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Abstract(s)
Desde os primórdios que as nascentes de água “especial”- ora por ser quente, ou por ter cheiro ou com gás, suscitam a curiosidade e estimulam a comunidade científica para a justificação desse fenómeno natural. Nesse contexto, surge o presente documento que se pretende que seja um contributo para o entendimento do escoamento subterrâneo da Bacia do Rio Dão onde ocorrem várias águas ditas “ especiais”(neste caso águas sulfúreas).
O Rio Dão é afluente da margem direita do Rio Mondego, desenvolve-se entre as Serras do Caramulo e da Serra da Estrela, com nascente em Eirado (Aguiar da Beira) e conflui com o Rio Mondego em plena Albufeira da Barragem da Aguieira em Santa Comba Dão. A bacia do Rio Dão tem uma forma próxima da elíptica, em que o eixo principal tem a direção próxima de NE-SW. Apresenta uma rede hidrográfica composta por vales retilíneos, que geralmente apresentam a direção de NE-SW.
A bacia do Rio Dão desenvolve-se na Zona Centro-Ibérica, cuja litologia é constituída essencialmente por elementos do maciço granítico de idade Hercínica. Na zona de jusante ocorrem elementos do Complexo Xisto-Grauváquico (Grupo das Beiras), que se entende servir de barreira aos fluxos que percolam no maciço granítico. Vários autores indicam a existência de uma extensa fratura ao longo do Rio Dão e que em profundidade condiciona e encaminha preferencialmente os fluxos que ocorrem na margem direita. Importa também destacar as extensas estruturas filonianas que interferem na circulação aquífera servindo de barreira por um lado e por outro conduzem os fluxos junto a si ao longo da sua direção.
Na bacia hidrográfica do Rio Dão registam-se de montante para jusante as águas indiciadoras de extenso circuito hidráulico: Caldas da Cavaca, Sezures, Termas de Alcafache, Caldas de Sangemil e água mineral do Granjal.
Ainda que sejam as águas minerais que melhor permitam a parametrização do modelo geohidráulico da Bacia do Rio Dão, importa analisar também as zonas de recarga. Com esse intuito foi feito um levantamento das nascentes com caudal perene em toda a extensão da Bacia, tendo sido caracterizadas 143 nascentes (fontanários, bicas). Outra componente com importante contributo na recarga aquífera é a precipitação, neste sentido foram colocados amostradores em vários pontos da bacia (montante, intermédia e jusante) para o estudo em detalhe daquela parcela.
Na bibliografia existem vários estudos sobre algumas das águas identificadas no presente trabalho; assim para otimizar os recursos disponíveis fez-se uma seleção de amostras a encaminhar para análise detalhada em ambiente laboratorial. As amostras foram encaminhadas para caracterização físico-química e parametrização da componente radiológica.
A composição química da água é resultante da interação do maciço, pelo que a técnica de fazer analogia da componente hidroquímica com a litologia é uma das metodologias mais utilizadas na definição do modelo geohidráulico conceptual. No presente trabalho foram aplicadas várias metodologias que indiciam várias correlações entre os parâmetros físico-químicos e consequentemente contributo para a definição do modelo (temperatura máxima, profundidade máxima, sentido de fluxo, etc.).
Contudo, a caracterização detalhada das unidades hidrogeológicas da bacia do Rio Dão por si só não representa a circulação dos aquíferos. Nesse contexto, entende-se que a representação gráfica da circulação em profundidade do recurso é considerada uma ferramenta fundamental para a conceptualização do modelo (ainda que de forma simplificada). Na representação gráfica do modelo em estudo foi utilizada uma das ferramentas tecnológicas existentes no mercado: o programa Feflow (Finite Element Subsurface Flow &Transport Simulation System) desenvolvido pelo DHI-WASY (2009).
Reconhecendo que a modelação de um aquífero subterrâneo é um processo dinâmico, apresentaram-se algumas das perspetivas futuras no complemento do modelo atualmente apresentado, assim como algumas considerações importantes face às expectativas iniciais.
