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Reports Help Governments Plan as Rising Seas Meet Roadways

Dec 4, 2019

As sea levels rise, roads that now flood only during the highest tides will be impacted more frequently, in some cases often enough to require they be raised or closed to traffic.

Reports funded in part by S.C. Sea Grant Consortium aim to help state and municipal planners by quantifying the potential problems and examining the legal complexities of maintaining roads in low-lying coastal counties. The decisions will not be easy or inexpensive.

In South Carolina, 108 miles of roads would face repetitive or severe damage with one foot of sea level rise (SLR), according to a 2019 report funded by the National Oceanic and Atmospheric Administration (NOAA) Office for Coastal Management and Sea Grant programs in South Carolina, North Carolina, Georgia, and Florida. The impact jumps to about 213 miles with two feet SLR and about 516 miles at three feet SLR.

University of South Carolina geography professor Kirstin Dow and graduate assistant Eleanor Davis were among the authors of the reports. The researchers used data from detailed maps of road systems layered on projections of sea level rise inundation. In South Carolina, scientists project seas will rise from .5 to 1.5 feet by 2030 and from .75 feet to 3.2 feet by 2050. Even at the low end of those ranges, many coastal roads will be impacted.

King tide flooding inundates a street in downtown Charleston. Photo by Sarah Watson, S.C. Sea Grant Consortium.

“Road Vulnerabilities to Projected Sea Level Rise by County: North Carolina, South Carolina, and Georgia” provides a general estimate of the scope of the decisions facing road maintenance agencies in South Carolina. About half of the potential roads impacted would be in two counties – Charleston (37 miles at one foot SLR, 82.2 miles at two feet SLR, and 229 miles at three feet SLR) and Beaufort (23.2 miles at one foot SLR, 47.5 miles at two feet SLR, and 132.2 miles at three feet SLR). The other impacted roads are spread throughout Berkeley, Colleton, Dorchester, Georgetown, Horry, and Jasper counties.  

The state maintains many roads in South Carolina, including about 57.5 miles that would be affected at one foot SLR, 97.1 miles at two feet SLR, and 188.1 miles at three feet SLR, according to the report. County and municipal governments and private entities also manage roads. In Charleston County, for instance, the state maintains 24.9 miles of the roads potentially impacted at one foot SLR, county and municipal governments are responsible for 11 miles, and 1.1 miles are privately managed.

The report’s authors say the data indicate adaptation planning on how to deal with road inundation must be focused locally and should involve multiple jurisdictions.

A separate report put together for the regional NOAA/Sea Grant project details the consequences of government action or inaction. “Legal Issues When Managing Public Roads Affected by Sea Level Rise” raises concerns about potential negligence liability if roads are not maintained or “takings” lawsuits if roads are abandoned, leaving owners with no access to their property. South Carolina law requires governments to compensate property owners if a  government action deprives them of use of their property.

The reports don’t suggest particular solutions. Instead, they are designed to provide data and legal precedent to inform discussions. “Sea level rise poses a significant threat to infrastructure in coastal areas of South Carolina,” the legal report notes. “Deciding how to adapt and manage roads in light of this threat is a question for all levels of government to consider.”