Estimating transmissivity fields and their influence on flow and transport: The case of Champagne mounts

Abstract

[1] This paper presents a flexible and general methodology that combines hydrogeological and geostatistical modeling techniques to estimate a set of transmissivity fields and their influence on flow and transport. The methodology may be applied to any case with only hydraulic head observations, even if most of them are concentrated inside a small part of the entire domain of interest. It is applied here to the case of the Champagne chalk aquifer (France), where it is shown to be very efficient. The methodology is decomposed in three independent parts. First, a reference head distribution is constructed by kriging in order to constrain the inverse problem. As hydraulic heads and elevations are correlated, a smoothed digital elevation model is used as external drift. The inverse problem is then solved by using a simplified pilot point method with an efficient and easy-to-use minimization algorithm. Finally, geostatistical simulations combined with flow simulations lead to a set of acceptable transmissivity fields. The induced uncertainty is evaluated by calculating tracer concentrations, pointing out areas where flow behavior is uncertain and where new borings would be advantageously drilled.

Reactive transport modelling of groundwater chemistry in a chalk aquifer at the watershed scale

“…The calculated mean Darcy velocities are 4.4 m year −1 (1.4×10 −7 ms −1 ) for the southern watershed (left-hand side of the grid) and 9.5 m year −1 (3.0×10 −7 ms −1 ) for the northern watershed (right-hand side). This is in fairly good agreement with a previous detailed hydrogeological study of the site (Renard and Jeannée, 2008). The corresponding effective flow velocities within the fracture network are 170 and 370myear −1 , respectively.…”

“…The annual effective infiltration rate was set to 120 and 60 mm year −1 at the southern watershed (left-hand side of the grid) and the northern watershed (right-hand side), respectively; soil clay layers reducing seepage in the latter case. These infiltration values, the hydraulic heads fixed as lateral boundary conditions as well as the estimated in situ hydraulic conductivity were slightly adjusted to be in fairly good agreement with a previous detailed hydrogeological study of the site (Renard and Jeannée, 2008).…”

“…The CO 3 2− / HCO 3 − ratio increases with pH, which decreases Ca concentration through the solubility product of calcite at equilibrium (as in the present case). Dilution is likely in view of the geometry of the site and hydrogeological modelling (Renard and Jeannée, 2008), the extent of which has not been fully assessed yet in lack of field tracer test or isotope analysis. Fig.…”

“…Geological and hydrogeological description of the area can be found elsewhere (Bourdon et al, 2009;Gillon et al, 2010;Hubert et al, 2006;Renard and Jeannée, 2008).…”

Process oriented use of geostatistics to analyse creeping para‐glacial features

“…Examples related to the use of geostatistics in environmental contexts can be found in Bourges et al . (), Hayet Chihi et al () or Renard and Jeannée (). Geostatistical processing was performed using Isatis® software (Geovariances, ).…”