| We applied 2D dense time-lapse electrical resistivity tomography (ERT) for monitoring groundwater seepage through a levee system. A small existing dike was used as a levee for the underseepage monitoring. First, we excavated a narrow channel underneath the dike and filled it with high-permeable coarse-grained river sands. The excavated portion of the dike body was re-mounded with backfill soils. After one-year curing, we conducted a seepage test in March 2018. A total of 14 m3 water was poured into a pond connected with the channel, intermittently for about 5 hours. Groundwater flow was monitored by the ERT at about 15-minute intervals along a survey line set just above the channel. A high-speed resistivity measurement tool was used for the ERT. The tool can transmit 24 individual current signals simultaneously and measure 24 potential responses. Electrode spacing was set to 25 cm to enhance spatial resolution at shallow depths. As a result, we could successfully delineate groundwater migration through the channel. Surface seepage was observed 220 minutes after the start of watering. The tests demonstrated that 2D dense time-lapse ERT was quite effective to detect migration of groundwater body and for the characterization of underseepage potential of a survey site. |
