MORPHODYNAMIC STUDY DURING AN EQUINOCTIAL SPRING TIDE IN A MACROTIDAL BEACH OF THE AMAZON LITTORAL (AJURUTEUA BEACH, PARÁ, BRAZIL)

Abstract

The Bragantinian coastal zone has been subjected to strong hydrodynamic processes, which continuouslyremodel its beach morphology. These energy fluctuations are more intense during the equinoctial spring tides,registered during the months of March/April and September/October. To understand the morphodynamic changesduring an equinoctial spring tide event (from 17 to 22 of March of 2003), morfodynamic studies were carried outdaily to characterize parameters such as current intensity and speed, wave break height (Hb), wave break period(T), wave break angle (αb), profile’s declivity (m), surf scaling parameter (ε), breaking coefficient (β) – and beachscarp variations. The currents were measured in the surf zone through a Sensordata SD30 current meter. Thewave break height, period and angle were measured by a graduate rule, chronometer and manual compassing,respectively. The topographic surveys were carried out in two perpendicular shoreline profiles by role andtopographic level. The analysis of these parameters showed that the studied area is, in its majority, dissipativewith a spilling type breaker, mainly in the SE sector. The observed erosive processes in the studied beach area consequence of natural causes (sometimes unknown) intensified by the human influence e.g. disorderedoccupation on dune areas and mangrove zones by edifices. The equinoctial macrotide energy was the principalfactor that contributed to the appearance of morphodynamic modifications at the Ajuruteua beach. These variationswere responsible for short-term sedimentary volume changes in the different beach sub-environments.