ABSTRACT
Preferential flow is the process whereby water and solutes move by preferred pathways through a porous medium (Helling and Gish, 1991). During preferential flow, local wetting fronts may propagate to considerable depths in a soil profile, essentially bypassing the matrix pore space (Beven, 1991). Under such conditions, classical methods, such as the convective-dispersive equation, for quantifying flow of water and solutes in uniform soils, may not be valid. Additionally, the presence of local flow channels complicates the problem of locating monitoring devices in the vadose zone. For example, random installation of suction lysimeters, used as point samplers of pore liquids, may result in some units being located within macropores, while other units are within the soil matrix. Kung et al. (1991) demonstrated that the concentrations of water-soluble constituents collected from macropores differ from concentrations within the soil matrix. Accordingly, by randomly installing sampling units, measurements of pore liquid chemistry will be highly variable and not a true representation of the spatial average (Kung et al., 1991).
