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Estudo do assoreamento do porto da Ericeira
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O assoreamento portuário diz respeito à agradação sedimentar do fundo e resulta na diminuição da profundidade no porto. O processo de assoreamento atinge grande parte dos portos marítimos em todo mundo e é um problema que pode condicionar a navegação. O estudo do assoreamento do porto da Ericeira é fundamental para compreender a evolução em litorais rochosos semelhantes, uma vez que ainda não existe um estudo dedicado à problemática da dinâmica sedimentar desta região. Esta dissertação tem como objetivo caracterizar o processo do assoreamento sedimentar do porto da Ericeira e compreender os processos de dinâmica sedimentares que estão na sua origem, através do estudo da evolução da linha de água numa escala plurianual. Outro objetivo baseia-se em fornecer uma perspetiva integrada do balanço sedimentar neste setor costeiro e compreender as causas do assoreamento. Numa fase inicial foi realizada a caracterização local de estudo e feita uma síntese de evolução do porto da Ericeira através de arquivos históricos e imagens antigas da região. De seguida, através da utilização das técnicas de aquisição geográfica, dos indicadores de linha de água e dos dados sedimentológicos avaliou-se a retenção sedimentar da praia dos Pescadores. Posteriormente, foram utilizados levantamentos de diferentes anos e o modelo do perfil introduzido para calcular o volume do assoreamento. Por fim, foi elaborado um modelo conceptual da dinâmica sedimentar, de modo a verificar a origem do assoreamento e perceber qual a sua evolução através dos processos sedimentares que o condicionam. A análise dos resultados baseia-se nos métodos utilizados para a extração da linha de água, aquisição de perfis topo-hidrográficos e dados da textura dos sedimentos, segundo um modelo teórico para o cálculo do volume de acreção de areia entre os anos de 2011 até 2020. Os resultados obtidos mostram que com a reconstrução e aumento do molhe de proteção de 2010, resultou num forte assoreamento no interior da bacia portuária e na praia. Este assoreamento não é uniforme em todo o porto correspondendo assim a um transporte de sedimentos diferente na bacia portuária e na praia intertidal, indicando um processo de seletividade nesta região. Segundo o modelo conceptual, observa-se que o transporte de sedimentos na praia submarina, equivalente à areia de dimensão fina e média, é mais intenso do que na praia intertidal formada por areia grosseira. O volume de acreção da praia intertidal e subtidal apresentam uma magnitude de assoreamento que ronda os 9400 m3 /ano e os 14400 m3 /ano respetivamente. Por isso, ao longo dos anos verifica-se que existe uma tendência de evolução do assoreamento como consequência do aumento do abrigo no porto. Os resultados do volume dos levantamentos estão em conformidade com o volume calculado no modelo de perfil introduzido, que se revelou uma boa ferramenta para estimar a magnitude do fenómeno de assoreamento em praias de plataforma rochosa. O modelo conceptual mostrou-se um instrumento útil no estudo do processo da evolução do assoreamento e no balanço sedimentar na gestão de troços costeiros, idênticos ao litoral do porto da Ericeira.
