Lowcountry residents are used to seeing roads flood when there are heavy rains, but a more dramatic problem this summer in South Carolina has been heavy rains getting underneath roads and causing them to collapse.

On Monday a sinkhole large enough to swallow a car opened in Dorchester County on rural, state-maintained Wire Road, near the Orangeburg County line. Meanwhile, S.C. Department of Transportation crews continued to work on repairing an equally large sinkhole on Interstate 26 in Berkeley County that was discovered July 5.

Both holes were described as being about 10 feet deep and at least 6 feet wide.

The I-26 hole is in the eastbound lane near Ridgeville, and the closure of that lane caused a 7-mile traffic backup for Charleston-bound traffic Friday. Lane closures are expected to continue through Wednesday, SCDOT spokesman James Law said.

Norman Levine was stuck in that traffic backup Friday, and took particular interest in the cause. Levine is a geology professor at the College of Charleston and director of the college’s Lowcountry Hazards Center.

Levine said parts of South Carolina are prone to sinkholes, caused when acidic rain water wears away at limestone near the surface — but that’s not what happened in these cases. Instead, the subsidences, or cave-ins, were caused by something called “piping.”

“What happened was, there was a change in the underground,” Levine said. “In this case there was fill around the pipes, and the excess water moved some of that fill away.”

Additional road subsidences have been reported during the past several weeks of unusually heavy rain across South Carolina. A hole opened up Monday in downtown Georgetown, and last week an Anderson sinkhole dramatically swallowed a utility repair truck.

In North Carolina, subsidences have claimed backyards in Asheville and a parking lot in Madison County. The Tanger Outlets mall in Blowing Rock, N.C., was shut down for a day in late June after a sinkhole opened near the mall entrance.

In most cases, large amounts of water flowing around underground pipes or utilities, or escaping from sub-surface pipes, was blamed.

Law, with SCDOT, said the hole on I-26 was caused by water escaping from a hole in a culvert under the highway. He said the hole was filled with concrete Monday, but additional repair work and lane closures could last through Wednesday.

“The one (on Wire Road) in Dorchester County should be fixed tomorrow afternoon,” Law said Monday. “With that one, a drain pipe under the road separated in two places.”

“The two problems we’ve had are definitely related to all the water,” he said.

Reach David Slade at 937-5552 or Twitter @DSladeNews.