Simultaneous estimation of the soil hydraulic conductivity and the van Genuchten water retention parameters from an upward infiltration experiment

This paper presents a new laboratory method to simultaneously estimate K-s and a and n parameters of the van Genuchten (1980) theta(h) from the inverse analysis of an upward infiltration curve measured in a 5-cm high soil column. The method was evaluated on synthetic 1D infiltration curves generated for a theoretical loamy sand, loam and clay soil. The influence of the soil initial condition on the inverse analysis was also studied. Next, an optimization method was presented and tested on eight theoretical soils (from loamy sand to clay). The method was subsequently applied to experimental curves measured on five sieved soils (from sand to clay) packed in 5-cm high and diameter cylinders. The K-s, alpha and n values estimated from the inverse analysis of the experimental curves were compared to those measured by Darcy and the pressure cell method (PC). The initial soil tension, h(i), which had an important influence on the optimization, was fixed to - 6.0.10(5) cm. The optimization method resulted robust and allowed accurate estimates of the actual hydraulic parameters. A close to one relationship (R-2 = 0.99) was observed between the theoretical a and n and the corresponding values obtained with the inverse analysis. Regarding to the experimental soils, significant relationships close to one were obtained between K-s and n (R-2 > 0.98) estimated from inverse analysis and those measured with Darcy and PC. A nonsignificant relationship with slope away from one was found for alpha.