Foredune formation and evolution on a prograding sea-breeze dominated beach

Abstract

This study investigates the mechanisms of dune formation and growth on a micro-tidal beach. The study area, located on a barrier island on the northern Yucatan peninsula, is characterized by persistent sea breeze conditions and a wide and shallow continental shelf. Beach topography data was collected over 5 years, on a prograding beach (0.5–7 m y-1), using a Real-Time Kinematic Differential Global Positioning System. The beach surveys (>100) cover from the subaerial beach (seaward from the existing foredune in 2015) to a 1.5 m water depth with a high spatial (0.2 m–0.5 m) and temporal (weekly to bi-weekly) resolution. Thus, shoreline evolution, offshore/onshore inner sandbar migration, and foredune initiation and growth can be analyzed from this data set. Moreover, environmental conditions, obtained from in situ observations and numerical model simulations, allow us to investigate the role of marine and aeolian processes on foredune morphodynamics. A net shoreline advance is observed, induced by the presence of a port's jetty, allowing the formation of a new foredune during the period of study. Field observations suggest that seasonal beach variability is explained by the onshore (offshore) sediment transport during fall-winter (spring-summer). The dune growth rate is well correlated with the monthly mean wind speed that reaches a maximum during spring months, when sea-breezes are more persistent and intense (W > 12 m s-1), the effective fetch length is larger, and the moisture content is lower. Empirical Orthogonal Function (EOF) analysis of beach profiles in the fast progradation area (>1 m y-1) shows that the variability is dominated by sustained beach width increase throughout the study period. On the other hand, at the slow progradation area the first and second EOF modes explain the seasonal beach and foredune variability, respectively. Thus, it is suggested that beach sand supply (during fall-winter) followed by aeolian transport (during spring) control the natural foredune growth in this region.