Electrical resistivity imaging and dye tracing test for joint investigation of reservoir leakage paths: a case study of loess area

The construction of reservoirs is a crucial method for humans to store and utilize water resources. Losing water resources due to reservoir leakage will hinder urban growth and jeopardize public safety. This paper investigated the leakage on the left bank of a reservoir with a high earth-filled dam in Shaanxi Province, China. Two springs erupted from the left bank’s slope toe of the neighboring valley following the impoundment of the reservoir. At the same time, a large amount of leakage was also discovered at the downstream drainage channel. Leakage continued after the reservoir stopped impounding. Electrical resistivity measurements along seven lines with Wenner arrays and three groups of dye tracing tests were carried out. The stratigraphic distributions of the river bed upstream of the dam and the mountain on the left side were revealed through the interpretation of electrical resistivity images. The high permeability zones corresponding to low electrical resistivity were found in the gravel and weathered sandstone stratum, which was supported by geological drilling data. The dye tracing test findings determined the groundwater velocities and hydraulic connectivity between the reservoir and the leakage outlets. Gravel stratum seepage was confirmed to be excessive. The joint investigation results of electrical resistivity imaging and dye tracing tests revealed three possible leakage paths from the reservoir, serving as a guide for the design of a seepage control plan.