Interpretation of pumping tests in a mixed flow karst system

Abstract

[1] A long-duration pumping test performed in the conduit of a mixed flow karst system (MFKS) is analyzed and interpreted. It constitutes a unique experiment of catchment wide response of a karst system, with drawdowns measured both in the pumped conduit and in the matrix. A modeling approach is proposed for this interpretation. The developed double continuum model consists of two reservoirs -karst conduits and the surrounding carbonate rocks -between which flow exchange is modeled using the superposition principle and the hypothesis of Darcian flow in the matrix considered as an equivalent porous media. The karst conduits are assumed to have an infinite hydraulic conductivity. Model calibration results in a very good match (relative root mean square [rRMS] = 2.3 %) with drawdown measured at the pumping well (karst conduit). It shows that the matrix hydrodynamic parameters (hydraulic conductivity and storativity) have a greater influence on the drawdown than the storage capacity of the conduit network. The accuracy of the model relies mostly on a very good knowledge of both pumping rate and natural discharge at the spring (with and without pumping). This type of approach represents an advance in double continuum modeling of karst systems. It also provides a methodology for the management of water resources from karst aquifers.

Comparison of the results of pumping and tracer tests in a karst terrain

“…Different values for hydraulic conductivity in one path may be due to the different hydraulic behavior of groundwater flow in the karst terrain during tracer and pumping tests. In a pumping test, groundwater mainly flows from the both macrofractures and matrix (Moench, 1984;Maréchal et al, 2008), while in a tracer test groundwater and dissolved dye mainly flow via the macrofracture and dissolution openings routes toward the observation points (Gouzie et al, 2010). In other words, transmission of dye in anisotropic media in tracer test is mainly via routes with minimum head loss (Salgado-Castro, 1988;Nassimi, 2011) such as dissolution-created channel and conduit (macrofracture) routes, while in a pumped well that taps anisotropic media, groundwater flows through both macrofractures and matrices in the cone of depression (Moench, 1984).…”

Revisiting Cent-Fonts Fluviokarst Hydrological Properties with Conservative Temperature Approximation

“…Since a few years, improved analytical models take better into account for the different behavior of the two types of reservoirs [34] or even three reservoirs [45]. However, despite the importance of calibration for the models, temperature has not been used probably because of the non-conservative character of this signal [26,34]. In the following we will take benefit of particular periods of the pumping test to get new constraints for the models.…”

“…According to Maréchal et al [34] we will considerer in the following the dewatering of the conduit network as a supplementary outgoing flow from the CS, Q CS .…”

“…A few decades ago, studies were often considering medium where CS was not disrupting the aquifer but continuous models were unsatisfactorily. Since a few years, improved analytical models take better into account for the different behavior of the two types of reservoirs [34] or even three reservoirs [45]. However, despite the importance of calibration for the models, temperature has not been used probably because of the non-conservative character of this signal [26,34].…”

“…It also opened the possibility of in situ timed volumetric gauging and geochemical sampling of Hérault River intrusions in the CS. This rich set of data has been extensively analyzed already [26,34]. The present work aims to revisit part of these data to assess the accuracy of conservative tracer assumption for water temperature.…”