Six series solute transport experiments were conducted with an objective to compare scale decency of fractional dispersion coefficient ( ) in space fractional advection-dispersion equation (s-FADE) with that of dispersion coefficient ( ) in advection-dispersion equation (ADE) at three flow rates. The experiments were performed in a 2.5 m×0.1 m×0.6 m (length×width×height) sandbox filled with a homogeneous or heterogeneous soil. The parameters of the s-FADE and ADE were estimated using an inverse method. The results indicated that the scale dependency of the was significantly less than that of the in the heterogeneous soil. The maximum variations of the and for the heterogeneous soil were observed at the flow rate of 200 cm3 min-1, in which the ratios of the maximum and to the minimum ones were, respectively, 6.009 and 39.039. However, in the homogeneous soil, the scale dependency of the was relatively similar to that of the . In this soil, the ratios of the maximum and to the minimum ones were, respectively, 3.109 and 5.041, which were observed at the flow rate of 548 cm3 min-1. Contrary to the and , the values of the s-FADE and ADE for both soils varied in relatively similar ranges at flow rates studied. Also, the fractional differentiation order (α) of the s-FADE described properly the heterogeneity degrees of the soils used. In a nutshell, the s-FADE is an efficient solute transport model to explain the solute transport process in natural porous media with different heterogeneity degrees.
