Vertical electric soundings characteristics of paleochannel in the Yuyao River Valley, Eastern China

Abstract

The Yuyao River Valley is located in the northwest of Ningbo basin, China. The confined aquifers in the study area show obvious spatial distribution characteristics, which are essentially controlled by the evolution and distribution of the paleochannel. Therefore, it is of great significance to determine the spatial geometric characteristics of the paleochannel for finding out the hydrogeological characteristics and establishing a sustainable groundwater management system. In order to confirm the geo-electric parameters (resistivity and thickness) of each geotechnical layer and the spatial geometric characteristics of the paleochannel in the Yuyao River Valley, 77 vertical electric soundings were performed on five profiles perpendicular to the valley. In addition, 13 geological boreholes distributed over the study area were collected, and the borehole-side electrical sounding measurements were carried out near the boreholes. In fact, the interpretations of borehole-side electrical sounding measurements indicate that the resistivity of each geotechnical layer in the survey area varies greatly in the vertical direction. After calibrated by the lithology of the boreholes, the results of the explication of VES and the electrical resistivity profiles demonstrated the existence of the paleochannel. The paleochannel corresponds to the sand gravel or round gravel aquifers whose particle diameter gradually increases from top to bottom. Thus, the buried depth of the paleochannel is about − 70 to − 35 m, and its width is more than 1000 m. This study corroborated the reliability of the VES method through combining electrical resistivity profiles and hydrogeological data to determine the spatial geometric characteristics of the paleochannel in terms of electrical differences.