7.1 Where is Retreat Preferable to Shore Protection?

There is both a private and public interest in whether a particular area is protected or given up to the rising sea. Most of the dry land along the shore is privately owned, while most shallow waters and intertidal lands are owned by the states (in trust for the public). Coastal hazards such as erosion and storms directly threaten the financial interests (and occasionally the safety) of private landowners, but public infrastructure is also threatened. Government programs often subsidize shore protection to prevent threats to private property[515] and cover the losses that do occur with flood insurance.[516] Severe storms often threaten public health, commerce, and the environment.

The private and public interests in shore protection may be aligned or they may diverge. They tend to be aligned in areas that are either very densely populated or very lightly populated. In densely developed coastal cities where land values are high, and private landowners and governments generally agree that shore protection is justified by both private investment and the welfare of the community.[517] In rural areas, neither governments nor landowners tend to be interested in shore protection of land that is mostly farm and forest.[518] The cost of shore protection is often greater than the value of the land that could be saved, making it a bad investment for the landowner. The government often has little reason to fund shore protection, because the slow loss of undeveloped land in rural areas does not cause perceptible harm to the state or the nation, while shore protection could harm the environment by preventing the inland migration of wetlands and beaches.

The private and public interests may diverge, by contrast, along moderately developed ocean beaches and estuarine shores—for opposite reasons. Along some barrier islands and spits, the cost of shore protection is greater than the value of the property that would be protected.[519] As with undeveloped farmland, shore protection would be a bad investment for the landowner. But government agencies often decide that shore protection has a social value greater than its cost,[520] and undertake publicly funded shore protection, with or without the support of adjacent landowners.[521] For example, in most states, erosion reduces the portion of the dry beach to which the public has access, while beach nourishment increases it. (See Section 2.2.)

Conversely, there are also cases where shore protection is a worthwhile investment to the landowner but counterproductive to society. For example, a group of homeowners would logically be willing to each spend $200,000 to delay the loss of their $600,000 homes by 20 years,[522] but doing so might not be a good investment for society overall. Perhaps the loss of those homes would otherwise increase the property values of the next row of homes by $325,000 (i.e., from $275,000 to $600,000) because they would now be waterfront. In that case, the shore protection would only be deferring a social cost of $275,000 ($600,000 minus $325,000), which would not be worth a current expenditure of $200,000.[523] Alternatively, perhaps shore protection would eliminate wetlands which serve an important ecological function, or would eliminate access along an important recreational beach. Or perhaps the least expensive measure of shore protection would be a dike which the community would gradually fortify as sea level rises, to the point where the entire community would eventually be below sea level and vulnerable to catastrophe during a severe storm.

Retreat policies have generally been implemented in two different types of situations:

• Shore protection has unacceptable impacts on public access and the environment.
• The cost of shore protection is high compared to the value of the assets likely to be lost as the shore retreats.

The decision to prohibit structures that harm beaches,[524] access along beaches,[525] or eroding-cliff habitat[526] can be viewed as a policy judgment that the value of the natural shore is greater than the net value of the private property lost to the rolling easement.[527] The merits of implementing a rolling easement will generally not depend on whether there is a right to hold back the sea (the Coase theorem makes this general point for other regulatory policies.[528]) If owning land does not inherently include a right to shore protection, retreat policies might be implemented without compensating landowners—but few governments will consciously give up taxable lands or anger property owners for the sake of a policy whose social benefits are less than the costs. Conversely, if there is a property right to shore protection, then logically a locality or conservancy should be willing to purchase the rolling easement from the property owner to preserve a natural resource whose value is greater than the price of the rolling easement (which would be the property owners' expected loss from not holding back the sea). This does not mean that adoption of a retreat policy is equally likely whether or not there is a right to shore protection—especially if the costs are likely to be high. But if the policy is considered with sufficient lead time for the immediate costs to be low, then whether to actually adopt the policy should logically depend on whether the benefits are greater than the costs, but not on who would have to pay several decades later if this generation does not adopt a policy.

The case for a retreat policy is different for areas where shore protection would be unlikely even without a policy (see Section 5.1.2). At first glance, there seems to be no need for a retreat policy in areas where development is uneconomical (e.g., unbridged islands) or shore protection is not cost-effective. But an explicit retreat policy might be worthwhile, for several reasons:

• State and local governments may want to discourage unwise investments that put communities at risk. Property owners may undervalue the likelihood of property loss; or the community may wish to avoid hazards or nuisances that individual property owners are willing to take on.
• Where no lands seem certain to be protected, a local government may prefer to designate some lands for protection and others for retreat, both to improve prospects for environmental preservation in some areas and to define an area with improved economics for shore protection. (That approach is similar to smart-growth policies and other approaches to land use planning where some lands are designated for agriculture and open space while others are designated for extensive infrastructure and other services.[529])
• A conservancy may prefer the certainty that a particular ecosystem will migrate inland over having to rely on property owners abandoning lands that do not seem worth protecting today, but might be so in the future.
• The cost of implementing a retreat policy is low in an area where no one expects shore protection today. Changing economics could make development and shore protection more likely in the future, by which time the cost of adopting a retreat policy would be high.

Although the need for a retreat policy seems less in areas where retreat is likely anyway, benefits may eventually accrue; and the cost of complying with regulations or purchasing easements there would be relatively low.

For localities interested in preparing for sea level rise, one of the most urgent tasks is to define the lands likely to be armored, elevated, or yielded to the rising sea.[530] In the context of a standard zoning ordinance, such a decision would involve designating shore protection, grade elevation, and retreat zones (see Figure 8). In many coastal areas, planning and community processes have already weighed the need for development against the need for open space and conservation land. The same planning process could also decide between armoring, elevation, and retreat, although it might be reasonable to supplement that process with an environmental assessment of areas where the inland migration is most important.[531] Areas where wetland migration is a priority may include habitat for endangered species and places where potential migration of habitat is greatest. How state and federal policies should modify local choices is beyond the scope of this primer; but a possible precedent is existing land use policy, where localities make most of the initial site-specific decisions, while private, state, and federal acquisition programs often preserve lands that could be developed under local regulations.