IDENTIFYING SOLUTE DISPERSIVITY IN UNSATURATED POROUS MEDIA USING A NON-INTRUSIVE TECHNIQUE

A non-intrusive methodology using spatial moment analysis linked with image processing of a dye tracer behavior in porous media was applied to identify time-series variation of dispersivities not only in longitudinal but in transverse directions under saturated and unsaturated conditions. Dye tracer experiments were carried out in a two-dimensional and vertically placed water tank with the dimensions of 100 cm width, 100 cm height and 3 cm thickness under saturated and unsaturated flow conditions. An image processing technique based on digitalized spatial distributions of dye tracer allowed to link with a spatial moment approach to identify the temporal change of the longitudinal and transverse dispersivities. Dispersivities exhibited an increasing and decreasing tendency associated with infiltration rates and showed a marked difference between estimates under saturated and unsaturated conditions. Transverse dispersivities under unsaturated conditions were approximately one order larger than those under saturated conditions. This attributed to the effect of air distributions in porous media on the temporal and spatial change of solute dispersion phenomena.