Use of geophysical methods to evaluate soil sediments behind gabion check dams in the dry regions of southern Tunisia.

This study aims to detect sediment at six gabions check-dams distributed in the upstream and downstream areas of the Koutine catchment located in an arid area in the southeast of Tunisia and characterized by an annual mean precipitation of less than 200 mm. The detection of sediment is based on the Electrical Resistivity Tomography (ERT) method associated with topographic measurements. About ten lines were arranged, with 72 electrodes. The results of resistivity data obtained during field measurements were inverted into subsurface structures using least squares inversion techniques. The preliminary results indicate that the sediment can be identified using an ERT contour method. The obtained results are calibrated based on samples collected for laboratory analysis. The accuracy of the high-density ERT method was justified. The density increases with the sediment deposit depth. Topographic methods were used to estimate the surface and the relief of deposed sediments in the area monitored by the gabions check-dams. This study provides an approach based on the high-density electrical resistivity tomography method and a topographic investigation to estimate sediment yield behind gabion check-dams that control catchments. The sedimentary deposit of eroded soils reduces the effectiveness of the recharge structures. Consequently, the improvement of permeability at the level of the retention basins (by cleaning the settlement basin and creating recharge wells) is of great importance. The study results are beneficial for decision-makers to evaluate the existing soil conservation and water management plans, which can be further adjusted using appropriate soil erosion mitigation options based on scientific evidence.