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Authors
Advisor(s)
Abstract(s)
O estudo do balanço sedimentar das zonas costeiras encontra-se dependente de
vários fatores interativos e retroativos, sendo o fornecimento sedimentar crucial para a
sua quantificação. Existem diversos métodos que permitam proceder à mesma, sendo que
são considerados respetivos fatores (clima, geomorfologia, geologia, ação humana etc.),
possibilitando a estimativa do sedimento que é transportado e exportado para o litoral
proveniente dos sistemas de drenagem. Na presente temática, os maiores problemas
encontram-se associados à escassez de dados fiáveis disponibilizados e à dificuldade em
considerar o efeito dos reservatórios sedimentares.
O principal objetivo na realização deste trabalho é estimar o potencial do
fornecimento sedimentar proveniente da erosão hídrica do solo que drena para a zona
costeira de Portugal continental e avaliar o efeito das barragens na retenção deste
fornecimento.
Deste modo, é pretendido fornecer uma aplicação metodológica coerente a nível
nacional. A metodologia abordada consiste na combinação dos modelos RUSLE, para
calcular a taxa de erosão do solo, e SDR, para estimar o fornecimento sedimentar às zonas
costeiras, tendo sido testadas e validadas algumas variantes referentes aos modelos
utilizados. Por sua vez, foram considerados cenários que permitissem mostrar o impacto
relativo que determinadas alterações, de natureza antrópica e climática, apresentam nesta
temática.
Segundo as condições de referência (cartografia de ocupação referente a 2018 e
uma erosividade da precipitação representativa de 2014), os resultados permitem inferir
que potencialmente sejam debitados 39.3 milhões de ton/ano de sedimento no litoral.
Dependendo da litologia aflorante nas bacias, a fração de sedimento de praia poderá
reduzir até aos 15% do sedimento total. Nos cenários modelados referentes ao impacto
das barragens, ocupação prístina, ocupação de 1990, incêndio extremo, medidas de
conservação do solo e evolução da erosividade da precipitação para 2070 apresentaram
efeitos relativos no fornecimento sedimentar de -82%, -38%, +6%, +261%, -50%, +10%,
respetivamente.
The study of the sediment budget in coastal zones depends on several interactive and retroactive factors, with sediment yield being crucial for its quantification. There are several methods to proceed with this quantification, (climate, geomorphology, geology, human activities, etc.). This approach allows for the estimation of sediment that is transported and delivered into the coast from drainage systems. In this regard, the main challenges area associated with the scarcity of reliable data and the difficulty in accounting the effect of sediment reservoirs. The main objective of this work is: to estimate/quantify the sediment supply from soil water erosion draining into to the entire coastal section of mainland Portugal, and assess the impact of dams on retaining this supply. In this sense, the goal is to provide a coherent methodological application at the national level. The methodology employed involves the combination of the RUSLE model, to calculate the soil erosion rate, and SDR, to estimate the sediment delivery ratio to coastal areas, with some variants relating to the models having been tested and validated. Additionally, various scenarios were considered to demonstrate the impact of certain changes, both anthropogenic and climatic, within the theme under study. Following the reference conditions, which include a land use map of 2018 and a representative precipitation erosivity for 2014, the results suggest that potentially 39.3 million tons/year of sediments could be discharged onto the Portuguese coast. Depending on the outcropping lithology of the basins, the fraction of beach sediment may reduce to as low as 15% of the total sediment. In the modelled scenarios related to the impact of dams, pristine land occupation, 1990 land occupation, extreme forest fire, soil conservation measures and rain erosivity evolution by 2070 show relative effects on sediment delivery of -82%, -38%, +6%, +261%, -50%, +10%, respectively.
The study of the sediment budget in coastal zones depends on several interactive and retroactive factors, with sediment yield being crucial for its quantification. There are several methods to proceed with this quantification, (climate, geomorphology, geology, human activities, etc.). This approach allows for the estimation of sediment that is transported and delivered into the coast from drainage systems. In this regard, the main challenges area associated with the scarcity of reliable data and the difficulty in accounting the effect of sediment reservoirs. The main objective of this work is: to estimate/quantify the sediment supply from soil water erosion draining into to the entire coastal section of mainland Portugal, and assess the impact of dams on retaining this supply. In this sense, the goal is to provide a coherent methodological application at the national level. The methodology employed involves the combination of the RUSLE model, to calculate the soil erosion rate, and SDR, to estimate the sediment delivery ratio to coastal areas, with some variants relating to the models having been tested and validated. Additionally, various scenarios were considered to demonstrate the impact of certain changes, both anthropogenic and climatic, within the theme under study. Following the reference conditions, which include a land use map of 2018 and a representative precipitation erosivity for 2014, the results suggest that potentially 39.3 million tons/year of sediments could be discharged onto the Portuguese coast. Depending on the outcropping lithology of the basins, the fraction of beach sediment may reduce to as low as 15% of the total sediment. In the modelled scenarios related to the impact of dams, pristine land occupation, 1990 land occupation, extreme forest fire, soil conservation measures and rain erosivity evolution by 2070 show relative effects on sediment delivery of -82%, -38%, +6%, +261%, -50%, +10%, respectively.
Description
Tese de mestrado, Geologia do Ambiente, Riscos Geológicos e Ordenamento do Território, 2024, Universidade de Lisboa, Faculdade de Ciências
Keywords
Fornecimento sedimentar RUSLE litoral Portugal Teses de mestrado - 2024