Measuring hydraulic properties using a line source: II. Field test

We designed and tested a field method to measure unsaturated soil hydraulic properties using multi-purpose time domain reflectometry (TDR) probes belo w a surface Line source with constant flux of water. The surface line sourc e was produced with a moving irrigation system at a field site sheltered fr om precipitation. Two hundred multi-purpose TDR probes were vertically inst alled in the soil beneath the Line source to measure soil water pressure he ad (psi), wafer storage (IV), and tracer travel time (T), The soil hydrauli c properties, the inverse macroscopic capillary length (alpha), hydraulic c onductivity at saturation (K-s), and soil water content at saturation (thet a(s)) were estimated by inverse procedures with new analytical expressions. Five combinations of measurement sets, namely IV-only, psi and W, psi and T, and W and T, and psi and W and T mere used. Approximate confidence conto urs in the alpha-K-s, plane were calculated to show the precision of the pa rameter estimates. For comparison, hydraulic properties were also measured by means of the Guelph Permeameter (GP) and the modified Guelph Pressure In filtrometer (GPI) systems, Hydraulic parameters estimated from only W measu rements were similar to those estimated from the combinations of W and psi, or W and T, or W and psi and T, The estimated hydraulic parameters were si milar to those obtained with three-dimensional (3-D) infiltration measureme nts by mesas of the GP and GPI systems.