The Public Trust Doctrine (PTD) is a legal concept that often has great impact on how governments manage their tidelands and nearshore waters. The government is the trustee of these areas for the benefit of the public and maintains this stewardship responsibility even though in some cases it may previously have decided to privatize some submerged sovereign lands (see NRC, 1999).

The original public trust interests included navigation, fishing, and commerce (Martin v. Lessees of Waddell, 41 U.S. 367 (1842) and Shivley v. Bowlby, 152 U.S. 48 (1894)). However, recent case law in some states since the early 1970s has produced an evolution in the interests that the PTD covers. Thus, depending on state law, the PTD interest may extend to open space protection, environmental quality, and recreation interests.

The PTD has implications for all decisions regarding shoreline erosion control options that inevitably produce an impact on public trust lands. The outcome will depend on the dominant interest at stake. For example, some erosion control options, such as wetland creation and “living shorelines” may impede the public trust interest of navigation while enhancing other public interests such as environmental quality and fishery habitat. Other responses, such as bulkheads, may degrade the quality of nearshore environments (e.g., reduce their quality as fish habitat), but maintain navigation. If protecting natural shorelines, wetlands, and beaches is a priority in an area, then some responses to erosion such as vertical walls may not be feasible. In other areas, protection of navigation interests might be paramount and lead to erosion responses that conflict with conservation of natural areas.

An additional issue that often complicates decision-making is public access. Not only does common law recognize the riparian right of access to navigable waters, it also guarantees the public’s right to navigate on waters. This later concept may create obstacles for proposals that interfere unreasonably with the public’s access to navigable waters, as well as the public navigation interest. Erosion control options, such as beach creation, may also create new opportunities for public access to the fringes of navigable waters. For example, in Mobile Bay, Alabama, property owners are warned by regulators that the construction of beaches—a mitigation option that increases habitat value as compared to a seawall which does not—will require that the public be granted access to the shoreline in places where it may not have had access previously (Douglass, 2005a).