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Governments Plan for Development of Land Vulnerable to Rising Sea Level: Virginia
J.G. Titus, Carl Hershner, et al. 2010. "Virginia". 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 also download either a low-resolution (5 MB) or a printer quality version of this Virginia sea level rise planning study (pdf 8.8 MB), which was originally prepared by the Virginia Institute for Marine Sciences.
Abstract
Sea level is rising 1 inch every 7 to 8 years (3-4 millimeters per year) along the coast of Virginia. Beaches are eroding along the Atlantic Ocean and Chesapeake Bay. Marshes are converting to open water, and low-lying farms, forests, and residential yards are gradually converting to marsh-including Jamestown and Tangier islands. Water levels in roadside ditches rise and fall with the tides in Poquoson and portions of Gloucester and Accomack counties. All of 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 8 mm/yr (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 is being pursued somewhere in Virginia. Wooden bulkheads and stone revetments are common along developed shores of Chesapeake Bay and the Potomac River. The federal or state government has placed sand on the eroding recreational beaches along the Atlantic Ocean, Chesapeake Bay, Hampton Roads, and the Potomac River. In the aftermath of Hurricane Isabel, homes have been elevated in many communities. The elevation of low-lying homes has become common during the last decade. Few homes have been lost to erosion recently, but farms and forests are converting to marsh in Virginia Beach and Gloucester and Accomack counties, and eroding in many areas.
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 low lands 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 by which society decides where to hold back the sea and where to yield the right of way to the inland migration of wetlands and beaches. A key step in evaluating whether new policies are needed is to evaluate what would happen under current policies. The maps in this report represent neither a recommendation nor an unconditional forecast of what will happen, but simply the likelihood that shores would be protected if current trends continue.
We obtained land use and planning data from the 12 coastal localities where it was available, digitized comprehensive plans for 4 other localities, and obtained land use/land cover and conservation data throughout the state. We also consulted with planners representing the six planning district commissions along Chesapeake Bay and the Potomac River, and the 30 localities most vulnerable to sea level rise within those districts, on how to best interpret the data given existing statutes, regulations, and policies. The result is a statewide series of maps that uses existing data, filtered through the local governments who plan and govern how land is used.
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 17-18 feet (5 meters) above the tides. (We did not project the fates of secured installations in rural areas 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, ande those shown in red and blue are most amenable to coastal planning. "Expected shore protection" is an intermediate scenario in which the areas depicted in brown and red are protected, while those shown in blue and light green are submerged.
Results
The summary map shows our assessment of the likelihood of shore protection for the coastal zone of Virginia and adjacent areas in North Carolina, Maryland, and the District of Columbia. The first summary table quantifies the area of land within approximately 3 feet (1 meter) above the tides for each of the shore protection categories by county. The second summary table quantifies the length of Virginia's shoreline along the Atlantic Ocean, Chesapeake Bay, and Potomac River by likelihood of shore protection.
Almost all of the Virginia Eastern Shore's 77-mile ocean coast is owned by either The Nature Conservancy or the federal or state government. Except for NASA's Wallops Island, all of these lands are managed by agencies committed to preserving natural shoreline processes. Behind the barrier islands, planners expect development to remain light in most areas. Hence shore protection is unlikely on the sea side of the Eastern Shore, except for Chincoteague, Wachapreague, and a few other communities.
The bay side of the Eastern Shore, by contrast, has very low land north of Onancock. The very low lands are gradually converting to marsh, and viewed by county officials as least promising for development. The 27.5 square miles of dry land close to sea level on the bay side of Accomack County is one of the two largest areas of land available for wetland migration as sea level rises. South of Onancock, by contrast, slopes are generally steeper, and the greater proximity to the Hampton Roads area makes development-and hence shore protection-more likely.
Across the mouth of Chesapeake Bay, the northern two-thirds of Virginia Beach's ocean shore is certain or likely to be protected. As the state's only ocean resort, this city has many different land uses along the shore, all with high property values. But the southern third of the ocean coast is within a state park or Back Bay National Wildlife Refuge, and shore protection would be precluded by current policies. Although the mainland opposite these conservation lands is privately owned, the city is committed to maintaining the rural character of the land south of its "Rural Line." In effect, the city expects that its land use plan to preserve rural areas is likely to preserve the coastal environment as sea level rises throughout the coming century and beyond. This area also has one of the two largest concentrations of very low dry land onto which wetlands are likely to migrate.
Along the western shore of Chesapeake Bay and several major tributaries, shore protection is becoming increasingly likely as shores become more developed. Of the nearly 100 square miles of dry land within 3 feet above the tides, more than 52 square miles are in the Hampton Roads area; the Guinea Neck in Gloucester County also has a large concentration of very low land. Elsewhere, most shore protection would involve erosion-control structures or beach nourishment rather than dikes or elevating land and buildings. Because erosion protection is relatively inexpensive compared with coastal property values, developed areas are almost certain to be protected. Nevertheless, planners view development as less imminent in the upstream areas of the Rappahannock, York, and some smaller rivers with substantial wetlands along the shore. Those areas appear to have the greatest potential for tidal wetland conservation as sea level rises. In the upper tidal Potomac River, shoreline armoring is commonplace-but a substantial portion of the shore is publicly owned and hence unlikely to be developed.
Findings
1. The prospects for shore protection appear to be largely established along 87percent of the 106-mile Atlantic Ocean coast.
--High property values and dense development make shore protection almost certain along 11 miles in Virginia Beach.
--Conservation policies preclude shore protection along approximately 76 percent of the ocean coast, including almost all of the barrier islands north of Cape Charles.
2. Shore protection is still uncertain along about 13 percent of the Atlantic Coast.
--This report did not examine the likelihood of shore protection for secured federal installations, including NASA's Wallops Island and the Navy's Surface Combat System Center.
--Wide beaches where shore protection is not immediately needed account for about 3 miles of shoreline in Virginia Beach. The land behind these beaches is almost certain to be protected if the beaches erode.
3. Along the 634 miles of estuarine shorelines, the prospects for shore protection are much less certain than along the ocean. These lands include approximately 120 square miles of dry land within about 3 feet (1 meter) above the tides.
--Only 50 square miles are developed enough for planners to view shore protection as almost certain to be protected.
--Less than 10 square miles of low lands are within conservation areas.
4. Despite the momentum toward coastal development, all of our options still appear to be open for about 70 square miles of low dry land in Virginia.
--Development and shore protection are likely on about 30 square miles within about 3 feet (1 meter) above the tides; but it is not too late to design land use plans that could accommodate both development and wetland migration.
--On the other 40 square miles, development and shore protection seem unlikely today; but people may want to move into many of these areas in the future.
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).