Simultaneous estimation of soil hydraulic and solute transport parameters from transient infiltration experiments

Abstract

Estimation of soil hydraulic and solute transport parameters is important to provide input parameters for numerical models simulating transient water flow and solute transport in the vadose zone. The Levenberg–Marquardt optimization algorithm in combination with the HYDRUS-1D numerical code was used to inversely estimate unsaturated soil-hydraulic and solute transport parameters from transient matric pressure head, apparent electrical conductivity, and effluent flux measurements. A 30 cm long soil column with an internal diameter of 5 cm was used for infiltration experiments in a coarse-textured soil. Infiltration experiments were carried out with both increasing and decreasing solute concentrations following a sudden increase in the infiltration rate. Matric pressure heads and solute concentrations were measured using automated mini-tensiometers and four-electrode sensors, respectively. The simultaneous estimation results were compared with independently measured soil water retention, unsaturated hydraulic conductivity, and solute dispersion data obtained from steady-state water flow experiments. The optimized values corresponded well with those measured independently within the range of experimental data. The information contained in the apparent electrical conductivity (which integrates information about both water flow and solute transport) proved to be very useful for the simultaneous estimation of soil hydraulic and solute transport parameters.