We pointed out in our paper that the two-dimensional Bruun model of beach erosion is controversial; the intensity of the controversy is amply illustrated by the responses printed in this Forum section of Eos. For example, at one end of the spectrum, Cyril Galvin derides beach erosion caused by sea-level rise as an article of faith, if not fact, while Pilkey et al. state that it is intuitive that sea-level rise is the primary factor causing shoreline retreat.
Pilkey et al. assert that we erred in confining our attention to the active beach profile rather than to the much flatter coastal plain. They claim that …we should expect rates of shoreline recession 10,000 times the rate of sea-level rise through simple innundation of the shoreline. We merely point out the obvious; such dramatic beach retreat has not occurred in the last 100 years, during which relative sea level has risen 20–40 cm along the U.S. east coast. In contrast to the Pilkey et al. assertions, we know of no U.S. barrier beaches that have retreated 2,000–4,000 m in the past century; we have the historical maps, and even crude comparisons show nothing approaching this magnitude of change! Many barrier beaches (for example, Nauset Spit, Cape Cod, Massachusetts; Ocean City, Maryland) are only a thousand meters wide or less and would have long eroded away or been sitting on the mainland shore if this were even close to being true.