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- Shore Protection Methods
Governments Plan for Development of Land Vulnerable to Rising Sea Level: Maryland
W.H. Nuckols, Peter Johnson, et al. 2010. "Maryland". 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 a printer quality version of this Maryland sea level rise planning study (pdf 4.0 MB, 156 pp).
Sea level is rising 3-4 millimeters per year (12 to 16 inches per century) along the Maryland coast. Beaches are eroding along the Atlantic Ocean and Chesapeake Bay. Especially in the lower Eastern Shore, marshes are converting to open water, and low-lying farms, forests, and residential yards are gradually converting to marsh. Water levels in roadside ditches rise and fall with the tides in Dorchester and Somerset 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 are being pursued somewhere in Maryland. Stone revetments are common along developed shores of Chesapeake Bay and the Potomac River. The federal and state governments have placed sand onto the eroding recreational beaches at Ocean City, Maryland. In the aftermath of Hurricane Isabel, homes have been elevated in many communities. Although few homes have been lost to erosion recently, some rural homes have been abandoned as rising water tables impair septic systems and convert yards to marsh; and substantial farm land is converting to marsh in Dorchester and Somerset counties.
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 statewide land use, planning, and conservation data, and comprehensive plans for the 9 coastal counties who thought that we needed it. We consulted with all 16 coastal counties and the City of Baltimore about how to best interpret the data given existing statutes, regulations, and policies. In some cases, hand renderings were necessary because of the unavailability of digital data. The result is a regionwide 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 (about 5 meters) above the tides. (We did not project the fates of military lands 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, while 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.
The summary map shows our assessment of the likelihood of shore protection for the coastal zone of Maryland and adjacent areas in Delaware, Virginia, and the District of Columbia. Table 1 quantifies the area of land within approximately 3 feet (1 meter) above the tides for each of the shore protection categories by county. Table 2 quantifies the length of Maryland's shoreline along the Atlantic Ocean, Chesapeake Bay, and Potomac River by likelihood of shore protection.
All of Maryland's 31-mile (51-km) ocean coast is part of either Ocean City (9 miles) or Assateague Island National Seashore (22 miles). City and state officials are committed to defending the current shoreline of Ocean City. National Park Service officials are generally committed to allowing natural shoreline retreat. (Our maps omit recent plans to nourish the northern portion of Assateague Island as part of an effort to protect developed areas.). The mainland behind the barrier islands includes developed and undeveloped lands. The areas opposite Ocean City and the northern third of Assateague Island are being developed. The mainland shore opposite the southern third of Assateague Island is subject to conservation easements that allow shore protection but preclude the development that would make shore protection likely. Aside from a few small settlements, the mainland opposite the middle third of Assateague Island is undeveloped. Although development is expected, efforts are under way to acquire conservation easements in some of these areas, and a countywide setback precludes the land immediately next to the shore from being protected.
Along Chesapeake Bay and its tributaries, the shore has been densely developed in and around Annapolis, Baltimore, and Washington, and areas with moderate density development can be found along most of the Western Shore. In the 1980s, the state legislature recognized that continuation of current trends would eventually lead to the development of most privately owned lands along the shore, to the detriment of Chesapeake Bay. It enacted the Critical Areas Act, which limits development to one home in 20 acres in resource conservation areas, i.e., about 90 percent of the land within 1,000 feet of the shore that had not been developed or subdivided by 1985. Shore protection is uncommon along agricultural shores in Maryland, though it does occur elsewhere. As a result, shore protection is unlikely in resource conservation areas. In an "enhanced shore protection scenario," however, these lands could be protected.
Maryland's Critical Areas Act has the greatest impact on the Eastern Shore, where most of the shore had not been developed before 1985 because of the greater distance from major population centers. Development--and expected future shore protection--are most concentrated in the northern areas near Interstate-95, Kent Island, and the various necks near Easton and St. Michaels. County planners view development--and hence shore protection--as unlikely or precluded along half of the Chesapeake Bay shoreline between the Susquehanna and Choptank Rivers rivers. Among the major tributaries, shore protection is unlikely along most of the Sassafras, Chester, and Choptank Riversrivers, but almost certain along most of the Wye, Elk, and North East Riversrivers. Given current policies, only 40% percent of the land area within one meter above spring high water is likely or certain to be protected.
