Contribuição metodológica à estimativa da vulnerabilidade natural e perigo de contaminação de aquíferos livres granulares
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Data
2018-04-10
Autores
Francisco, Richard Fonseca [UNESP]
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Editor
Universidade Estadual Paulista (Unesp)
Resumo
Diante da importância das águas subterrâneas para os diversos usos, particularmente o abastecimento público, e considerando os crescentes impactos nas reservas subterrâneas decorrentes de superexplotação, bem como a degradação da qualidade da água por atividades antrópicas, torna-se imprescindível o estabelecimento de instrumentos de planejamento, gestão do uso e proteção dos recursos hídricos subterrâneos. Por esta razão, o objetivo principal desta pesquisa foi apresentar uma proposta metodológica para avaliar a vulnerabilidade natural e perigo de contaminação de aquíferos livres granulares, a partir de uma abordagem centrada na integração entre o parâmetro de Dar Zarrouk denominado condutância longitudinal unitária e demais fatores que interferem na estimativa destes processos. Para tanto, os métodos SDR e SDR-PERIGO foram desenvolvidos e aplicados experimentalmente no Aquífero Rio Claro, no município de Rio Claro/SP, a fim de estimar a vulnerabilidade natural e perigo de contaminação, respectivamente. A espessura e a resistividade elétrica da zona não saturada, utilizadas para o cálculo da condutância longitudinal unitária, foram obtidas através do processamento e análise de sondagens elétricas verticais. Os demais fatores empregados foram a declividade, taxa anual de recarga do aquífero e uso e cobertura do solo. Os pesos de influência dos fatores foram determinados com o auxílio da Análise Hierárquica de Processos, a fim de reduzir a subjetividade e eventuais erros inerentes à tomada de decisão. Em seguida, os mapas de fator foram integrados em ambiente SIG, com base na Análise Multicritério, por meio da aplicação do método da Combinação Linear Ponderada. No que se refere ao método SDR, toda a área de estudo apresentou vulnerabilidade natural alta, resultado compatível com aqueles reportados em trabalhos anteriores e conforme o esperado, considerando as características dos sedimentos areno- argilosos da Formação Rio Claro. Com relação ao método SDR-PERIGO, o perigo é alto em aproximadamente 72% da área de estudo, devido à associação entre a alta vulnerabilidade natural e atividades potencialmente poluidoras. De modo geral, locais com alto perigo de contaminação foram relacionados, principalmente, à área urbano- industrial e aos cultivos de cana-de-açúcar e de cítricos. Áreas com perigo de contaminação baixo ou nulo foram encontradas onde ocorrem tipos de uso e cobertura da terra com potencial de contaminação insignificante, como vegetação natural e áreas úmidas. No que se refere aos métodos SDR e SDR-PERIGO, a análise integrada da condutância longitudinal unitária e demais parâmetros forneceu resultados robustos, sendo vantajosos sob o ponto de vista da praticidade na utilização e do número reduzido de parâmetros requeridos. Assim, estes métodos poderão ser empregados como alternativas àqueles considerados tradicionais e já consagrados na literatura pertinente, podendo constituir, futuramente, importantes ferramentas para a proteção de aquíferos livres granulares.
