Measuring hydraulic properties using a line source: I. Analytical expressions

In situ measurement of soil hydraulic properties remains a challenge. This study presents new analytical expressions for estimation of soil hydraulic properties below a surface Line source by means of multi-purpose time domai n reflectometry (TDR) probes and existing quasi analytical, steady state so lutions for infiltration from a surface line source. Inverse procedures are used to estimate the inverse macroscopic capillary length scale, alpha, an d the hydraulic conductivity at saturation, K-s, from pressure head (psi), water storage (W), and conservative ionic tracer travel time (T) measured v ia multi-purpose TDR probes placed at several depths below a line source wi th constant flax of water. Soil water content at saturation, theta(s), ran also be estimated if prior information is available, The parameter and spat ial sensitivities of each solution were calculated by means of sensitivity coefficients. The uniqueness of possible combinations of measurements to es timate alpha, K-s, and theta(s) was tested by means of two-dimensional resp onse surfaces, Significant correlation exists between K-s and theta(s), and thus it is not possible to estimate both K-s and theta(s) by globally mini mizing the objective function. Combination approaches with W (i.e., psi and W, T and IV, or psi and W and T) give unique estimates of alpha and K-s if either theta(s) is known or prior information on theta(s) is available.