Parameter Estimation of the Coefficients in Soil Hydraulic Equations from Steady-State Unsaturated Flow

Abstract

A parameter estimation procedure which determines the coefficients of soil hydraulic equations (soil-water characteristic and hydraulic conductivity curves) is developed. The parameters are determined by nonlinear least-squares regression of steady-state water potential measured at several points along an unsaturated horizontal soil column to an equation, herein derived, which describes water potential continuously along the column. To estimate parameter values, total mass of water in the soil column at steady-state, saturated water content, and steady-state flow rate must also be measured. The parameter estimation procedure is verified using synthetic data and is applied in the laboratory. The coefficients appearing in the van Genuchten and Campbell soil hydraulic equations are estimated by the procedure. Alternative methodologies are proposed to augment this procedure and to provide user flexibility. The coefficients in the difficult-to- measure wet range can be determined from measurements taken at steady-state without independently measuring water retention.