Morfologia e Sedimentação em Praias Oceânicas da Amazônia Oriental durante a Variação Anual de Chuvas

Abstract

Este artigo buscou analisar os efeitos dinâmicos da sazonalidade climática sobre a morfologia e sedimentação de praias oceânicas da Amazônia durante as estações chuvosa e menos chuvosa. A importância deste estudo foi demonstrar um comportamento deposicional de sedimentos nestas praias de uma estação climática à outra. A metodologia consistiu em perfilagem topográfica nas praias dos setores: oeste (Corvina e Maçarico), central (Farol Velho) e leste (Atalaia) de Salinópolis (PA), amostragem de sedimentos, análise granulométrica com aplicação de parâmetros estatísticos e medições de altura e período de ondas. O diâmetro médio dos sedimentos consistiu predominantemente de areia fina (2,6 a 2,8 phi), muito bem a bem selecionada (0,2 a 0,5). A assimetria variou, principalmente, entre positiva (0,10 a 0,30) e aproximadamente simétrica (-0,10 a 0,10). O grau de curtose entre muito platicúrtica (<0,67) a muito leptocúrtica (1,50 a 3,00). As alturas de ondas foram mais elevadas no setor leste (máximo de 1,05 m) e períodos de ondas foram mais curtos (< 4,5 s) no setor oeste. As praias apresentaram declives suaves (< 1,5°) e grandes variações na largura entre as estações do ano (9,6 a 88,4 m). Predominou o estado morfodinâmico dissipativo (Ω>5,5), mas com ocorrência do estado de banco e calha longitudinais (4,7<Ω<5,5) no setor oeste. Foi observada acreção sedimentar da estação chuvosa a menos chuvosa em todas as praias. O transporte transversal de sedimentos foi elevado, especialmente no sentido onshore (máximo: 11x10-3 kg/s/m, setor leste). No setor central foi baixo (mínimo: 0,72x10-3 kg/s/m), favorecendo tendências erosivas neste local. Morphology and Sedimentation in Ocean Beaches in the Eastern Amazon during the Annual Rain Variation A B S T R A C TThis paper aimed to analyze the dynamic effects of climatic seasonality on the morphology and sedimentation of oceanic beaches in the Amazon during the rainy and less rainy seasons. The importance of this study was to demonstrate a depositional behavior of sediments on these beaches from one climatic season to another. The methodology consisted of topographic profiling on the beaches of the sectors: west (Corvina and Maçarico), central (Farol Velho) and east (Atalaia) of Salinópolis (PA), sediment sampling, grain-size analysis with application of statistical parameters and measurements of height and wave period. The mean diameter of the sediments consisted predominantly of fine sand (2.6 to 2.8 phi), well sorted and very well sorted (0.2 to 0.5). The asymmetry varied, mainly, between positive (0.10 to 0.30) and nearly symmetrical (-0.10 to 0.10). The degree of kurtosis between very platykurtic (<0.67) to very leptokurtic (1.50 to 3.00). The wave heights were higher on the eastern sector (maximum 1.05 m) and wave periods were shorter (<4.5 s) on the western sector. The beaches presented smooth slopes (<1.5°) and great variations in width between the seasons (9.6 to 88.4 m). The dissipative morphodynamic state (Ω > 5.5) predominated, but with the occurrence of the longshore bar and trough (4.7 < Ω <5.5) in the western sector. Sedimentary accretion from the rainy to less rainy season was observed on all beaches. Cross-shore sediment transport was high, especially in the onshore (maximum: 11x10-3 kg.s-1.m-1, east sector). In the central sector it was low (minimum: 0.72x10-3 kg.s-1.m-1), favoring erosive trends in this location.Keywords: Beach, Morphodynamic, Grain-Size, Amazon.

Coastal dynamics on equatorial beaches of amazonian coast during extreme tide events

“…These sediments are associated with tidal influence, characterizing the current plains of rivers, mangroves, and beaches (Sá, 1969). On the latter, there is a predominance of fine sands, with moderately to poorly selected medium grain-size in isolated points of the beaches, close to the rocky outcrops of the Pirabas Formation (Ranieri & El-Robrini, 2020).…”

Morphometric Characterization of Banho and Caúra Beaches in the Municipality of São José De Ribamar, São Luís Island, State of Maranhão, Brazil

“…Despite the ecological and social importance of these ecosystems, sandy beaches are significantly impacted by human interference, chemical and organic pollution, tourism and global climate change (Amaral et al, 2016). Sandy beaches are for erosion, transportation and, finally, granulometric distribution (Ranieri and El-Robrini, 2020).…”

“…Structural interventions on the coast, such as containment engineering projects designed to minimize or even impede erosive processes, need to be monitored by studies that consider climatological and oceanographic forces to avoid irreversible environmental harm as well as material losses due to poorly designed projects (Oliveira et al, 2011). For Ranieri and El-Robrini (2020) the coastal currents, waves, tidal currents are the main conditions for topography and sediment transport on macro-tidal beaches (range> 4 m).…”