Clemson students devise rising sea level responses

Imagine the historic Charleston peninsula becoming a Lowcountry version of Venice, Italy, with canals replacing major streets in response to rising sea levels.

Clemson School of Architecture students devised that concept and other thought-provoking scenarios while examining how global warming could affect Charleston and how the city could respond if money were no object.

Their concepts included elevating the Crosstown Expressway and building a series of retention ponds underneath, a sea wall running along the Ashley River and creating a massive levy jutting out from the coast to protect the harbor and barrier islands.

Don't laugh, said professor Ray Huff, who noted the extensive dike system in Holland.

Most scientists agree that sea levels will rise at a faster pace this century due to global warming. The U.S. Environmental Protection Agency's most recent estimate says the sea level in Charleston will likely rise 19 inches by 2100.

That would submerge marsh and wetlands, erode beaches, increase flooding and amplify storm surges, according to the EPA.

Clemson students considered how Charleston might respond if sea levels rose by 1, 3, 6 or 12 feet. Charleston's top city planning officials attended a presentation of their conclusions last week.

With a 1-foot rise in sea level, which is just three inches more than the sea level rose in the 1900s, Charleston's downtown flooding problems would worsen and marsh areas would be threatened.

Clemson students suggested creating a series of retention ponds to trap floodwater and then slowly release it, and new pervious roadways that would allow water to pass through the pavement into drainage systems below.

They also proposed elevating the Crosstown Expressway, a major evacuation route that could become unusable if submerged.

City officials have considered retention ponds before but rejected the concept because they would likely fill with groundwater, essentially becoming tidal pools and defeating their purpose.

Charleston's drainage improvement efforts have so far focused on massive tunnels and pumping stations. Construction is starting this year, for example, on a more than $20 million project to address Market Street flooding.

If sea levels rise by 3 feet, Charleston's peninsular marshes could be submerged and property would be threatened. At that point, Clemson's students proposed building a 9-foot sea wall along the Ashley River, with pedestrian access on top, like the Battery.

"These 1-foot and 3-foot scenarios are things we should be thinking about," said Greg Carbone, a University of South Carolina professor who frequently lectures on climate change issues and attended the Clemson presentation.

"Do we want walls here? Do we want retention ponds? These are things that ought to be discussed now rather than later," Carbone said.

If the seas rose by 6 feet, something the students concluded was possible during the next 150 years, student Melissa Discepolo said the southwestern tip of the peninsula below Calhoun Street could be rebuilt to allow the sea in.

The land would have to be raised to the elevation of King Street, about 13 feet above sea level, and roads would become canals.

"It would be like a historic Charleston-Venice kind of thing," she said.

At 12 feet, a sea level rise that would submerge most of the peninsula, Charleston would be in a New Orleans situation, requiring a 30-foot wall encircling the peninsula. Or, said student Tim Hoskins, a massive levy could run through the ocean from Mount Pleasant to Johns Island.

Hard to picture? The project will be exhibited at the Charleston Civic Design Center, 85 Calhoun St., from May 24 to June 29.

Reach David Slade at 937-5552 or dslade@postandcourier.com.