Author(s): F. Stauffer; P. Jussel; M. Rauber; T. Dracos
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Abstract: The description of heterogeneities in prealpine aquifers yielded statistical information on the coherent sedimentary structures of gravel deposits. Unweathered outcrops in gravel pits were investigated. Distinct sedimentary structures appearing as lenses and layers could be specified. The variability of the hydraulic properties of the different structures (hydraulic conductivity and porosity) was determined in the laboratory on the basis of disturbed and undisturbed samples. The data revealed large differences in hydraulic conductivity between distinct structure elements. The statistical information obtained was used to numerically generate distinct realizations of synthetic block size aquifers having the same statistical properties with respect to the hydraulic parameters as the investigated deposits. Numerical flow and transport experiments were performed with the help of a three-dimensional finite element flow model and a corresponding random walk transport model. A series of stochastic numerical transport experiments with synthetic gravel aquifers allowed the estimation of effective parameters as the effective hydraulic conductivity and the effective macrodispersivity of the investigated formation. These estimated values were compared with estimates from stochastic theories. The simulated effective hydraulic conductivity values correspond well with Dagan's theory (Dagan, 1989). Deviations are apparent in the effective macrodispersivity values and their dependence on the transport distance. It is expected that the reason for the discrepancies mainly lies in the existence of the coherent sedimentary structures which can not be completely de-scribed by the variance and the correlation length of hydraulic conductivity.
Year: 1993