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Governments Plan for Development of Land Vulnerable to Rising Sea Level: Accomack County, Virginia
Vulnerability to Sea Level Rise
Rising sea level is already converting farmlands to tidal wetlands. Oftentimes one can observe corn and other crops on low land near the Bay or a tributary, and on closer inspection some of the rows of crops will be broken by wetland vegetation. Land that might have been arable a few years ago gradually becomes nonarable because of salt contamination from tidal flooding. Given the 14.1 square miles of dry land within 2 feet above the wetlands, a linear interpolation implies that the county has 47 acres within one eighth of an inch (3 millimeters) above the tides. As a result, it may be realistic to assume that 474 acres of wetland are created per year from the gradual inundation of low-lying farms.
The county's land use policies recognize the low-lying character in several ways that will tend to influence the ultimate response to sea level rise. Currently, only Onancock and Tangier have sewage treatment plants. Because of the reliance on septic tanks, soils determine where development goes. Moreover, densities are restricted in the coastal floodplain. Because of these factors, along Chesapeake Bay, development is mostly occurring toward the southern half of the county, where elevations are relatively high. The barrier islands are all owned by the federal government, state government, or The Nature Conservancy. Along the coastal bays on the Atlantic side, the combination of county policies, environmental factors, and economic trends tends to encourage development in the northern areas near Chincoteague, Wallops Island/NASA, and the Maryland line while discouraging development along the bays opposite The Nature Conservancy's lands. The county continues to grow.
Accomack's three developed islands, Tangier, Saxis, and Chincoteague, have their own town governments with land use authority. Tangier Island is in the middle of Chesapeake Bay, with passenger ferries to Crisfield, Maryland, on the Eastern Shore, Onancock in Accomack County, and Reedville on the Northern Neck of Virginia. The town is built on several ridges that once represented the highest ground, but now represent the only dry land. Channels separate each of these ridges now, so that strictly speaking there are several islands. Shore erosion is also severe, necessitating shoreline armoring, particularly on the north side. Approximately 90 percent of the structures are within the 100-year floodplain. USGS topographic maps show the entire island as below the 5-ft contour, except for about half of Canton Ridge. Given the tide range and historical sea level rise, the USGS maps imply that the entire island would be flooded by the tides with a rise in sea level of 2 to 3 feet.
Tangier is as vulnerable as many of the "Small Island States" that researchers and the news media often discuss as potential victims of rising sea level, such as Tuvalu, Marshall Islands, and the Republic of Maldives. Like those atoll republics, here a unique culture is threatened with extinction, only it may be even more immediately vulnerable than those nations. Although one might normally assume that a picturesque island in the United States would have greater resources for holding back the sea, Tangier is a fishing community. The decline of oysters and other shellfish in Chesapeake Bay has reduced incomes, and the fill dirt necessary to enable the island to keep pace with rising sea level is relatively expensive given the island's remote location. Town officials believe that subsidence is exacerbating the effects of sea level rise on some portions of the island.
Yet despite its vulnerability, there are reasons to believe that Tangier could survive rising sea level. First, the island has a sewage treatment system, so homes will not be condemned as yards are saturated. It also has a new K-12 school, and a small but viable summer tourism industry. Thus the state has shown a willingness to invest a level of resources that presumed the continued existence of this community. Moreover, the U.S. Army Corps of Engineers has an ongoing project to halt erosion on Tangier Island, based in part on the historical significance of the island.
Saxis is also vulnerable island community. Fortunately, two-thirds of the developed part of the island is above the 5-ft contour, but the northern portion of the island is only about 4 feet above NGVD, that is, approximately 2 feet above the tidal wetlands. The island has a severe erosion problem. The community is actively attempting to secure Corps assistance with its erosion problem.
Moreover, the population is at risk during storms because the nearest high ground is 15 miles away, and the evacuation route along Saxis Road runs through Sanford, which is lower than Saxis; slow drainage there can leave water a foot or so above the water level in the Bay. The causeway through the marsh appears to be compacting, possibly because the fill includes pine logs. Moreover, the marsh through which the road passes is starting to degrade, increasing the threat of waves and washout during storms even today. Although protection of infrastructure is outside the scope of this study, Saxis officials communicated a strong concern that infrastructure planners consider whether the road needs to be redesigned to withstand and possibly mitigate problems associated with marsh degradation, subsidence, and rising sea level.
