North Carolina: The Likelihood of Shore Protection

Clark, Walter C.; Kassakian, Jennifer; Titus, James G.

Governments Plan for Development of Land Vulnerable to Rising Sea Level: North Carolina

Walter Clark et al. 2010. "North Carolina". In The Likelihood of Shore Protection along the Atlantic Coast of the United States. Edited by James G. Titus and Daniel Hudgens. Report to the U.S. Environmental Protection Agency.

The summary is on this page. You can download either a monitor quality version of the North Carolina sea level rise planning study (pdf 4.8 MB) or a printer-quality version (pdf 15 MB, 168 pp.)

Abstract

Sea level is rising about one inch about every eight years along the coast of North Carolina. Ocean shores are eroding along the Atlantic coast, threatening homes along the Outer Banks. Wetlands are converting to open water, and wind-generated tides flood several communities in the low-lying lands between Albemarle and Pamlico sounds. These effects would become more commonplace if rising global temperatures cause the rate of sea level rise to accelerate. The Intergovernmental Panel on Climate Change, for example, estimates that by the end of the next century, sea level is likely to be rising 0 to 3 inches per decade more rapidly than today (excluding the possible impacts of increased ice discharges from the Greenland and Antarctic ice sheets).

Rising sea level erodes beaches, drowns wetlands, submerges low-lying lands, exacerbates coastal flooding, and increases the salinity of estuaries and aquifers. Coastal communities must ultimately choose between one of three general responses:
--Armor the shore with seawalls, dikes, revetments, bulkheads, and other structures. This approach preserves existing land uses, but wetlands and beaches are squeezed between the development and the rising sea.
--Elevate the land and perhaps the wetlands and beaches as well. This approach can preserve both the natural shores and existing land uses, but often costs more than shoreline armoring
--Retreat by allowing the wetlands and beaches to take over land that is dry today. This approach can preserve natural shores, but existing land uses are lost.

Each of these approaches are being pursued somewhere in North Carolina. Dikes protect some low-lying farms in Tyrill County, and another dike is planned for Swan Quarter. Many estuarine shores have been armored with wooden bulkheads or stone revetments. The Corps of Engineers has placed sand onto ocean beaches. In the aftermath of Hurricane Floyd, many homes in Carteret County were elevated. Homes have been lost to retreating ocean shores in Kitty Hawk and Nags Head, and after Hurricane Floyd destroyed homes in eastern Pamlico County, local officials discouraged rebuilding in the most vulnerable locations.

Nevertheless, there is no explicit plan for the fate of most low-lying coastal lands as sea level rises. Environmental planners do not know whether to assume that the coastal wetlands will be lost or simply migrate inland. Those who plan coastal infrastructure do not know whether to assume that a given area will be submerged by rising waters or protected from the sea. And even in developed areas that will presumably be protected, public works departments do not know whether to assume that the land surfaces will gradually be elevated or that the area will be protected with a dike.

This report develops maps that distinguish shores that are likely to be protected from the sea from those areas that are likely to be submerged, assuming current coastal policies, development trends, and shore protection practices. Our purpose is primarily to promote the dialogue necessary to decide where people will yield the right of way to the inland migration of wetlands and beaches, and where we will hold back the sea. The authors consulted with the state regional coastal divisions and planners from 17 coastal county governments on existing and future development (4 counties provided digital planning data and 2 provided hard copies that we digitized). All of the counties provided advice on how to best interpret expectations and existing statutes, regulations, and policies. The result is a statewide series of county maps that uses available understanding and planner expectations.

By "shore protection" we mean activities that prevent dry land from converting to either wetland or water. Activities that protect coastal wetlands from eroding or being submerged were outside the scope of this study. This study does not analyze the timing of possible shore protection; it simply examines whether land would be protected once it became threatened. Nor do we analyze whether shore protection is likely to be a transitional response or sustained indefinitely.

The sea level rise planning maps divide the dry land close to sea level into four categories of shore protection:
--Shore protection almost certain (brown);
--Shore protection likely (red);
--Shore protection unlikely (blue); and
--No shore protection, i.e., protection is prohibited by existing policies (light green).

For reasons related to data quality, our study area includes lands within about 17 to 18 feet (5 meters) above the tides. (We did not project the fates of secured federal installations but depicted them in red so that they stand out.)

