Combining time-lapse electrical resistivity tomography and air injection to detect agricultural subsurface drains

Abstract

Subsurface drainage (SD) techniques are widely used for agricultural purposes. In France, this practice has expanded since the 1960s; however, the maps and designs of SD networks have disappeared over time. During the past two decades, the number of industry operator requests for SD network detection has been increasing. This study evaluates a new methodology for detecting SD networks by the use of time-lapse electrical resistivity tomography (ERT) monitoring in combination with air injection from the SD outlet. The air is injected at different pressure levels and temperatures. This detection method has been tested on both a laboratory model and a small experimental plot drained by tile drains. The results of these experiments show that the injection of high-pressure air instantaneously modifies the soil electrical resistivity around the drains, thereby creating a sufficiently visible electrical resistivity contrast on the ERT images. However, air injection under high temperature and low pressure yields inconclusive results. Air injection under high pressure coupled with ERT monitoring allows for an accurate detection of the SD network at the plot scale and moreover offers new perspectives for the detection of buried pipes.