A Comprehensive Model for Single Ring Infiltration II: Estimating Field-Saturated Hydraulic Conductivity

In this study, we explored four approaches to infer field-saturated hydraulic conductivity (K-fs) from both early-time and steady-state infiltration measurements using an explicit expression for three-dimensional flow. All approaches required an estimate of the soil capillary length, lambda. Approach 1 estimated K-fs via optimization, in which all other infiltration parameters (9 in total) were known. The remaining approaches constrained lambda through different interpretations of coefficients generated by linear regression between infiltration and time. Approach 2 utilized these coefficients plus estimated soil water content to simultaneously quantify both lambda and K-fs. Approach 3 used an analytical expression in which lambda was estimated based on water retention/unsaturated hydraulic conductivity parameters, while Approach 4 adopted a universal lambda value of 15 cm. The accuracy of these four approaches were tested using numerical and laboratory infiltration data. Approach 1 had the highest accuracy but also required the most auxiliary data, making it most suitable for laboratory and numerical experiments. Approach 2 was the least consistent, providing negative estimates for lambda and K-fs under certain conditions. Approach 3 also gave accurate predictions of K-fs, but may be inaccurate in instances where the water retention model parameters are uncertain or do not describe soil hydraulic behaviors well. Approach 4 provided reasonable estimates of K-fs (within a factor of three from the actual value in most cases), while not requiring additional observational data. The optimal approach for interpreting K-fs will thus vary depending on the type and quality of available auxiliary data.