Hydrogeological conditions of karst leakage and locating of leakage channels in Biyun lake,Guizhou
China is a country with the widest distribution area and the most complete karst development type in the world,and its karst area accounts for about one third of China's territorial area.Finding leakage channels of lakes and reservoirs in karst areas has been an urgent problem for the lake and reservoir construction and the control of leakage disasters.In this study,Biyun lake in Zhijin county of Guizhou Province was taken as an example to analyze the hydrogeological conditions around the lake in response to the problem of watershed shrinkage.Furthermore,with the combination of tracer tests and geophysical detection methods,the hydrogeological conditions of leakage in Biyun lake and the location of the main leakage channel were determined and verified by drilling test results.The results of the tracer test show that Moion concentration increased significantly 32 hours after the tracer was put into Biyun lake,and the value peaked 68 hours after the setting of tracer,and then decreased.The tracer results confirm that Biyun lake flows along the karst leakage zone in the north-east direction after seeping through the sinkhole,and is finally discharged at the outlet of the Babu underground river.In the results of high-power charging method,the potential curve and gradient curve show a relatively maximum potential value and a relatively minimum value of potential gradient at the measuring point of 540 m,where the main leakage channel of Biyun lake was inferred to be located and a large-scale karst cave is likely developed in the vicinity.The rest of the anomalous sections of the curves is inferred to be a strong karst development zone,which can provide conditions for the storage and transport of groundwater.A relatively strong reflective surface of electromagnetic wave shown by geological radar exploration at the depth of about 20-28 m is inferred to be a contact surface between mudstone and greystone.A strong reflection surface of relative electromagnetic wave at the depth of 36-48 m is inferred to be a strong karst development zone.These results are basically in line with the location of the strong karst leakage zone detected by high-power charging method.The borehole drilled at the measuring point of 540 m has verified the strong karst leakage zone inferred from the physical exploration.Based on the correction of the data from the borehole,the parameter of geological radar,V,is taken to be 0.060 m·ns-1 which is applicable to the study area.The study results indicate that Biyun lake belongs to the oblique tectonic basin,where leakage points and underground river pipes are mainly developed close to the axis of the Babu compound oblique,along the lithological interface of three sections of greystone and the second section of the mudstone of Jialingjiang Group.The mudstone constitutes a water separating plate of the karst leakage zone.After lake water seeps along the zone,it flows northwest,and is discharged in the end at the outlet of the Babu underground river.In addition,the leakage of Biyun lake is mainly of the karst pipeline type.The karst leakage zone is located at the measuring point of 540 m,with a 40-meter-deep of karst pipeline;therefore,the leakage section is relatively narrow,and it is feasible to plug the leakage by grouting.The drilling test results confirm the reliability of the technical method used in karst areas,which is combined by hydrogeological investigation,tracer test and physical exploration,because this method can well determine the direction of the leakage channel and the location of the leakage zone,and thus providing guidance on the leakage control of lakes or reservoirs in karst areas.
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