USING MULTI-DIMENSIONAL ERT MODELLING TO PROVIDE NEW INSIGHT INTO THE HYDROGEOLOGICAL STRUCTURE OF A VERY SLOW-MOVING LANDSLIDE IN GLACIAL SEDIMENTS, THOMPSON RIVER VALLEY, BRITISH COLUMBIA, CANADA

Landslides in the Thompson River valley, southwestern British Columbia, are monitored by the railway industry, universities and government agencies to better manage geohazard risks in the primary national transportation corridor. The consequences of landslide activity in this study area include adverse impacts on: 1) vital railway infrastructure and operations; 2) sensitive ecosystems and natural freshwater resources; and 3) public safety, local communities, cultural heritage features and Canada’s economy. Current research efforts are focused on the 0.04 km² Ripley Landslide. Surface displacement, tension cracks and scarps on active slopes are monitored by experimental global positioning systems, satellite radar interferometry and photogrammetry using unmanned aerial vehicles. Slope inclinometers, acoustic emission monitors and piezometers capture changes in sub-surface movement and changes in groundwater levels. Merged 2D and 3D ERT datasets have captured a clear static proxy image of soil moisture and groundwater conditions in surficial deposits and bedrock for November 2013 (land) and 2014 (river). Continuous (real-time) ERT monitoring has now been deployed to characterize the long-term hydrological behaviour of geological units in the landslide. In November 2017, an array of 74 electrodes were positioned across the slide body and connected to a proactive infrastructure monitoring and evaluation (PRIME) system with internet access via a modem. This installation captures dynamic changes in electrical resistivity of the hydrogeological units, and is helping to better define surface water and groundwater flow paths in the main slide body, and their relationship to fluctuating porewater pressures and landslide activity. A greater understanding of the composition and internal structure of slope failures in the valley is gained at the test site from terrain analysis and modelling of 2D, 3D and 4D geophysical datasets. This insight helps with the interpretation of multi-year monitoring datasets and guides future efforts to monitor landslide activity in the valley.