About 10 miles of brick archways were built below some of Charleston's streets before they became historic, and the city is studying what parts of this 19th century infrastructure could be repaired to help ease flooding in the 21st century.
Many of these underground archways have fallen into disrepair and occasionally have needed emergency patchwork. This summer, city leaders will prioritize which ones should be refurbished for stormwater drainage.
The arches were installed in the mid-1800s in response to the yellow fever epidemic. They helped carry waste from the city into the harbor.
The arches were built just above the water table but low enough so tides could flush out their contents. They are built with brick and mortared together into an arch form, strong engineering according to Charleston's Director of Stormwater Management Matthew Fountain. But the mortar has disintegrated over time.
If a utility company works underground and punches through an archway, there's a chance it could collapse, creating a street closure such as the one on Coming Street earlier this spring.
The city's longest archway starts at Meeting and Spring streets and ends off the battery, and part of it has been cleaned and fortified with mesh and concrete piping. The fortified arch would also take in stormwater during heavy rain, helping ease the street flooding the city sees.
To say these archways have been ignored, other than emergency repairs, might be an understatement. The most information the city has about the archways is from a paper written by James Dingle, a civil engineering student at Cornell University in 1892, according to Fountain.
Dingle, at that time, estimated the cost of about 16 miles of brick arches at roughly $235,000 in 1856 for 16 miles of brick arches, more than $6 million today.
"Even at that time he was saying that they were starting to fall into disrepair and they were starting to have problems then," Fountain said. "Those arches have been there for 150 years just slowly deteriorating, and over the last 10 to 20 years they've started to have more noticeable problems."
The arches "unintended purpose" is to support downtown streets, Fountain said. In some areas, there are buried trolley tracks that help support the space under possibly collapsed archways.
"The problem with an arch is that it works really, really well, but it relies on all the other pieces of the arch," Fountain said. "If you take a piece out, it collapses."
Mayor John Tecklenburg said he is excited about the project and its potential to improve drainage in the city.
"It's kind of remarkable, I'm a big believer in recycling and we're basically recycling a sewer system from 160 years ago or so and using it to augment our existing drainage system," Tecklenburg said.
"The archway tunnels are much larger than your typical 18- and 24-inch pipes, that we lay through drainage systems the last 100 years," he added. "These will carry a good bit of water if they're put in full use even to the point that they're going to provide a reasonable amount of storage."
Tecklenburg said the new use of the archways will be similar to work he saw being done in the Netherlands as part of his research into drainage and sea level rise.
"To the extent that we can get these fully functional again, it would be a great bang for the buck and also in line with our renewed maintenance efforts," he said.
The city already has mapped out the locations of all the archways, which vary in size between 5 feet by 3 feet to as small as 1½ feet by 2¼ feet. Some arches have outflows through the city's battery wall at its southern tip; others empty off of East Bay Street.
City employees will compare the lists before identifying the next project. Fountain said the project will be expensive, but the preventative measure would be more cost effective than making pricey emergency repairs.
"Since we're spending a decent amount of money to go in and fix all of these arches as they fail, since you can't obviously have a major hole in the middle of a downtown road, why don't we try to do a more proactive maintenance approach and come up with a plan to actually go in and line and repair all the arches?" Fountain said.
"In order to kind of make that work from a cost perspective, let's say while we're doing that, let's tie in the surface drainage."
The first project might be the arch that starts at Coming and Spring streets and winds toward Logan, Tradd and Council streets before it flushes out the battery. Initial work shows it could provide good drainage, and early cost estimates put the project between $1-3 million.
"It's not a perfect solution," Fountain said. "It's an improvement to the existing situation."
The city also is working on South Adgers Wharf, cleaning that archway out before lining it with mesh and spray-on concrete.
Fountain said the city will apply for funding through the South Carolina Transportation Infrastructure Bank and work with the county and state since those roads are maintained by the state and county.
His staff will work the rest of the summer finalizing a plan, then applying for funding. Ideally, the city will have clarity about funding by year's end. He said the soonest work on the arches could begin would likely be early next year.