Three-dimensional inversion of in-line resistivity data for monitoring a groundwater recharge experiment in a pyroclastic plateau. Issue 3 (1st September 2017)

• Record Type: Journal Article
• Authors: Inoue, Keisuke; Nakazato, Hiroomi; Kubota, Tomijiro; Takeuchi, Mutsuo; Sugimoto, Yoshihiro; Kim, Hee Joon; Furue, Koji
• Is Part Of: Exploration geophysics. Volume 48:Issue 3(2017)
• Page Start: 332
• Page End: 343
• Publication Date: 2017-09-01
• Subjects: groundwater recharge experiment, in-line resistivity data, pyroclastic plateau, three-dimensional inversion, time lapse.; Geophysics -- Periodicals; Prospecting -- Geophysical methods -- Periodicals; 622.15
• DOI: 10.1071/EG16035
• Languages: English
• ISSNs: 0812-3985

Abstract

Abstract : An artificial groundwater recharge experiment was conducted in a pyroclastic plateau in Kagoshima Prefecture in Japan, and time-lapse electrical resistivity data were collected to monitor the recharge process. In the experiment, time-efficient in-line resistivity surveys were performed along four intersecting lines, because a large amount of water was released from two recharge areas and a relatively fast migration of water into the vadose zone was expected. The migration of recharged water may be estimated from changes in electrical resistivity because resistivity in the vadose zone is largely controlled by water saturation variations there. The geological setting at the experiment site was interpreted from the resistivity distribution inverted from the in-line survey data, which were obtained before the recharge experiment. The resistivity distribution showed an approximately layered structure, which could be correlated with four borehole logs in the area. Three-dimensional (3D) distributions of the resistivity change ratio were derived through constrained nonlinear ratio inversion. Three-dimensional inversion of the in-line resistivity data was more suitable than two-dimensional inversion to describe the 3D phenomena associated with groundwater recharge. During the recharge experiment, the zones of decreased resistivity shifted with time, indicating non-uniform penetration of water from the recharge areas into the ground and a horizontal flow of the recharged water, especially in the secondary Shirasu layer, which comprises lacustrine or marine sediments of pyroclastic origin. These interpretations agree with the variation in water content observed in a borehole. Abstract : An artificial groundwater recharge experiment was conducted in a pyroclastic plateau in Kagoshima Prefecture in Japan, and time-efficient in-line resistivity surveys were performed along four intersecting lines. The zones of decreased resistivity shifted with time, indicating non-uniform penetration of water from the recharge areas and a horizontal flow of the recharged water.