Satellites Reveal Sinking High-Risk Dams Across US

A new look from space is raising fresh questions about some of America's biggest dams. Virginia Tech researchers who used data from European weather satellites say they've detected subtle sinking at dozens of high-risk hydropower dams across the United States, including one in Texas that later triggered a "potential failure watch," the Washington Post reports.

• Geophysicist Mohammad Khorrami told colleagues at a December scientific meeting that satellite data show part of Livingston Dam, north of Houston, has been settling about 8 millimeters a year. The structure is already rated "high hazard potential," meaning a failure could cause deaths and major damage, and is now listed in "unsatisfactory" condition in the National Inventory of Dams. After heavy rains last summer eroded parts of the dam, its owner, the Trinity River Authority, issued a failure watch.

• Khorrami and fellow Virginia Tech geophysicist Manoochehr Shirzaei examined 41 large hydropower dams in 13 states and Puerto Rico that are both in poor condition and rated capable of causing fatalities if they fail. All showed some vertical movement, from near-imperceptible subsidence to more worrisome "differential settlement," where sections shift at different rates.
• The team stresses that the detections, made with Interferometric Synthetic Aperture Radar (InSAR), are an early-warning tool, not a diagnosis; only on-site inspections can reveal whether changes detected by satellites are the result of cracks or structural problems.
• "We need to do further analysis to have a concrete answer," Shirzaei said, per Popular Science. "But some of the observations may suggest that some of these infrastructures are undergoing internal degradation."
• One operator, Dominion Energy, disputes the findings at its Roanoke Rapids Dam in North Carolina, saying it sits on solid rock and that significant settlement is "highly unlikely if not physically impossible."

• The work comes as aging US dams face intensifying rainfall linked to climate change. The US has just over 92,000 dams and according to the National Inventory of Dams, their average age is 61, Gizmodo reports. Of the 16,500 considered high hazard, around 2,500 are in poor condition. A recent report by state dam officials estimated it would cost more than $165 billion to repair roughly 89,000 dams controlled by states or private entities, far beyond current funding levels, the Post reports. Regulators say satellite monitoring could help prioritize which high-hazard dams need attention first.
• John Roche, president of the Association of State Dam Safety Officials, says use of InSAR is "absolutely helpful as a first tool" to spot potential problems. "Just a visual, hands-on inspection of your dam is not necessarily sufficient to understand the full health of the dam and underlying risks," he says.
• The Virginia Tech team hopes to build a national, publicly accessible map showing movement at high-risk dams as part of what Shirzaei calls a "health care" model for critical infrastructure.