Coupling geophysical measurements and hydrological modeling for the determination of longitudinal dispersivity.

The knowledge of the longitudinal dispersivity parameter is necessary to simulate solute transport in porous media. The direct measurement of this parameter is expensive and time consuming. Indirect methods based on the inverse modelling procedure provide an easier and reliable alternative, if measurements of solute concentration and soil water content are available. In this study, Hydrus 1D model was coupled with apparent electrical conductivity measured by means of the simple and rapid electromagnetic induction (EMI) technique in order to determine the longitudinal dispersion parameter in a sandy soil. By means of forward Hydrus 1D simulations the temporal distribution of soil water content in 1 m depth soil profile was obtained. The soil water content and the inverted soil electrical conductivity were implemented in the Rhoades linear equation in order to determine the distribution of the soil solution electrical conductivity. Thereby, the longitudinal distribution parameter was finally determined by carrying out Hydrus 1D inversions. The estimated dispersion parameter was 10.23 cm. The proposed procedure allows to obtain reasonable values of longitudinal dispersion with a good degree of approximation.