Map of Coastal Change-Potential

Background of CPI

The Change-Potential Index (CPI) for assessing susceptibility to coastal change associated with sea level fall was derived from a similar methodology called the Coastal Vulnerability Index (CVI), which was developed to highlight the vulnerability of a coast to sea-level rise impacts (Thieler and Hammar-Klose, 1999). Potential impacts associated with sea-level rise include shoreline erosion, saltwater intrusion into groundwater aquifers, inundation of wetlands and estuaries, and threats to cultural and historic resources as well as infrastructure. Impacts from sea-level fall in an area like southeastern Alaska could include grounding of tidewater glaciers, dewatering of wetland areas, decreases in harborage area, channel shoaling, stream and river mouth erosion, and habitat loss. A goal of the USGS/NPS cooperative project was to apply the CVI methodology in a variety of sea-level settings, and GBNPP was selected as a location where relative sea-level is falling. Because the impacts associated with sea-level fall are different from impacts associated with sea-level rise, a slightly different index was developed to differentiate assessments in areas with falling sea-level from areas experiencing sea-level rise. In this study, we considered that impacts are often evaluated from a human perspective and a human connection to the coast. Threats to infrastructure, for example, are a major concern along coastlines that are experiencing sea-level rise. Alternatively in areas where sea-level is falling, the potential subaerial exposure of polluted marine sediments may be a primary concern. For the purposes of this cooperative project, we chose to reserve the word 'vulnerability' for coastlines that may succumb to loss of land, infrastructure, or natural and cultural resources as a result of sea level rise. Alternatively, for areas where sea level is falling and associated impacts are not as well-understood or researched, we address the likelihood that coastal change may occur without assigning a subjective term such as risk, hazard, or vulnerability.

One assumption that is made in order to apply the CPI method to an emerging coast is, that independent of the net movement of sea level relative to the land surface, the variables that are most important to coastal change and shoreline evolution will be the same. That is, the six variables defined in the CPI methodology will be important for both submerging (experiencing relative sea-level rise) and emerging (experiencing relative sea-level fall) coastlines. Since the CPI is designed to highlight change-potential based on variables that are common to almost all coasts without directly indicating a physical effect, it should be amenable to application in a variety of geologic settings. Although this methodology can be applied anywhere that physical change is likely to occur as a result of changing sea-level, the physical changes that may occur are not addressed and should be considered by planners in the context of resources utilization and preservation. This report illustrates that CPI methodology can be applied along the southeastern coast of Alaska. The usefulness of the data for planning purposes, however, will be a function of the nature of potential environmental change and whether such change is desirable from a resource management perspective