Identification of groundwater sources of a local-scale creep slope: Using environmental stable isotopes as tracers

Water plays an important role for slope stability and typically consists of local precipitation (LP) and original slope groundwater (OSGW); high amount of the OSGW leads the slope groundwater (SGW) easily to exceed the critical level that causes slope failure in a heavy raining event. This study was to verify the source and significance of the OSGW for a creep slope adjoining a hydropower plant, northern Taiwan by an environmental stable isotope approach. Isotope results indicate that the source of the OSGW derived from leaking of the water-transporting system of the power plant; the leaking fraction in the SGW is as high as 70–80%. High leaking component in the SGW indicates that the leaking water rather than local precipitation is the crucial factor for the mass movement of the creep slope. Since the mass movement poses a potential threat to the hydropower plant safety, the most important measure for the remedial project is to perform a comprehensive check and repair the leak of the water-transporting system.