Guerreiro, J.S., Ranieri, L. A., El-Robrini, M., Vila-Concejo. Seasonal changes of a dynamic macrotidal beach: Case Study of Marieta beach(Amazon Coast/Brazil)
The Amazon Atlantic Coast is a very dynamic area due to the large discharge associated to a large network of rivers that include the Amazon River. Many of the beaches in this area are located within the area of influence of macrotidal range. There is a large sediment availability that creates extensive tidal flats. Waves are moderate with average offshore of 1.8m. The area has a tropical climate with two seasons, rainy and dry, and is under influence of moderate SE/NE trade winds. This paper presents topographic and hydrodynamic data from one of these beaches, Marieta Beach, and shows that while it undergoes severe erosion during the rainy season, accretion and recovery occurs during the dry season. Erosion seems to be associated to the large river discharge in the rainy season (10 3 to 10 4 m3/s−1), high water levels coupled with strong ebbing currents that remove the sediment from the beach. The beach accumulates large volumes of sediment during the dry season (averaging 15.2 m3); the processes that drive sediment transport are not clear but given that onshore winds occur during this period, it is hypothesized that locally wind- generated waves are capable of transporting sediment back to the beach. Seasonal behavior in this case is associated to the tropical seasonality of the rivers instead of traditional storm/fair weather conditions cycles that are often found in the literature.