Date of Award
Master of Science (MS)
Civil and Environmental Engineering
George F. Pinder
Inherent in the continuum equations that describe flow and transport in porous media is a component of scale. This is an artifact of the underlying assumptions necessary for transforming the complex pore-scale characteristics of soil into manageable state variables and parameters that are readily measurable in the field (e.g., piezometric head and hydraulic conductivity). The mechanism used to formulate the upscaled porous medium equations involves Averaging Theory in which a representative elementary volume (REV) is used. This REV acts as an integration volume where pore-scale quantities are averaged over a macroscale volume.
The REV defines all aspects of the modeling process—from the coefficients that describe the soil parameters, to the state variables that the models predict. Despite its ubiquity, knowledge of its actual size or its impact on numerical model outputs is unknown. The work presented here includes five experiments involving a highly instrumented physical bench-top sandbox model that provide insights into the impact scale plays on a physical groundwater system. State variable measurements including piezometric head and solute concentration are determined at different scales using an areal averaging technique. These measurements are used to calculate the relevant soil hydraulic and transport parameters at well-defined scales. The resulting parameters are then employed in an equivalent numerical simulation.
Comparisons between the measured and simulated outputs at the same scale show that the REV averaging size plays an important role in model results. A convergence of simulated head and solute concentration data with consistently averaged measured values occurs at larger REV sizes, however at a loss of some macroscale heterogeneities. The results of this work suggest that the optimal REV for modeling flow and transport in porous media is dependent on the soil type as well as the characteristics of the entire system to be modeled. They also reveal the importance of interpreting numerical models in the context of the scale at which they are created.
Number of Pages
Ulrich, Evan Norris, "The Impact of Representative Scale in Groundwater Modeling" (2024). Graduate College Dissertations and Theses. 1812.
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