Análise da dinâmica morfo-sedimentar da praia da Marieta – Ilha do Marco-Maracanã (NE do Pará)

Abstract

This study aims the investigation of the morphological and sedimentological variations occurred in Marieta’s Beach- Marco Island (NE of Pará) during the rainy season (March) and rainyless season (November) of 2007, seeking to identify the main factors responsible by these variations. The Marieta’s beach has 3 km long, with NW-SE direction, and is supported by the sediments of the Barreiras Group, Post-Barreiras and the recent sediments that provide much of the sediment at the mouth of the estuary Urindeua. Topographic profiles were conducted in June in the following subdivisions Beach Marieta: Sector sandy spit - profiles I and II (tgβ = 0.0015); central section - profiles III, IV (tgβ = 0.0017) and NW sector - and V profiles VI (tgβ = 0.005). We applied the following morphological beach models: Inmam & Guza (1975), Sandy Spur -        in the rainy season         in the rainyless period, Sector Central -      12 in the rainy season        during rainyless. These results show a strong reflection with some dissipation, characterized as Intermediate Bar and Longitudinal with the NW sector, which indicated a Dissipative behavior during the two periods studied, According to Wright & Short (1984) had a whole beach Dissipative behavior during the two periods studied -       in the rainy season         in the less rainy period; And following Masselink & Short (1993) showed the profiles to be modified by tides, with dissipative bars RTR = 4 in the rainy season and RTR= 3.6 in the rainyless period. The beaches are predominantly covered by very fine sand, very well selected and moderately selected, with mesocurtic and platicurtic kurtosis and negative asymmetry at the supratidal zones during the rainy season and in areas of infratidal in the rainyless season in other areas of the beach Marieta were approximately symmetrical and positive asymmetries. The Marieta’s beach has been profiled morpho-sedimentary influenced by the displacement of the Convergence Zone Inter-Tropical (ITCZ) in the rainy season (1736.6 mm) and at rainless (2.4 mm). The speed of the wind was weaker during the rainy season with an average of 6.7 nodes while in the less rainy period the average speed was 11.3 knots with preferential direction NE, and therefore, buckled with higher energy (Hb = 1 , 5 m in the rainy season in March). Coupled with an amplitude of 5.5 m tide reaching the innermost areas of the beach. In the less rainy period, the waves were smaller, compared to the rainy season, which reached 1.2 m combined with an amplitude of 4.8 m tide. Through these parameters showed that the major changes in the beach profile were associated mainly to the interaction of the effects of winds, waves and tides, showing the strong relationship between the shape and orientation of the beach and the incidence of these agents.