A physically based model for the hydrologic control on shallow landsliding

Both rainfall intensity and duration take part in determining the hydrologic conditions favorable to the occurrence of shallow landslides. Hydrogeomorphic models of slope stability generally account for the dependence of landsliding on soil mechanical and topographic factors, while the role of rainfall duration is seldom considered within a process-based approach. To investigate the effect of different climate drivers on slope stability, we developed a modeling framework that accounts for the variability of extreme rainfall rate with the duration of rainfall events. The slope stability component includes the key characteristics of the soil mantle, i.e., angle of shearing resistance, void ratio, and specific gravity of solids. Hillslope hydrology is modeled by coupling the conservation of mass of soil water with the Darcy’s law used to describe seepage flow. This yields a simple analytical model capable of describing combined effect of duration and intensity of a precipitation episode in triggering shallow landslides. Dimensionless variables are introduced to investigate model sensitivity. Finally, coupling this model with the simple scaling model for the frequency of storm precipitation can help in understanding the climate control on landscape evolution. This leads to predict the temporal scale of hillslope evolution associated with the occurrence of shallow landslides. Model application is shown for the Mettman Ridge study area in Oregon, United States.