Abstract
Groundwater flow in karst aquifers are particularly located in the main conduits fractures. In this work, we aim to describe and investigate the behavior of the flow at different scales. At the local scale, the flow modeling considers a continuum approach. At the regional scale, discrete features such as conduits are added to the continuum model (hybrid approach). For the continuum approach, we use a double-porosity flow model. The analytical solution of this model allows to investigate the transitions phases while a constant pressure boundary conditions is applied. Such a boundary condition, in a well may represent a constant head hydraulic test. In order to specify different boundaries conditions (for instance impervious barriers) and an irregular geometry of the flow domain, we developed and applied a numerical code based on the boundary element method. This allows to put into practice the hybrid method (continuum model with discrete conduits) in which we consider the local vertical and horizontal conduits intersections. This type of modeling allows to consider a larger and more complex domain than analytical solution alone. Moreover in this work we conceived and developed an experimental laboratory model. This model has been used in order to investigate the transitions phases which appears from the outflow of heterogeneous media. This approach is complementary to the analytical and numerical modeling. Last, part of this work was dedicated to the development and preliminary experiment of a new probe system. This new probe is an autonomous sensor which aim to map inaccessible drowned karst conduits. With this new tool, the geometry of the discrete conduit network in the aquifer could be known. The gathered informations could be used to represent the geometry of the conduit network used more realistically in the hybrid modeling approach. The main conclusions of this work are the following : at the local and regional scales, the transitions phases of the flow depends on the hydraulic properties of the continuum (when a continuum approach is used). The numerical solution developed allows to investigate the influence of the domain's geometry and complex boundaries conditions on the flux response. The experimental model used in the laboratory allows to reproduce qualitatively different transition phases of the flux at the outlet. Finally, the probe proved the feasibility to map its path in controlled experimental conditions. These new methods contribute to the characterization of the hydrodynamical behavior that takes place in karstified limestone aquifers.