Since the earliest times, the "special" water springs - whether they be hot, with smell, with gas, etc. - arouse curiosity and encourage the scientific community to explain this natural phenomenon. In this context, this document is intended as a contribution to the understanding of the underground flow of the Dão river basin where several so-called "special" waters (in this case, sulphur waters) exist. The Dão river is an affluent of the right bank of the Mondego River. It develops between the Serra do Caramulo and the Serra da Estrela, with its source in Eirado (Aguiar da Beira) and merges with the Mondego River in the middle of the Aguieira dam in Santa Comba Dão. The Dão river basin has an almost elliptical shape, where the main axis runs in an almost NE-SW direction. It presents a hydrographic network composed of rectilinear valleys, which are usually facing in a NE-SW direction. The Dão river basin develops in the Central-Iberian Zone, whose lithology consists essentially of elements of the Hercynian granite massif. In the downstream zone, elements of the Schist-Greywacke Complex occur, which is seen to serve as a barrier against the flows that percolate in the granite massif. Several authors indicate the existence of an extensive fracture along the Dão river which, in deep waters, conditions and preferentially directs the flows that occur in the right margin. It is also important to point out the extensive philonian structures that also interfere with the aquifer circulation (they serve as a barrier on the one hand and on the other hand they carry the streams alongside each other along their course). In the Dão river basin there is an upstream and a downstream, indicating an extensive hydraulic circuit: Caldas da Cavaca, Sezures, Termas de Alcafache, Caldas de Sangemil and mineral water of Granjal. Although it is the mineral waters that best allow the parameterization of the geo-hydraulic model of the Dão river basin, it is also important to analyse the recharge zones. For this purpose, a survey of the springs with perennial flow throughout the Basin was carried out, and 143 springs (fountains, spouts, etc.) were characterized. Another component with an important contribution in the aquifer recharge is precipitation, in this sense, sampling devices were placed in several points of the basin (upstream, intermediate and downstream) for the detailed study of that plot. In the bibliography there are several studies on some of the waters identified in this work, so to optimize the available resources, a selection of samples to be sent for detailed analysis in a laboratory environment was gathered. The samples were sent for physical-chemical characterization and parameterization of the radiological component. The chemical composition of the water is the result of the interaction of the massif, so the technique of making an analogy of the hydrochemical component with the lithology is one of the methodologies most used in the definition of the conceptual model. In this work, several methodologies have been applied which indicate several correlations between the physical-chemical parameters and consequently the definition of the model (with for example the maximum temperature, the maximum depth, direction of flow, among others). However, the detailed characterization of the hydrogeological units of the Dão river basin alone does not represent the circulation of the aquifers. In this context, it is understood that the graphical representation of the in-depth circulation of the resource is considered a fundamental tool for the conceptualisation of the model (albeit in a simplified form). In the graphical representation of the model, one of the technological tools on the market was used: the programme Feflow (the Finite Element Subsurface Flow & Transport Simulation System) developed by DHI-WASY (2009). Recognizing that the modelling of an underground aquifer is a dynamic process, some of the future perspectives were presented in the supplement to the model presented today, as well as some important considerations in response to the initial expectations.
Since the earliest times, the "special" water springs - whether they be hot, with smell, with gas, etc. - arouse curiosity and encourage the scientific community to explain this natural phenomenon. In this context, this document is intended as a contribution to the understanding of the underground flow of the Dão river basin where several so-called "special" waters (in this case, sulphur waters) exist. The Dão river is an affluent of the right bank of the Mondego River. It develops between the Serra do Caramulo and the Serra da Estrela, with its source in Eirado (Aguiar da Beira) and merges with the Mondego River in the middle of the Aguieira dam in Santa Comba Dão. The Dão river basin has an almost elliptical shape, where the main axis runs in an almost NE-SW direction. It presents a hydrographic network composed of rectilinear valleys, which are usually facing in a NE-SW direction. The Dão river basin develops in the Central-Iberian Zone, whose lithology consists essentially of elements of the Hercynian granite massif. In the downstream zone, elements of the Schist-Greywacke Complex occur, which is seen to serve as a barrier against the flows that percolate in the granite massif. Several authors indicate the existence of an extensive fracture along the Dão river which, in deep waters, conditions and preferentially directs the flows that occur in the right margin. It is also important to point out the extensive philonian structures that also interfere with the aquifer circulation (they serve as a barrier on the one hand and on the other hand they carry the streams alongside each other along their course). In the Dão river basin there is an upstream and a downstream, indicating an extensive hydraulic circuit: Caldas da Cavaca, Sezures, Termas de Alcafache, Caldas de Sangemil and mineral water of Granjal. Although it is the mineral waters that best allow the parameterization of the geo-hydraulic model of the Dão river basin, it is also important to analyse the recharge zones. For this purpose, a survey of the springs with perennial flow throughout the Basin was carried out, and 143 springs (fountains, spouts, etc.) were characterized. Another component with an important contribution in the aquifer recharge is precipitation, in this sense, sampling devices were placed in several points of the basin (upstream, intermediate and downstream) for the detailed study of that plot. In the bibliography there are several studies on some of the waters identified in this work, so to optimize the available resources, a selection of samples to be sent for detailed analysis in a laboratory environment was gathered. The samples were sent for physical-chemical characterization and parameterization of the radiological component. The chemical composition of the water is the result of the interaction of the massif, so the technique of making an analogy of the hydrochemical component with the lithology is one of the methodologies most used in the definition of the conceptual model. In this work, several methodologies have been applied which indicate several correlations between the physical-chemical parameters and consequently the definition of the model (with for example the maximum temperature, the maximum depth, direction of flow, among others). However, the detailed characterization of the hydrogeological units of the Dão river basin alone does not represent the circulation of the aquifers. In this context, it is understood that the graphical representation of the in-depth circulation of the resource is considered a fundamental tool for the conceptualisation of the model (albeit in a simplified form). In the graphical representation of the model, one of the technological tools on the market was used: the programme Feflow (the Finite Element Subsurface Flow & Transport Simulation System) developed by DHI-WASY (2009). Recognizing that the modelling of an underground aquifer is a dynamic process, some of the future perspectives were presented in the supplement to the model presented today, as well as some important considerations in response to the initial expectations.
Description
Keywords
Rio Dão - Características hidrográficas Rio Dão - Modelo geohidráulico