Field monitoring of preferential infiltration in loess using time-lapse electrical resistivity tomography

• Published in: Journal of hydrology (Amsterdam) Vol. 591; p. 125278
• Main Authors: Zhao, Kuanyao, Xu, Qiang, Liu, Fangzhou, Xiu, Dehao, Ren, Xiaohu
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.12.2020
• Subjects: Infiltration process; Preferential paths; Subsurface; Time-lapse electrical resistivity tomography; Preferential paths; UES; Infiltration process; GWT; ERT; PMF; SRI; UAV; PF; Time-lapse electrical resistivity tomography; HFT; MF; LF; Subsurface; SWC
• ISSN: 0022-1694; 1879-2707
• DOI: 10.1016/j.jhydrol.2020.125278

•Electrical resistivity tomography was useful to monitor infiltration process in loess.•Day-time temperature fluctuation affected electrical resistivity in loess.•Matrix flow in loess stagnated at near-surface under constant influx.•Preferential flow transferred to matrix flow for downward progression in deeper soil.•Flood irrigation recharged groundwater via hidden cracks over intact surface. The effect of preferential flow (PF) in loess is of direct interest as flood irrigation is commonly found in loess regions where precipitation is scarce. This study was to assess the applicability of time-lapse electrical resistivity tomography (ERT) data on monitoring infiltration in loess and to analyze the effects of preexisting preferential path on infiltration process at a localized scale. An in situ single-ring infiltrometer (SRI) test was conducted above a preexisting near-surface crack under a constant influx (10 cm water head for 8h), and the test was monitored by the means of 2-D time-lapse ERT and validated by an exploratory trench. The ERT results observed some increasing uncertainties in the electrical resistivity in part due to daily temperature variation; however, they showed that the infiltration process under the presence of preferential path can be effectively monitored by time-lapse ERT with a combination of unit electrode spacing (UES). The test results showed a high relative reduction of electrical resistivity (>80%) due to matrix flow (MF) and PF within 0–0.5h of the test, and followed by a transformation of preferential flow to a more matrix-dominated unsaturated flow, i.e. preferential-to-matrix flow (PMF), with continuous downward progression into the deeper subsurface (greater than 1.2 m) while MF stagnated at the near-surface (about 0.4 m). The results suggested that the presence of even a near-surface preferential path significantly accelerate the infiltration into the deeper loess by the means of PMF, as compared to observed slow infiltration of pure matrix flow in previous studies.