Abstract

The development and maintenance of beach cusps were studied along a shore segment of the Delaware coast from June 5 through June 28, 1979. On three occasions, a berm and a series of beach cusps developed together on the foreshore as part of rebuilding processes following an erosional event. After the beach was rebuilt and cusps were established, the spacing between horns and the elevation of horns remain fixed. Although the processes which govern the spacing between cusps are still in question, the elevation of cusps was controlled by the elevation of swash runup. When wave dimensions were fairly constant, the elevation of the runup, and thus of the cusps, was determined by the water level of the spring high tide. As processes fluctuated back and forth from depositional to erosional events, the horns, as compared to the bays, responded to a greater extent. For example, when sediments were being deposited on the cusps, the rate of deposition on the horn crest was greater than in the bays. When waves eroded the seaward portion of a berm with cusps, however, most of the sediments lost from the cusps came from the horns; the results frequently left beach scarps at former positions of horns and no scarps at bays. After an erosional event had left beach scarps at former positions of horns, the remnant topography of beach cusps controlled the action of the swash so as to reconstruct horns at their former positions. As the beach was being rebuilt, the swash was diverted sideways by the beach scarps, and the energy of the swash was sufficiently decreased to cause deposition in front of the scarps. In turn, horns were rebuilt, and a new set of cusps was constructed at approximately the same position as of the old set of cusps.

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