Flood maps show potential hazards, development proposals differ

Charleston County’s five to 10-year plan for conservation and growth will be publicly available online Dec. 1, but some say they worry it won’t adequately respond to the county’s 2021 flood maps. The maps show a considerable flood risk in much of the county, including areas heavy with commercial and residential development.

The maps by the Federal Emergency Management Agency (FEMA) indicate a significant part of Charleston County is within either a coastal A zone or an inland V zone. Translated, that means both are classified as high-risk flood zones, which the United States Geological Survey (USGS) reported have a 1% “chance of occurring in any given year.” So a 30-year mortgage on a home in one of these areas has at least a one-in-four chance of experiencing such an event.

In Charleston County, all homeowners seeking a mortgage in zones A or V must have flood insurance, but the requirement doesn’t apply to existing structures. As the city’s Chief Resilience Officer Dale Morris told the Charleston City Paper, the insurance requirement is “actually very narrow,” because it only applies to mortgages, not leases or rentals.

Flood risk may be understated, experts say

“A lot of people think the [FEMA] mapping is out of date because of how quickly development is occurring in Charleston, the city, the county and the region,” Morris said. In other words, many who worry about coastal flooding believe FEMA’s maps understate the area’s flooding. The Woodwell Climate Research Center, for example, a prominent climate institute in Massachusetts, illustrates much higher rates of inland riverine flooding in Charleston by 2050 than the FEMA maps predict.

Morris added the reason these fairly recent maps might be outdated is because sea level rise is also worse than initially expected. The sea level, he said, “has risen 13 inches in the last 100 years here. Seven of that 13 was in the last 30 [years].”

The city of Charleston, according to Morris, is adapting its policies to assume an additional 14 inches of sea level rise by 2050. The resulting coastal inundation, paired with accelerated flooding, is only expected to threaten more homes and commercial buildings. The Woodwell Center in June reported that between 2040 and 2060 the number of at-risk structures in Charleston County is projected to be over 87,000 — about 58% of county developments.

Edisto Island resident Fred Palm, a retired professor of oversight and investigations at the John Jay College School of Public Management, said he became interested in Charleston’s severe flood risk after he heard the phrase “nuisance flooding” and felt it was an oxymoron.

Palm said a dirt-filling practice by developers to raise land to build on is common in floodplains — particularly when flood insurance regulations are dependent on base elevation. So those “who bought their houses not needing flood insurance are the ones needing flood insurance” later, after a rainfall or storm surge, he added.

But Morris said the city has “required two more feet of elevation of that foundation,” which adds resilience to its infrastructure. He told the City Paper that Charleston is a part of the Community Rating System, an economic incentive by FEMA to make cities more resilient to climate change. Every time the city’s rating improves — by implementing more regulatory policies and measures — homeowners get discounts on their flood insurance premiums.

Funding for I-526 expansion gets in the way

Despite all of the data about how many businesses and homes are at risk for severe flooding, Charleston County Council plans to propose a 2024 referendum for a half-cent sales tax, much of which would go toward extending the Interstate-526 Corridor (I-526), also known as the Mark Clark Expressway.

Moreover, the most recent update of the county’s comprehensive plan in 2017 included the highway extension. While the plan isn’t a set of enforceable legislation, it’s a “guide for future decision-making” for the public, government, developers and landowners. Given the proposed sales tax referendum, it seems that the council isn’t planning to cut the I-526 expansion out of the 2023 version.

County Council Chairman Herb Sass of Mount Pleasant defended the tax referendum, a measure he referenced when asked about raising money to prevent flooding for Charleston residents. As for the extension the referendum is also funding, Sass said it would help to alleviate traffic congestion and save time for commuters. He told the Charleston City Paper that the increase in sales tax, which has also been the subject of a 2004 and 2016 referendum, has funded necessary roads no other jurisdiction planned to build. Sales taxes also invest in the county’s Greenbelt program and improve public transportation, Sass said.

But the cost of extending the interstate is growing — and not just by a little. Four years ago, it was priced at $725 million. Now, it’s more than $2.35 billion. Sass, however, said the sales tax, which is predicted to raise around $5.4 billion, will “more than cover Mark Clark and other road projects as well as CARTA [public transportation] and Greenbelt” projects.

Sass told the City Paper that the tax also funded the county’s preservation of “44,000 acres of land from ever being developed.” The council chairman added that the county does not “build any roads to a place that’s not developed. We build roads because we already need them.”

But according to a 2023 petition opposing the extension, it seems some residents are concerned about growth on James and Johns islands, two already partially developed areas. They’re worried I-526 would make these places vulnerable to the negative impacts of additional mass infrastructure, citing Daniel Island as an example.

In general, both highways and development exacerbate flooding by replacing soil with “impermeable surfaces” like concrete and asphalt, which “accelerate runoff to ditches and streams,” according to USGS.

Palm said for the expressway not to be impacted by future flooding, the county would need to build high above ground level. Charleston County, he added, would have to build elevated access roads too, upping the project’s price tag to closer to $3 billion.

Sass said he hopes the county will construct the I-526 extension and its access roads above floodplain elevation. “I would think we’d be foolish to build a road that we thought was going to be covered by water.”

Progress at the city level

The city of Charleston in April 2023 passed an ordinance to ban slab-on-grade construction starting next year, a practice the Southern Environmental Law Center noted “disturbs the ecosystem” and can “exacerbate growing flood risk.” But the ordinance does not apply to residents of any town outside the city’s jurisdiction.

The city of Charleston — alongside the U.S. Army Corps of Engineers — is also planning to build a sea wall, said Dale Morris, its chief resilience officer.

“If you don’t do [the sea wall], the peninsula is not manageable in 2050 or 2060,” he said, adding that when people think of a sea wall, they usually imagine something ugly — even though it may not be. The lower Battery, he noted, is one example that challenges public misconceptions. What’s more, Morris said, the peninsula sea wall is going to be complemented with nature-based features for aesthetics and conservation.

He added despite concerns that the wall doesn’t adequately address environmental justice, the city has mapped the location of communities most vulnerable to the effects of environmental racism to design focused resiliency plans.

Federal policy for a sea wall is based on a cost-benefit analysis, however, so any land without development won’t be protected. “There’s no financial reward right now for the city — for the federal government, which pays 65% of the costs — to extend the wall” to these areas, Morris added.

Flood policy watcher Fred Palm of Edisto Island said this is all part of the way economic policy values the things around us. Nature here, he said, is worth zero dollars.

“When we take nature out of circulation by putting an ‘improvement’ on it,” there’s no cost, per se, of destroying the land. “But if we take a life, then that becomes an economic discussion.”