Jump to main content.

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

Chris Linn. 2010. "Pennsylvania". 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 Pennsylvania sea level rise planning study (pdf 2 MB), which was originally prepared by the Delaware Valley Regional Planning Commission.


Sea level is rising about 1 inch every 9 years (2.7 millimeters per year) along the coast of Pennsylvania. Sea level rise in this area will continue to be approximately 0.05 inches per year (1.2 mm/year) greater than the global rise in sea level because of land subsidence in the Mid-Atlantic region. Given the small amount of low-lying land along Pennsylvania's coast, rising seas threaten only a relatively small portion of the state's coastal communities. However, the impacts of sea level rise go beyond inundation to include increased erosion, increased flooding, and the migration of the salt line farther up tidal rivers and streams.

Land use is diverse along the Pennsylvania portion of the Delaware Estuary. Most of the coast is heavily developed; only about 18 percent of the coastal area is classified as undeveloped. Much of the natural shoreline has already been filled in or modified many times over with bulkheads, docks, wharfs, piers, riprap shorelines, and other hard structures during the past two centuries.

As a result of the developed and altered character of the Delaware Estuary, the natural ebb and flow of the tide is, in many places, already restricted by hard edges and vertical structures. Shoreline armoring with bulkheads establishes a vertical boundary that separates uplands on one side from open water, wetlands, or mudflats on the other. As the sea rises, these armoring structures prevent the high protected uplands from becoming progressively transformed into a wetlands or intertidal environment. If fronting marshes or tidal flats do not accrete enough sediment to keep pace with rising sea level, they will drown.

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. 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. The author obtained land use and planning data from Delaware, Philadelphia, and Bucks County and consulted with county planners as well as participating agencies in the Pennsylvania Coastal Zone Management program.

"Shore protection" here means 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 does it 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, the study area includes lands within about 17-18 feet (about 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. "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 Pennsylvania. 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 Pennsylvania's shoreline along the Delaware River.


1. Shore protection is likely or certain along most of the Pennsylvania coast.
---All but 24 miles of the state's 60-mile Delaware River shore is likely or certain to be protected.
---Of the 10.5 square miles of dry land within approximately 3 feet above the tides, 6.1 square miles is likely or almost certain to be protected.

2. Wetland migration will not be possible along a majority of the shores that our maps depict as likely or certain to be protected.
---Development along the Delaware Estuary already restricts the natural ebb and flow of tides through hard edges and vertical armoring structures. Fronting marshes or tidal flats must accrete enough sediment to keep pace with rising sea levels, or be drowned.
---Approximately 40 percent of Pennsylvania's coastline is unlikely to be protected or abuts nontidal wetlands, allowing for the inland migration of tidal wetlands.

Top of page

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).

Top of page

| Main study | Elevation Maps | Planning Maps | Related Links

Local Navigation

Jump to main content.