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Modelação da susceptibilidade à rotura e propagação de desabamentos na Arrábida
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Resumo(s)
Na presente dissertação foi desenvolvido um estudo relacionado com a
instabilidade de vertentes na Serra da Arrábida (Península de Setúbal), focado nos
desabamentos, sob a forma de queda de blocos rochosos e numa área aproximada de
117.5 km2. Todos os procedimentos foram desenvolvidos em ambiente de Sistemas de
Informação Geográfica.
Foram definidos dois objectivos específicos: (i) análise da susceptibilidade à
ocorrência de desabamentos: através da criação de um inventário de movimentos de
vertente e da utilização de seis variáveis explicativas foram aplicados os
procedimentos necessários à utilização do método do Valor Informativo, o que
possibilitou a criação de nove modelos de susceptibilidade; (ii) análise da
susceptibilidade à propagação dos desabamentos: com base nos resultados obtidos
em (i) foram definidas quatro áreas de teste onde se procedeu à modelação da
propagação dos desabamentos a partir das fontes, recorrendo ao software CONEFALL
1.0 e utilizando duas variáveis, o Modelo Numérico de Elevação, que contém as
características morfológicas das áreas de teste, e as fontes de desabamentos
inventariadas e/ou determinadas a partir da localização dos blocos e dos depósitos
desabados. O CONEFALL assenta no Ângulo da Linha de Energia e implica que sejam
determinados ângulos de alcance para cada área de teste. Para tal, foram definidos
ângulos mínimos e máximos com variações 0.5°, com vista à determinação do ângulo
que gera o melhor ajustamento entre a classificação da susceptibilidade determinada
com base nas áreas de propagação e a distribuição dos blocos e/ou depósitos de
desabamento reconhecidos por foto interpretação e trabalho de campo. Deste modo,
foram criados sete modelos de propagação para cada uma das áreas de teste e
obtiveram-se as densidades de trajectórias e respectivas áreas de propagação.
Os resultados obtidos e a modelação em duas fases distintas permitiu identificar
“onde” os desabamentos poderão ocorrer e “até onde” este se poderão propagar.
ABSTRACT In this thesis a study related to the slope instability focused on rockfalls was developed for the Arrábida mountain (117.5 km2) located in the Setúbal Peninsula. All the procedures were developed in Geographic Information Systems. Two main specific objectives were defined: (i) the assessment of rockfall rupture susceptibility; by creating a rockfall inventory and using six explanatory variables. The Information Value method was used to weighted variable classes and nine rockfall susceptibility models were produced covering the entire study area; (ii) the assessment of rockfall propagation: based on the results obtained in (i), four test areas were defined, where the procedures to model the propagation of the rockfalls from the departure zone (sources) were applied. The software CONEFALL 1.0 was selected to model rockfall propagation by considering two variables: the Digital Elevation Model, which contains the morphological characteristics of the test areas, and the sources of rockfalls inventoried. The inventoried rockfall blocks and deposits were used to validate the results. The method CONEFALL is based on Line of Energy Angle and it is mandatory that a range of angles of reach are defined for each test area. Therefore, minimum and maximum angles were defined with variation of 0.5° with the objective to determine which angles allow the best adjustment between susceptibility classes ranked on the propagation areas and the distribution of the rockfall blocks and/or deposits. Seven rockfall propagation models were built for each test areas allowing the definition of paths and propagation areas. The final results of rockfall modeling in two distinct phases allow us to identify "where" future rockfalls may occur and "how far" they may propagate.
ABSTRACT In this thesis a study related to the slope instability focused on rockfalls was developed for the Arrábida mountain (117.5 km2) located in the Setúbal Peninsula. All the procedures were developed in Geographic Information Systems. Two main specific objectives were defined: (i) the assessment of rockfall rupture susceptibility; by creating a rockfall inventory and using six explanatory variables. The Information Value method was used to weighted variable classes and nine rockfall susceptibility models were produced covering the entire study area; (ii) the assessment of rockfall propagation: based on the results obtained in (i), four test areas were defined, where the procedures to model the propagation of the rockfalls from the departure zone (sources) were applied. The software CONEFALL 1.0 was selected to model rockfall propagation by considering two variables: the Digital Elevation Model, which contains the morphological characteristics of the test areas, and the sources of rockfalls inventoried. The inventoried rockfall blocks and deposits were used to validate the results. The method CONEFALL is based on Line of Energy Angle and it is mandatory that a range of angles of reach are defined for each test area. Therefore, minimum and maximum angles were defined with variation of 0.5° with the objective to determine which angles allow the best adjustment between susceptibility classes ranked on the propagation areas and the distribution of the rockfall blocks and/or deposits. Seven rockfall propagation models were built for each test areas allowing the definition of paths and propagation areas. The final results of rockfall modeling in two distinct phases allow us to identify "where" future rockfalls may occur and "how far" they may propagate.
Descrição
Tese de mestrado, Geografia - Geografia Física e Ordenamento do Território, Universidade de Lisboa, Instituto de Geografia e Ordenamento do Território, 2012
Palavras-chave
Movimentos de vertente - Arrábida (Portugal) Modelos em geologia Teses de mestrado - 2012