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.