Beach oscillation and rotation: local and regional response at three beaches in southeast Australia

Abstract

Short, A.D., Bracs, M.A., Turner, I.L., 2014, Beach oscillation and rotation: local and regional response on three beaches in southeast Australia. In: Green, A.N. and Cooper, J.A.G. (eds.), Proceedings 13th International Coastal Symposium (Durban, South Africa), Journal of Coastal Research, Special Issue 70, pp. 712-717, ISSN 0749-0208.Six years of monthly subaerial surveys across three embayed beaches in southeast Australia located 270 km apart are utilized to compare the response of the beaches at the local and regional scale. The three beaches (Narrabeen, Moruya and Pedro) are exposed to a similar deep water wave climate (Hs ~1.5 m, T~10 s), identical tides (spring range 1.6 m) and have similar lengths (~3 km), easterly orientation and medium to fine sand. Over the six years all three beaches had synchronous oscillation and rotation, though at different magnitudes. The lower energy Moruya beach undergoes greater beach oscillation (up to 100 m) and rotation than the higher energy Narrabeen and Pedro. The results highlight the regional scale of synchronous beach response, as well as have implication for our understanding of sediment transport and shoreline stability in relation to beach state, with the lower energy beach having a more dynamic shoreline. Furthermore the six years of data is insufficient to detect longer term trends observed at Narrabeen since 1976.