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Publication
Análise geomorfológica da propensão de cheias: casos de estudo dos Concelhos de Câmara de Lobos, Santa Cruz, São Vicente e Porto Moniz
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Abstract(s)
As cheias são fenómenos que têm vindo a impactar a ilha da Madeira de forma relativamente
recorrente ao longo dos últimos séculos. Na verdade, nas décadas mais recentes, a regularidade
com que este tipo de fenómeno ocorre nesta região tem vindo a aumentar. Se, por um lado, a
preponderância do crescente alcance e difusão dos meios de comunicação não pode ser ignorada,
o impacto de fatores como as alterações climáticas, o excessivo grau de impermeabilização dos
solos, sobretudo nas áreas urbanizadas, ou o surgimento tardio de instrumentos de ordenamento
de território na ilha deverá ser também tido em conta.
Durante o fenómeno de precipitação, a água precipitada que cai sobre uma determinada bacia
hidrográfica, à medida que a taxa de infiltração diminui, irá ser conduzida, por meio dos cursos
de água que compõem essa mesma bacia, até à secção de saída – a foz. Assim, é percetível que o
maior ou menor grau de exposição de uma determinada bacia hidrográfica à ocorrência de cheias
está, em grande medida, relacionado com as características da mesma; aspetos como a rugosidade,
a altura e a largura dos cursos de água, o material com que este é constituído, o declive da bacia
ou a presença de sedimentação e/ou vegetação nos canais são fundamentais para uma correta
análise à propensão de ocorrência de cheias numa determinada região.
Do ponto de vista da ilha da Madeira, o presente estudo virou atenções para os casos específicos
dos concelhos de Câmara de Lobos, Santa Cruz, São Vicente e Porto Moniz, mais concretamente
para as seguintes bacias hidrográficas: Ribeira dos Socorridos, Ribeira do Vigário, Santa Cruz,
Porto Novo, Ribeira da Vargem, São Vicente, Seixal e Ribeira da Janela. Assim, considerando
parâmetros como o tempo de concentração, a densidade e o padrão de drenagem, por exemplo,
em adição a fatores relacionados com a quantificação da forma das bacias (fatores de forma e de
alongamento e índice de compacidade) e com a caracterização das mesmas, é realizada uma
análise à probabilidade de ocorrência de transbordo, tendo em conta o caudal de ponta de cheia
de cada uma das bacias hidrográficas.
Para esse efeito, e de modo a obter dados com um maior grau de fiabilidade, recorre-se ao software
ArcGIS, desenvolvido pela Esri; num segundo momento, perante a incapacidade de escoamento
que os cursos de água em análise apresentam, considerando o caudal precipitado estimado para
um período de retorno de 100 anos, é sugerida, como medida de prevenção, a construção de uma
bacia de detenção, procedendo-se, posteriormente, ao seu dimensionamento. Esta medida surge
com o intuito de evitar que ocorra o transbordo na zona da foz do curso de água, assegurando que
esta funcionará adequadamente perante um fenómeno de precipitação extrema.
Floods are events that have been impacting Madeira on a relatively recurrent basis over the last few centuries. In fact, in recent decades, the regularity with which this type of phenomenon occurs in this region has been increasing. If, on the one hand, the importance of the media’s growing reach and diffusion power cannot be ignored on this matter, the impact of factors such as climate change, the excessive degree of soil sealing, especially in urbanized areas, or the late appearance of urban planning on the island should also be considered. During precipitation, as the infiltration rate decreases, the precipitated water that falls on a certain watershed will be conducted, through the water courses that make up that same basin, to the mouth of the river. Thus, it is noticeable that the degree of exposure of a river basin to the occurrence of floods is, to a large extent, related to its characteristics. Aspects such as its roughness, its height and width, the material with which it is made, the slope of the basin or the presence of sedimentation and/or vegetation in the channels are fundamental for a correct and precise analysis regarding the propensity of flooding. From Madeira’s perspective, the present study turned its attention to the specific cases of four cities – Câmara de Lobos, Santa Cruz, São Vicente and Porto Moniz – more specifically to the following river basins: Ribeira dos Socorridos, Ribeira do Vigário, Santa Cruz, Porto Novo, Ribeira da Vargem, São Vicente, Seixal and Ribeira da Janela. Therefore, considering factors such as concentration time, density and drainage pattern, for example, in addition to factors related to the quantification of the shape of the basins (shape and elongation factors and compactness index) and with their characterization, an analysis is carried out on the probability of transhipment, taking into account the peak flow of each of the hydrographic basins. For this purpose, and in order to obtain reliable data, ArcGIS software, developed by Esri, is used; secondly, given the inability of the watercourses under analysis to flow, considering the precipitated flow estimated for a return period of 100 years, it is suggested, as a preventive measure, the construction of a detention basin, proceeding, later, to its dimensioning. This step aims to prevent transhipment at the mouth of the watercourse, ensuring that it will function properly in the event of extreme precipitation.
Floods are events that have been impacting Madeira on a relatively recurrent basis over the last few centuries. In fact, in recent decades, the regularity with which this type of phenomenon occurs in this region has been increasing. If, on the one hand, the importance of the media’s growing reach and diffusion power cannot be ignored on this matter, the impact of factors such as climate change, the excessive degree of soil sealing, especially in urbanized areas, or the late appearance of urban planning on the island should also be considered. During precipitation, as the infiltration rate decreases, the precipitated water that falls on a certain watershed will be conducted, through the water courses that make up that same basin, to the mouth of the river. Thus, it is noticeable that the degree of exposure of a river basin to the occurrence of floods is, to a large extent, related to its characteristics. Aspects such as its roughness, its height and width, the material with which it is made, the slope of the basin or the presence of sedimentation and/or vegetation in the channels are fundamental for a correct and precise analysis regarding the propensity of flooding. From Madeira’s perspective, the present study turned its attention to the specific cases of four cities – Câmara de Lobos, Santa Cruz, São Vicente and Porto Moniz – more specifically to the following river basins: Ribeira dos Socorridos, Ribeira do Vigário, Santa Cruz, Porto Novo, Ribeira da Vargem, São Vicente, Seixal and Ribeira da Janela. Therefore, considering factors such as concentration time, density and drainage pattern, for example, in addition to factors related to the quantification of the shape of the basins (shape and elongation factors and compactness index) and with their characterization, an analysis is carried out on the probability of transhipment, taking into account the peak flow of each of the hydrographic basins. For this purpose, and in order to obtain reliable data, ArcGIS software, developed by Esri, is used; secondly, given the inability of the watercourses under analysis to flow, considering the precipitated flow estimated for a return period of 100 years, it is suggested, as a preventive measure, the construction of a detention basin, proceeding, later, to its dimensioning. This step aims to prevent transhipment at the mouth of the watercourse, ensuring that it will function properly in the event of extreme precipitation.
Description
Keywords
Escoamento superficial Gestão ambiental Hidrologia Inundações Planeamento urbano Câmara de Lobos, Madeira (Portugal) Santa Cruz, Madeira (Portugal) São Vicente, Madeira (Portugal) Porto Moniz, Madeira (Portugal) Environmental management Floods Hydrology Surface runoff Urban planning Engenharia Civil . Faculdade de Ciências Exatas e da Engenharia