Combined Effect of Infiltration, Capillary Barrier and Sloping Layered Soil on Flow and Solute Transfer in a Heterogeneous Lysimeter

Abstract

<span>This aim of this paper is to describe a study of the combined effect of infiltration, capillary barrier and sloping layered soil on both flow and solute transport processes in a large, physical model (1</span><span> </span><span><span>×</span></span></a><span></span><span></span><span> </span><span>1</span><span> </span><span>×</span><span> </span><span>1.6 m³</span><span>) called LUGH (Lysimeter for Urban Groundwater Hydrology) and a 3D numerical flow model. Sand and a soil composed of a bimodal sand-gravel mixture were placed in the lysimeter to simulate one of the basic structural and textural elements of the heterogeneity observed in the vadose zone under an infiltration basin of Lyon (France). Water and an inert tracer (KBr) were injected <span>from the top of the lysimeter using a specific water sprinkler system and collected at 15 different outlets at the bottom. The outlet flows and the 15 breakthrough curves obtained presented high heterogeneity, emphasising the establishment of preferential flows resulting from both capillary barrier and soil layer dip effects. Numerical modelling led to better understanding of the mechanisms responsible for these heterogeneous transfers and it was also used to perform a sensitivity analysis of the effects of water velocity (water and solute flux fed by the sprinkler) and the slope interface. </span>The results show that decreasing velocity and increasing the slope of the interface can lead to the develop<span>ment of preferential flows. In addition, the offset of the centre of gravity of the flow distribution at the output increases linearly as a function of the slope angle of the layered soil. </span></span><span>This paper provides relevant information on the coupling between hydrodynamic processes and pollutant transfer in unsaturated heterogeneous soil and emphasizes </span><span>the role of the geometry of the interfaces between materials and boundary conditions as key factors for preferential </span><span>flow.</span><span></span> <p> </p

Combined effect of capillary barrier and layered slope on water, solute and nanoparticle transfer in an unsaturated soil at lysimeter scale

“…A portion of flow arriving at the interface between the two materials is deflected along the slope producing simultaneously an increase in volumetric water content at the interface (Figure 3a). Bien et al, (2013) found similar results for studies in the same lysimeter.…”

“…This proportion is chosen to ensure the bi-modality of particle size in the mixture. The sizes of the three materials are similar to those observed in the most common lithofacies encountered in East Lyon (Prédélus et al, 2014a;Bien et al, 2013;Goutaland et al, 2008Goutaland et al, . 2013 (Figure 1a).…”

“…4 Big size Lysimeters are commonly used in laboratory to measure the coupled transfer of water -solute (Bien et al, 2013, Ityel et al, 2013Li et al, 2012;Anguela, 2004;Bussière et al, 2003, Schoen et al, 1999Walter et al, 2000). Experiments using lysimeters give results that are closer to reality than those carried out in columns as the lysimeter allows preferential flow conditions to be taken into account.…”

“…where a fine material deposited on coarse material leads to the development of a capillary barrier (Bien et al, 2013). Materials were embedded in the lysimeter by successive layers of 3 cm.…”

Tracing Water Flow and Colloidal Particles Transfer in an Unsaturated Soil

“…The choice of materials was made to replicate a glaciofluvial type soil similar to that observed in an unsaturated zone, in the region of Lyon (France) [22] [23]: that is to say, having the same particle size distribution and the same chemical composition ( Table 1). The selected materials are sand (0 -0.2 cm) and gravel (0.4 -1.1 cm) with which a bimodal mixture, which was formed in mass fraction 50% -50% (Figure 1).…”