Estimativa do transporte longitudinal de sedimentos a partir da modelagem de ondas para a Costa Brasileira
Resumo
A ocorrência de mudanças morfológicas nos ambientes costeiros é decorrente da interação dos processos terrestres, oceânicos e atmosféricos. A mobilidade dos sedimentos, transportada pe- los efeitos constantes das ondas, correntes litorâneas, marés e ventos, resulta em processos de acreção e/ou erosão praial. A falta de planejamento e gestão com relação ao transporte de sedimentos ao longo da costa, seja por causas naturais ou antropogênicas, pode alterar a curto ou longo prazo o equilíbrio existente em regiões costeiras, ocasionando ou acelerando processos erosivos e resultando em prejuízos econômicos e ambientais. Inserido neste contexto, o presente trabalho tem como finalidade identificar as médias anuais do transporte de sedimentos ao longo de toda a costa brasileira, a direção dominante da deriva litorânea e a sua variabilidade espaço- temporal. Para isso, foi considerada a modelagem de ondas geradas por vento, utilizando o modelo Tomawac (pertencente ao consórcio open Telemac-Mascaret), para um período de 37 anos (1979 a 2015), além de quatro metodologias para o cálculo do transporte sedimentar. Para a análise de variabilidade espaço-temporal foi aplicada a análise de ondaletas, relacionando o efeito dos ciclos de curto e longo período sobre o comportamento do transporte longitudinal de sedimentos. Os resultados mostraram que três metodologias aplicadas nos cálculos se mos- traram satisfatórias, e apenas uma superestimou os resultados, sendo considerada inadequada em todos os trechos. As maiores taxas calculadas para o transporte longitudinal de sedimentos ocorreram na Região Nordeste, destacando-se o trecho entre Pina (Pernambuco) e Piaçabuçu (Alagoas), com médias de até 844 320 m3 ano−1 . Além disso, destaca-se os pontos em Maraú e Ilhéus, ambos na Bahia, com médias de aproximadamente 650 000 m3 ano−1 . Por outro lado, as menores médias ocorreram em Meia Praia (Santa Catarina), com 13 497 m3 ano−1 , seguida por Mucurí (Bahia), com 22 577 m3 ano−1 , e Ilha Comprida (São Paulo), com 24 067 m3 ano−1 . Em relação ao efeito dos ciclos de variabilidade no transporte sedimentar, foi observado que na Região Nordeste, os ciclos anuais e interanuais resultaram mais frequentes e energéticos que na Região Sul, onde os ciclos de período curto apresentaram importância similar aos ciclos mais longos, durante os 37 anos do estudo. Entretanto, no contexto global da análise, os ciclos de longo período são mais significativos para o transporte longitudinal de sedimentos, por se tratar de um processo que ocorre a longo prazo. Desta forma, o presente estudo contribui com informações sobre o transporte longitudinal de sedimentos, destacando-se as médias anuais e a deriva dominante. Além disso, questões importantes relacionadas à influência dos ciclos de variabilidade na região de estudo são discutidas, ressaltando a importância dos eventos de mais longo período para o controle do transporte sedimentar no litoral brasileiro. Ademais, tais informações podem ser consideradas em projetos futuros, que envolvem a gestão e o manejo sustentável das zonas costeiras, possibilitando uma identificação preliminar do movimento dos sedimentos ao longo de toda a costa brasileira.
