Caracterização dos padrões morfodinâmicos em cristas de praias na costa amazônica

Abstract

Knowledge of beach environments requires an integrated morphodynamic approach using different spatio-temporal scales, in order to understand the role of coastal and marine processes in modifying beach morphology. There are some important peculiarities about these processes on the beaches of the Amazon region, such as the large hydro-sedimentary discharge from the estuaries, high rainfall rates and the high amplitude and intensity of the tidal currents, which shape the often complex beach systems, such as beach ridges. The objective of this research was to analyze the morphological dynamics of a beach ridge segment located north of the mouth of the Amazon River, in Goiabal (city of Calçoene), in the coastal ocean sector of the state of Amapá.The hypothesis is that the morphological changes in the segment of beach crest under study are influenced by the hydrosedimentary dynamics of the Amazon River. The research methodology was based on three stages: (1) determining the morphology of beach ridges and their changes (beach profile variation, sedimentary deposits and beach classification); (2) analysis of morphosedimentary processes (physical coastal agents such as tides, waves and currents, and sediment supply such as sediment plumes; (3) data integration (correlation between the processes analyzed in stage one and two). The results indicate significant average variations in the morphosedimentation of the Goiabal beach ridge system, with seasonal migration (~24 to ~42 meters) towards the mainland. Erosion and deposition on the ridges and subsequent channels averaged less than 0.30 m along the beach profiles during the seasonal cycle. The oceanographic parameters indicate an average wave height of 0.25 m and an average tidal range of 5 m. Coastal currents are directed west-southwest and there is a predominance of ebb tide currents during the rainy season. The sediment plume of the Amazon River was closer to the study area during the rainy season (~15 to 25 km), with a predominance of ebb tide currents. Thus, it can be concluded that the segment of beach crest studied has a greater influence from the Amazon River sediment plume during the rainy season, intensifying the deposition of fine sediments. The displacement of beach ridges and the supply of sediment have a strong relationship with tidal dynamics in the region.