Exploration of the Confined Aquifers in the Yuyao River Valley (Eastern China) Using Electrical Sounding Method

With abundant groundwater resources and obvious spatial distribution characteristics of confined aquifers, the Yuyao River valley is located in Ningbo, a coastal city in eastern China. It is greatly significant for studying the formation, movement and recharge of groundwater and establishing a sustainable groundwater management system to determine the spatial distribution of confined aquifers. In this paper, the spatial distribution of confined aquifers in the Yuyao River valley are studied by combining the symmetrical quadrupole electrical sounding method with hydrogeological data. Through analysis of the existing hydrogeological data, it is corroborated that there are sand gravel and round gravel confined aquifers in the study area. Then, the results of borehole-side electrical sounding measurements show that significant electrical differences are found among each rock-soil layer in the study area, and the resistivity of sand gravel and round gravel confined aquifers varies from 10 to 20 Ω·m. Finally, 77 symmetrical quadrupole electrical soundings on 5 lines were carried out perpendicular to the Yuyao River valley, and the data of electrical sounding were inverted and analyzed by the analysis software of GeoElectro. After calibration with boreholes, the confined aquifers in the study area were determined to be zonally distributed along the middle line of the valley, with buried depth ranging from -65 to -25 m and width exceeding 1000 m