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Laborers working for Audubon South Carolina loaded 400 trees at a time in to the bags to plant in Four Holes Swamp. Cori McIntyre from ASC/ASC staff

Cypress trees, swamp oaks, tupelo — more than 215,000 native wetland trees have just been planted to restore 500 acres in Four Holes Swamp near Holly Hill. 

Think of them as a solution to flooding.

The Audubon South Carolina seedling effort will create a couple of hundred-thousand more tall straws in the swamp's ability to suck up floodwaters that otherwise would deluge the rapidly developing Charleston suburbs downstream.

The massive swamp collected or bogged down some 230 billion gallons of the historic 2015 flood that was the remnants of Hurricane Joaquin, according to an Audubon analysis — no small share of some of the 11 trillion gallons that rained over the Carolinas combined.

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Seedlings for 215,000 wetlands bottom trees were planted across 500 acres in Four Holes Swamp. Cori McIntyre from ASC/ASC staff

That's the value of "green infrastructure," a longtime focus of preservation groups that is getting new attention as suburban growth packs around metro areas and extreme weather, like flooding, becomes more common.

"We have to be prepared for a a new normal, a changing weather system that's going to affect our communities as well as our habitats, birds and other animal species for the foreseeable future," said Sharon Richardson, the Audubon South Carolina director.

The trees were planted on an obscure tract south of U.S. Highway 15 near the Orangeburg-Dorchester county line that Audubon is reclaiming to wetlands from previously ditched and drained commercial pine timberland.

Over the centuries, wetland trees adapted for this volatile region, where in the past the undammed lower Santee River sometimes would flood 5 miles wide.

The trees meant a lot more than flood control: They were a key canopy for the staggeringly diverse environs of Lowcountry plants and animals. 

They also provide carbon storage to mitigate the climate warming effect of today's fossil fuel burning.

Floods have started coming frequently and severely enough that Gov. Henry McMaster in 2018 formed a Floodwater Commission to promote mitigation and other solutions.

The planting is one of the first demonstration projects. Tom Mullikin, the floodwater commission chairman, called it common sense and win-win.

 "Approaches that protect restore and mimic natural systems not only protect against the worst effects of flooding, but also provide rich and productive habitat for our wildlife," he said.

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The huge, water absorbing cypress in Four Holes Swamp near Harleyville provide flood protection for populated Charleston areas downstream. Provided/Mac Stone

Projects like the one Audubon is doing are one of the best defenses the region has against floods, said Mark Robertson, director of the South Carolina chapter of the Nature Conservancy.

"We’ve seen that when these floodplains get developed, neighborhoods that never used to flood will start flooding," he said.

"Two of the best things we can do to protect our existing healthy floodplains are not build on them and then — as Audubon is doing — restore those floodplains to a more natural condition. The types of trees do make a difference, and replanting native cypress and hardwoods is a good long-term solution," he said.

The Four Holes Swamp might be the largest remaining virgin cypress-tupelo swamp forest in the world. From a few springs near Orangeburg it flows in a wide bend some 60 miles to the Edisto River near Ridgeville. Its wetlands cover some 45,000 acres — about the size of Washington, D.C. — and at points spread 2 miles wide.

Nearly 2 feet of rain fell in spots in less than a week during the 2015 flood. More than 20 rivers broke or nearly matched records for the volume of water streaming. The people who manage these crises in the state roundly agreed the floodwaters would have overflowed any artificial defenses that could have been built.

The Edisto River’s gauge recorded the heaviest volume of flow in 87 years of record-keeping. Without the swamp it could have been a lot worse. About one-third of the water in the lower Edisto comes out of Four Holes. 

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Reach Bo Petersen at @bopete on Twitter or 843-937-5744.

Science and environment reporter. Author of Washing Our Hands in the Clouds.