Shoreline Periodicities and Linear Offshore Shoals

Felder, W.; Hayden, B.; Dolan, R.

Linear shoals off the Delmarva coast are believed to have evolved on the shoreface of Assateague Island in response to inshore processes. Analyses of shoreline rate of-change data and the spatial distribution of the linear shoals indicate several spatial periodicities. The shorelineperiodicities correspond to hypothetical standing edge waves. The linear shoals, however, do not have wave-Lenqt.hs consistent with either the shoreline periodicities or the edge waves. The strongest periodicity in the shoal field has an orientation parallel to relict beach ridgeson Assateague Island dated ca 2000 BP. Thus, the linear offshore shoals may have formed at a time when Assateague Island was shorter and edge waves of a different wavelengthwere present. Where sedimentary shorelines are strongly concave, such as the 123 km Arc between Cape Hatteras and Cape Lookout, i~shore currents associated with standingedge waves seem to inhibit the development of linear shoals. Where the shoreline is c9nvex, such as along the Delmarva coast, currents associated with standing edge waves are lessprevalent and thus likely to inhibit the development of linear shoals.