The objective of this research is to assess the seepage problems in the Ghordanloo dam foundation and to present a proper method of water-proofing. The dam will be built on the Atrak river in the northeast of Iran. The abutments of this dam will be contructed on limestone and shale that belong to the lower Cretaceous. The maximum thickness of the alluvium in the dam axis is up to 60 meters. Due to the presence of large thickness of alluvium, with various permeabilities in the dam foundation, it is necessary to prevent seepage through the dam foundation. Hence, based on the results of Lofran tests the permeability of alluvium was determined. According to the results, the permeability of the alluvium was between 10-2 to 10-6 cm/s. Then, the dam body and its alluvial foundations were modeled using the SEEP/W software. Potential of water seepage, at different positions and depths of the cutoff wall, was also determined on the basis of numerical analyses. Finally, based on the amount of seepage, values for hydraulic gradient and safety factors, a proper method of water-proofing was proposed.

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