Constructed four generations ago, the massive rock and clay dam at El Capitan Reservoir is capable of storing over 36 billion gallons of water, enough to supply every resident in San Diego for most of a year. Today, it's three-quarters empty, intentionally kept low because of concerns it could fail under the strain of too much water. Seismic instability and a spillway in need of "significant repair" led El Capitan to be added to a growing list of dams rated in poor condition or worse that will likely cause deaths downstream if they fail. An AP analysis tallied more than 2,200 high-hazard dams in poor or unsatisfactory condition across the US—up substantially from a similar AP review conducted three years ago.
The actual number is likely even higher, although it's unclear, because some states don't track such data, while many federal agencies refuse to release details about their dams' conditions. The US Army Corps of Engineers lists about 92,000 dams in its nationwide database, most of which are privately owned and regulated by states. The nation's dams are, on average, over a half-century old and often present more of a hazard than envisioned when designed because homes, businesses, or highways have cropped up below them. Decades of deferred maintenance has worsened the problem. But a changing climate and extreme floods have brought a renewed focus to an often overlooked aspect of America's critical infrastructure.
Del Shannon, president of the US Society on Dams, says that without investment in upgrades, the number of "deficient, high-hazard dams" will continue to rise. However, repairs can be costly and take years to complete. Attempts to remove dams—and empty the lakes they hold back—can spawn legal battles and a public outcry from those who rely on them for recreation or to sustain property values. The $1 trillion infrastructure bill signed last year by President Biden will pump about $3 billion into dam-related projects. Yet that's just a fraction of the nearly $76 billion needed to fix the almost 89,000 dams owned by other entities besides the federal government. They're "ticking time bombs if they are not addressed," says a Michigan lawmaker. (Read much more here.)