Bridging hydraulic diffusivity from aquifer to particle-size scale: a study on loess sediments from southwest Hungary

Abstract

In situ megascale hydraulic diffusivities (D) of a confined loess aquifer were estimated at various scales (10 ≤ L ≤ 1500 m) by a finite difference model, and laboratory microscale diffusivities of a loess sample by empirical formulas. A scatter plot reveals that D fits to a single power function of L, providing that microscale diffusivities are assigned to L = 1 m and that differences in diffusivity observed between micro-and megascales are assigned to medium heterogeneity appraised by variations in the curvature and slope of natural hydraulic head waves propagating through the aquifer. Subsequently, a general power relationship between D and L is defined where the base and exponent terms stand for the aquifer storage capability under a confined regime of flow, for the microscale hydraulic conductivity and specific yield of loess, and for the changes in curvature and slope of hydraulic head waves relative to values defined at unit scale.Relier les diffusivités hydrauliques de l'aquifère à l'échelle particulaire : une étude sur les loess du Sud-Ouest de la Hongrie Résumé Les diffusivités hydrauliques (D) in situ d'un aquifère captif loessique ont été estimées à différentes méga-échelles (10 ≤ L ≤ 1500 m) par un modèle aux différences finies tout comme les diffusivités de laboratoire l'ont été à la micro-échelle d'un échantillon de loess à partir de formules empiriques. Un diagramme montre que D s'ajuste à une fonction puissance de L à condition que les diffusivités microéchelle soient affectées à L = 1 m et que les différences de diffusivité observées chez les micro et les méga-échelles soient attribuées à l'hétérogénéité du milieu éstimée par les variations de courbure et de pente des ondes naturelles de charge hydraulique se propageant dans l'aquifère. En conséquence, une relation générale exponentielle entre D et L a été définie, où le terme de base et l'exposant représentent la capacité d'emmagasinement en nappe captive, la conductivité hydraulique et la porosité efficace du loess à microéchelle, et les changements de courbure et de pente des ondes de charge hydraulique par rapport aux valeurs définies à l'échelle unitaire.

Effects of microarrangement of solid particles on PCE migration and its remediation in porous media

“…Results are essential to the macroscopic aquifer composed of porous media without large heterogeneity, such as sandy aquifers containing rich groundwater resources. However, there are many problems associated with the upscaling of aquifers in real-world conditions (Dagan et al, 2013;Pacheco, 2013;Pacheco et al, 2015). Due to the large heterogeneity of natural aquifers, research results may be very different and can not be extrapolated to complex regional aquifer on a large scale.…”

Influence of the scale range width on the determination of the hydraulic conductivity and effective porosity. The case of a porous aquifer in southern Italy

“…Furthermore, according to the specific problem, considering laws of variation at different scales (small, medium, large) for each parameter can be of interest [25].…”

Response to Dr. Pacheco FLA’s Comments on Manuscript hess-2017-493 “Effects of Micro-Arrangement of Solid Particles on PCE Migration and Its Remediation in Porous Media” by Ming Wu, Jianfeng Wu, Jichun Wu, and Bill X. Hu

“…Results are essential to the macroscopic aquifer composed of porous media without large heterogeneity, such as sandy aquifers containing rich groundwater resources. However, there are many problems associated with the upscaling of aquifers in real-world conditions(Dagan et al, 2013;Pacheco, 2013;Pacheco et al, 2015). Due to the large heterogeneity of natural aquifers, research results may be very different and can not be extrapolated to complex regional aquifer on a large scale.…”