Determination of hydraulic conductivity using the inverse problem of the hydrus-1d software.

Knowledge of soil hydraulic conductivity is essential for any study that involves the movement of water in soil. The hydraulic conductivity decreases considerably with decreases in the volumetric water content (θ), or increases in the matric potential modulus (h). The relationship among these variables may be represented by the functions K(θ) and K(h). Field or laboratory methods for determining the values of the parameters that describe these functions are time consuming, costly and involve considerable uncertainty. An alternative method to determine these parameters is to employ the reverse process (inverse method). In the inverse method, the causes are determined based on their effects. This study aimed to determine the Ks parameter (saturated hydraulic conductivity) of functions K(θ) and K(h), defined according to the van Genuchten model, by solving, with the use of the Hydrus-1D software, an inverse problem based on cumulative infiltration data collected in the field. It was found that there is great variability in the value of the Ks estimates. The proposed inverse problem method allows the unsaturated hydraulic conductivity to be determined based on data collected under a wide range of soil moisture values and matric potential moduli. The inverse problem was adequately defined for the estimates of Ks in the 0-0.20 and 0.20-0.60 m layers but did not allow for a reliable Ks estimate of the 0.60-1.00 m layer.