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Shore Protection and Retreat: What influences this decision?

From Shore Protection and Retreat by James G. Titus and Michael Craghan (2009), which was chapter 6 of the Bush Administration's published sea level rise assessment, entitled Coastal Sensitivity to Sea Level Rise

Outline of the Chapter

6.2 What factors influence the decision whether to protect or retreat?

6.2.1 Site-Specific Factors

Private landowners and government agencies who contemplate possible shore protection are usually motivated by either storm damages or the loss of land (NRC, 2007). They inquire about possible shore protection measures, investigate the costs and consequences of one or more measures, and consider whether undertaking the costs of shore protection is preferable to the consequences of not doing so. For most homeowners, the costs of shore protection include the costs of both construction and necessary government permits; the benefits include the avoided damages or loss of land and structures. Businesses might also consider avoided disruptions in operations. Regulatory authorities that issue or deny permits for private shore protection consider possible impacts of shore protection on the environment, public access along ocean shores, and whether the design minimizes those impacts (NRC, 2007). Government agencies consider the same factors as private owners as well as public benefits of shore protection, such as greater recreational opportunities from wider beaches, increased development made possible by the shore protection (where applicable), and public safety.

Accelerated sea-level rise would not change the character of those considerations, but it would increase the magnitude of both the benefits and the consequences (monetary and otherwise) of shore protection. In some areas, accelerated sea-level rise would lead communities that are unprotected today to protect the shore; in other areas, the increased costs of shore protection may begin to outweigh the benefits. No published study provides a comprehensive assessment of how sea-level rise changes the costs and benefits of shore protection. However, the available evidence suggests that the environmental and social impacts could increase more than proportionately with the rate of sea-level rise (see Sections 6.3 and 6.4). A case study of Long Beach Island, New Jersey (a densely developed barrier island with no high-rise build buildings) concluded that shore protection is more cost-effective than retreat for the first 50 to 100 cm of sea-level rise (Titus, 1990). If the rise continues to accelerate, however, then eventually the costs of protection would rise more rapidly than the benefits, and a strategic retreat would then become the more cost-effective response, assuming that the island could be sustained by a landward migration (see Box A1.2 in Appendix 1). An economic analysis by Yohe et al. (1996) found that higher rates of sea-level rise make shore protection less cost-effective in marginal cases.

6.2.2 Regional Scale Factors

Potential benefits and consequences are usually the key to understanding whether a particular project will be a-dopted. At a broader scale, however, land use and shoreline environment are often indicators of the likelihood of shore protection. Land use provides an indicator of the demand for protection, and the shoreline environment provides an indicator of the type of shore protection that would be needed.

Most land along the mid-Atlantic ocean coast is either developed or part of a park or conservation area. This region has approximately 1,100 kilometers (almost 700 miles) of shoreline along the Atlantic Ocean. Almost half of this coastline consists of ocean beach resorts with dense development and high property values. Federal shore protection has been authorized along most of these developed shores. These lands are fairly evenly spread throughout the mid-Atlantic states, except Virginia (see Section A1.E.2.1 in Appendix 1). However, a large part of the coast is owned by landowners who are committed to allowing natural shoreline processes to operate, such as The Nature Conservancy, National Park Service (see Section 11.2.1), and U.S. Fish and Wildlife Service. These shores include most of North Carolina’s Outer Banks, all of Virginia’s Atlantic coast except for part of Virginia Beach and a NASA installation, more than two-thirds of the Maryland coast, and New York’s Fire Island. The rest of the ocean coast in this region is lightly developed, yet shore protection is possible for these coasts as well due to the presence of important coastal highways.

Development is less extensive along many estuaries than along the ocean coast. The greatest concentrations of low-lying undeveloped lands along estuaries are in North Carolina, the Eastern Shore of Chesapeake Bay, and portions of Delaware Bay. Development has come more slowly to the lands along the Albemarle and Pamlico Sounds in North Carolina than to other parts of the mid-Atlantic coast (Hartgen, 2003). Maryland law limits development along much of the Chesapeake Bay shore (Section A1.F.2.1 in Appendix 1), and a combination of floodplain regulations and aggressive agricultural preservation programs limit development along the Delaware Bay shore in Delaware (Section A1.D.2.2 in Appendix 1). Yet there is increasing pressure to develop land along tidal creeks, rivers, and bays (USCOP, 2004; DNREC, 2000; Titus, 1998), and barrier islands are in a continual state of redevelopment in which seasonal cottages are replaced with larger homes and high-rises (e.g., Randall, 2003). If threatened by rising sea level, these developed lands (e.g., urban, residential, commercial, industrial, transportation) would require shore protection for current land uses to continue. Along estuaries, the costs of armoring, elevating, or nourishing shorelines are generally less than the value of the land to the landowner, suggesting that under existing trends shore protection would continue in most of these areas. But there are also some land uses for which the cost and effort of shore protection may be less attractive than allowing the land to convert to wetland, beach, or shallow water. Those land uses might include marginal farmland, conservations lands, portions of some recreational parks, and even portions of back yards where lot sizes are large. Along the ocean, shore protection costs are greater—but so are land values. Shore protection is likely along much of the coastal zone, but substantial areas of undeveloped (but developable) lands remain along the mid-Atlantic estuaries, where either shore protection or wetland migration could reasonably be expected to occur (NRC, 2007; Yohe et al., 1996; Titus et al., 1991). Plans and designs for the development of those lands generally do not consider implications of future sea-level rise (see Chapter 11). A series of studies have been undertaken that map the likelihood of shore protection along the entirety of the U.S. Atlantic Coast as a function of land use (Nicholls et al., 2007; Titus, 2004, 2005; Clark, 2001; Nuckols, 2001).

6.2.3 Mutual Reinforcement Between Coastal Development and Shore Protection

Lands with substantial shore protection are more extensively developed than similar lands without shore protection, both because shore protection encourages development and development encourages shore protection. People develop floodplains, which leads to public funding for flood control structures, which in turn leads to additional development in the area protected (e.g., Burby, 2006). Few studies have measured this effect, but possible mechanisms include:

The impact of coastal development on shore protection is more firmly established. Governments and private landowners generally implement a shore protection project only when the value of land and structures protected is greater than the cost of the project (see Sections 6.1 and 12.2.3).

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