Estimation of groundwater levels with vertical electrical sounding in the semiarid area of South Keerqin sandy aquifer, China

To develop a simple, accurate, and non-destructive method for estimating the groundwater level (GWL) in an unconfined sandy aquifer, field measurements of soil electrical resistivity were conducted at the Daqinggou Ecological Station (DES) in 2005 and the Experimental Base of the Institute of Wind-Sand Land Improvement and Utilization (IWLIU) in 2009. The resistivity data were acquired through a series of vertical electrical soundings (VES) using a Wenner array. For comparison with the VES method, the GWLs were also manually monitored in wells. The results showed that the thirty VES profiles decreased or first increased and then decreased with increasing electrode spacing (i.e., becoming more conductive with depth). The depth of the GWL was obtained by calculating the turning points, as inferred from inflections in the apparent resistivity profiles. The GWL variations between the VES method and manual measurement ranged from 0.22 to 1.03 m at the DES, with a mean value of 0.52 m, and from 0.03 to 0.82 m at the IWLIU, with a mean value of 0.10 m. The significant differences between the GWLs obtained by the VES method and manual measurement at the DES were due to the higher GWLs with capillary action; there were no significant differences in the GWLs obtained at the IWLIU. The linear regression coefficient of determination was 0.97 for the IWLIU GWL values, indicating a good agreement between the VES method and manual measurements. Therefore, we conclude that the VES method is a sound measuring tool for estimating GWLs in unconfined sandy aquifers when the GWL is sufficiently deep (e.g., GWL > 3.98 m).

► We estimate groundwater levels using vertical electrical sounding with a Wenner array. ► For comparison with the VES method, the GWLs were also manually monitored in wells. ► Estimated groundwater levels were close to measured ones (GWL > 3.98 m). ► No significant differences and a high coefficient of determination were between them. ► VES method is a sound measuring tool for estimating groundwater level (GWL > 3.98 m).