Historic flooding raises questions about dam safety

CHARLESTON, SC (WCSC) - Dam failures across South Carolina last month caused catastrophic damage, raising new questions for many Lowcountry residents.

A total of 36 dams statewide breached during last month's historic rainfall. Homes and businesses flooded, roads washed out, and many bridges weren't safe for travel.

In the aftermath come new worries: How many dams are here, how did we escape the damage and could the same thing happen to us?

Safety measures at the Santee Cooper Project 

Forty miles of dams and dikes surround Santee Cooper's Lakes Marion and Moultrie. It is Mark Carter's job to oversee them, keeping an eye on the inspection process and the weather, not just in the Lowcountry, but also in the upstate and parts of North Carolina. Rainfall there flows into Lake Marion.

"The lake system has a 15-thousand square mile drainage basin," Carter said as he took our crew to the Pinopolis Dam in Berkeley County.

To prevent catastrophe such as an overflow or dam break, water is released  through the Santee Spillway to the Santee River. Carter said no water is routed toward Charleston because of the Pinopolis Dam.

"The potential for flooding on the Cooper River is almost non-existent because we can't release a significant amount of water here," Carter said.

Santee Cooper engineers inspect at least monthly.  They've used stakes to mark some shallow slides caused by the historic rainfall.

"It saturated the soil and that water and that added weight causes the soil and water to slide down the hill," he said. Carter calls it maintenance, and repairs will prevent further erosion. "And grass can provide protective cover."

A backup dam built in the 1980s below the primary dam built in the 1940s serves as an earthquake safety measure. But no threat, he believes, is greater than another.

"Because the consequences of failure are very severe, and so from our point of view we try to look at all the threats and address them appropriately," Carter said.

There are three levels of inspections: year round by company engineers, an independent inspector every five years, and a yearly inspection by the federal government. While that federal report is classified, a government spokeswoman said the 2015 inspection in June found "No outstanding dam safety issues."

Santee Cooper plans to share its Emergency Action Plan for Dam Failure to residents living on the Santee River floodplain below the Santee North Dam. The company will explain what to do in the event of a dam failure at Sampit Elementary School in Georgetown on Tuesday at 6 p.m.

Tracking hazard potential for neighborhood dams

While that may ease your mind, don't relax just yet.  There are more than two thousand dams regulated by our state, 86 percent of them are privately owned and maintained. They look more like grassy dikes than dams.

One of them is in a Moncks Corner subdivision, and at least one person who lives there said there is no dam in his neighborhood.

But the state government says there is, and considers it to have significant hazard potential. A high-hazard dam is only feet away from a major highway thousands of you travel every day. It is one of several state-regulated dams in the Lowcountry many of you may not know exist.

The Lowcountry is home to seven state regulated dams. Three are in Dorchester County and four are in Berkeley County.

One is in a Moncks Corner subdivision, but some people who live there have no idea it's classified C-2, having significant hazard potential.

The Moss Grove Plantation Dam was in "fair" condition when inspected last December, with the inspector noting it had been "neglected."

The Homeowner's Association president said bids are in hand to clear the vegetation, as outlined in a post-inspection letter. He said the dam had no issues during the record rainfall.

Whitesville Rural Fire Department Chief Timothy Stephenson said when most of us think of a dam breach, we think of catastrophic failure.

"But that's not what usually happens," he said. "Although we did have some levies or dikes that failed, they didn't actually fail at the dam or dike portion itself. They failed because of the erosion from the overflow of the water."

He said that happened at Compton Road, which runs atop Crystal Springs Lake Dam.  While the dam didn't break during the historic rainfall in October,  "The amount of rain overwhelmed the lake," Stephenson said. And through erosion, a water main broke, closing the road.

The Crystal Springs Lake Dam passed state inspection in November of 2014 with a satisfactory rating. That dam, the Moss Grove Plantation Dam and the Lake Hastie Dam in Pimlico in Berkeley County are classified C-2, having significant hazard potential.

A dam considered to have high hazard potential, classified as C-1, is just off Highway 61 at Middleton. Traveling Highway 61 daily are 7,700 vehicles according to the South Carolina Department of Transportation. A dam break could flood, even take out the highway, and that's why the Middleton Lake Dam carries the highest hazard rating.

"We take the responsibility seriously and DHEC does as well," Middleton's Colby Hollifield said.

DHEC, the Department of Health and Environmental Control oversaw construction of the Middleton Dam when it was rebuilt about ten years ago.

"We packed it with clay every six inches," Middleton's Josh Hair said. "It is a very solid wall of clay."

DHEC inspects it.

"They look for rodents, they look for large trees growing, so we keep it all mowed down, we like to have grass," Hollifield said.

A watershed drains into the lake from a mile around.

Video of the swamp during the historic rainfall showed water rushing toward Middleton Lake during October's deluge. Hollifield said the Friday before the storm, DHEC notified them to lower the lake level, if possible.

"So we opened the spill gates, we opened that up," he said.

Through the spill gates, the flow of water is controlled. The lake water is piped under the dam to the other side. Hollifield said during the storm, DHEC called constantly and he could hear conversations on the other end of the line.

"They almost didn't believe that it was working as well as it was, and so they kept asking, are you out there, have you seen it, how close is it to going over 61?" he said. No water flooded the highway there: the Middleton Lake Dam held. "It worked as designed here for sure," he said.

National dam experts say our state needs to fund more inspectors.  While it costs money, they point out, the consequences of dam failure are far more expensive.  Of the 36 dams that breached last month, 31 are regulated by the state, one by the federal government, and four others were unregulated dams.

For information on dam safety, check out the website www.livingneardams.org.

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