An investigation of seepage was conducted at the Golfaraj Reservoir Dam with a particular emphasis on determining the seepage areas based on regional and site-specific hydrogeological studies. The primary goal of the investigation was to develop strategies intended to minimize dam and reservoir seepage. Leakage from the reservoir is a serious problem and of considerable concern to the local populace. Substantial reduction of seepage from the Golfaraj Reservoir Dam is the ultimate goal of the investigations conducted. The Golfaraj Reservoir Dam, located in the East Azerbaijan province, NW Iran, was built to provide water for agricultural and industrial needs in the Golfaraj plain and neighbouring lands. The Golfaraj Reservoir was constructed through the Miocene Upper Red Formation, which consists of sequences of sandstone, mudstone, conglomerate and gypsiferous marl. Following reservoir filling, seepage of water into adjacent formations was found to occur at an estimated rate of 70 l s−1. After reservoir impoundment, groundwater levels in Shahmar village, 2 km downstream and just north of the dam axis, rose and land surfaces became abnormally wet. Lugeon values in some boreholes drilled around the Golfaraj Dam before and after dam construction were high enough to indicate that the dam base had sufficient permeability to allow water to escape by underflow. Twenty-four Casagrande piezometers installed around the dam axis at four sectors provided additional information on seepage pathways through the dam body and underneath or through the cutoff wall. Water-level variations in the Casagrande piezometers confirmed the seepage routes. Study results showed that reservoir water is likely to seep through the reservoir bottom, and beneath and through the cutoff wall. The west side of the dam and near the reservoir reflected water-level rises in accordance with the rise in reservoir-water level. Seepage in this area is probably due to its proximity to the Golfaraj Reservoir. Hydrogeochemical analyses further suggest that the water source at the Shahmar Drain, c. 1800 m north of the Golfaraj Dam, cannot be from the east or west embankments of the dam because the electrical conductivity in the Shahmar Drain water approximates to the electrical conductivity of the Golfaraj Reservoir water and is lower than the electrical conductivity of groundwater in some of boreholes. Potential future seepage mitigation measures will focus on methods to seal the reservoir floor and cutoff wall sections I2–I2 and I3–I3, although some efforts may be directed at the west side of the dam. Such measures could take the form of the installation of a geomembrane barrier over the west side of the dam, concrete cutoff walls downstream of the dam and pumping wells to intercept seepage.

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