The Application of Self-Potential Method on Top of Water Surface for the Detection of Karst Leakage Channel in the Morbid Reservoir

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As a result of karst development, water leakage from reservoirs and waste water leakage from mine tailings impoundments often occur in karst region of southwestem China. The geophysical prospecting methods commonly used in the investigation of karst leakage passage are mostly located in the dam, abutment and other land of the reservoir area, which are fail to detect and evaluate the karst collapse at the bottom of the reservoir directly. This will result that the effect of detection and governance are often poor. This paper takes the detection of karst leakage passage beside culvert of the first class hydropower station in Jinjihe reservoir in North Guangxi as an example, studying the principle, field working method and detection effect of detecting karst leakage passage in reservoir by self-potential method on the water. Outcropping formation in the study area mainly consist by the limestone clipped dolomite, dolomitic limestone of Devonian Liujiang formation (D3L) and dolomite, limestone, argillaceous limestone of the Devonian Donggangling order (D2d). The hidden karst is secondary development. That outlet pipe of the first class hydropower station in the district releases water can cause a strong negative center regional field of self-potential on the water. By dividing the regional field of self-potential on the water using the circumferential mean method and calculating the residual local anomaly separate 6 secondary negative center residual local anomaly of self-potential on the water covered by a strong regional field like an equiaxed or elliptical shape. After check in the reservoir by the diver, the 6 negative center residual local anomaly zone correspond to karst collapse, karst opening or leaking skylight at the bottom of the reservoir. Among them, the negative center residual local anomaly like an equiaxed shape near the survey points 46-48 of line 16 correspond to the largest karst collapse at the bottom of the reservoir. Through the simple connected experiment of internal and external water and the engineering geological drilling, the effect of geophysical anomaly detection is good. The self-potential method on the water can be used in the investigation of karst geological problems, such as the emergency on the water of the karst sick reservoir, and the rapid delineation of the range of the shallow karst leakage passage.