Qualitative experiment of unsaturated water vadose through two-layer porous media

The method and main results of qualitative experiment of unsaturated water vadose through two-layer porous media is introduced in this paper. Two types of compositions of porous media, i.e. coarse-fine quartz sand (Type I) and quartz sand-loess (Type II), were used for the experiment. The experiment box is made of glass. And tracers used for the experiment are Rhodamine B and Eosin Y. The vadose path and expansion of tracers through two-layer porous media were observed under artificial sprinkling from top surface for 'top release' of Type I and II as well as for 'middle release' of Type II, respectively. The detouring flow phenomenon of unsaturated water through two-layer porous media is observed, whether they are made up of coarse and fine quartz sand or quartz sand and loess, even though the coarse particle layer is very thin. An obvious space is formed at the lower part of the coarse particle layer at longer time of releasing tracer from the top. And a narrow tracer zone is formed at the lower part of coarse particle layer for releasing tracer from mixed tracer and quartz sand layer in the middle of loess. The complementary scenario is observed for both mentioned above. Moreover, the tracer, which is initially put in coarse particle layer within loess, expanded up and down into loess and the expansion extent increases with retention period under no water sprinkling