Considering the importance of groundwater for several uses, particularly the public supply, and considering the increasing impacts on groundwater reserves due to overexploitation, as well as the degradation of water quality by anthropogenic activities, it becomes essential to establish tools for planning, management of the use and protection of groundwater resources. For this reason, the aim of this research was to present a methodological proposal to assess the natural vulnerability and hazard to contamination of the granular unconfined aquifers, by means of an approach focused on the integration between the Dar Zarrouk parameter denominated Longitudinal Unit Conductance and other factors that interfere in the estimation of these processes. In order to evaluate the natural vulnerability and hazard to contamination, the SDR and SDR-HAZARD methods were developed and experimentally applied in the Rio Claro Aquifer, in the Rio Claro municipality, São Paulo State, Brazil. The longitudinal unit conductance results from the ratio between the thickness of the unsaturated zone and its electrical resistivity, which were obtained by processing and analysis of vertical electrical soundings. Other factors were used, such as slope, annual rate of aquifer recharge and land use. Factor weights were determined with the aid of the Analytic Hierarchy Process, in order to reduce the subjectivity and eventual inconsistencies in the decision-making process. Posteriorly, the factor maps were integrated into GIS based on Multicriteria Analysis, through the application of the Weighted Linear Combination method. Regarding the SDR method, the entire study area presented high natural vulnerability, a result compatible with those reported in previous studies and as expected, considering the characteristics of sandy-clay sediments of the Rio Claro Formation. With respect to the SDR-HAZARD method, the hazard is high in approximately 72% of the study area, due to the association between high natural vulnerability and potentially polluting activities. Generally, places with high contamination hazard were mainly related to industrial and urban areas, including sugarcane and citrus crops. Areas with low or null contamination hazard were found where there are types of land use with negligible potential contamination, such as natural vegetation and wetlands. As regards the SDR and SDR-HAZARD methods, the integrated analysis of the longitudinal unit conductance and other parameters provided robust results, whose advantages are the practicality use and reduced number of required parameters. Thus, these methods may be employed as alternatives to those considered traditional and already established in the related literature, providing, in the future, important tools for the protection of granular unconfined aquifers.
Considering the importance of groundwater for several uses, particularly the public supply, and considering the increasing impacts on groundwater reserves due to overexploitation, as well as the degradation of water quality by anthropogenic activities, it becomes essential to establish tools for planning, management of the use and protection of groundwater resources. For this reason, the aim of this research was to present a methodological proposal to assess the natural vulnerability and hazard to contamination of the granular unconfined aquifers, by means of an approach focused on the integration between the Dar Zarrouk parameter denominated Longitudinal Unit Conductance and other factors that interfere in the estimation of these processes. In order to evaluate the natural vulnerability and hazard to contamination, the SDR and SDR-HAZARD methods were developed and experimentally applied in the Rio Claro Aquifer, in the Rio Claro municipality, São Paulo State, Brazil. The longitudinal unit conductance results from the ratio between the thickness of the unsaturated zone and its electrical resistivity, which were obtained by processing and analysis of vertical electrical soundings. Other factors were used, such as slope, annual rate of aquifer recharge and land use. Factor weights were determined with the aid of the Analytic Hierarchy Process, in order to reduce the subjectivity and eventual inconsistencies in the decision-making process. Posteriorly, the factor maps were integrated into GIS based on Multicriteria Analysis, through the application of the Weighted Linear Combination method. Regarding the SDR method, the entire study area presented high natural vulnerability, a result compatible with those reported in previous studies and as expected, considering the characteristics of sandy-clay sediments of the Rio Claro Formation. With respect to the SDR-HAZARD method, the hazard is high in approximately 72% of the study area, due to the association between high natural vulnerability and potentially polluting activities. Generally, places with high contamination hazard were mainly related to industrial and urban areas, including sugarcane and citrus crops. Areas with low or null contamination hazard were found where there are types of land use with negligible potential contamination, such as natural vegetation and wetlands. As regards the SDR and SDR-HAZARD methods, the integrated analysis of the longitudinal unit conductance and other parameters provided robust results, whose advantages are the practicality use and reduced number of required parameters. Thus, these methods may be employed as alternatives to those considered traditional and already established in the related literature, providing, in the future, important tools for the protection of granular unconfined aquifers.
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Palavras-chave
Aquífero Rio Claro, Vulnerabilidade, Perigo, Método SDR, Método SDR-PERIGO, Condutância longitudinal unitária, Rio Claro aquifer, Vulnerability, Hazard, SDR Method, SDR-HAZARD Method, Longitudinal unit conductance