Estudo geofísico em uma área na zona de recarga do sistema aquífero Guarani
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Data
2021-08-04
Autores
Oliveira, Mariana Vieira Galvão de
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Universidade Estadual Paulista (Unesp)
Resumo
O problema da crise hídrica é uma preocupação até em países com grandes quantidades de água doce, como o Brasil. No Estado de São Paulo, após o longo período de estiagem nos anos de 2014 a 2015, a problemática acerca das crises hídricas passou a ser foco de diversos estudo. Alguns destes estudos propõem o uso de águas subterrâneas para evitar crises hídricas, todavia muitos destes não compreendem ou ignoram os processos hidrológicos de recarga e descarga dos aquíferos. Há uma grande defasagem cientifica acerca dos processos hidrológicos dos aquíferos, e esse déficit dificulta o planejamento de uso sustentável dos reservatórios. Entender os processos de recarga e descarga é fundamental para prevenir problemas relacionados a aquíferos e compreender melhor as relações de trocas entre os reservatórios superficiais e subterrâneos. Estudos geofísicos são usados para estudar esses processos hidrológicos, entretanto existe pouca bibliografia acerca do uso do método da Eletrorrestividade neste tipo de estudo. O presente trabalho delimitou uma área próxima da escarpa do front da Cuesta Basáltica no município de Ipeúna (SP), para estudar os processos de recarga e descarga por meio do método da Eletrorrestividade e de um levantamento estratigráfico. A área escolhida está em uma área de afloramento do Sistema Aquífero Guarani (SAG), local conhecido por ser importante na recarga desse aquífero transfronteiriço. O levantamento estratigráfico foi feito por meio de um caminhamento pela estrada de acesso à área de estudo. No levantamento geofísico foi necessário realizar 10 linhas pararelas de tomografia elétrica em arranjo Schlumberger. Os valores de resistividade medidos variaram entre 5000 Ω.m e 20 Ω.m. Os dados coletados em campos foram processados e representados em modelos logarítmicos bidimensionais e tridimensionais. Com a correlação entre a estratigrafia e os modelos 2D foi possível localizar onde estavam localizados os aquíferos porosos e fraturados, assim como relacionar os valores de resistividade com as rochas presentes na área, que são: Basaltos, Arenitos e Arenitos silicificados. O aquífero poroso funciona como um grande reservatório, a água é armazenada nele antes de fluir para o aquífero fraturado abaixo. O 3D permitiu uma melhor visualização da presença de água no arcabouço geológico, e a visualização dos valores de resistividade nas cotas. O modelo de bloco 3D possibilitou visualizar a água dentro de uma grande lente arenítica que flui em direção ao front da Cuesta, e não para o reverso como era esperado. A análise conjunta entre a geofísica e estratigrafia permitiu compreender sobre o arcabouço geológico, a relação do mesmo com o fluxo de água subterrânea e os processos hidrológicos. O trabalho também diminui a lacuna de estudos geofísicos no SAG e de uso de Eletrorrestividade para compreender os processos hidrológicos dos aquíferos.
The problem of the water crisis is a concern even in countries with large amounts of fresh water, such as Brazil. In the State of São Paulo, after the long period of drought in the years 2014 to 2015, the issue of water crises became the focus of several studies. Some of these studies propose the use of groundwater to avoid water crises, however many of them do not understand or ignore the hydrological processes of aquifer recharge and discharge. There is a large scientific gap regarding the hydrological processes of aquifers, and this deficit makes it difficult to plan the sustainable use of reservoirs. Understanding the recharge and discharge processes is essential to prevent problems related to aquifers and to better understand the exchange relationships between surface and underground reservoirs. Geophysical studies are used to study these hydrological processes, however there is little bibliography about the use of the Electrorestivity method in this type of study. The present work delimited an area close to the escarpment of the Cuesta Basáltica front in the municipality of Ipeúna (SP), in order to study the recharge and discharge processes using the Electrorestivity method and a stratigraphic survey. The chosen area is in an upwelling area of the Guarani Aquifer System (SAG), a place known to be important in the recharge of this transboundary aquifer. The stratigraphic survey was carried out by walking along the access road to the study area. In the geophysical survey, it was necessary to carry out 10 parallel lines of electrical tomography in Schlumberger arrangement. The measured resistivity values ranged between 5000 Ω.m and 20 Ω.m. Data collected in fields were processed and represented in two-dimensional and threedimensional logarithmic models. With the correlation between stratigraphy and 2D models, it was possible to locate where the porous and fractured aquifers were located, as well as to relate the resistivity values with the rocks present in the area, which are: Basalts, Sandstones and Silicified Sandstones. The porous aquifer acts as a large reservoir, water is stored in it before flowing into the fractured aquifer below. The 3D allowed a better visualization of the presence of water in the geological framework, and the visualization of resistivity values in the dimensions. The 3D block model made it possible to visualize the water inside a large sandstone lens that flows towards the front of the Cuesta, and not to the reverse as expected. The joint analysis between geophysics and stratigraphy allowed us to understand the geological framework, its relationship with groundwater flow and hydrological processes. The work also reduces the gap in geophysical studies in the SAG and the use of Electrorestivity to understand the hydrological processes of aquifers.
The problem of the water crisis is a concern even in countries with large amounts of fresh water, such as Brazil. In the State of São Paulo, after the long period of drought in the years 2014 to 2015, the issue of water crises became the focus of several studies. Some of these studies propose the use of groundwater to avoid water crises, however many of them do not understand or ignore the hydrological processes of aquifer recharge and discharge. There is a large scientific gap regarding the hydrological processes of aquifers, and this deficit makes it difficult to plan the sustainable use of reservoirs. Understanding the recharge and discharge processes is essential to prevent problems related to aquifers and to better understand the exchange relationships between surface and underground reservoirs. Geophysical studies are used to study these hydrological processes, however there is little bibliography about the use of the Electrorestivity method in this type of study. The present work delimited an area close to the escarpment of the Cuesta Basáltica front in the municipality of Ipeúna (SP), in order to study the recharge and discharge processes using the Electrorestivity method and a stratigraphic survey. The chosen area is in an upwelling area of the Guarani Aquifer System (SAG), a place known to be important in the recharge of this transboundary aquifer. The stratigraphic survey was carried out by walking along the access road to the study area. In the geophysical survey, it was necessary to carry out 10 parallel lines of electrical tomography in Schlumberger arrangement. The measured resistivity values ranged between 5000 Ω.m and 20 Ω.m. Data collected in fields were processed and represented in two-dimensional and threedimensional logarithmic models. With the correlation between stratigraphy and 2D models, it was possible to locate where the porous and fractured aquifers were located, as well as to relate the resistivity values with the rocks present in the area, which are: Basalts, Sandstones and Silicified Sandstones. The porous aquifer acts as a large reservoir, water is stored in it before flowing into the fractured aquifer below. The 3D allowed a better visualization of the presence of water in the geological framework, and the visualization of resistivity values in the dimensions. The 3D block model made it possible to visualize the water inside a large sandstone lens that flows towards the front of the Cuesta, and not to the reverse as expected. The joint analysis between geophysics and stratigraphy allowed us to understand the geological framework, its relationship with groundwater flow and hydrological processes. The work also reduces the gap in geophysical studies in the SAG and the use of Electrorestivity to understand the hydrological processes of aquifers.
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Palavras-chave
Aquífero, Eletrorresistividade, Modelagem 3D, Recarga e descarga, Cuesta, Groundwater, Electrorestivity, 3D modeling, Recharge and discharge