The effect of scale on the water leakage from the reservoir and abutment of Beheshtabad Dam

Dam construction on karstic carbonate formations usually involves leakage problems from their abutments and reservoirs. Constructing a dam in such formations can lead to reservoir leakage to downstream or adjacent basins. In karstic areas, hydraulic conductivity has a direct correlation with scale. In other words, hydraulic conductivity is far lower in sub-local scales (Slug test and Lugeon test) in comparison with local scales (pumping test) and large scales (dye tracing test and recession curve). The present study was conducted to investigate the scale effect on water leakage from the reservoir and abutment of Beheshtabad Dam. This dam is located approximately at the end of an anticline axis named Sangvil, which is mainly composed of dolomite-limestone with a thickness of about 700 m. The righthand side of the reservoir is in contact with this formation. Several methods have been used for the evaluation of hydraulic conductivity and for determining the reservoir leakage in the righthand side of the dam, including Lugeon tests, Uranine tracer, a gradient approach, and spring recession curves. Also, a pumping test was carried out by considering pumping well assumptions. The results showed a range of hydraulic conductivity values for the rock mass from 2.1×10⁻⁶ m/s at the sub-local scale (Slug test) to 1.7 × 10⁻⁴ m/s at the regional scale (dye tracing test). In such a context, reservoir leakage is calculated at approximately 0.1 l/s iayn the sub-local scale to 2.7 l/s at a regional scale. By considering that reservoir scale is correlated with regional scale, leakage in the righthand side of Beheshtabad dam is calculated according to a regional scale, and the leakage amount was predicted to be within the range of 5.4 to 7.8 m³/s.