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Dam Disaster: State’s inspection program under scrutiny following catastrophic floods

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cary lakefront 1 web
One of the 48 single-family homes on Cary Lake now looks over an empty 56-acre lake bed. The lake, located between Decker Boulevard and Trenholm Road, was emptied after the dam broke during the historic flood. (Photos/Chuck Crumbo)

By Mike Fitts
Published Nov. 2, 2015

From the Oct. 26 – Nov. 8 issue of the Columbia Regional Business Report

South Carolina can and should do more to oversee dams on private property in the wake of deadly flooding in the Midlands, according to two experts on the state’s waterways.

According to Erich Miarka of the Gills Creek Watershed Association, the state’s staff of less than a half-dozen inspectors, while skilled at what they do, cannot hope to check frequently on the hundreds of small dams around the state that are their responsibility. Miarka points out that just the Gills Creek Watershed in Richland County contains dozens of bodies of water and dams that fall under state inspection, enough to keep the DHEC dam staff busy.

The state’s staff has almost 2,500 dams to regulate statewide, according to the national Association of State Dam Safety Officials. That’s about 380 dams per staff per staff member, according to the organization’s estimate.

“DHEC is understaffed on this,” Miarka said.

Elected officials, while coping with the flooding’s immediate aftermath, also have begun to look toward a review of how DHEC regulates most of the state’s dams. (The biggest dams, such as the one on Lake Murray, fall under the authority of the federal government, not the state.)

Gov. Nikki Haley has announced that the state is checking on the 600-plus state-regulated dams considered to pose the highest damage risk in case of failure. Those checks are expected to be complete by the end of October, and include the assistance of outside consultants from the HDR engineering firm.

The governor also said that the way that the state oversees dams would be under review. “Do we have enough engineers to monitor those dams? How are we going to go and maintain those dams going forward?” she said during a mid-October press briefing at the S.C. Emergency Management Division.

S.C. Department of Health and Environmental director Catherine Heigel added at the same briefing there appears to be support for bolstering the agency’s dam inspection program.

“These are private dams,” Heigel said, pointing out one of the key challenges involved in revamping the program.

“They are owned by private property landowners so we will have a lot we have to work through,” she said.

However, Heigel added, “we have a strong commitment” from many dam owners, General Assembly members, and the governor to fix the problem.

Rep. Beth Bernstein, a Democrat whose Richland County district includes some of the hardest-hit areas in Forest Acres and Arcadia Lakes, believes that the legislative and executive branches – and both political parties – will have to cooperate to correctly review dam safety in the state. “I hope we can work together to get it done,” Bernstein said.

Legislators will be interested, of course, to see if DHEC had been doing what it should to regulate dams in the state. But to her, any such review needs to be focused more on improving safety going forward and less on what happened this October. “We can point fingers all day long, but I hope we can lessen the impacts on people,” she said.

In the first few days after the flooding, her constituents were more focused on rescue, recovery and cleanup than on any issues with the state’s waterways. “People have been displaced, lost everything and are in a bit of shock,” Bernstein said.

What Did Happen?

To Miarka, the dam failures in the Gills Creek watershed were stunning and unexpected, even though he had first-hand knowledge of many of the structures.

Of course, he had not imagined more than a foot of rain falling in a weekend’s time, as a storm front was energized by moisture pouring inland from Hurricane Joaquin, which was lashing the Bahamas. The Gills Creek area particularly was drenched with rain estimated at 20 inches or more.

cary lake dam web
Cary Lake dam is one 17 dams in Richland County that were washed away in the historic Oct. 4 flood. A road atop the dam also was destroyed, isolating 14 homes.
That much rain might have been simply impossible for the watershed’s earthen dams, many of which are decades old, to withstand, Miarka said. With that much rain, dam failures likely were “inevitable,” he said.

So much water was piled up in the ponds on Oct. 4 that it began to flow over tops of dams. That’s very destructive for an earthen dam, Miarka said, because of the force of the water flowing over the backside of the dam. That water running down erodes the dam, which can fail because it already is under so much pressure. “It was the erosion of the dam (that broke them) because there was so much water,” he said.

Some dams even had concrete spillways added to let water overflow without erosion, but there was just too much water too fast, he said. Five dams in the Gills Creek watershed failed, with at least one of them causing the next dam downstream to fail by unleashing so much sudden extra water. Across the state, it’s reported that 17 dams failed.

What should the state do?

The rains associated with the flood were remarkable, by historical standards. According to meteorologists, that kind of rainstorm occurs only once per 1,000 years, on average. That doesn’t mean that the state can assume that nothing like this can happen again, said Gerrit Jobsis, senior director for conservation at the American Rivers group. “Intense storms will happen,” he said.

To protect those who live downstream, DHEC must invest more in inspections and look at the construction standards of these dams, Jobsis said. As dams are inspected and failed ones rebuilt, it’s time to look at how they are built and whether the materials are sufficient, he said.

If an earthen dam is made of sand, it will have a weaker resistance to erosion than if it is made out of clay, he said. “Earthen dams can be safe, if constructed in the right way,” he said.

If state inspectors find issues with a dam’s safety, they do have the powers to require improvements, even on private land, Miarka said. One dam in Richland County failed inspection in the past couple of years and the owners were required to take the water level down until improvements are made, he said.

In a state that will face other storms in the future and also is vulnerable to earthquakes, there needs to be a more vigorous inspection regime, Jobsis said. “It shouldn’t be seen as an isolated event that won’t happen again.”

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