High-resolution time-lapse DC-IP imaging of a green infrastructure’s response to a flooding test and a heavy rain event

Stormwater management is an escalating challenge in urban areas worldwide. Green Infrastructures (GIs), such as vegetated roadside areas with lowered curbs, are gaining recognition in Quebec as an effective solution to reduce the burden on urban sewage systems. However, the widespread use of de-icing salt during winter raises concerns about increased contaminant infiltration into the ground, potentially leading to infrastructure deterioration. Despite the growing adoption of GIs, a research gap persists regarding their impact on water and chloride infiltration.
In this study, a 50m-long GI was equipped with a large range of hydrogeological sensors such as water content and pore pressure sensors, thermistors, barometer and piezometers equipped with level, temperature and conductivity loggers. In addition, a time-lapse electrical resistivity tomography (TL-ERT) monitoring system was installed to extend spatially and temporally the coverage of the hydrogeological monitoring of the GI. In total, 113 electrodes were installed in boreholes and connected to an autonomous resistivity meter. In this study, 64 electrodes located within and around a 6m × 1.8m grid were used to recover the spatial and temporal distribution of electrical resistivity perpendicularly to the GI.
A controlled flooding test (CFT) using bromide salt as a saline tracer was conducted to evaluate the GI’s response to infiltration. A multi-method surveying and sampling program was implemented, integrating ERT and induced polarization (IP) geophysical measurements, hydrogeological monitoring (piezometers), and geochemical analyses (continuous groundwater sampling). In addition, a heavy rainfall event (HRE) was monitored using DC-IP surveys conducted every two hours. In total, approximately 90 DC surveys were completed during the CFT, with a temporal resolution of approximately 10 minutes and 50 DC-IP surveys were performed during the HRE, with a temporal resolution varying  from 2 to 4 hours. 
This study presents geophysical imaging results from these events, showcasing time-lapse imaging interpreted using laboratory analyses of the soil in-situ. Preliminary results suggest that the geophysical results are consistent with hydrogeological and geochemical data, offering valuable insights into the 2D distribution and temporal evolution of water and chloride movement in and around the GI. These findings contribute to understanding the performance and potential limitations of GIs in mitigating stormwater impacts under saline conditions.