In 2018, the U.S. Army Corps of Engineers, Charleston District embarked on a $3 million, federally funded study of coastal flooding in downtown Charleston. The result? Researchers concluded that the most economically + environmentally viable solution to combat coastal flooding downtown would be to build a protective wall around the perimeter of the peninsula.
How we got here: Conversations about flood management in Charleston began long before global warming became a mainstream concern. In fact, the city’s first tide gauge was installed in 1899. Since then, the sea level has risen in the Charleston Harbor by 1.07 feet.
The tentatively selected plan laid out by the Army Corps of Engineers proposes the following structural measures:
○ A storm surge wall along the perimeter of the peninsula. The combined elevation of the wall and the ground beneath it would reach 12 feet. Two types of walls would exist: “t-walls” – which are basically large, concrete barriers supported by steel piles – would be built over areas where there is hard ground water; and “combo-walls”, which are more aesthetically pleasing, would be used in marshland and areas with softer ground.
○ Various storm surge gates that could be closed during low tide prior to the arrival of a major storm in order to make way for water storage.
○ A wave attenuator – a floating structure designed to reduce the intensity of waves when they reach the peninsula – would be constructed about 230 feet offshore. The height of that structure is TBD.
○ 10 pump stations to prevent rainfall runoff from pooling within the storm surge wall. Half of those stations would be permanent, and half would be mobile.
More minimal, non-structural measures are recommended for residential communities (such as the Bridgeview Village apartments and the Rosemont neighborhood) that would not fall within the area protected by the proposed wall due to their higher elevation, but are still at risk of flooding. Other than the placement of temporary barriers and ring dikes, it is unclear what those non-structural measures would include.
Additional considerations laid out by researchers include a possible walkway along the battery, which would look similar to the existing walkway.
What happens if nothing is done?
Experts project that the sea level could continue to significantly rise by the end of this century – and that flooding events will continue to increase in both frequency and intensity. According to potential storm surge maps created by the NOAA, a CAT5 hurricane could put the entire peninsula under 9 ft. of water.
Upwards of 500 properties within the study area have been identified as “Repetitive Loss” structures because of repeated flooding. Between 2010-2018, the city’s population grew at more than three times the rate of the U.S. (18.5% compared to 6%). Researchers say they assume that as development and population increase, so will the number of structures damaged by flooding.
If nothing is done, the Army Corps of Engineers says that between now and 2075, a major storm could put nearly 67% of the peninsula at risk of 9 feet of water elevation. Contained in those at-risk areas are hospitals, police and fire stations, culturally significant landmarks, businesses, and homes.