ABSTRACT

Observations at Westbrook, Connecticut, suggest that the following conditions are necessary for the formation and preservation beyond one tide period of sandy and pebbly beach cusps and of pebble ridges, developing perpendicular to the shoreline:

1. Adequate amount of available and transportable source material.
2. Sufficient breaker energy for the accumulation of prospective cusp and ridge material.
3. Maintaining of balance between the swash energy and the source material for a certain amount of time to allow the construction of the cusps and preventing their erosion. In the case of fine sandy cusps the still-stand of the sealevel for 30-45 minutes is held to be necessary for this purpose.
4. Subsequent lowering of the sealevel without breaker energy increase.

Pebbly-coarse sandy cusps are forming in a much shorter time than fine sandy cusps of the same dimensions do. Pebble ridges, perpendicular and oblique to the beach trend develop if the beach contains an abundant amount of coarse material below the high tide level and the swash energy is in balance with the material during the receding tide. Oblique ridges form during strong longshore drift. Fine sand cusps were found to have been built by the combination of erosion and accumulation.