RESUMO
Analytical and semi-analytical models for stream depletion with transient stream stage drawdown induced by groundwater pumping are developed to address a deficiency in existing models, namely, the use of a fixed stream stage condition at the stream-aquifer interface. Field data are presented to demonstrate that stream stage drawdown does indeed occur in response to groundwater pumping near aquifer-connected streams. A model that predicts stream depletion with transient stream drawdown is developed based on stream channel mass conservation and finite stream channel storage. The resulting models are shown to reduce to existing fixed-stage models in the limit as stream channel storage becomes infinitely large, and to the confined aquifer flow with a no-flow boundary at the streambed in the limit as stream storage becomes vanishingly small. The model is applied to field measurements of aquifer and stream drawdown, giving estimates of aquifer hydraulic parameters, streambed conductance, and a measure of stream channel storage. The results of the modeling and data analysis presented herein have implications for sustainable groundwater management.
RESUMO
Groundwater constitutes a critical component in providing fresh water for various human endeavors. Never-theless, its susceptibility to contamination by pollutants represents a significant challenge. A comprehensive understanding of the dynamics of solute transport in groundwater and soils is essential for predicting the spatial and temporal distribution of these contaminants. Presently, conventional models such as the mobile-immobile (MIM) model and the rate-limited sorption (RLS) model are widely employed to describe the non-Fickian behavior of solute transport. In this research, we present a novel approach to solute transport that is founded on the temporally relaxed theory of Fick's Law. Our methodology introduces two relaxation times to account for solute particle collisions and attachment, leading to the derivation of a new advection-dispersion equation. Our findings indicate that the relaxation times possess similar properties to the transport parameters in the MIM and RLS models, and our solution can be applied to accurately predict transport parameters from soil column experiments. Additionally, we discovered that the relaxation times are proportional to the magnitude of Peclet number. This innovative approach provides a deeper insight into solute transport and its impact on groundwater contamination.
RESUMO
In the last few years, several articles have studied heat as a groundwater tracer and developed analytical geothermal solutions to predict the subsurface temperature and groundwater fluxes. These solutions can be sorted into steady-state and transient solutions. The steady-state solutions cannot describe the time-varying subsurface temperature, while the transient solutions ignore subsurface thermal boundary effects. Moreover, soil type may be another crucial factor significantly affecting the prediction results. This study compares six existing classical analytical solutions to examine the effects of soil types and subsurface thermal boundaries on simulating temperature-depth profiles and estimating groundwater fluxes. Several synthetic cases are built by considering the common soil types, sand and clay, to demonstrate their effects on predicting the profiles. A field case is used to show the effect of subsurface thermal boundaries on the groundwater flux estimated by an inverse approach. The study results indicate that the soil types have significant influences on simulating the profiles, and the influences grow with time. Some existing solutions may give inaccurate estimations of the field groundwater flux since they merely consider the heat source from the temperature variations on the ground surface but ignore possible thermal boundary effects in the subsurface. These findings will be valuable to those applying heat as a tracer to investigate infiltration.