One can also view these maps as representing three shore protection scenarios. For example, in an "enhanced wetland migration" scenario, only the areas depicted in brown would be protected; but in an "enhanced shore protection" scenario, only the areas depicted in light green would be submerged. Thus the prospects for shore protection are best understood in the areas shown in brown and light green, while those shown in red and blue are most amenable to coastal planning.

Results

The summary map shows our assessment of the likelihood of shore protection for the coastal zone of North Carolina, and adjacent areas in Virginia. The first summary table quantifies the area of land within approximately three feet (one meter) above the tides for each of the shore protection categories by county. The second summary table quantifies the length of North Carolina's shoreline along the Atlantic Ocean, the Pamlico and Albemarle sounds, and the back barrier sounds by likelihood of shore protection.

Ocean Coast

North Carolina's ocean coast, like most states, includes moderate and densely developed communities that will almost certainly be protected, and undeveloped roadless barrier islands that will almost certainly retreat. Unlike the other mid-Atlantic states, however, North Carolina's coast also includes a roadless coastal barrier that is nevertheless being developed, densely populated areas that nevertheless have been yielding homes to the sea, and a major lighthouse that has been relocated landward. Of the 303 miles of ocean shore, shore protection is almost certain along 118 milesand precluded by environmental management policies along 106 milesApproximately 48 miles (77 kilometers) of shoreline are along National Park Service lands where shores will be allowed to retreat, but the existence of a major coastal highway are likely to lead officials to fill inlet breaches and otherwise prevent the island from disintegrating. Shore protection is uncertain for another 89 miles of shoreline: likely along 53 miles and unlikely along the other 26.

The northern 14 miles of the state's coastline is a designated undeveloped coastal barrier and hence ineligible for most federal programs. This stretch of barrier island includes two sections of Currituck National Wildlife Refuge, each about 1 mile long, which are both off-limits to development and make it infeasible for the County to even consider a road along the barrier island. Nevertheless, the privately owned areas are gradually being developed, even though they are accessible only by boat or four-wheel drive vehicles traveling along the beach. Given the lack of eligibility for beach nourishment and flood insurance, county planners view shore protection as unlikely in the roadless area. The rest of the Currituck County ocean shore will almost certainly be protected.

Dare County officials view most of the coast from Kitty Hawk to Nags Head as almost certain to be protected, given both the development density and recent authorizations for beach nourishment. Homes have been condemned as shores erode and septics fail; but now that the through streets parallel to the shore are at risk, officials have decided to hold the line. Nevertheless, the beaches in some of the communities north of Kitty Hawk are not yet open to the public, and hence currently ineligible for beach nourishment. Although officials expect that property owners along the shore will eventually provide easements for public access, until that happens shore protection is likely but not certain. Roanoke Island is also certain to be protected, aside from conservation lands owned by The Nature Conservancy.

From Nags Head to Hatteras Island, most of the coast is part of Cape Hatteras National Seashore, with a coastal highway the entire length from which one can catch a ferry to Ocrakoke Island. The National Park Service generally allows shores to retreat, and the road has been relocated inland in places. Congress appropriated $9.8 million to move the Cape Hatteras Lighthouse 1,600 feet inland. Nevertheless, county and state officials view the coastal highway as essential infrastructure. While the gradual landward migration of the barrier islands may be tolerated, the barrier island itself will not be allowed to disintegrate. The various isolated communities within the barrier island system are likely to be protected, but protection is not certain because beach nourishment may not be cost-effective for the relatively short stretches of developed beach. Similarly, the town of Ocracoke is certain to be protected, but most of the island is part of Cape Hatteras National Seashore and hence shore protection would not occur under current policies.

South of Ocracoke lie the undeveloped Portsmouth Island and Core Bank, which constitute Cape Lookout National Seashore. Given the lack of a bridge to the mainland, shores would not be protected under current policies. To the southwest, the rest of the coast consists mostly of developed barrier islands where shore protection is certain, conservation lands will not be protected, and designated "undeveloped coastal barriers" are nevertheless being developed and likely to be protected even without federal subsidies.

Pamlico and Albemarle Sounds.

The lands along these two sounds account for 70 percent of the nontidal wetlands, 40 percent of the dry land, and 55 percent of all land within 1 meter above spring high water in the entire mid-Atlantic. This area has about 50 percent of the dry land within about three feet (one meter) above the tides where protection is precluded or unlikely. If nontidal wetlands are included, this area has 63 percent of the land that would be submerged (and potentially converted to tidal wetland) if sea level rises three feet.

