Flaws likely in dams that failed, researchers find

Some of the earthen dams that broke during Columbia’s historic flood this month likely were not designed well, relied on suspect materials and were not properly maintained, says a Georgia Tech researcher who recently assessed the failures with a team of experts.

The research team, which included federal officials and experts from Clemson University, likened some of the dam failures in the Columbia area to levee breaches that occurred in New Orleans during Hurricane Katrina 10 years ago, Georgia Tech officials said.

Flawed dams identified by researchers included those at Cary Lake and Lake Elizabeth in Columbia, the Old Mill in Lexington and the Columbia Canal, the main water supply for thousands of city residents. They all failed during the storm. Researchers spent four days in Columbia examining numerous dams before Georgia Tech released the preliminary findings over the weekend.

One of the chief researchers, Hermann Fritz of Georgia Tech, said some of the dams in South Carolina need to be better constructed and maintained in the future. A concrete-reinforced dam at Forest Lake is an example of a sturdy design, he said. The concrete probably helped prevent the dam from failing, he said.

“Forest Lake is one that worked, compared to some of the others,” Fritz said.

Fritz said some of the most obvious problems the research team identified were at Cary Lake in the Arcadia Lakes area.

Fritz said the Cary Lake dam, by all accounts, should not have failed.

The dam at one point was refurbished in the past 30 years and should have been able to withstand the water better than some older dams that did not fail, he said. He said substandard soil could have played a role in the dam failure.

“You would not expect a modern structure to fail like that,” he said. “Something went wrong, either in the design or the construction or the maintenance of that dam.”

A sign of potential problems at Cary Lake was that the dam never was overtopped by rising water during the storm, Fritz said.

Typically, when water overtops an earthen dam, it begins to erode. In turn, that can weaken it and ultimately cause the dam to break.

The residential pond’s dam burst the morning after heavy rainfall on Oct. 4, sending a wave of water downstream that eventually washed out the bridge at Rockbridge Road and contributed to flooding for miles along Gills Creek. Thousands of people fled their homes as flood waters rose.

Some two feet of rain fell over five days in parts of South Carolina, Georgia Tech researchers said. More than three dozen dams in South Carolina, including 17 in the Columbia-area, broke during the torrential rains.

State records show that the S.C. Department of Health and Environmental Control gave the Cary Lake dam a satisfactory rating in its 2014 inspection report. The report noted slight erosion on the downside slope that needed monitoring. But the report said the “dam is in good visible condition.’’

In an email Monday evening, department officials called the torrential rains a “1,000 year flood event” that many dams were not designed to withstand.

The department said it is continuing to assess all high-hazard and significant-hazard dams to identify problems. The agency also said Monday it had issued emergency orders for 75 dams, an action that requires water levels behind dams to be lowered and improvements made to the dams.

Meanwhile on Monday, DHEC said the Windsor Lake dam in northeast Richland County is safe, despite concerns by some residents that it is unstable. Water levels in the lake had not been lowered Monday afternoon, but DHEC said the lake’s owners have a deadline at 5 p.m. Tuesday.

Fritz, who researched levees following Hurricane Katrina in 2005, said other dams in the Midlands also had problems that his group found. All told the group focused on about 10 dams during its four-day examination, although the team looked at more structures.

Researchers took soil samples of failed dams. The group is expected to complete its research in about a month.

Among the dams with problems cited by Fritz:

▪  The Old Mill dam in Lexington was overtopped with water and eventually blew out, he said. The blowout also could have resulted because water got through a seam between two different types of materials in the dam.

▪  The Columbia Canal wall broke, apparently because it was made of varying materials, he said. Part of the wall has stone in it, but other parts of were made of earth. Water found the weak spot between the different materials and broke through, he said.

“The South Carolina flooding was characterized by local dam failures of mostly earthen dams, which was reminiscent to the aging infrastructure and poorly maintained levees in New Orleans during Hurricane Katrina 10 years ago,” Fritz said. “In both cases, earthen dams or levees were aging and poorly designed with soils of limited strength, resulting in breaches prior to reaching their design heights or being overtopped by water.’’

This story was originally published October 20, 2015 at 7:49 AM with the headline "Flaws likely in dams that failed, researchers find."