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Development boom in Columbia area contributed to dam failures, researchers say

Old Mill in Lexington Recovers after Flood

Ryan Condon and Laban Chappell, co-owners of Lexington's Old Mill mall, talk about damage to the historic structure during this year's flood. The high waters damaged the Old Mill dam, the Old Mill Brewpub and other businesses at the mall.
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Ryan Condon and Laban Chappell, co-owners of Lexington's Old Mill mall, talk about damage to the historic structure during this year's flood. The high waters damaged the Old Mill dam, the Old Mill Brewpub and other businesses at the mall.

Booming growth and development in parts of the Columbia area likely contributed to the failure of dams during last fall’s devastating floods, researchers at the College of Charleston have concluded.

Instead of soaking into the ground, rain that fell during last October’s massive storm ran off pavement in areas that have grown dramatically since 2001 – and that increased the force of water working its way toward dams downstream, according to research presented Friday during a conference in Columbia.

When runoff-swollen creeks hit the dams, the impact likely contributed to their failure, said Norm Levine, a College of Charleston associate professor who supervised the student research project. The research focused on development upstream of failed dams at lakes Covington and Elizabeth in Richland County and of the broken Old Mill dam in Lexington County.

“This shows that we need to be looking at land-use changes both above and below dams,’’ Levine said. “We need to make sure we actually have knowledge of the amount of water that could possibly trigger problems, so we can start planning for the future.’’

Such planning could mean building up earthen dams constructed when parts of the Columbia area were more rural, said student researchers Kelsey Culbertson and Mary Eaton. Some of the area’s dams weren’t built to withstand runoff that increased when upstream watersheds urbanized, they said.

“The main takeaway is the dams need to be upgraded to keep up with the demand,’’ said Culbertson, a graduate student at the College of Charleston.

The research she and Eaton conducted is the first to surface that examines how developed land upstream affected the stability and safety of dams downstream during the storm.

Last fall’s flood caused at least 36 dams across South Carolina to fail – more than half of them in the Columbia area – as sheets of rain blasted the state for days, according to the state Emergency Management Division. South Carolina has about 2,400 regulated dams, but state emergency officials estimate up to 20,000 are not overseen by the state.

Erich Miarka, director of the Gills Creek Watershed Association, said the College of Charleston research highlights a problem he’s been concerned about for some time. Although the college’s study looked at several developing areas outside of Gills Creek, Miarka said his watershed has the same challenges with runoff.

“These kids nailed it,’’ Miarka said. “The root cause of the problem is storm water runoff from all the development upstream.’’

Some property owners might find it difficult to build up private dams because of the expense, but Miarka said several owners in the Gills Creek watershed likely will repair or replace dams to better withstand future storms. The S.C. Department of Health and Environmental Control is weighing whether to approve the repair or replacement of dams battered by the storm.

Miarka, however, said development upstream also needs to be more tightly controlled to limit runoff. That could be done with tougher storm water management standards that would require commercial developments to retain more water, he said.

In making their conclusions, Culbertson and Eaton used rainfall data from the October storm and compared that to areas of both counties with some of the most dramatic increases in development. The research assumed that 35-70 percent of the rain falling in early October would run off of pavement and other development in areas above Covington Lake and the Old Mill Pond.

Above Covington Lake, for instance, maps showed moderate urbanization in 2001, but by 2011, urbanization above the lake had expanded sharply. The lake is close to Killian Road near the increasingly popular Blythewood area of northern Richland County. Maps of the Twelve-Mile Creek area of Lexington County showed similar increases in development.

Some property owners in Columbia have complained that runoff from upstream development increased pressure on dams such as the one at Lake Elizabeth on U.S. 21 north of Columbia. Culbertson said the condition of dams could also have contributed to their failure.

The recently completed College of Charleston study was unveiled Friday at the Geological Society of America’s annual Southeastern conference. Researchers from the University of South Carolina, the U.S. Forest Service and the S.C. Emergency Management Division also discussed research they have conducted about the effects of the storm.

Last fall’s storm dropped nearly 17 inches of rain in the Gills Creek watershed in 24 hours, one of the highest rainfall amounts in the state. The heavily urbanized watershed has a string of dams, most of which are classified as posing a high or significant hazard because of surrounding development.

The storm killed 19 people statewide, displaced 20,000 others and left 40,000 people without drinkable water, according to the Emergency Management Division. At the height of the flood, more than 500 roads and bridges were closed, although most have since reopened, a division official said.

During Friday’s presentations, USC engineer Inthuorn Sasanakul said about 60 percent of the dams in South Carolina are more than 50 years old. Most of the dams are made of earth and are privately owned. Research she is heading is examining failures of both dams and culverts that run beneath roads. Worldwide, erosion causes dam failures more than 90 percent of the time, according to data she presented.

Of the state’s regulated dams, Sasanakul said about 28 percent are considered high or significant hazard structures, meaning they present a danger to life and property downstream.

Photographer Matt Walsh contributed to this story

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