| The Salmon Falls landslide, a deep-seated rotational slump, previously exhibited the counterintuitive finding of increased sliding velocity during dry summer months, but the suspected attribution to irrigation water was never tested. In this study, we explore drivers of slide velocity at Salmon Falls Creek using contemporaneous daily measurements of GPS positions and water levels. Between 03/2017 and 06/2018, the most consistent, robust predictor of landslide velocity was water level in Bluegill Lake on the slide body, which explained three of four acceleration events. Lake water level was directly associated with initiation and termination of flow in an unlined canal which overflows the canyon rim and supplies the lake. One unexplained acceleration was correlated with a rain-on-snow precipitation event. Regional groundwater failed to explain higher frequency velocity variations. These findings highlight the value of surficial water measurements in predicting landslide velocity and the impact of anthropogenic water redistribution on hillslope stability.
Keywords: slow-moving rotational slump, landslide, pore-water pressure, Salmon Falls Creek, Idaho, canyon formation, geomorphology, hydrogeology, landslide kinematics, static GPS, Global Positioning System, GNSS, irrigation water |