Regression and Inverse Analyses in Regional Ground-Water Modeling
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Abstract:
Numerical models of ground-water flow within the regional aquifer underlying Lambton County, Ontario, Canada, are constructed by the conjunctive application of methods of regression and inverse analyses. Regression analysis of physiographic and hydraulic head data reveals a distinct relation between ground-water levels and ground-surface topography that is used to condition the aquifer models that are subjected to inverse analysis. Inverse analysis determines the variation of hydraulic head along the perimeter of the region and the distribution of ground-water recharge and discharge within the region that optimally replicate the observed hydraulic head data. The use of physiographic data as a substitute for geologic data in the construction of the aquifer models is defended on the basis of the constraints that apply to the investigation and the opportunity to invoke hydrogeologic judgment in the evaluation of the results. Interpretation of the results of the analyses reveals important characteristics of the hydrogeology of Lambton County, including an area of elevated ground-water recharge and the partitioning of ground-water discharge to the Saint Clair River.Keywords:
Hydraulic head
Groundwater model
Depression-focused recharge
Water balance
Groundwater discharge
Groundwater model
Infiltration (HVAC)
Cone of depression
Environmental isotopes
Overexploitation
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Groundwater discharge
Groundwater model
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The present study deals with the problem of evaluation of the recharge mechanism and the characterization of the groundwater flow system in the basement shallow aquifer, which is one of the groundwater resource in the semi-arid South region of Madagascar. Stable isotopes (deuterium and oxygen-18) and tritium are used to achieve with accuracy the hydrogeological and geochemical dynamics study. Chemical analysis is used to provide complementary information to the investigation. A space distribution of tritium concentration and isotopic composition in groundwater shows evidence of two opposite categories of aquifers, which is confirmed by the chemical analysis results and by the geological features of the study site. Some groundwater flow path directions have been identified in the study area thanks to the tritium concentration space distribution and the geological formation. Besides, the groundwater recharge of the shallow aquifers in the South of Madagascar has been characterized by the exponential mixing model.
Environmental isotopes
Depression-focused recharge
Groundwater model
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MODFLOW
Hydraulic head
Groundwater model
Aquifer properties
Groundwater discharge
Drawdown (hydrology)
Aquifer test
Depression-focused recharge
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Groundwater model
MODFLOW
Groundwater discharge
Aquifer test
Specific storage
Cone of depression
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Groundwater model
Sustainable yield
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Depression-focused recharge
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A multi-component geochemical dataset was collected from groundwater and surface-water bodies associated with the urban Fountain Creek alluvial aquifer, Colorado, USA, to facilitate analysis of recharge sources, geochemical interactions, and groundwater-residence times. Results indicate that groundwater can be separated into three distinct geochemical zones based on location within the flow system and proximity to surface water, and these zones can be used to infer sources of recharge and groundwater movement through the aquifer. Rare-earth-element concentrations and detections of wastewater-indicator compounds indicate the presence of effluent from wastewater-treatment plants in both groundwater and surface water. Effluent presence in groundwater indicates that streams in the area lose to groundwater in some seasons and are a source of focused groundwater recharge. Distributions of pharmaceuticals and wastewater-indicator compounds also inform an understanding of groundwater–surface-water interactions. Noble-gas isotopes corroborate rare-earth-element data in indicating geochemical evolution within the aquifer from recharge area to discharge area and qualitatively indicate variable groundwater-residence times and mixing with pre-modern groundwater. Quantitative groundwater-residence times calculated from 3H/3He, SF6, and lumped-parameter modeling generally are less than 20 years, but the presence of mixing with older groundwater of an unknown age is also indicated at selected locations. Future investigations would benefit by including groundwater-age tracers suited to quantification of mixing for both young (years to decades) and old (centuries and millennia) groundwater. This multi-faceted analysis facilitated development of a conceptual model for the investigated groundwater-flow system and illustrates the application of an encompassing suite of analytes in exploring hydrologic and geochemical interactions in complex systems.
Depression-focused recharge
Groundwater discharge
Groundwater model
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