The Bruun Theory of Sea-Level Rise as a Cause of Shore Erosion

Laboratory and field tests have been undertaken in order to test the new theory proposed by Bruun which offers dimensional relationships to the process of sea-level rise as a cause of shore erosion, in contrast to the classic Johnsonian concept. Bruun holds that when an equilibrium profile is developed, (a) there is a shoreward displacement of the beach profile as the upper beach is eroded; (b) the material eroded from the upper beach is equal in volume to the material deposited on the nearshore bottom; (c) the rise of the near-shore bottom as a result of this deposition is equal to the rise in sea level, thus maintaining a constant water depth in that area. In field investigations, the variation between neap and spring low tide was utilized as a short-term model of sea-level rise in obtaining profiles on two dissimilar Cape Cod beaches. Scuba gear and a newly devised profiling technique were employed to obtain precise control in this phase of the study. Laboratory tests were conducted on two small-scale wave basins in coordination with the beach surveys. First-order determinations, based on combined field and laboratory data, affirm the Bruun theory of predic table shore erosion following a rise in sea level.