Beach Imaging Through the Time Evolution of Topographical Profiles

Abstract

Beaches are among the most important transitional environments on the Earth's surface. The Armacao beach in Salvador, Brazil, presents peculiar characteristics. Those characteristics allow us to evaluate the influence of the atmospheric circulation system and the consequent longitudinal and transversal variation in the energetic response acting on it. Employing the power spectrum, the Argand complex plane, the return and the phase plots, instead of other common forms of graphical representation of beach shape and topography, greatly improved imaging of the beach profiles results. A sequential analysis of these four representations showed both the purely deterministic and the non-linear, possibly chaotic, components of the phenomenon. They also enhanced some aspects and disclosed others, which previous investigations with the same temporal data set did not show. Both the lunar cycle and a 29-month cycle related to "EI Nino" have been identified. Three, four, six, and seven-month cycles have been significantly depicted on the lower beachface. The combined analysis of the four types of representations, with the energy content versus cycle time of those cycles, show that these phenomena are manifestations of chaotic systems. Therefore they are unpredictable, without a simple explanation of causal relationships. The employed procedure can be adapted to the investigation of other natural dynamical systems.