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Communication Dans Un Congrès Année : 2019

Aquifer structure at the catchment scale inferred from a geostatical analysis of compressional wave velocity images

Résumé

The use of compressional wave velocity (Vp) images is widely recognized to supply a strong insight on the depth variability of interfaces structuring the critical zone. Indeed, Vp is highly sensitive to the porosity and to the degree of weathering of the sub-surface. Here, we deduce from ten Vp profiles covering a watershed, the respective geometry of interfaces separating the regolith, the saprolite and the weathered bedrock. We reconstruct then the catchment geometry using a geostatistical analysis of the Vp images, considering the geomorphological characteristics of the studied site. An adapted geostatistical model (truncated power variogram) is used to consider the scale variability of the Vp measurement support. A sensitivity analysis is performed to study the impact on hydrogeophysical data of the Vp limits used to identify the interfaces’ depth, the randomness of the geostatistical interpolation as well as the porosity and hydraulic conductivity parameters. The simulated hydrogeophysical data correspond to flow rate at the catchment outlet and magnetic resonance soundings (MRS) distributed on the catchment. Then, the likelihood of the hydrologic model parameters is estimated by comparing the simulated hydrogeophysical data to field measurements. The fitting of both flow rate and MRS data show an equifinality issue as the thickness of the aquifer layers is strongly correlated with the aquifer’s porosity and hydraulic conductivity when simulating such hydrogeophysical signals. This equifinality is greatly reduced by the analysis of the Vp characteristics that helps determining the aquifer layers thicknesses distribution. So the aquifer porosity and hydraulic conductivity are determined more reliably when fitting the outlet flow rate and the MRS data after constraining the aquifer geometry from Vp images. The methodology proposed here is assessed on the small 1 km² Strengbach headwater catchment, located in a mid-mountain environment and laying on hard-rock
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Dates et versions

hal-03570947 , version 1 (13-02-2022)

Identifiants

  • HAL Id : hal-03570947 , version 1

Citer

Nolwenn Lesparre, Sylvain Pasquet, Philippe Ackerer. Aquifer structure at the catchment scale inferred from a geostatical analysis of compressional wave velocity images. AGU fall meeting, Dec 2019, San Francisco, United States. ⟨hal-03570947⟩
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