Downward Water Flow and Solute Transport in an Unsaturated Soil with Gradually Decreasing Head on the Ground Level - 21060

The downward movement of water and solute transport due to a suddenly imposed head condition on the ground surface are investigated by solving the Richards equation and the transport equation in an unsaturated soil by using the software HYDRUS 1D. While the head decreases gradually, the concentration of the contaminant is maintained constant over a finite duration of time on the ground surface. The moisture migration is solved and then the contaminant transport, which is coupled to moisture movement, is solved. Downward penetrations of the hydraulic head, the moisture content, and the contaminant concentration are slowed down as the penetrations proceed vertically. The coupled processes are discussed with special emphasis on the effects of sorption coefficient. Specifically as the sorption coefficient increases the region of contamination tends to be confined in shallow depths. (authors)