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Equivalent mean flow models for fractured aquifers: Insights from a pumping tests scaling interpretation
Author(s) -
Le Borgne T.,
Bour O.,
de Dreuzy J. R.,
Davy P.,
Touchard F.
Publication year - 2004
Publication title -
water resources research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.863
H-Index - 217
eISSN - 1944-7973
pISSN - 0043-1397
DOI - 10.1029/2003wr002436
Subject(s) - piezometer , scaling , aquifer , hydraulic head , hydraulic conductivity , aquifer properties , geology , flow (mathematics) , mechanics , electrical conduit , geotechnical engineering , mathematics , soil science , physics , geometry , groundwater , engineering , mechanical engineering , groundwater recharge , soil water
We investigate if a mean equivalent flow model can be defined to describe hydraulic head variations in a crystalline aquifer characterized by multiscale heterogeneity. We analyzed in particular the hydraulic response of a crystalline aquifer to pumping tests covering a large range of spatial and temporal scales. Pumping tests appear to be well designed to test the medium hydraulic properties and to track scaling effects, since the perturbation induced by pumping grows with time and samples increasingly large volumes. We tested well‐test interpretation frameworks underpinned by equivalent media models that basically contain scaling information. Interpretations of drawdown time series, recorded in piezometers located at distances ranging from 2 to 400 m from the pumping well and of durations ranging from 5 to 90 days, show that the temporal evolutions of drawdown are well modeled by fractional flow models [ Barker , 1988; Acuna and Yortsos , 1995]. Estimates of flow dimensions are consistent across the whole site and lie in the range [1.4–1.7]. To investigate the nature of diffusion, we defined a methodology based on the evolution of the characteristic time or amplitude of hydraulic head variations with the distance from the pumping well. For most of the piezometers, those aligned along the main fault, it is possible to define a scaling law for all piezometers with a unique set of parameters. The derived exponents imply that hydraulic head diffusion is anomalously slow, a characteristic that is taken into account only in the model of Acuna and Yortsos [1995], based on diffusion in fractals.