Given the large areas of land available for potential wetland creation, this area represents an environmental planning opportunity that is national in scope. Nevertheless, development continues, particularly along the shores of the sounds. Significant urbanization has been slow to come to this area for many reasons. Most of it is farther from population centers than the Delaware and Chesapeake estuaries. Development along coastal bays often intensifies only when inexpensive land along the barrier islands becomes exhausted. The Outer Banks were slower to develop than the barrier islands of New Jersey, Delaware, and Maryland. And most important, the land is mostly low and wet.

Unlike the Delaware Estuary, this region does not have a long history of diking tidal wetlands to reclaim land from the sea for agricultural purposes. But it is starting to gain experience with dikes to protect agricultural lands from flooding. In Tyrell County, the Gum Neck has been protected with a dike for two decades. A dike is now planned for the town and farms around Swan Quarter, the county seat of Hyde County. Especially in Tyrell County, officials expect substantial amounts of agricultural lands to be protected with dikes as sea level rises. With most the county below the 5-meter contour, shore protection is a matter of self-preservation to this county. Hurricane Floyd led Pamlico County, by contrast, to encourage people to gradually abandon the eastern portion of the county, by working with FEMA to relocate people rather than rebuild damaged homes. In parts of Carteret County, by contrast, people learned the opposite lesson and elevated homes.

Caveat

This report relies less on digital land use and planning data than the companion studies of the other mid-Atlantic States. When the study was initiated, county land use data was generally unavailable-and the land use/land cover data then available was dated. With the exception of 6 counties, these maps rely on hand-drawn renderings of existing and expected development based on interviews with state and local officials. As a result, the precision of the maps is less than for the other mid-Atlantic studies.

This report may overstate the amount of land where shore protection is unlikely compared to the other mid-Atlantic states in this volume, for two reasons. First, the more densely developed counties that dominate the other states generally expect development everywhere that a policy is not in place to prevent it; the rural counties that dominate North Carolina tend to expect development in priority growth areas, but not in privately owned farms and forests where no one is yet planning to develop. Second, the interviews for this report took place between 2001-2003. Since that time, people have decided to develop areas where development was not expected a few years ago.

These caveats do not change the fundamental finding that North Carolina has more undeveloped lands potentially available for wetland migration than the other mid-Atlantic States. They may suggest, however, that this environmental planning opportunity is diminishing as the lands around North Carolina's sounds are developed.

Conclusions

1. The prospects for shore protection appear to be largely established along 74percent of the 303 miles of open ocean coast.
---High property values and dense development make shore protection almost certain along 39 percent of the Atlantic Coast. [118 miles]
---Policies would preclude shore protection along approximately 35 percent (106 miles) of the ocean coast.

2. Shore protection is still uncertain along about 26 percent of the Atlantic Coast.
---Approximately 48 miles of shoreline are along National Park Service lands where shores will be allowed to retreat, but the existence of a major coastal highway are likely to lead officials to fill inlet breaches and otherwise prevent the island from disintegrating
---About 17 percent (53 miles) of the shore is likely-but not certain-to be protected. Most of these areas are developed, but planners are not certain whether those areas would qualify for federal beach nourishment due to high shore protection costs, insufficient development density, or lack of public access to the beach.
---About 9 percent of the ocean shore (26 miles) is unlikely to be protected. Most of these lands are designated undeveloped barrier islands under the Coastal Barrier Resources Act.

3. Along the 1,192 miles of estuarine shorelines, the prospects for shore protection are much less certain than along the ocean. These lands include approximately 526 square kilometers of dry land within one meter above the tides.
---Only 29 percent of the estuarine shore is developed enough for planners to view shore protection as almost certain to be protected
---Less than 9 percent of the estuarine shores are within conservation areas.

4. Despite the momentum toward coastal development, all of our options still appear to be open for more than half of the dry land in the mid-Atlantic.
---Development and shore protection are likely on about 74square miles; but it is not too late to design land use plans that could accommodate both development and wetland migration.
---In the other 286 square miles, development and shore protection seem unlikely today; but people may want to move into these areas in the future.

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Governments Plan for Development of Most Land Vulnerable to Rising Sea (PDF, 7 pp., 1.3 MB) was originally published in Environmental Research Letters , Issue 3, Volume 4 (2009).