3D cross-hole resistivity tomography to monitor water percolation during irrigation on cracking soil
Author(s): Greve, AK, Acworth, RI, Kelly, BFJ
Publication Name: Soil Research
Date: December 2011
Irrigation water entering soil cracks can quickly move past the root-zone without being utilised by plants. To assess the efficiency of irrigation practices, reliable methods to monitor water percolation are needed. Three-dimensional (3D) cross-hole electrical resistivity tomography (ERT) was carried out during three irrigation events on soil with different surface-crack intensities. Changes in the resistivity distribution during the irrigation events were related to water movement. The propagation of resistivity change during irrigation events differed for different degrees of soil cracking. For surface cracks of <2 mm width before the irrigation, the resistivity change propagated evenly down-gradient, indicating matrix flow. During irrigation on soil with 30-mm-wide surface cracks, the resistivity change first occurred in the lower parts of the profile before propagating to the top. This suggests preferential flow filling cracks from the bottom up. The differences in initial soil moisture that resulted in these two flow behaviours were reflected in the pre-irrigation resistivity profile. Subsurface temperature changes during the irrigation confirmed the different flow behaviour. 3D Cross-hole ERT allows monitoring of percolation patterns as well as the pre-irrigation moisture states that cause these patterns. This makes 3D cross-hole ERT an excellent tool for researching irrigation management.