Three-dimensional hydrogeological parametrization using sparse piezometric data

Abstract. When modelling contamination transport in the subsurface
and aquifers, it is crucial to assess the heterogeneities of the porous
medium, including the vertical distribution of the aquifer parameter. This
issue is generally addressed thanks to geophysical investigations. As an alternative, a method is proposed using estimated hydraulic parameters
from a 2D calibrated flow model (solely reliant on piezometric series) as
parametrization constraints for a 3D hydrogeological model. The methodology
is tested via a synthetic model, ensuring full knowledge and control of its
structure. The synthetic aquifer is composed of five lithofacies,
distributed according to a sedimentary pattern, and functions in an
unconfined regime. The level of heterogeneity for hydraulic conductivity
spans 3 orders of magnitude. It provides the piezometric chronicles used
to inverse 2D flow parameter fields and the lithological logs used to
interpolate the 3D lithological model. Finally, the parameters of each
facies (hydraulic conductivity and porosity) are obtained through an
optimization loop, which minimizes the difference between the 2D calibrated
transmissivity and the transmissivity computed with the estimated 3D facies
parameters. The method estimates values close to the known parameters, even with sparse
piezometric and lithological data sampling. The maximal discrepancy is
45 % of the known value for the hydraulic conductivity and 6 % for the
porosity (mean error 26 % and 3 %, respectively). Although the
methodology does not prevent interpolation errors, it succeeds in
reconstructing flow and transport dynamics close to the control data. Due to
the inherent limitations of the 2D inversion approach, the method only
applies to the saturated zone at this point.
