ABSTRACT
Lysimeters are generally classified according to their size, filling method and effluent collection method (Bergstrom, 1990). Those for which the soil profile is reconstructed are acceptable for gravelly or sandy soils and have a low-construction cost (Lanthaler, 2004). On the other hand, with a reconstructed soil, it is possible to control both the structural arrangement and texture of the materials. According to how the water is drained, there are two popular types of lysimeters: free drainage systems and suction-controlled (i.e., pressure-controlled) systems. For the first type, water flows freely outside the lysimeter by gravity. For the suction-lysimeter, percolated water is collected by applying suction pressure at the outlets
1 INTRODUCTION
The structure of the vadose zone plays a major role in the transfer of water and solute. Its high heterogeneity is the cause of so-called preferential flow which is the source of a wide disparity in time of occurrence of pollutants in groundwater (Parker & Albrecht, 1987; Flury et al., 1994). It is therefore necessary to understand how the soil structural heterogeneity impacts both water and mass transfer in order to preserve the groundwater resource. From a hydrodynamic point of view, it is possible to consider that these preferential flows occur in areas involving significant variation of unsaturated hydraulic conductivity with respect to adjacent materials (Miyazaki, 1998; Kung, 1990; Steenhuis et al., 1990; Heilig et al., 2003).
