Experimental study of solute transport in an artificially drained shallow water-table ; Etude du transfert d'eau et de solutés dans un sol à nappe superficielle drainée artificiellement

The comprehension of solute transport mechanisms in a shallow water table drained soil is essential in order to improve impacts of drained systems on the quality of surface water. Experiments have been carried out in steady state conditions on two physical models at the laboratory, allowing a control of the initial and boundary conditions. The first part of the thesis is dedicated to the one-dimensional studies, in order to characterize the unsaturated zone. A soil column (1*0,15 m²) and a soil tank (1*2*0,5 m3) have been used, both filled with a loamy-sand soil. The tracers used are the H218O and Cl-. The second part of this PhD studies two-dimensional flow in a drained soil. Experiments have only been realized in the soil tank. Two tracer applications have been selected: a pulse input applied at the soil surface and an uniformly distributed tracer in soil. Only Cl- has been then used as tracer. Tracer has been measured in soil by means of EC-probes (measurement of the electrical conductivity of water) and at the tank outlet (analysis of soil solution). The experimental results have been confronted with a numerical code (HYDRUS-2D) using the transport parameters obtained in the one-dimensional studies. A second method, particle tracking (Lagrangian approach), has been utilised to obtain the advance of water and the transfer time of the particles in the soil. ; La compréhension des mécanismes de transport de solutés dans un milieu poreux variablement saturé tel que les sols à nappe drainée par tuyaux enterrés, est essentielle afin de répondre aux interrogations concernant l'impact de ces systèmes sur la qualité des eaux de surface. L'approche choisie repose sur des expériences de traçage réalisées en régime permanent sur modèle physique de sol au laboratoire, permettant un contrôle des conditions initiales et aux limites. La première partie de la thèse est dédiée aux études monodimensionnelles, afin de caractériser la zone non saturée du sol. Nous avons utilisé une colonne de sol (1*0,15 m²) et un modèle ...