Using sparse polynomial chaos expansions for the global sensitivity analysis of groundwater lifetime expectancy in a multi-layered hydrogeological model
Résumé
The study makes use of polynomial chaos expansions to compute
Sobol’ indices within the frame of a global sensitivity analysis of hydrodispersive
parameters in a simplified vertical cross-section of a segment
of the subsurface of the Paris Basin. Applying conservative ranges,
the uncertainty in 78 input variables is propagated upon the mean lifetime
expectancy of water molecules departing from a specific location
within a highly confining layer situated in the middle of the model domain.
Lifetime expectancy is a hydrogeological performance measure
pertinent to safety analysis with respect to subsurface contaminants,
such as radionuclides. The sensitivity analysis indicates that the variability
in the mean lifetime expectancy can be sufficiently explained
by the uncertainty in the petrofacies, i.e. the sets of porosity and hydraulic
conductivity, of only a few layers of the model. The obtained
results provide guidance regarding the uncertainty modeling in future
investigations employing detailed numerical models of the subsurface
of the Paris Basin. Moreover, the study demonstrates the high efficiency of sparse polynomial chaos expansions in computing Sobol’
indices for high-dimensional models.
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