Estimation of main aquifer parameters using geoelectric measurements to select the suitable wells locations in Bahr Al-Najaf depression, Iraq

Abstract

The aquifer parameters like hydraulic conductivity and transmissivity are extremely important for the management and development of groundwater resources. Vertical Electrical Sounding (VES) and 2D Electrical Resistivity Imaging (ERI) techniques were adopted for geophysical investigation in Fadaq plantation area within Bahr Al-Najaf depression, Iraq. A total of 22 VES point distributed as a grid along six profiles in the plantation with half-current electrode spacing (AB/2) is 400 m are used to evaluate the aquifer geoelectric and hydraulic parameters, where six 2D ERI profiles were conducted and concatenated as one 2D ERI profile with a total length of 4525 m to verify the results of VES. The average formation factor of the aquifer is 22.33 with porosity and water saturation average of 22.62% and 0.59% respectively. Geoelectric and hydraulic parameters estimated values are; apparent resistivity 2.17–2.92 Ω, formation factor 6.23–31.18, porosity 17.91–40.06%, water saturation 0.18–0.85, longitudinal conductance 1.60–10.06 Ω-1, transverse resistance 3258–27200 Ωm2, hydraulic conductivity 0.62–0.68 m2/day and transmissivity 70.68–198.05 m2/day. The thickness and bulk resistivity vary between 112 and 320 m and 18–85 Ωm respectively. About 26% of the aquifer in the study area has an intermediate designation, while 73.91% of the aquifer has high designation. There is a linear relationship between transmissivity and water saturation. Based on designation, protective capacity, and groundwater supply potential VES 6C, VES 7A, VES 4C and VES 2E were recommended for new drilling sites.