Alternation of beach erosion/accretion cycles related to wave action off Rosarito, Baja California, Mexico

Abstract

A total of 1860 beach profiles were surveyed monthly from October 1995 to December 2003 at 29 control points along the coast of Rosarito (Baja California, Mexico). Sand volumes were estimated for the subaerial beach and related to deep-water wave records off California and nearshore waters at two localities off Rosarito. The spectral analysis of the sand volume time series revealed two main spectral peaks of 12- and 36-month periods. The latter cycle was identified for the first time along Rosarito beaches, showing a slightly larger amplitude on the beaches near the Federal Electricity Commission´ s breakwater and in the southern part of the study area. The contribution to sand movement produced by the annual cycle was 80 m³ m^–1, while the transport induced by the 36-month cycle was 50 m³ m^–1. The erosion and accretion cycle corresponded to winter and summer, respectively, but this pattern was inverted at two localities. The annual or seasonal cycle of sand volume change, defined in terms of the Dean number (Ω = H_s/w_sT), is controlled by the seasonal wave pattern, while the inverted cycle is due to local changes in beach morphology and approach angle of breaking waves. The factor that accounted for this cycle is associated with interannual wave pattern variations and this, in turn, with ENSO events.