Three-dimensional, time-dependent modeling of rainfall-induced landslides over a digital landscape: a case study

Physically based approaches for the regional assessment of slope stability using digital elevation model (DEM) topography usually consist of one-dimensional (1D) descriptions and often include more simplifying assumptions than realistic, three-dimensional (3D) analyses. We investigated a new application of the well-known, publicly available software TRIGRS (Transient Rainfall Infiltration and Grid-Based Regional Slope-Stability Model) in combination with Scoops3D to analyze 3D slope stability throughout a digital landscape in a time-dependent fashion, typically not implemented in three-dimensional models. TRIGRS simulated the dynamic hydraulic conditions within slopes induced by a rainstorm, and Scoops3D used the resulting pore water pressure for 3D stability assessment. We applied this approach to the July 2011 landslide event at Mount Umyeon, South Korea, and compared the results with the landslide initiation locations reported for this rainfall event. We described soil depth in the study area by three different simple models. Stability maps, obtained by the 1D (TRIGRS only) and 3D (TRIGRS and Scoops3D) time-dependent approaches, were compared with observations to assess the timing and locations of unstable sites via a synthetic index, previously developed specifically for dealing with point landslide locations. We highlight the performance of the 3D approach versus the 1D method represented by TRIGRS alone, as well as the consistency of the time dependence of the results obtained using the combined approach with the observations.