Port siltation refers to the sedimentation of the bottom and results in the decrease of the depth in the port. The silting process affects a large part of the seaports around the world and is a problem that can condition navigation. The study of the silting of the Ericeira harbor is fundamental to understand the evolution in similar rocky coastlines, since there is not a study dedicated to the problem of sediment dynamics in this region. This dissertation intends to characterize the sediment silting process in the Ericeira harbour and to understand the sediment dynamics processes that are at its origin, through the study of the waterline evolution on a multi-annual scale. Another objective is to provide an integrated perspective of the sediment balance in this coastal sector and to understand the causes of siltation. In an initial phase the local characterization of the study site was developed and a synthesis of the evolution of the port of Ericeira was obtained through historical archives and old images of the region. Next, through the description of geographic acquisition techniques, waterline indicators, and sedimentological data, the sediment retention of Pescadores Beach was evaluated. After that, surveys from different years and the profile model introduced were used to calculate the volume of siltation. Finally, a conceptual model of the sediment dynamics was developed in order to verify the origin of the siltation and to understand its evolution through the sedimentary processes that condition it. The analysis of the results is supported by the methods used for waterline extraction, acquisition of top hydrographs profiles and sediment texture data, according to a theoretical model for the calculation of sand accretion volume between the years 2011 to 2020. The results achieved demonstrate that with the reconstruction and enlargement of the 2010 protection pier, strong siltation has resulted within the harbor basin and on the beach. This siltation is not uniform throughout the harbor corresponding to a different sediment transport in the harbor basin and on the intertidal beach, indicating a selectivity process in this region. According to the conceptual model, it is observed that sediment transport on the subtidal beach, equivalent to fine and medium-sized sand, is more intense than on the intertidal beach formed by coarse sand. The accretion volume of the intertidal and subtidal beach has a siltation magnitude of about 9400 m3 /year and 14400 m3 /year respectively. Therefore, over the years there is a tendency for the siltation to evolve as a consequence of the increase in the harbor shelter. The results of the volume of the surveys are in accordance with the volume calculated in the profile model introduced, which proved to be a good tool for estimating the magnitude of the siltation phenomenon on rocky shelf beaches. The conceptual model proved to be a useful tool in the study of the siltation evolution process and sediment balance in the management of coastal stretches, identical to the Ericeira harbor coastline.
Port siltation refers to the sedimentation of the bottom and results in the decrease of the depth in the port. The silting process affects a large part of the seaports around the world and is a problem that can condition navigation. The study of the silting of the Ericeira harbor is fundamental to understand the evolution in similar rocky coastlines, since there is not a study dedicated to the problem of sediment dynamics in this region. This dissertation intends to characterize the sediment silting process in the Ericeira harbour and to understand the sediment dynamics processes that are at its origin, through the study of the waterline evolution on a multi-annual scale. Another objective is to provide an integrated perspective of the sediment balance in this coastal sector and to understand the causes of siltation. In an initial phase the local characterization of the study site was developed and a synthesis of the evolution of the port of Ericeira was obtained through historical archives and old images of the region. Next, through the description of geographic acquisition techniques, waterline indicators, and sedimentological data, the sediment retention of Pescadores Beach was evaluated. After that, surveys from different years and the profile model introduced were used to calculate the volume of siltation. Finally, a conceptual model of the sediment dynamics was developed in order to verify the origin of the siltation and to understand its evolution through the sedimentary processes that condition it. The analysis of the results is supported by the methods used for waterline extraction, acquisition of top hydrographs profiles and sediment texture data, according to a theoretical model for the calculation of sand accretion volume between the years 2011 to 2020. The results achieved demonstrate that with the reconstruction and enlargement of the 2010 protection pier, strong siltation has resulted within the harbor basin and on the beach. This siltation is not uniform throughout the harbor corresponding to a different sediment transport in the harbor basin and on the intertidal beach, indicating a selectivity process in this region. According to the conceptual model, it is observed that sediment transport on the subtidal beach, equivalent to fine and medium-sized sand, is more intense than on the intertidal beach formed by coarse sand. The accretion volume of the intertidal and subtidal beach has a siltation magnitude of about 9400 m3 /year and 14400 m3 /year respectively. Therefore, over the years there is a tendency for the siltation to evolve as a consequence of the increase in the harbor shelter. The results of the volume of the surveys are in accordance with the volume calculated in the profile model introduced, which proved to be a good tool for estimating the magnitude of the siltation phenomenon on rocky shelf beaches. The conceptual model proved to be a useful tool in the study of the siltation evolution process and sediment balance in the management of coastal stretches, identical to the Ericeira harbor coastline.
Descrição
Tese de mestrado, Geologia do Ambiente, Riscos Geológicos e Ordenamento do Território, Universidade de Lisboa, Faculdade de Ciências, 2022
Palavras-chave
Porto da Ericeira assoreamento linha de água perfis topo-hidrográficos volume sedimentar Teses de mestrado - 2022