It has been found that irregular infiltration is often observed at the wetting front in soil under unsatu-rated conditions. This concept is known as fingered flow. Macroscopic dispersion occurs in the solute transport pro-cess due to the heterogeneity of the flow field. In the conventional convective-dispersion analysis, macroscopic dispersivity has been known to be an important parame-ter when reproducing this phenomenon. However, quan-titative evaluation of the macroscopic dispersivity in the vadose zone is still problematic, because the dispersivity depends on the infiltration conditions. In this study, the nu-merical simulations of infiltration and solute transport pro-cesses are performed in the artificial heterogeneous field of hydraulic conductivity. The heterogeneous field are gener-ated using the stochastic fractal model. Then, the quantita-tive evaluation of macroscopic dispersivity under fingered flow conditions and its characteristics are discussed. The results of this study show that the difference in averaged permeability between upper and lower formations affects the shape of the infiltration profile, or finger shape. The macroscopic dispersivity of the media seems to depend on this finger shape. Also, a large infiltration surplus inhibits the generation of fingered flow.
Soil moisture plays the critical role in land-surface processes. But it is not well understood, in part because of its strong spatial variability that makes diffi-cult obtaining representative measurements. The recently developed cosmic-ray soil moisture probe provides the means for such representative measurements and therefore has the potential to provide useful area-average data for land-surface hydrology.