Natural tracing for concentrated leakage detection in a rockfill dam

Abstract

During two field visits to the Renzonghai dam at the southeast edge of the Qinghai-Tibet Plateau in China, a large amount of leaking water was observed downstream of the dam. In particular, at the high reservoir water level, the leakage amount reached 754.33 L/s, >10 times the maximum allowable leakage limit, which seriously threatens the dam safety. Therefore, it is essential to identify the leakage paths quickly and efficiently, so that they can be stopped. The natural tracers of temperature and conductivity are combined with water stable isotope and chemistry compositions for dam leakage investigation. For comparison analysis, in-situ measurements and sample collections were completed in September 2015 at a high water level and in April 2016 at a low water level. The results obtained from temperature and conductivity logging are improved by measuring the water stable isotope and chemistry compositions, which showed at least three concentrated leakage paths. Two of them were located on each side of the dam abutment through the developed faults, and the other one went through the concrete cut-off wall and dam foundation. Due to the low cost, efficiency, and simple operation of this natural tracer technique, it is suggested that the technique should be utilized by engineers for dam leakage investigation, especially for concentrated leakage path delineation, at least at the preliminary stage.