Numerical modeling of free-drainage water samplers in the shallow vadose zone

A finite element model was used to simulate the performance of a free-drainage sampler. This device may be used to collect soil water by free drainage in the shallow vadose zone. A unique feature of this sampling device is that it serves as a barrier to flow and creates a locally saturated region in an otherwise unsaturated system. Steady and unsteady flows were modeled assuming the hydraulic functions of van Genuchten and Gardner. Results include flux into the sampler and distribution of hydraulic head as functions of soil hydraulic properties, background soil flux and sampler size.