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标题：Finite Difference Model For Evaluating The Recharge Of The Guaraní Aquifer System On The Uruguayanbrazilian Border
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作者：Andrea A. Gómez ; Leticia B. Rodríguez ; Luis S. Vives 等
期刊名称：Mecánica Computacional
印刷版ISSN：2591-3522
出版年度：2007
页码：1479-1496
语种：English
出版社：CIMEC-INTEC-CONICET-UNL
摘要：Part of the precipitation that falls over a region infiltrates through soil layers and eventually migrates deeper reaching the groundwater reservoir known as aquifer. The water that makes its way to the aquifer becomes recharge. The magnitude of recharge constitutes an upper bound to the amount of water that can be extracted from a groundwater reservoir without causing a major impact on it. The recharge can not be measured directly therefore it has to be determined by an indirect method, and as such, is one of the most difficult hydrological variables to calculate. The Guaraní Aquifer System (GAS) is an international transboundary groundwater reservoir. Its area is about 1200000 km2 distributed in Brazil, Argentina, Paraguay and Uruguay. This aquifer is contained within the pores and cracks of sandstones (rocks of mostly sandy nature). The Uruguayan- Brazilian border nearby the cities of Rivera (Uruguay) and Sant´Ana do Livramento (Brazil) is of special interest as this area receives a significant amount of recharge, both direct from precipitation and indirect from fractured basalts overlying the GAS, that compensates water ions. This study focuses in this particular area of the GAS, covering about 650 km2 surrounding both cities. The well known numerical code MODFLOW that solves the parabolic groundwater flow equation by the finite difference method was used. A steady state condition was simulated representing the current hydraulic behavior of the groundwater system. The finite different grid consists of 135 rows and 156 columns, 250 m x 250 m in both, x and y directions. Vertically, the model contains three layers coincident with the aquifer units defined in the conceptual model, which are basalts, shallow sandstone aquifer and deep sandstone aquifer. The calibration was performed by the trial-and-error method, matching simulated hydraulic heads with the observed data. Boundary conditions, recharge rates, stream/aquifer interphase conductances and hydraulic conductivities were adjusted during the calibration process. The conceptual model was correctly validated. Model results approximately match existing data, although they highlighted data scarcity and the dubious reliability on many available data. In the deep aquifer the model reproduces adequately the cone of depression detected near the two cities, surveyed in the field, caused by intensive groundwater pumping. Regarding flow directions, model results would indicate that most of the streams in the area drain the groundwater reservoir, in agreement with field evidence. Downward flows were simulated between model layers. In terms of the simulated recharge rates for the current calibration of the model, the rate over basalts resulted in a meager 1.3 mm/year, and the rate over the outcropping areas of sandstones resulted in 140.2 mm/year, equivalent to 0.08 % and 8.55 %, respectively, of the mean annual precipitation of 1639 mm estimated at Rivera.
其他摘要：Part of the precipitation that falls over a region infiltrates through soil layers and eventually migrates deeper reaching the groundwater reservoir known as aquifer. The water that makes its way to the aquifer becomes recharge. The magnitude of recharge constitutes an upper bound to the amount of water that can be extracted from a groundwater reservoir without causing a major impact on it. The recharge can not be measured directly therefore it has to be determined by an indirect method, and as such, is one of the most difficult hydrological variables to calculate. The Guaraní Aquifer System (GAS) is an international transboundary groundwater reservoir. Its area is about 1200000 km2 distributed in Brazil, Argentina, Paraguay and Uruguay. This aquifer is contained within the pores and cracks of sandstones (rocks of mostly sandy nature). The Uruguayan- Brazilian border nearby the cities of Rivera (Uruguay) and Sant´Ana do Livramento (Brazil) is of special interest as this area receives a significant amount of recharge, both direct from precipitation and indirect from fractured basalts overlying the GAS, that compensates water abstractions. This study focuses in this particular area of the GAS, covering about 650 km2 surrounding both cities. The well known numerical code MODFLOW that solves the parabolic groundwater flow equation by the finite difference method was used. A steady state condition was simulated representing the current hydraulic behavior of the groundwater system. The finite different grid consists of 135 rows and 156 columns, 250 m x 250 m in both, x and y directions. Vertically, the model contains three layers coincident with the aquifer units defined in the conceptual model, which are basalts, shallow sandstone aquifer and deep sandstone aquifer. The calibration was performed by the trial-and-error method, matching simulated hydraulic heads with the observed data. Boundary conditions, recharge rates, stream/aquifer interphase conductances and hydraulic conductivities were adjusted during the calibration process. The conceptual model was correctly validated. Model results approximately match existing data, although they highlighted data scarcity and the dubious reliability on many available data. In the deep aquifer the model reproduces adequately the cone of depression detected near the two cities, surveyed in the field, caused by intensive groundwater pumping. Regarding flow directions, model results would indicate that most of the streams in the area drain the groundwater reservoir, in agreement with field evidence. Downward flows were simulated between model layers. In terms of the simulated recharge rates for the current calibration of the model, the rate over basalts resulted in a meager 1.3 mm/year, and the rate over the outcropping areas of sandstones resulted in 140.2 mm/year, equivalent to 0.08 % and 8.55 %, respectively, of the mean annual precipitation of 1639 mm estimated at Rivera.