Chincoteague is a coastal resort community just inland of the southern portion of Assateague Island, a barrier island that extends into Maryland and is entirely within Assateague Island National Seashore. As the southern gateway to the national seashore, Chincoteague provides overnight accommodations for people making day trips to the barrier island, and many restaurants and shops. The island also has both recreational and commercial fishermen, and it somewhat higher than both Saxis and Tangier. Given the tourism revenues, Chincoteague has the economic ability to maintain itself in the face of rising sea level, and erosion protection costs are less than those for Tangier and Saxis because the wave climate is more benign in Chincoteague Bay than in Chesapeake Bay.
Anticipated Sea Level Rise Responses
Most of the development is being concentrated either along Chesapeake Bay (bayside) in the southern half of the county or along the coastal bays (seaside) in the northern and southern portions of the county (but not along the central portion). With some exceptions, those are the primary areas that county officials expect to be protected. Our map shows the three populated islands as almost certain to be protected.
The island towns of Saxis and Tangier are confronting erosion and inundation and are committed to their own continued existence. The county planners are unsure about whether Tangier and Saxis can economically justify holding back the sea if the rate of sea level rise accelerates, and hence were inclined to classify those communities as likely-but not certain-to be protected. Nevertheless, for purposes of these maps, they agreed to defer to the responsible town officials, who have primary land use authority. Although Chincoteague is not currently threatened, the planners all agree that the revenues it generates make it more likely to survive almost any reasonable sea level rise scenario than the other two islands.
Our maps show NASA-owned lands as red because of the study's general approach of showing secured federal installations as protection uncertain, unless we have additional information showing that another classification is appropriate.
On the mainland seaside, the planners of Accomack County generally expect the growing communities of Greenbackville and Captains Cove to be protected. Those areas are thus shown as brown. Development there is likely to be extended south to the entrance to NASA, and hence that area is shown as likely to be protected. In the southern portion of the county along the coastal bays, Accomack planners also consider protection to be almost certain for Wachapreague and Quinby, and for Bradford Neck in between those two communities. Along Chesapeake Bay, the historic villages of Harbortown and Onanock are sure to be protected, as well as Broadway Neck and other areas around Onancock.
Protection is likely, but less certain, for a number of more lightly developed areas. Local planners suggested that interior areas in and around Whitesville are in the likely-to-be-protected category, as is Custis Neck on the mainland opposite Cedar Island. They suggested that although these communities are reasonably well developed, they have not demonstrated a commitment to taking measures to hold back the sea and therefore cannot be listed as certain. Sanford is also marginal. The demand to live in this remote, nonwaterfront community is not great, and the costs of maintaining an operating septic system and elevating homes may encourage the abandonment of this community, particularly if a severe hurricane were to destroy it. Still, as long as Saxis survives, the state's commitment to maintaining Saxis Road will provide Sanford with an anchor of dry land. Moreover, rising sea level may eventually convert the miles of marsh between Sanford and Saxis to open water, in which case the value of buildable waterfront lots would be greater than the value of today's marshfront lots.
Most of the farms and forests in this county seem unlikely to be protected. Nevertheless, Accomack County planners identified two areas where agricultural productivity is great enough to justify protection even if they are not developed: the areas southwest of Onancock and west of Wachapreague.
To protect the rural way of life, subdivisions are discouraged in some of the traditionally agricultural areas. Yet development is likely to continue in this coastal county, especially in waterfront areas. Given the areas where growth is generally being directed, the planners agreed that a reasonable way to account for future growth in undeveloped areas would be to assume that those areas south of Onancock with shore-parallel roads will probably be developed over time with waterfront homes, and that those homes will probably be protected. Because of the high ground in that region, protecting waterfront homes from erosion has the effect of protecting the inland areas as well.
The remaining undeveloped areas are unlikely to be protected. Along the sea side, The Nature Conservancy has a policy of allowing the barrier islands to respond to natural processes, so the barrier islands south of Wallops Island are light green. Because development is directed toward the bayside in southern Accomack, the land along the coastal bays is unlikely to be protected. Similarly, most private farms and forests on the bayside in the northern part of the county will probably continue to gradually convert to wetlands as sea level rises.
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).