Abstract: Using the North Carolina barrier island shoreline as the test area, a variety of simple geometric recession models has been applied to predict shoreline erosion rates for various sea-level rise scenarios. All sea-level rise scenarios assume no acceleration in rate of rise. South of Cape Lookout, the Bruun Rule, Generalized Bruun Rule and the slope of the migration surface all lead to similar recession predictions. North of Cape Lookout, the slope of the migration surface predicts a much greater recession than Bruun-related models. This suggests the possibility that the islands are in an “out-of-equilibrium position” with respect to present sea level. If this is the case, the possibility exists that very rapid migration of the northern islands will soon occur. The assumptions used in the present mathematical models depicting shoreline retreat are generally weak. Better models are needed, especially for shorelines where recession is part of the barrier island migration process. The large number of types of islands in a wide variety of geologic and oceanographic settings makes a universally applicable model difficult, if not impossible, to formulate.

Abstract Over 75 percent of the United States ocean shoreline is eroding retreating landward Shoreline progradation where occurring is generally assumed to be a temporary phenomenon When affecting a developed area shoreline retreat is usually termed erosion but considerable confusion remains over the use of this term Retreat and progradation refer to achange in shoreline position whereas erosion and accretion refer to volumetric changes in the subaerial beach As used in this paper however erosion refers to any form of shoreline retreat consistent with common usage. Coastal erosion is a fundamental and widespread process on U S and world shorelines Evidence particularly on barrier island coasts indicates that in the past few decades or millenia erosion may have become a more widespread process Possible causes of this change include the effect of humans shoreface steepening or an increase in the rate of eustatic sea level rise. Mechanisms responsible for shoreline erosion are highly variable both temporally and geographically. In addition, our understanding of shoreline sediment transport dynamics is incomplete. Consequently, we are presently unable to predict accurately future shoreline-retreat rates related to continued sea-level rise. The Bruun Rule, for example, predicts little shoreline retreat relative to using, as a predictive tool, the slope of the land surface over which sea level is expected to rise.