Rainfall thresholds for the occurrence of shallow landslides determined for slopes in the Nowy Wiśnicz Foothills (Polish Flysch Carpathians)

Abstract

Values of rainfall thresholds on selected shallow landslide slopes (Dzial, Gwoździec) located in the Nowy Wiśnicz Foothills are determined using a physically-based slope stability model considering a long-term period of analysis (GeoSlope Inc. software). Slope stability analysis included determination of the impact of rainfall on changes of stress state within the soil substrate and their influence on estimation of mass movement risk. The slope stability calculation results have shown that the rainfall threshold values are a function of many variables, primarily the hydraulic properties of soil and rock substratum, temporal distribution of precipitation, and soil moisture content conditions in the period proceeding rainfall. The results of the calculations indicate that, in extreme cases, accumulated rainfall threshold values for the same slope can range from ~100 to 500 mm. Estimated rainfall threshold values were lower than those values reported in the literature for the Polish Carpathians, but are similar to those determined by Guzetti et al. (2007) for Central and Southern Europe.