In Search for Flooding Solutions, Conway Looked to Carolina BaysJan 09, 2024 01:01PM ● By David Caraviello
The worst of it was 2018 and the aftermath of Hurricane Florence, whose torrential rains swelled upland rivers and sent all that water rushing back toward the coast. But that wasn’t the only flooding event that April O’Leary has experienced since moving to Conway — now even sustained heavy rains can overwhelm Crabtree Canal, a waterway which runs near her home in the Sherwood Forest community.
“If there’s an event that has both localized rain and rain moving downstream from our headwaters, it’s a compound flood — and that’s particularly problematic for Crabtree Canal,” O’Leary said. “It can’t handle that much water or rainfall.”
The flooding was so bad after Florence that water filled living rooms, and residents of the area had to park their cars on a patch of high, dry ground nearby, and paddle kayaks to get to their vehicles and go to work. The city began acquiring properties near Crabtree Canal through a FEMA buy-out program, and one day former Conway public works director Kevin Chestnut looked at the open land left behind and wondered about creating a stormwater retention project that would help mitigate flooding in the area.
That once-aspirational goal reached a major milestone recently when FEMA awarded Conway a $2.17 million grant to build a stormwater and park project in the area most affected by flooding near Crabtree Canal and the surrounding swamp of the same name. Robinson Design Engineers, the Charleston-based environmental engineering firm attached to the project, plans for the retention area to mimic a Carolina bay, which is a shallow, elliptical depression common in the state. The project was named Chestnut Bay after the former Conway administrator, who retired after being diagnosed with ALS.
“He was such a great asset to the city,” said Mary Catherine Hyman, Conway’s deputy city administrator. “He always could see things that others didn’t. He could look at a project from different angles, and find solutions and problems that others didn’t see. And he’s sorely missed here, but we’re so glad we can honor him with this project.”
A ‘constructed wetland’
While Carolina bays are not exclusive to South Carolina, the S.C. Department of Natural Resources reports that around 5,000 of them have been mapped in the Palmetto State. No one is certain how they were formed—one theory is that they are the remains of ancient, shallow lakes—yet they are universally ovular in shape, aligned along a northwest-to-southeast axis, with sand rims on either side. They range from 30 feet to 3 miles in diameter, and their interiors may be filled with swamps, water, or remain dry.
Undisturbed Carolina bays also collect rainwater and help prevent flooding. The artificial Carolina bay crafted by Robinson Design Engineers, which will replace what is currently the intersection of Freeman and Godfrey avenues, will have a permanent pool depth ranging between 12 and 18 inches, but can store a maximum of three feet of water during a storm event.
Chestnut Bay will include vegetation of various heights, in addition to flood protection berms built from excavated material. The area around the man-made bay will also include a boardwalk, children’s play area, fishing pond, and restrooms, allowing the 7.8-acre site to function as a community park when it’s not being employed as a flooding mitigation device.
Currently, “runoff in the neighborhood is going through stormwater pipes and ditches and straight into the canal,” Hyman said. “This will bring it into a constructed wetland, so it’s infiltrated into the ground. Some of it will be taken up by the trees and the plants, and that will slow it down and filter the water before it reaches the canal — which is where we see the problem now, because that’s where the flash flooding comes from.”
The other part of the project involves resorting Crabtree Swamp’s natural floodplain. Crabtree Canal was dug in the 1960s by the U.S. Army Corps of Engineers in an effort to help drain nearby tobacco farms. The resulting sediment was simply piled onto the adjacent banks, “creating a very steep, unstable levee system with failing banks and an unstable channel bottom that isolated the remaining floodplain, increased water velocities, and eliminated habitat and fish spawning grounds,” according to researchers at Coastal Carolina University, which is located in Conway.
Conceptual designs by Robinson Design Engineers call for adding features like flow-through channels, side slopes, and depressions, all of them designed to help mitigate the effects of post-storm riverine flooding by allowing the swamp’s floodplain to hold more water.