Along the western shore of Chesapeake Bay, by contrast, approximately 55 percent of the shoreline is almost certain to be protected, and shore protection is likely along another 20 percent. Compared with the Eastern Shore, Maryland's Critical Areas Act is unlikely to preserve a major portion of the Western Shore, which was largely developed before the Act was passed. Along the Western Shore, parks--not state regulation--account for most of the shoreline where protection is unlikely.
The land along the Western Shore of Chesapeake Bay is generally higher than along the Eastern Shore. With the exceptions of the Deal/Shady side area in Anne Arundel and military lands near Aberdeen, the 10-ft contour is generally within a few hundred feet of the shore--and often only tens of feet inland. Although very little land is being submerged by the rising sea, many shores are eroding. Stone revetments are common along the mostly developed shores of Anne Arundel and Baltimore counties.
Yet the Western Shore also has one of the only shore protection policies in the nation that prohibits shore protection along an estuary, even when the prohibition means that homes will be lost. Calvert County's cliff erosion policy is designed to preserve the unique cliff areas that border Chesapeake Bay. These cliffs provide habitat to plants and wildlife, including endangered species, and also contain one of the largest exposures of fossils from the Miocene Age. Along approximately 7 miles of cliff, the county County requires homes to be set back 300 feet and bans shore protection. Along another 5 miles, shore protection is allowed to protect only homes built before 1997.
The land along the Potomac River is generally steep, with only a few small communities below the 10-ft contour. With the state's first capital at St. Mary's City, several small longstanding resorts, and boating equivalent to that of Chesapeake Bay, the Potomac shore below the U.S. 301 bridge was largely developed or subdivided before passage of the Critical Areas Act. Above the bridge, however, almost all of Charles County is within a resource conservation area or owned by the military. Thus, the amount of Potomac River shoreline where shore protection is unlikely in Charles County alone (30 miles) is greater than the amount of shoreline along the entire Western Shore of Chesapeake Bay (16 miles) where shore protection is unlikely. Given its proximity to the nation's capital, about half of the Potomac shore in Prince George's County is developed; but 36 miles of shoreline along the Potomac and its tributaries are owned by the National Park Service and other conservation entities that preclude shore protection.
1. The prospects for shore protection appear to be largely established along all of the 31- mile Atlantic Ocean coast.
a. High property values and dense development make shore protection almost certain along 9 miles in Ocean City.
b. Conservation policies preclude shore protection along the other 71 percent of the ocean coast, which is part of Assateague Island National Seashore.
2. Along the 768 miles of estuarine shoreline, the prospects for shore protection are much less certain than
along the ocean. These lands include approximately 173.3 square miles of dry land within about 3 feet (1 meter) above the tides.
a. Only 36 percent of the estuarine shore is developed enough for planners to view shore protection as almost certain.
b. Approximately 1 percent of the estuarine shores are is within conservation areas.
3. Despite the momentum toward coastal development, all of our options still appear to be open for more than 72 percent of the low dry
land in Maryland.
a. Development and shore protection are likely on about 27 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.
b. In the other 97 square miles, development and shore protection seem unlikely today. Most of these lands are agricultural areas with conservation easements, or resource conservation areas in which state law limits development to no more than one home in 20 acres. Although shore protection is unlikely given today's practices, regulations and conservation easements generally allow shore protection.
4. The areas where shore protection is unlikely are concentrated along the Eastern Shore of Chesapeake Bay, the southern portion of Worcester County, and Charles County along the Potomac River.
a. Shore protection is likely or almost certain along 76 percent of the 117 mile Western Shore, but only 40 percent of the 133- mile eastern shore.
b. Shore protection is likely or almost certain along 58 percent of the Potomac River's 97 mile shoreline, but only 41 percent of Charles County's 56- mile shore.
c. Shore protection is likely or almost certain along 99 percent of northern Worcester County's 28-mile shoreline, but only 25 percent along Worcester's southern, 112-mile coastline.
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).