Two-dimensional ERT simulations to compare different electrode configurations in detecting qanats

We present the results of two-dimensional electrical resistivity tomography (ERT) modellings to detect qanats hosted by different soils. Synthetic models of qanats at varying depths were defined in RES2DMOD once for a sand-dominated environment and once for a clayey medium. For each model, ERT profiles were calculated for the Wenner, Wenner-Schlumberger, and dipole-dipole arrays. The calculated apparent resistivity pseudosections, both without noise and with high levels of noise, were then inverted in RES2DINVx64. Based on the final resistivity sections, graphs of the percentage of resistivity contrast between qanat and its hosting material versus qanat depth were plotted. The results showed that although the dipole-dipole array was more severely affected by noise, it has the highest resolution in detecting qanats, and it could resolve qanats as deep as about 11-13m with resistivity contrasts around 4% in sand and 3% in clay. Wenner and Wenner-Schlumberger arrays could clearly detect qanats shallower than 5m and hardly down to about 7m and 9m, respectively. Our study shows that ERT method can be efficient in detecting qanats down to about 11-13m, provided that proper electrode array is selected and modern equipment for using large number of electrodes are available. Future studies can focus on simulations using optimized arrays to explore how the resolution at depth might be improved.