Breaching of a Beach Ridge and the Formation of Beach Cusps

Abstract

The development of beach cusps was observed on Mont‐St‐Pierre beach on the southern shore of the St Lawrence estuary on the Gaspé peninsula, in July 1979. Local observations and sediment analyses showed that the cusp material originated from a beach ridge located in the upper part of the tidal area. The initial stage in the formation of cusps was the breaching of this beach ridge by the swash. Material transported by the swash and backwash formed the cusp horns. No cusps were observed to develop on the western part of the beach where the beach ridge was not breached by the swash. Le développement des croissants de plage a été observé sur la plage de Mont‐St‐Pierre, la céte méridionale de l'estuaire du Saint‐Laurent, sur peninsule de la Gaspésie, en juillet 1979. Les observations faites sur l'aire de recherche et les analyses skdimentaires ont révélé que les matériaux des croissants de plage étaient essentiellement originaires d'une crtte de plage qui se trouvait dans la partie supérieure de la zone de rnarée. La formation des croissants de plage a commencé par la rupture de la crtte de plage que les bas‐fonds avaient causées. Ces matkriaux transportés par les bas‐fonds et les bas‐fonds revenants ont produit les parties pointues des croissants. Aucun croissant de plage ne s’était produit dans la région ouest de la plage ou les bas‐fonds n'ebrkchaient pas la crtte de plage.

Efficacy of beach dewatering — Alassio, Italy

“…Cusp formation by edge waves (Guza and Inman, 1975;Inman and Guza, 1982) is also an erosive process. The breaching of the beach ridge or berm, as a trigger for cusp development was suggested by Sallenger (1979), Dubois (1978) and Pyokari (1982). Cusps, although not as small as ours, have been also reported by Wright and Short (1983) as indicators of the early stage of beach front truncation.…”