The satellite signal was subtle but persistent. A decade of observations suggested that part of the Livingston Dam – a 2.5-mile-long earth and concrete structure about 70 miles north of Houston – was sinking by roughly 8 millimeters per year.
This deformation could indicate the structure is unstable, said geophysicist Mohammad Khorrami, who presented the findings in December at the annual meeting of the American Geophysical Union. Though the observation is preliminary, he said it was cause for concern; regulators consider the dam to have “high hazard potential,” meaning it could lead to deaths and significant property damage if it ever failed.
Livingston is not the only U.S. dam that appears to be sinking into the earth, said Khorrami, a postdoctoral associate at Virginia Tech. Using radar from satellites to survey hydropower dams in 13 states and Puerto Rico, he and his colleagues detected subtle shifts in the height of all 41 structures they studied. The observations ranged from barely perceptible subsidence to more worrying “differential settlement” – cases like the Livingston where parts of the dam are moving at varying rates.
The team’s findings don’t necessarily indicate that downstream communities are in immediate danger, cautioned Manoochehr Shirzaei, a fellow Virginia Tech geophysicist who contributed to the research. There can be benign explanations for small changes in a dam’s elevation, and the dams must be inspected in person to determine whether the satellite detections are a sign of cracks or other structural issues.
He compared the satellite findings to an anomaly on a routine medical screening – something that prompts doctors to look more closely for potential problems.
“The purpose of the study is to help create a health care approach toward maintaining infrastructure,” Shirzaei said.
In the case of the Livingston Dam, 10 years of satellite observations proved prescient: In 2024, heavy rains caused erosion around the dam, prompting the Trinity River Authority – which owns and operates the structure – to declare a “potential failure watch.” According to the National Inventory of Dams, which is maintained by the Army Corps of Engineers, the Livingston Dam is classified as being in “unsatisfactory” condition.
The Trinity River Authority has spent more $45 million on emergency repairs to address the erosion problem, according to general manager Kevin Ward. The organization now conducts annual safety reviews and is making additional upgrades to allow the dam to withstand more intense floods.
Ward said the most recent assessment at the Livingston Dam didn’t identify any safety issues related to subsidence. He added that the small movements detected by satellite could be connected to innocuous factors, such as traffic on the road that runs on top of the dam.
“I agree you need surveillance like that when we have so many dams across the country,” Ward said. But any satellite survey will be imprecise, he said, and should be confirmed by investigators on the ground.
According to the Association of State Dam Safety Officials (ASDSO), there are nearly 92,000 dams in the United States, ranging from behemoths like the Hoover Dam to more modest earthen structures used to hold back reservoirs, tailings ponds and other small water bodies. The majority of these dams are more than 50 years old – an age at which many structures begin to show signs of wear and tear.
The research presented last week has not yet been published in an academic journal. But it uses the same methodology as other peer-reviewed studies, including an analysis of a deadly 2023 dam collapse in Libya that Shirzaei published in 2025.
The Virginia Tech researchers focused their analysis on large hydropower dams that are classified as being in poor or unsatisfactory condition and that could cause fatalities if they failed. Any weaknesses in these structures could make them vulnerable to severe weather fueled by climate change, Shirzaei said.
A Washington Post investigation found that the flow of water vapor through Earth’s atmosphere – a crucial ingredient for extreme rainfall – is on track to hit a record high for 2025. Increasingly intense rain events can rapidly fill reservoirs and put dams under unprecedented strain, experts say.
The researchers say their remote sensing technique, known as Interferometric Synthetic Aperture Radar (InSAR), could be used to identify potentially problematic structures among thousands of high hazard potential dams across the country – many of which require rehabilitation to meet modern safety standards and cope with rising climate risks.
“We know the infrastructure in the United States is in poor condition,” Shirzaei said. “Our technology, our data is a very affordable and accurate way of creating a priority list.”
In a report published in March, the ASDSO concluded it would cost $165.2 billion to rehabilitate the 89,000 dams controlled by states and private entities. Fixing problems at federally controlled dams could cost billions more. Yet state and federal funding for dam safety and maintenance typically amounts to tens of millions of dollars per year – orders of magnitude less than what experts say is required.
John Roche, a dam regulator in Maryland and ASDSO president, said the ability of InSAR to detect minute changes in dams is “absolutely helpful as a first tool” for resource-strapped officials, helping point out problems that aren’t evident from the ground.
“Just a visual, hands-on inspection of your dam is not necessarily sufficient to understand the full health of the dam and underlying risks,” Roche said.
But a spokeswoman for Dominion Energy, which operates one of the other dams where the Virginia Tech team found evidence of deformation, criticized the scientists’ methodology, saying it was not applicable to the dam in question.
The satellite observations suggested that parts of Roanoke Rapids Dam in North Carolina were sinking by about 7 millimeters per year. But the dam is built on “very sound rock”, spokeswoman Cherise Newsome wrote in an email, “and significant settlement is highly unlikely if not physically impossible.”
Khorrami and Shirzaei’s research utilized radar observations taken by the European Space Agency’s Sentinel-1 satellites over the past decade. The instruments emit radio waves that bounce off the Earth’s surface, then measure the time it takes for the reflection to return – allowing them to detect minute changes in the height of whatever lies below.
The scientists hope to eventually create an interactive map that shows movement at all high hazard potential dams in the U.S.
“This work is motivated by a simple question, which is how to detect early warning of the signs and signatures of dams’ instability at a national scale before an actual disaster happens,” Khorrami said.
