Could an earthquake break the Lake Murray dam? It’s unlikely, but not impossible

Experts say it’s unlikely, but a powerful Midlands earthquake could threaten the Lake Murray dam and unleash up to 650 billion gallons of water.

If the two 213-foot tall dams comprising the Dreher Shoals Dam facility — known locally as the Lake Murray dam — were fractured after a powerful earthquake, the resulting failure would unleash a massive amount of water. A breach of the structure — which holds back nearly 650 billion gallons of water — would subject the Midlands area to catastrophic flooding, with water reaching south of I-20 into the Congaree Swamp, according to Kim Stenson, the director of the South Carolina Emergency Management Division, and Dominion Energy.

The nearly 8,000-foot-long main dam, which is owned by Dominion Energy, provides hydroelectric power generated from Lake Murray’s 50,000 acres of water.

The Gervais Street Bridge could be under water, with places like the Vulcan Quarry or the Riverbanks Zoo being inundated.

John Davis, the director of animal care and welfare at the Riverbanks Zoo, told The State there is essentially nothing the Zoo isn’t prepared for. The facilities and team are well-equipped and trained for any disaster, and Davis has connections with facilities around the Southeast should animals need to be evacuated.

Jimmy Fleming, a vice president for permits and external affairs at Vulcan Materials, said the quarry has experienced flooding and natural disasters before and doesn’t see anything to be worried about.

“There’s nothing that would occur to our side that we would consider catastrophic to something else. In other words, if something on our site broke, it wouldn’t cause danger to anyone outside of our site,” Fleming said.

The dam has never suffered damage or failures. But in the early 2000s, local officials were ordered to devise a strategy for if the dam broke.

The decision came after federal officials concluded the initial dam would not survive the potentially strongest earthquake in the area. In their planning, they envisioned the worst case situation: a flood would be unleashed, covering a 210-square-mile area as far as 35 miles away within half a day and raising river levels to 125 feet above normal.

To remedy the potential calamity, a 213-foot tall backup dam that can withstand a 7.3-magnitude earthquake was built.

“The backup dam was completed in 2005 at the Saluda Hydro facility as an additional measure of safety to withstand an unlikely event of major seismic activity,” a Dominion spokesman, Matthew Long, said in an email. “The Saluda Hydro facility meets the Federal Energy Regulatory Commission’s rigorous safety criteria, and both dams undergo frequent, thorough inspections to ensure their readiness to perform as designed.”

The largest recorded earthquake in South Carolina history — and one of the largest in the history of eastern United States — struck Charleston in 1886 and was thought to be around 7.3 magnitude or stronger.

Experts say an earthquake of that magnitude in the Lake Murray area is improbable, even after a recent string of South Carolina earthquakes.

“The problem is that there haven’t been enough that we really see any patterns at this point,” said Tom Pratt, a research geologist for the U.S. Geological Survey. “But we have no idea whether it’s going to lead to something bigger or not, it’s unlikely.”

There are a number of fault lines that run under Lake Murray and South Carolina, but a fault line must be proven active before it is considered hazardous. The faults running under Lake Murray have had no history of activity.

Several minor to moderate earthquakes have rattled South Carolina in the last few months, with the largest reaching a magnitude 3.5. Since December, at least 64 earthquakes have struck the Columbia area, typically between Elgin and Lugoff. Pratt said significant damage only happens after a 6-magnitude earthquake.

Instead of worrying about disaster, Pratt urged residents to think of the recent activity as a wake-up call for preparation.

“It’s always a reminder to keep emergency plans updated,” Pratt said. “They (recent earthquakes) might die off and do nothing. They might make something bigger. They might just keep going the way they are. We just don’t know.”

South Carolina has a state emergency operations plan used for all disasters as well as plans for specific types of disasters. They include a dam-focused plan that interprets disaster modeling from Dominion Energy. The South Carolina Emergency Management Division has used that data to create a plan that includes evacuation routes, evacuation zones and shelter locations.

According to a baseline of the model, more than 150,000 people would be affected, said Stenson.

“Now the likelihood of something happening affecting the Lake Murray dam is probably fairly low,” Stenson said.

Stenson said the Federal Energy Regulatory Commission mandates periodic exercises testing the emergency plans. The latest exercise was in March 2021.

Emergency preparedness has greatly changed since the 2000s, Stenson said, with smart phone and alert systems. He said the number one concern in South Carolina is hurricanes. Lake Murray and the probability of a breach are of less concern, but still accounted for.

“SCE&G spent a lot of time and effort building that other backup dam. We’re fairly confident that that will do the trick if we have a problem,” Stenson said.

South Carolina Electric & Gas Co. and its parent company, SCANA, were purchased by Dominion Energy in early 2018.

Brandon LaVorgna, the public information officer for the Division, said an update for the emergency plan will most likely be concluded sometime next year and hasn’t been updated since around 2010. It was planned for an update but stopped when COVID became an obstacle. Stenson said it is now on the “front burner,” although not much has changed in the near 20 years since its creation.

He said the agency has tested flooding plans and have always executed them well, and he said 2015’s response to the historic flood in Columbia showed that.

2015 posed a number of flooding problems after nearly 17 inches of rain fell on the Columbia area in just a few hours in October. Scores of small dams broke in the 2015 rain bomb, with the failures showing how even small dam breaks can swamp areas below.

To stay safe in the case of an emergency, Stenson said to listen to local and state authorities and devise a personal plan of emergency preparedness of resources, education and evacuation.

“It’s very unlikely, I think, we think, but there’s always the potential to be flooded from some sort of dam break. They should have a plan,” Stenson said.