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Desenvolvimento de um método paramétrico semiautomático de recuo do perfil topográfico da costa devido aos efeitos cumulativos de erosão e subida do nível médio do mar
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Resumo(s)
Uma das consequências da subida do NMM é o aumento da erosão costeira e o recuo da linha de
costa. A modelação e o acompanhamento das alterações costeiras revelam-se de extrema importância
para uma melhoria da adaptação do território a estas alterações. Grande parte dos estudos que projetam
cenários futuros da subida do NMM, têm em conta os perfis de costa e os respetivos modelos
altimétricos atuais. Este estudo procura colmatar esta limitação, explorando uma nova metodologia de
determinação do recuo da LC, recorrendo a princípios básicos da formulação modificada de Bruun,
estimando a topografia modificada. Sobre esta topografia são criados cenários de inundação futura
colmatando as incertezas dos cenários de inundação habituais.
Para validar a aplicabilidade desta metodologia, selecionou-se uma área de estudo na região da Costa
Nova. A precisão dos resultados foi avaliada usando dados históricos de fotografia aérea, datados de
1958. Efetuou-se uma aerotriangulação dum bloco de fotografias aéreas, coordenando PF’s no terreno,
derivando-se o recuo da LC até à data atual. A comparação entre esta LC e a obtida pelo algoritmo
evidenciou a existência de alterações antropogénicas à duna, conduzindo à necessidade de retificação
dos parâmetros do algoritmo para validá-lo. Contudo, esta retificação impõe demasiada influência da
subida do NMM no recuo de costa obtido, desconsiderando os efeitos do défice sedimentar e
impossibilitando a realização da validação desta metodologia. Porém, foi possível estimar o volume de
sedimentos perdidos e ganhos, devido ao recuo da costa, produzir cenários futuros de inundação
extrema e quantificar o recuo da linha de costa. O volume de sedimentos que potencialmente serão
perdidos é estimado em aproximadamente 629 mil m3 e o recuo médio obtido rondou os 1.4 m/ano. Os
cenários de inundação com a topografia ajustada à época do cenário revelaram resultados
consideravelmente diferentes dos produzidos anteriormente, evidenciando o recuo obtido.
One of the consequences of rising MSL is increased coastal erosion and shoreline retreat. Modeling and monitoring coastal changes is extremely important for improving the territory's adaptation to these changes. Most of the studies that project future scenarios for the rise of the MSL consider the coast profiles and the respective current altimetric models. This study seeks to overcome this limitation, exploring a new methodology for to determine the shoreline setback, resorting to the basic principles of Bruun's modified formulation, estimating the modified topography. Future flood scenarios are created over this topography, bridging the uncertainties of usual flood scenarios. To validate the applicability of this methodology, a study area in the Costa Nova region was selected. The accuracy of the results was evaluated using historical aerial photography data, dated 1958. An aerial-triangulation of a block of aerial photographs was carried out, coordinating FP’s on the ground, deriving the shoreline retreat to the present date. The comparison between this shoreline and the one obtained by the algorithm showed the existence of anthropogenic alterations to the dune, leading to the need to rectify the parameters of the algorithm to validate it. However, this rectification measures too much influence of the MSL rise on the coast retreat obtained, disregarding the effects of the sedimentary deficit, and making it impossible to carry out the validation of this methodology. However, it was possible to estimate the volume of sediments lost and gained due to shoreline retreat, produce future scenarios of extreme flooding, and quantify shoreline retreat. The volume of sediments that will potentially be lost is estimated at approximately 629 thousand m3 and the average retreat obtained was around 1.4 m/year. The flood scenarios with the topography adjusted to the time of the scenario revealed results considerably different from those previously produced, evidencing the retreat obtained.
One of the consequences of rising MSL is increased coastal erosion and shoreline retreat. Modeling and monitoring coastal changes is extremely important for improving the territory's adaptation to these changes. Most of the studies that project future scenarios for the rise of the MSL consider the coast profiles and the respective current altimetric models. This study seeks to overcome this limitation, exploring a new methodology for to determine the shoreline setback, resorting to the basic principles of Bruun's modified formulation, estimating the modified topography. Future flood scenarios are created over this topography, bridging the uncertainties of usual flood scenarios. To validate the applicability of this methodology, a study area in the Costa Nova region was selected. The accuracy of the results was evaluated using historical aerial photography data, dated 1958. An aerial-triangulation of a block of aerial photographs was carried out, coordinating FP’s on the ground, deriving the shoreline retreat to the present date. The comparison between this shoreline and the one obtained by the algorithm showed the existence of anthropogenic alterations to the dune, leading to the need to rectify the parameters of the algorithm to validate it. However, this rectification measures too much influence of the MSL rise on the coast retreat obtained, disregarding the effects of the sedimentary deficit, and making it impossible to carry out the validation of this methodology. However, it was possible to estimate the volume of sediments lost and gained due to shoreline retreat, produce future scenarios of extreme flooding, and quantify shoreline retreat. The volume of sediments that will potentially be lost is estimated at approximately 629 thousand m3 and the average retreat obtained was around 1.4 m/year. The flood scenarios with the topography adjusted to the time of the scenario revealed results considerably different from those previously produced, evidencing the retreat obtained.
Descrição
Tese de Mestrado, Engenharia Geoespacial, 2022, Universidade de Lisboa, Faculdade de Ciências
Palavras-chave
Recuo da costa Erosão costeira Alterações climáticas Regra de Bruun Modificada Subida do Nível Médio do Mar Teses de mestrado - 2023