The occurrence of morphological changes in coastal environments is caused by the interaction of terrestrial, oceanic and atmospheric processes. Sediment mobility, carried by the constant effects of waves, coastal currents, tides and winds, results in processes of accretion and/or be- ach erosion. The lack of planning and management in relation to sediment transport along the coast, whether by natural or anthropogenic causes, can alter the existing or short-term equilibrium in coastal regions, causing or accelerating erosive processes and resulting in econo- mic and environmental damages. Within this context, the present work aims to identify the annual sediment transport averages along the entire Brazilian coast, the dominant direction of the coastal drift and its spatial variability. In this way, a wind-generated wave modeling was considered, using the Tomawac model (from open Telemac-Mascaret consortium), with 37 years of data (1979 to 2015), as well as four sediment transport formulations. For the spatiotemporal variability, the analysis of wavelets was applied, relating the effect of cycles of variability over the behavior of longitudinal sediment transport. The results showed that three methodologies applied in the calculations were satisfactory, and only one overestimated the re- sults, being considered inadequate in all the sections. The largest annual volumes of sediment transport occurred in the Northeastern Region of Brazil, highlighting the stretch between Pina (Pernambuco) and Piaçabuçu (Alagoas), with averages up to 844 320 m3 year−1 . In addition, the points in Maraú and Ilhéus, both in Bahia, are highlighted, with averages of approximately 650 000 m3 year−1 . On the other hand, the smallest transport averages occurred in Meia Praia (Santa Catarina), with 13 497 m3 year−1 , followed by Mucurí (Bahia), with 22 577 m3 year−1 , and Ilha Comprida (São Paulo), with 24 067 m3 year−1 . In relation to the effect of cycles of variability on sedimentary transport, it was observed that in the Northeast region, annual and interannual cycles were more frequent and more energetic than in the Southern Region, where short cycle cycles presented similar importance to longer cycles, during the 37 years of study. However, in the overall context of the analysis, the long period cycles are more significant for longitudinal sediment transport, since this is a long term process. In this way, the present article contributes with information on longshore sediment transport, highlighting the annual methods and the dominant drift. In addition, important questions about the influence of cycles of variability in the study region are discussed, emphasizing the importance of longer period events for the control of sedimentary transport in the Brazilian coast. Such information can be considered in future projects, which involve the sustainable management of coastal zones, allowing a preliminary identification of the sediment movement along the entire Brazilian coast.
The occurrence of morphological changes in coastal environments is caused by the interaction of terrestrial, oceanic and atmospheric processes. Sediment mobility, carried by the constant effects of waves, coastal currents, tides and winds, results in processes of accretion and/or be- ach erosion. The lack of planning and management in relation to sediment transport along the coast, whether by natural or anthropogenic causes, can alter the existing or short-term equilibrium in coastal regions, causing or accelerating erosive processes and resulting in econo- mic and environmental damages. Within this context, the present work aims to identify the annual sediment transport averages along the entire Brazilian coast, the dominant direction of the coastal drift and its spatial variability. In this way, a wind-generated wave modeling was considered, using the Tomawac model (from open Telemac-Mascaret consortium), with 37 years of data (1979 to 2015), as well as four sediment transport formulations. For the spatiotemporal variability, the analysis of wavelets was applied, relating the effect of cycles of variability over the behavior of longitudinal sediment transport. The results showed that three methodologies applied in the calculations were satisfactory, and only one overestimated the re- sults, being considered inadequate in all the sections. The largest annual volumes of sediment transport occurred in the Northeastern Region of Brazil, highlighting the stretch between Pina (Pernambuco) and Piaçabuçu (Alagoas), with averages up to 844 320 m3 year−1 . In addition, the points in Maraú and Ilhéus, both in Bahia, are highlighted, with averages of approximately 650 000 m3 year−1 . On the other hand, the smallest transport averages occurred in Meia Praia (Santa Catarina), with 13 497 m3 year−1 , followed by Mucurí (Bahia), with 22 577 m3 year−1 , and Ilha Comprida (São Paulo), with 24 067 m3 year−1 . In relation to the effect of cycles of variability on sedimentary transport, it was observed that in the Northeast region, annual and interannual cycles were more frequent and more energetic than in the Southern Region, where short cycle cycles presented similar importance to longer cycles, during the 37 years of study. However, in the overall context of the analysis, the long period cycles are more significant for longitudinal sediment transport, since this is a long term process. In this way, the present article contributes with information on longshore sediment transport, highlighting the annual methods and the dominant drift. In addition, important questions about the influence of cycles of variability in the study region are discussed, emphasizing the importance of longer period events for the control of sedimentary transport in the Brazilian coast. Such information can be considered in future projects, which involve the sustainable management of coastal zones, allowing a preliminary identification of the sediment movement along the entire Brazilian coast.
Descrição
Dissertação (Mestrado)
Palavras-chave
Modelagem Numérica, Tomawac, CERC, Kamphuis, Transporte Sedimentar, Numerical Modeling, Sedimentary Transport
Citação
TROMBETTA, Thaísa Beloti. Estimativa do transporte longitudinal de sedimentos a partir da modelagem de ondas para a Costa Brasileira. 2019. 115f. Dissertação (Mestrado) - Programa de Pós-Graduação em Engenharia Oceânica, Escola de Engenharia, Universidade Federal do Rio Grande, Rio Grande, 2019.