Impacts of aquifer's geometry estimated from seismic refraction
tomography on hydrogeophysical variables
Abstract
Understanding the critical zone processes related to groundwater flows
relies on underground structure knowledge and its associated parameters.
We propose a methodology to draw the patterns of the underground
critical zone at the catchment scale from seismic refraction data. The
designed patterns define the structure for a physically based
distributed hydrological model applied to a mountainous catchment. In
that goal, we acquired 10 seismic profiles covering the different
geomorphology zones of the studied catchment. We develop a methodology
to analyze the geostatistical characteristics of the seismic data and
interpolate them over the whole catchment. The applied geostatistical
model considers the scale variability of the underground structures
observed from the seismic data analysis. We use compressional seismic
wave velocity thresholds to identify the depth of the regolith and
saprolite bottom interfaces. Assuming that such porous compartments host
the main part of the active aquifer, their patterns are embedded in a
distributed hydrological model. We examine the sensitivity of classical
hydrological data (piezometric heads) and geophysical data (magnetic
resonance soundings) to the applied velocity thresholds used to define
the regolith and saprolite boundaries. Different sets of hydrogeological
parameters are used in order to distinguish general trends or
specificities related to the choice of the parameter values. The
application of the methodology to an actual catchment illustrates the
interest of seismic refraction to constrain the structure of the
critical zone underground compartments. The sensitivity tests highlight
the complementarity of the analyzed hydrogeophysical data sets.