“Big rivers in my mind are like interstates, and some of these smaller rivers feeding into them are kind of like on-ramps,” said Joy Brown, resilient communities program director for the South Carolina chapter of The Nature Conservancy, which has partnered with Conway on the project. “So, the water was having a problem draining out of some of these communities, because that interstate was draining those big floodwaters, and these on-ramps were getting backed up. So, the hope is that this project can more safely hold that water while these big rain events have the time to drain out.”
Added O’Leary: “Any enhancements we can make to Crabtree Canal in conjunction with projects like manmade Carolina bays would make a big difference, especially for flash flood events and even riverine flood events.”
‘Do we want to do something?’
Since 2016, the South Carolina chapter of The Nature Conservancy has engaged in a program called the North Coast Initiative that explores potential environmental issues in Georgetown and Horry counties. It was in community meetings involved with that project that the organization was first made aware of the flooding problems in Conway, where the city was buying out homes to move people away from the areas most affected by flooding from Crabtree Canal.
“That area has been razed. It’s been taken all the way back to green,” said Brown, of The Nature Conservancy. “The city will have to maintain that property in perpetuity. So, do you just want to send people out and let them mow grass forever? Or do we want to do something? Because it was situated very near Crabtree Swamp, we saw some opportunities to maybe utilize that as kind of a storage area.”
A $40,000 grant from Boeing allowed The Nature Conservancy to contract with Robinson Design Engineers for a conceptual design on the Chestnut Bay project — which in turn, helped the city land the Building Resilient Infrastructure and Communities grant from FEMA. A dedication ceremony for the Chestnut Bay initiative was held in November, although breaking ground on the project — much less finishing it — remains still to come.
Under the terms of the BRIC grant, Hyman said, all engineering and design on the project must be completed by December of 2025. “However, we’re hoping to be done prior to that date,” she added. “And once that engineering and design is done, we will procure a contractor to begin construction.”
To residents like O’Leary, who started a group called Horry County Rising to lobby for wetland protections to help stem flooding, it can’t come soon enough. “The Chestnut Bay project will help slow, store, absorb, and evaporate rainwater before it discharges into Crabtree Canal. It will help prevent flash flooding, and improve water quality,” she said.
“I believe the project will help improve flood conditions, but it’s not going to reduce our risk. If we could replicate this project on a much larger scale and scope, it could make a real difference, but one project will not solve the flooding we experience.”
Replacing lost value
As a bio-retention area designed to hold stormwater, Chestnut Bay is the type of nature-based approach that The Nature Conservancy tries to encourage — one that falls in line with similar efforts like the restoration of sand dunes and oyster reefs, and the “living shoreline” created on Gold Bug Island near Mount Pleasant, which transformed a heavily eroded area into one that now supports oysters and marsh grass.
In the case of Chestnut Bay, “everybody brought some creativity to the table,” Brown said. “The city of Conway was already thinking through new and different solutions — like putting boat cleats on the roofs of some buildings down by the river so people could access them through the top if they got flooded, and making portable fuse boxes people could remove if there was flooding in certain areas. So, they already had a lot of creativity going into this, but by bringing in Robinson Design Engineers and The Nature Conservancy and thinking through more natural options, it was just a great partnership. And we would love to see more of these projects.”
Hyman, who lived in Sherwood Forest during Hurricane Florence, said residents of the area are eager to see the project started. “It’s not only a stormwater infrastructure project, but it’s also going to serve a lot of other roles,” she said. “I think it will really improve the value of a neighborhood that has been hit so hard by these floods and will really help with the property values and just the overall morale of the neighborhood. They’re really excited.”
O’Leary said she’d like to see the project replicated throughout the watershed, in addition to Crabtree Canal widened. But for someone who’s endured three 500-year flooding events in five years, Chestnut Bay offers a hopeful first step.
“Our community has lost a tremendous amount of value because it flooded,” she said. “Creating an amenity like the Carolina bay that will include a park for recreation helps communities like ours recover some of what has been lost. Also, there’s no such thing as recovery when you flood. There is a grief that’s unspeakable, and many families feel forgotten about. Projects like these, supported by our elected officials and created by municipal staff, show affected communities that they care about us, even this many years later.”