Experimental assessment of preferential flow paths in a field soil

Abstract

Preferential flow paths in the subsoil can cause an accelerated movement of solutes in unsaturated-saturated transport systems. To visualize these zones of preferred flow, an iodide-coloring technique was applied to ten plots in a field. Results indicate the existence of a nonuniform solute front in the subsoil. However, this nonuniformity could be adequately accounted for by using the convection-dispersion equation for describing the relative amount of colored area in the system. Pore water velocities agreed well with measured volumetric water contents, while dispersivities were roughly of the same order of magnitude as those reported in the literature for field-scale experiments. Results did not agree with the accelerated movement found in a previous unsaturated-saturated flow experiment on the same field. The study indicates that the antecedent moisture regime and rainfall intensity have an important effect on the formation of preferential flow paths in a subsoil, thus showing the dynamic nature of this physical phenomenon.