Establishing the magnitude of landslide triggering rainstorm events within the Cayaguas River watershed: A proposed methodology

This research study focuses on evaluating slope stability within the watershed during rainfall events. Detailed slope water flow and stability analyses were performed in order to determine the rainfall duration and intensity which most probably led the slope towards failure. Slope models were determined based on a case study slope failure and fictitious slope failures consisting of typical soils and slope angles within the watershed.Results from simulated slope failures demonstrated that these intensities were lower than those depicted by both Pando et al. (2005) and Larsen and Simon (1993) generalized landslide triggering rainfall thresholds. A lower bound threshold was defined by these intensities as i = 22.06D -0.72, where i was the triggering rainfall intensity (mm/hr) of D duration (hrs). Still, this threshold was only found reliable once an initial accumulated precipitation amount exceeded precipitation values depicted by rainstorms from Larsen and Simon (1993) threshold.