Botanical Garden weathers the storm — precisely as planned
CLEMSON — Thanks to a 2013 flood that wreaked havoc at the South Carolina Botanical Garden, the prized 295-acre venue was able to escape this past weekend’s historic storm relatively unscathed.
On July 13, 2013, more than 11 inches of rain fell in just a few hours. Sixty-four million gallons of water rose out of the Duck Pond and blasted through the Natural Heritage Garden Trail, leaving destruction in its wake. But lessons learned and actions taken after the 2013 event paid off this year, when more than 9 inches fell Thursday-Sunday. Except for a few downed trees, some cracked asphalt roads and minor damage to a couple of newer exhibits, the garden avoided catastrophe.
“We learned from what happened in 2013 and applied what we learned – and it worked,” Botanical Garden director Patrick McMillan said. “Volunteers, staff and faculty put a tremendous amount of effort into projects designed to work with Mother Nature. This past weekend really shows what happens when you do things right. Instead of destroying the trail and surrounding areas, the floodwaters passed through without causing major damage.”
Though changes and improvements were made throughout the garden after 2013, The Hunt Cabin and the nearby Natural Heritage Garden Trail received most of the attention. From a parking area well above the cabin, a paved road leads steeply downward and runs between the historic cabin and the Duck Pond. This impervious surface served as a racetrack for rushing water, so McMillan and his team decided it was time to lower the speed limit.
“We wanted to slow the water down and have it go where we wanted it to go instead of where it wanted to go,” McMillan said. “So we built speed bumps on the road that acted as water bars, with each bar guiding water into a designed system, such as a bio-swale rain garden. The last two speed bumps feed into a ditch that is lined with a special material provided by Clemson researcher Cal Sawyer and then planted over with monkey grass. This ditch worked really well to slow down the water, infiltrate as much of it as possible into the groundwater and then direct the remainder into the Duck Pond rather than over the shoulder of the road into the Hunt Cabin area.”
Though other parts of South Carolina received more than 20 inches of rain this past weekend, the garden certainly received a sizable share, with most of it falling during ferocious spurts on Thursday and Sunday. In 2013, the Natural Heritage Garden Trail — which had first opened just two months before that year’s storm struck — was smothered by 16 feet of water. The deluge destroyed approximately half of the collection of more than 1,000 varieties of plants and washed away all but one bridge. Silt and debris could be seen clinging to high tree branches for days afterward. The total damage was estimated at more than a quarter million dollars. But despite the horrors the flood inflicted, it ended up providing the impetus to rethink and rebuild. As a result, the trail and its surrounding areas rode out the 2015 storm precisely as planned.
“It really is kind of a miracle that Hunt Cabin and the National Heritage Garden Trail remained intact,” McMillan said. “We had more than 9 inches of rain here overall. On Thursday we got about 5 inches, and the Duck Pond came within just a couple inches of going over the top. And the rain that we had on Sunday — another 4-plus inches — didn’t take it over the dam, so we dodged a bullet there.”
Other post-2013 improvements included nature-friendly bridges designed by a team of architecture, art and engineering students from Clemson. The bridges, which are made of Cor-Ten steel, are designed to allow water to flow through the structure and snap away if overwhelmed by a flood surge or struck by a falling tree, thus avoiding tearing out an entire bank. McMillan and his team also prepared canals, swales and other features to divert floodwaters away from sensitive areas.
“It all worked, and that’s really the amazing thing,” McMillan said. “Rockie English with Sustainable Trails here at Clemson University devised the heritage trail so well, nothing was washed away. Kudos to his group. And there are so many others who deserve credit. Because of the 75-plus projects we’ve completed since 2013, the garden remains intact.”
Still, massive storms almost always cause some level of destruction. Events of this caliber can alter the appearance of the natural world.
“Rain and floods of this magnitude are becoming more and more common,” McMillan said. “We have had a ‘1,000-year’ event, a ‘640-year’ event and a ‘250-year’ event all in the past three years. It seems like we might need to recalculate the periodicity of such flooding. Change is happening all the time and you don’t need to look only to gardens and parks to see its impacts. It is being felt in the natural communities as well.”
At the garden, a large yellow poplar was among the dozen or so trees that fell this past weekend, its gnarled roots tearing up a portion of a nearby trail. And even worse, a 150-year-old white oak might also collapse. Cracks in the trail caused by the majestic tree’s rising roots are a bad sign.
“These cracks are indicating that this oak is going to go,” McMillan said sadly. ”And what’s worrying me even more is that the oldest tree in the garden — a 300-year-old shortleaf pine — is in the oak’s path. If the oak goes down, it could take out that ancient shortleaf, which is my favorite tree in the entire garden.”