UNSATURATED HYDRAULIC CONDUCTIVITY MEASURED BY TIME-DOMAIN REFLECTOMETRY UNDER A RAINFALL SIMULATOR

We used time domain reflectometry (TDR) probes installed vertically at the soil surface beneath a constant-rate rainfall simulator to measure cumulative water storage and the soil's unsaturated hydraulic conductivity. The slope from linear regression of water storage on time before any applied water infiltrates to the bottom of the TDR probe gives an estimate of the local infiltration rate. Local filtration rates measured by TDR in the field were plotted against the corresponding local steady state water contents to give an estimate of the soil's unsaturated hydraulic conductivity over a range in water content of 20% using only two applied rainfall rates. The spatial variability in local infiltration rates may be the result of infrequent high-intensity pulses of rainfall leading to temporary pending and redistribution of water at the soil surface. Nonlinear optimization was used to estimate the saturated hydraulic conductivity and inverse capillary length scale from TDR data.