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Stormwater flooding in South Carolina an expensive problem and a hot issue

Jun 20, 2017

By David Slade [email protected]

{Workers with American Bridge and R.H. Moore Company install one piece of a stormwater drainage system in North Myrtle Beach in 2013. The city plans to eventually install 50 new systems, which will treat stormwater and send it 1,200 feet offshore, to replace stormwater pipes that empty onto the beach. Patrick Dowling, city of North Myrtle Beach/Provided}

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When it starts raining hard in South Carolina's cities, elected officials' phones start ringing because of rising frustration about stormwater flooding.

"The homeowners, they are done," said Columbia Councilman Daniel Rickenmann. "I’ve probably had more calls this year on stormwater than any other subject."

More frequent extreme weather, combined with rapid development and historically weak regulation, have resulted in costly and sometimes deadly flooding in unexpected places, and water quality problems in popular spots, such as the Grand Strand beaches and picturesque Shem Creek in Mount Pleasant. 

{An $18.2 million plan to improve Coleman Boulevard in Mount Pleasant should reduce the amount of untreated stormwater runoff flowing into Shem Creek. File/Grace Beahm/Staff}

Columbia is finalizing a budget, unanimously given initial approval Tuesday, that would raise annual stormwater fees by $60 per household starting July 1 and more in the following years, to help fund $93 million of improvements. Mount Pleasant, the state's fourth-largest city, plans to temporarily stop issuing building permits in some areas while stormwater flooding is studied.

Charleston is asking the Federal Emergency Management Agency to fund a buyout of 32 townhomes that have repeatedly flooded, and is working on a system of huge drainage tunnels and pumps for part of the Charleston peninsula costing more than $150 million. North Myrtle Beach expects to spend as much as $100 million over the next 35 years to finish a long-running stormwater drainage improvement plan, partly to keep the ocean from getting so polluted that tourists will be scared off.

"Statewide, the science of stormwater management is catching up with the development that’s occurred," said Eric Larson, board president for the S.C. Association of Stormwater Managers. Larson is also director of environmental engineering and stormwater manager for Beaufort County, which adopted tougher standards for new development last year.

"We are seeing nuisance flooding and downstream flooding because of runoff," Larson said. "In Beaufort County we have shellfish closures, which we believe is directly related to development."

When property is developed, roofs and roads and driveways cover up water-soaking ground. Rain flows across those impervious surfaces, picking up pollution — pesticides, oil, animal waste — as the water flows to lower points. That could be a nearby creek, a pipe outfall on a beach, a dip in a nearby road, a stormwater retention pond or the ground floor of someone's house.

By some estimates used in a city of Charleston presentation, one inch of rain falling on one acre of forest would result in 750 gallons of runoff, but if the same rain were to fall on one acre of paved parking lot there were be 27,000 gallons of runoff. Charleston is working on a grant-funded study to determine if planting more trees and creating more green space would help with stormwater issues.

"We are doubling down on our stormwater policies," said Jacob Lindsey, director of the city's Department of Planning, Preservation & Sustainability. "We think it will need every possible tool."

That includes zoning incentives in a portion of the city, allowing taller new buildings if they include environmentally friendly stormwater features, such as porous pavement, "green" roofs with water-absorbing plants, and features to capture and reuse rainwater. Columbia offers stormwater fee discounts to include such features in new development.

"It’s very common now if you’re building something — and this helps us out — that people want to have green spaces in urban areas," said Columbia Stormwater Manager Mike Jaspers. "They don’t just want concrete and asphalt."

Along the Grand Strand, stormwater from some major roads was originally piped directly onto the beach, and in many cases it still is. North Myrtle Beach has replaced 21 of those pipes with drainage systems meant to reduce flooding, treat stormwater and send that water into the ocean 1,200 feet offshore.

The huge, expensive construction and engineering project was launched after reports of high bacteria levels in the ocean along the Grand Strand, said North Myrtle Beach spokesman Patrick Dowling.

"Tourism is the state’s number one industry, and bacteria counts in the ocean are a great threat to that," he said. 

{Work to replace one of the 50 stormwater drainage systems in North Myrtle Beach, in 2013. Patrick Dowling, city of North Myrtle Beach/Provided}

Due to high bacteria counts, mostly related to animal and pet waste carried by stormwater, long-term swimming advisories started in Myrtle Beach in 2007, and in Surfside Beach and Horry County in 2008, and remain in place, according to the S.C. Department of Health and Environmental Control. The department warns that bacteria levels are typically higher after heavy rains, particularly within 200 feet of drainage pipe outfalls — a direct link between stormwater and water pollution.

"We’ve removed 21 ocean drainage pipes from the beach, and we’ve got 29 left," Dowling said. "They’re very expensive."

A single pipe replacement due to start this fall is expected to cost more than $12 million.

Modern stormwater controls were not required by South Carolina until the 1990s, and current federal stormwater pollution rules just came into play for most large cities across the state during the past decade, so many efforts to address stormwater are focused on older subdivisions and road systems. In Mount Pleasant, despite concern that new development is causing flooding, older subdivisions are where most stormwater funds are spent each year.

"These developments pre-dated the state’s Sediment and Erosions Reduction Act of 1991," said staff comments in an email from Christiane Farrell, the town’s director of planning. "Prior to this, not much emphasis was placed on proper management and stormwater planning."

One challenge for stormwater managers and elected officials is that, while new developments are required to control stormwater, the requirements are based on assumptions about rainfall. If stormwater controls are designed for a 100-year storm, the kind of storm there's a one percent chance of in any year, larger storms could overwhelm stormwater features and cause flooding related to the additional development.

{More than 14,000 stormwater ponds are estimated to have been dug for development on the coast, and more are coming. File}

"Here in Columbia, we had 100-year floods, 200-year floods and a 1,000-year flood, on top of a hurricane," said Rickenmann, the city councilman.

Individual property owners can take small steps to help: installing rain barrels and rain gardens, using porous pavement for driveways and sidewalks, limiting pesticide use and removing animal waste. 

"Every little bit makes a difference," Jaspers said. "One big rain event, and people start talking about how more needs to be done."

 

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

 © 2017, Post and Courier, an Evening Post Industries company.

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