Estudo da recarga subterrânea de sistemas aquíferos em diferentes escalas: aplicações de modelagem hidrogeológica
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Data
2022-06-03
Autores
Gonçalves, Roger Dias [UNESP]
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Universidade Estadual Paulista (Unesp)
Resumo
A recarga subterrânea é um fluxo vital, visto que os recursos hídricos subterrâneos compreendem significativa parcela das reservas de água potável, além do abastecimento de água depender dos aquíferos, e estes sofrerem com crescentes depleções e contaminações. Há diversos fatores que precisam ser considerados na estimativa de recarga, e hoje temos diferentes técnicas que empregam distintos parâmetros nos cálculos. Ademais, as escalas de tempo e de espaço são cruciais dado que diferentes objetivos requerem estimativas de recarga em diferentes escalas de análise. O objetivo principal recai sobre compreender o comportamento do fluxo de recarga em aquíferos em diferentes escalas de análise, avaliando os métodos mais utilizados e propondo melhorias e/ou novos métodos, a partir de três estudos de caso: Aquífero Rio Claro, Sistema Aquífero Urucuia (SAU) e Sistema Aquífero Guarani (SAG). Para aquíferos locais, porosos e livres que apresentam grandes flutuações do NA, efeitos de trapeamento de ar não são negligenciáveis, assim recomenda-se o uso da porosidade preenchível no método WTF, descontando a fração volumétrica de ar trapeado, e modelagem numérica de fluxo com a discretização de uma camada quasi-saturada para estimativa de recarga. Para aquíferos livres de grande escala, com complexo e intenso uso e ocupação, é sugerido o uso de balanço hídrico e sensores remotos com foco na variação do armazenamento em detrimento da recarga apenas. Foram validados o GRACE e análises de tendências com Mann-Kendall e Sen’s slope. Em aquíferos de grande porte, parcialmente confinados, o emprego do WTF nas porções livres pode estimar a recarga total na área de afloramento, enquanto o fluxo de base estima a descarga local, valores que podem ser usados no balanço hídrico local. Já a recarga profunda é mais bem calculada, integralmente, com o emprego de simulação numérica tridimensional de fluxo acoplada a datações de águas subterrâneas, sendo validada em regime estacionário com o uso de particle tracking.
Groundwater recharge is a vital flow, as groundwater resources comprise a significant portion of drinking water resources. In addition, water supply relies on aquifers, and those are currently suffering from increasing rates of depletion and contamination. There are several factors that need to be considered when estimating recharge, and nowadays we have different techniques that employ distinct parameters when calculating recharge. Furthermore, time and space scales are crucial as different goals require recharge at different scales. The main objective is to understand the behavior of the groundwater recharge in aquifers at diverse scales, evaluating the most used methods and proposing improvements and/or new methods, based on three case studies: Rio Claro Aquifer, Urucuia Aquifer System (UAS) and Guarani Aquifer System (GAS). For local aquifers, porous and unconfined, presenting great water table fluctuations, entrapped air effects are not negligible, so it is recommended to use fillable porosity in the WTF method, using the volumetric fraction of entrapped air, and numerical modeling with a quasi-saturated layer discretized to properly estimate recharge rates. For large-scale unconfined aquifers, with complex and intense use and land cover changes, water balance and remote sensing techniques are suggested, focused on water storage changes instead of only recharge. GRACE satellites and trend analysis were validated, also Mann-Kendall and Sen's slope analysis. In large and partially-confined aquifers, the use of WTF in unconfined portions can estimate total recharge fluxes in the outcrop areas, while the baseflow estimates the local discharge. Those values may be applied in the local water balance. Deep recharge, on the other hand, is better calculated, completely, with three-dimensional numerical simulation coupled with groundwater dating, being validated in steady state with the application of particle tracking technique.
Groundwater recharge is a vital flow, as groundwater resources comprise a significant portion of drinking water resources. In addition, water supply relies on aquifers, and those are currently suffering from increasing rates of depletion and contamination. There are several factors that need to be considered when estimating recharge, and nowadays we have different techniques that employ distinct parameters when calculating recharge. Furthermore, time and space scales are crucial as different goals require recharge at different scales. The main objective is to understand the behavior of the groundwater recharge in aquifers at diverse scales, evaluating the most used methods and proposing improvements and/or new methods, based on three case studies: Rio Claro Aquifer, Urucuia Aquifer System (UAS) and Guarani Aquifer System (GAS). For local aquifers, porous and unconfined, presenting great water table fluctuations, entrapped air effects are not negligible, so it is recommended to use fillable porosity in the WTF method, using the volumetric fraction of entrapped air, and numerical modeling with a quasi-saturated layer discretized to properly estimate recharge rates. For large-scale unconfined aquifers, with complex and intense use and land cover changes, water balance and remote sensing techniques are suggested, focused on water storage changes instead of only recharge. GRACE satellites and trend analysis were validated, also Mann-Kendall and Sen's slope analysis. In large and partially-confined aquifers, the use of WTF in unconfined portions can estimate total recharge fluxes in the outcrop areas, while the baseflow estimates the local discharge. Those values may be applied in the local water balance. Deep recharge, on the other hand, is better calculated, completely, with three-dimensional numerical simulation coupled with groundwater dating, being validated in steady state with the application of particle tracking technique.
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Palavras-chave
Recarga de águas subterrâneas, Hidrogeologia, Recursos hídricos, Simulação numérica de fluxo, Modelagem hidrogeológica, Groundwater recharge, Hydrogeology, Water resources, Groundwater modeling, Hydrogeology modeling