高密度电法和音频大地电磁测深法在西南岩溶地区地下水勘探中的应用

Application of high-density electrical resistivity tomography and audio magnetotellurics for groundwater exploration in the karst area in southwestern China

云南省会泽县属西南岩溶地区,岩溶地下水是该地区主要的供水水源。为解决当地群众饮水困难的问题,在充分认识会泽地区水文地质条件的基础上,总结出该区地下水赋存概念模型,并结合岩石物性测量结果,对物探方法的适用性和组合优选进行评价。根据地方实际需求,选择在会泽县拖姑村布设了一条高密度电法和音频大地电磁测深法结合的综合剖面,通过电阻率异常圈定了地下水富集部位,有效指导钻孔的布设,单孔最大涌水量为20.76 m3/d,有效解决了当地居民饮水困难的问题。通过该项研究认为,高密度电法和音频大地电磁法相结合的探测方式是在碳酸盐岩地区寻找地下水的优选方法。高密度电法能够精细刻画风化层厚度、基岩界面、裂隙发育程度及地层含水情况,对地下水的补给通道进行约束,弥补了音频大地电磁测深法对近地表地层结构识别能力不足的缺陷。而音频大地电磁测深法能够准确反映断裂破碎带的空间结构和地层的宏观结构,对储水构造的边界条件(隔水层)进行限定,弥补了在高阻地层区,高密度电法探测深度不足的缺陷。二者分别从精度和深度上相互补充,对地下水运移、存储和富集的空间赋存条件进行识别和约束。

Huize County of Yunnan Province is situated in the karst area in southwestern China,where karst groundwater is its primary water source.To conquer local difficulties in drinking water,this study constructed a conceptual model of groundwater occurrence by fully investigating the hydrogeological conditions of the Huize area.Moreover,this study evaluated the applicability and optimal combination of geophysical methods based on the measurement results of petrophysical properties.According to the actual local needs,this study deployed a comprehensive profile combining high-density electrical resistivity tomography(HDERT)and audio magnetotellurics(AMT)in Tuogu Village,Huize County.The groundwater enrichment site was delineated relying on resistivity anomalies,effectively guiding the layout of boreholes.The boreholes achieved the maximum single-borehole water yield of 20.76 m 3/d,thus effectively alleviating the local drinking water problem.The HDERT-AMT combined exploration method proves to be optimal for prospecting for groundwater in carbonate rock areas.HDERT can accurately characterize weathered layer thicknesses,bedrock boundaries,fissure evolutionary degrees,and water-bearing properties of strata,constraining groundwater recharge channels,thus counteracting AMT's defects for identification of near-surface stratigraphic structures.AMT can accurately reflect the spatial structures of fracture zones and the macrostructures of strata,limiting the boundary conditions(aquicludes)of water-bearing structures,thus making up for the defects of insufficient detection depths of HDERT in high-resistivity stratigraphic regions.HDERT and AMT,which are complementary to each other in terms of accuracy and depth,can be applied to identify and constrain the spatial occurrence conditions of groundwater migration,storage,and enrichment.