Valley has more industries than any other valley in Texas. Its industrial development can be greatly increased when assurance is given against devastating floods. Better flood control is needed, too, to protect crops, livestock and even human inhabitants of the valley. With the flood danger checked, many lowlands now wasted can be reclaimed and put to productive use. Steps taken to prevent floods will also be of help in readying the river for navigation.
Combined with the sister projects, Lake Lewisville, which was known as the Garza-Little Elm Reservoir until a certain Denton County municipality successfully lobbied to have it changed, quintupled Dallas' water supply. Officials were downright cocky. Dallas' water superintendent predicted the reservoirs would adequately supply a Dallas population of 1.2 million even if it didn't rain for five consecutive years. In 1952, as a drought-stricken city struggled to conserve water, the regional commander of the Corps called it "inconceivable" that Dallas would ever again face a water shortage once the new lakes were filled.
Something similar was happening throughout the country. During the period, the Corps and Bureau of Reclamation dammed up just about every waterway of any consequence in the name of some combination of flood control, water supply, hydroelectric power and recreation. State and local governments and private landowners filled in the gaps. Today there are some 84,000 dams in the U.S. with an average age of 50 years. The Lewisville Dam and about 15,000 others are classified as "high hazard," which doesn't mean that they are likely to fail, just that people will probably die if they do.
The existence of high-hazard dams isn't a problem in and of itself, though it's worrisome that the number has jumped 50 percent from the 10,000 high-hazard dams of a dozen years ago as more and more people have decided to live in the path of potential disaster. Dams are designed not to fail, and, with the exception of the Teton Dam in Idaho, which breached and killed 11 people almost as soon as it was built in the mid-1970s, they basically never do. But the dams were also designed for a 50-year lifespan. The Corps says so itself: "Approximately 95 percent of the dams managed by USACE are more than 30 years old, and 52 percent have reached or exceeded the 50-year service lives for which they were designed."
Lewisville, if you haven't done the math, is 10 years past its design life and counting.
That certainly sounds like the entire country is clutching a giant time bomb that's already ticked to zero, but dams don't work like that, according to John France, who leads the dam and hydropower arm of the infrastructure firm AECOM. "An embankment dam like [Lewisville] physically doesn't necessarily wear out," he says. The concrete spillways, metal gates and other components of the dam may need to be replaced after 50 years, but the giant mound of dirt and rubble that does the actual work of holding back the water tends not to change much over the decades.
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The problem, says France, is that the dam builders of the 1950s didn't know as much as engineers today. Whereas now engineers build dams to prevent the type of sand boil recently discovered on the Lewisville Dam, they didn't back then. So when problems like that arise, the Corps has to go back and do expensive fixes. The cost of addressing sand boils varies depending on the individual dam but the price tag can easily grow to tens of millions of dollars or more. And it's not just preventing sand boils. Old dams also fall short of modern standards on other measures, like withstanding large floods and earthquakes.
Dam-safety advocates put the price tag for repairing the nation's dams well into the tens of billions. According to the American Society of Civil Engineers, it will take $21 billion just to bring the country's high-hazard dams up to snuff. At current investment levels, the Corps has estimated that it will take half a century to fund necessary repairs. Any specific estimates should be taken with a grain of salt, since they are generally peddled by civil engineers whose livelihoods depend on ensuring a robust flow of infrastructure spending, but the general idea is on point, says Todd Shallat, a Boise State University history professor who has written a pair of books on the history of the Corps.
It's important to understand, Shallat says, that Corps projects are the product of an intensely political process. The local voices lobbying most strongly for a lot of dam projects are typically the housing developers or agricultural interests or industrialists who hope to profit by turning a former floodplain into productive use. In addition, the dam-building boom was spurred along by intense rivalry between the Corps, the Bureau of Reclamation, and the half-dozen other federal dam-building agencies, all of them jockeying for projects. Corps projects always come with maintenance costs baked into the cost-benefit analysis, which theoretically ensure that dams are kept in decent shape well beyond their design life. But it's all "really fuzzy, fuzzy math," and in reality, the government has not spent enough maintaining dams, which will inevitably lead to larger costs in the future. "It's like a pothole in the road," Shallat says. "If you don't maintain it over time ... you're going to have a sinkhole." That's what Dallas is currently seeing with the Lewisville Dam and, um, with its actual potholes.
On the plus side, France says the Corps has gotten much better over the past decade at managing dam safety. Previously, each of the Corps' several-dozen districts would compile a roster of needed fixes and lobby headquarters for funding. Now, there is a centralized system that rates all Corps dams according to risk. Funding is distributed accordingly. Everyone agrees that there's still not enough of it to go around, but it's not so bad that dams are going to start to collapse.