Measuring shoreline erosion rates: Strategy, techniques and accuracy

When coastal change in populated areas manifests itself as a landward migration of the shoreline occurring on a human time scale, quantification of erosion rates becomes important. Numerous techniques to measure shoreline change have been developed over the last 25 years (Stafford, 1971; Dolan, et al., 1978; Glow and Leatherman, 1984; McBride et al., 1991; Thieler and Danforth, 1994, Fisher and Overton, Per. Com.). These methods have been used to study beach erosion, barrier island migration and dune/bluff erosion. Although applied to the investigation of similar problems, these techniques vary considerably in approach, accuracy and cost. They range from qualitative approaches such as the measurement of shoreline position from ground or oblique photos to the very precise quantitative approach of "softcopy photogrammetry." Along with an increase in accuracy provided by the more quantitative techniques is an increase in cost and project duration. This, among other factors, has likely prevented the emergence of a standard technique for measuring shoreline change. While many coastal mapping studies would benefit from application of more advanced and accurate techniques, not all studies of the changing coastal zone require the high resolution these techniques offer. Thus, choosing appropriately from among the available methods is challenging. The many factors to be considered when selecting a shoreline mapping technique are outlined in this paper along with a framework for technique selection. Two applications of this framework are presented using studies of the California coast.