The Effect of Cut-off Walls on the Contaminant Transport through the Porous Medium under a Dam

Contaminants trapped behind dams can gradually migrate and affect the downstream aquifers negatively. Cut-off walls are practical means for controlling contamination in the aquifers. In this study, the effect of length, location and number of cut-off walls on the contaminant transport under a dam (with laboratory dimensions) was numerically investigated. Cut-off walls with the lengths of ۱۰, ۱۵ and ۲۰ cm at the dam heel and toe and in the middle of the foundation were examined. The concentration of a contaminant, migrating from the upstream toward the downstream, was obtained at the far downstream of the stilling basin at different times using the Hydrus-۲D model. The results showed that when there were no cut-off walls, the peak concentration occurred at the downstream ۱۵ hours after the contaminant started to migrate from the upstream. This time for the cut-off walls with the lengths of ۱۰, ۱۵ and ۲۰ cm at the heel was ۳۰, ۴۰ and ۵۰ hours, and at the toe was ۵۰, ۵۶ and ۶۴ hours, respectively. The cut-off walls delayed the contaminant transport, and as their distance from the upstream increased, the delay also increased. Also, the longer the cut-off wall was, the more time the contaminant stagnated behind it. Using two cut-off walls at the heel and the toe resulted in a better performance than the single cut-off wall in the middle of the foundation, with the peak concentration occurring after ۸۸ and ۳۲ hours, respectively

کلیدواژه ها:

Contaminant transport ، Cut-off wall ، Dam ، Hydrus-۲D ، Numerical simulation