2022, 41(1): 88-99.
doi: 10.11932/karst20220104
Abstract:
Xiaohewei reservoir is an important centralized drinking water source in Wenshan Prefecture， Yunnan Province. It is also the reservoir with the highest sea level in Wenshan City. The reservoir dam is a concrete double curvature arch dam， with a total storage capacity of 3.9892 million m3， a profitable storage capacity of 3.7892 million m3 and a dead storage capacity of 200 thousand m3. Xiaohewei reservoir， supplying 220，000 people with drinking water， has been plagued by leakage problems for years because the geological survey work in the stage of reservoir site selection is insufficient. According to the 1∶200，000 geological survey data and results of the geological drilling conducted at the dam site， a wrong judgment was made that there are mudstone and silty mudstone clastic rock strata of Devonian Pojiao formation （D1pj） and there is no carbonate rock distribution at the dam site and at the bottom of the reservoir basin. Therefore， it is not likely to occur the leakage caused by karst development in reservoir construction of this area. However， this article presents a new understanding of the hydrogeological conditions of karst seepage in Xiaohewei reservoir based on hydrogeological investigations. The siliciclastic rocks of the Devonian Pozheluo formation and those of the Liujiang formation form the water barrier between the north and south sides， with the limestone of the watershed zone formation about 40 m thick in the middle forming the seepage zone. A northeast-southwest compressional and torsional reverse fault F1 forms the western water barrier， with water seeping mainly to the northeast. （1） The tracer experiment was carried out between leakage point X01 and collapse pit Tx02. The results show that surface water leaks from the bottom of Xiaohewei reservoir， flows northeast along the karst leakage zone， passes through carbonate rock strata such as Carboniferous Weining formation， Maping formation and Permian Yangxin formation， and finally discharges into the karst spring S01 by the Shundian river. （2） Two physical methods， the high-power charging and the audio geomagnetic method， have been used to detect the locations and depth of karst leakage pipes. The potential curve of high-power charging method reaches the local peak at point 460， point 525 and point 545， and the potential gradient value is close to 0， which is speculated to be the location of karst leakage pipeline. The local peak near points 525-545 is wider， and the width at point 460 is relatively small. The results of the audio magnetotelluric method show that the points 450-480 and 510-560 constitute two extremely low resistance closure loops， and the depth of the anomaly zone is less than 120 m. The positions of these two extremely low resistance closure loops are basically consistent with the positions of the strong karst seepage zone detected by the high-power charging method. （3） Boreholes were respectively drilled at point 460 and point 545. The results show that karst caves are exposed in both boreholes， which verifies the strong karst leakage zone speculated by geophysical exploration. （4） The results of hydrogeological survey， geophysical exploration and drilling have been comprehensively analyzed. It is considered that there are two strong karst seepage zones near the lithologic contact zones between the watershed limestone and the upper Liujiang siliceous rock and lower Pozheluo siliceous rock respectively. The scale of these two karst leakage zones varies greatly， small at point 460 and large at points 525 to 545. ZK01 borehole at point 460 is a semi-filled mud karst cave with drill falling at 51.5-53.7 m， which is located near the lithologic boundary between the limestone of Fenshuiling formation and the siliceous rock of lower slope folding formation. At point 545， ZK06 borehole exposed karst caves at the lithologic boundary of 24.9-26.9 m and 52.4-56.4 m respectively， of which the karst caves at the lithologic boundary of 24.9-26.9 m Fenshuiling formation limestone and Liujiang formation siliceous rock are completely filled with mud； the karst caves at the lithologic boundary of 52.4-56.4 m Fenshuiling formation limestone and lower slope break formation are semi-filled； the bottom is filled with mud at 56.1-56.4 m， with high water content at 52.4-56.1 m depth. The research results will provide a basis for the control of leakage in Xiaohewei reservoir and a reference for the investigation and prevention of similar reservoir leakage problems in karst areas in the future.
LIU Tianyun,LUO Ruiheng,HU Shunqiang,et al.Hydrogeological conditions of karst leakage and identification of pipeline location in Xiaohewei reservoir, Wenshan[J].Carsologica Sinica,2022,41(01):88-99.. doi: 10.11932/karst20220104.
