Old Village flooding (copy) (copy)

David Lynn trudged though a flooded street in Mount Pleasant to check on his mother-in-law during Tropical Storm Irma on Sept. 11, 2017. The storm was the latest in a series of major flooding events in South Carolina. Wade Spees/Staff

Following three consecutive years of serious flooding in South Carolina, towns and cities are increasingly taking steps to limit the amount of rain-soaking ground covered with pavement and rooftops.

In Columbia, significant increases in stormwater fees have created a powerful financial incentive to limit impervious surfaces such as pavement, which increase stormwater runoff, flooding and pollution of waterways. Along the coast, Mount Pleasant has joined some barrier islands that limit the portion of a residential property that can be covered with such surfaces.

“Clearly, the more impervious surface you put on the ground, the less places water can go," said Mount Pleasant Assistant Town Administrator Christiane Farrell.

Pawleys Island was an early adopter, with rules adopted in the 2000s that not only limit impervious ground cover to 40 percent of any property but also prohibit impervious driveways. Any new or replacement driveways on Pawleys Island must use materials water can run through, ranging from gravel to pavers and pervious concrete.

“The whole point is so that the water can penetrate the ground, and have less runoff," said Pawleys Island Administrator Ryan Fabbri.

In Beaufort County, commercial properties must be developed in ways that mimic having no more than 10 percent impervious ground cover. That means most of the property might be covered with buildings and parking, but engineered stormwater systems limit the volume and rate of runoff.

"Stormwater runs off a parking lot much faster than a meadow or a forest, so you can get flash floods," county Stormwater Manager Eric Larson said. "We use all different kinds of best management practices to capture and retain the stormwater on site."

For example, a more than 40-acre site in Bluffton is home to both a Walmart and a Sam's Club, with parking for both. But the parking area has rain gardens within landscaped medians, some areas with pervious pavement, and a pond system that collects runoff and uses it for irrigation.

In Mount Pleasant, the state's fourth-largest municipality, Town Council in September imposed an impervious surface limit on hundreds of residential properties in one of the oldest parts of town, in an effort to combat stormwater flooding.

Like Pawleys Island, Mount Pleasant requires that in a 900-acre, flood-prone section of town, new construction including building additions can't result in more than 40 percent of a property being covered by impervious surfaces. That includes buildings, driveways, patios and swimming pools.

Previously, the town regulated how much of a property could be covered by buildings, but only the Old Village Historic District had a limit on impervious coverage.

“I’m seeing it a whole lot more," said Chuck Jarman, water resources engineer for the Clemson Cooperative Extension. "That’s becoming a more popular means of managing stormwater."

Columbia has taken a more aggressive stance on stormwater but is relying on a financial carrot-and-stick approach. The state's second-largest city charges a monthly stormwater fee that's based on impervious coverage, and that fee is rising fast.

For example, a large commercial property with 100,000 square feet of impervious surface, which is about 2.3 acres, would now pay $483.80 each month. That works out to $2,460 more, yearly, than the city charged at the start of this year.

“It’s going to continue to increase over the next couple of years," said Columbia Stormwater Manager Mike Jaspers. “With the increase in the fee, the incentive is higher.”

Businesses can cut costs by having less impervious surfaces, by using pervious pavement, for example, and they can get stormwater credits by taking steps to reduce stormwater runoff, such as rain gardens and green roofs.

For a large organizations in Columbia, such as University of South Carolina, stormwater fees can add up to hundreds of thousands of dollars each year.

“With the new fee, what may not have been cost-effective before could be now," Jaspers said.

Limits on impervious surfaces, or fees to discourage them, go hand in hand with other efforts to address stormwater flooding. In Charleston, the state's largest city, efforts range from massive drainage tunnel and pumping systems to a recently announced study, looking at how trees can be used to reduce stormwater problems.

“I think it’s all part of a bigger picture, a bigger effort," Farrell said. “Resiliency is going to become more and more of a discussion."

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Reach David Slade at 843-937-5552. Follow him on Twitter @DSladeNews.

David Slade is a senior Post and Courier reporter. His work has been honored nationally by Society of Professional Journalists, American Society of Newspaper Editors, Scripps foundation and others. Reach him at 843-937-5552 or dslade@postandcourier.com

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