Those hoping to fathom the complexities facing Charleston from flooding and rising seas should consider the “weeping sidewalks.”
Anyone walking along the east side of Lockwood Boulevard at high tide on Thursday couldn’t help but notice water bubbling upwards from the path near the town’s marina and Alberta Sottile Long Lake. The swollen Ashley River was pressing hard towards the lake, with more force than their shared underground pipe could handle. This pushed the water up creating a small bubbling puddle on a perfectly sunny day.
A similar weeping sidewalk along Murray Boulevard just south of the Coast Guard Station was tackled when this section of the weak battery was rebuilt and raised nearly 3 feet.
These examples illustrate the sheer scale of Charleston’s flood challenge: it’s not just about collecting and directing rainwater falling from the sky, or preventing ever-higher tides or future storm surges. to spread on our lands. The other challenge, much less discussed and probably less understood, is to ensure that groundwater does not seep from below.
Meeting the challenge of rising groundwater will be crucial to the city’s overall success in staying dry and livable. As the tides have gotten higher and higher in recent years, the city has managed to respond by installing dozens of new backwater valves. These backflow prevention devices helped prevent higher water from rivers and harbors from backing up through storm drains onto city streets, creating the phenomenon known as “sunny weather flooding.” “.
But as the sea continues to rise, flooding on sunny days can also be expected in people’s yards, local parks and other places due to shallow aquifers and rising groundwater. This has already been noticed on playgrounds in Charleston’s Rosemont community, which got muddy even days after the most recent rain, says Dale Morris, Charleston’s resilience manager.
“If the river is connected to a shallow aquifer, and it most likely is, the water pressure in the river will force the water back up onto the land,” he says. “That’s where you get those muddy baseball or soccer fields. In the future, it could be people’s backyards. … It’s going to start happening in more places because of the nature of shallow aquifers. This is what we have to study.
Although the federal government and academic institutions such as the College of Charleston have conducted analyzes on these aquifers, the available data has not been aggregated and likely has gaps. The City’s Water Management Plan, work on which should begin soon, should help complete the picture and see things more clearly.
If the city goes ahead with plans for a billion-plus dollar perimeter protection system for the peninsula, groundwater investigation should also be a key focus. There is no point in building a wall along Lockwood Boulevard, attractive as it is, if groundwater during a storm saturates the peninsula to a point where levels rise dramatically in Alberta’s Sottile Long or Colonial Lake. – or in parks and backyards. “If you put a structure in place to handle surges, and the water pressure during a hurricane is so high outside the wall and there’s a direct groundwater connection under the wall to inside the city, the water would go right under the wall,” Morris said. “That’s not good.
Not well indeed. The next phase of the perimeter protection study, known as PED (preconstruction, engineering and design), is to determine where sheet piling or other steps will be needed to complete any above ground surge barrier. To complicate matters further, the increasing salinity of aquifers and groundwater can threaten trees and other vegetation established when that water was softer.
It is imperative that the city learn more about what is happening with the water immediately below our feet. Although largely hidden – save for the occasional weeping sidewalk or muddy field – it is very much about the challenge of dealing with unwanted water from clouds, high tides and angry seas.