Incorporating The Effect Of Root Systems Of Forest Species Into Spatially Distributed Models Of Shallow Landslides

In this paper, the stability model SINMAP was applied to a mountainous study area in order to include soil reinforcement exerted by root systems of forest species. Including root cohesion information in slope stability models, in fact, can lead to a better description of the shallow landsliding process and decrease the requirement for information on past landslides that is needed for model calibration. The study area is located in northern Italy (Lombardy Region) and was classified in seven forest regions with different species composition. A two-phase procedure was applied: first of all, a standard calibration approach led to a realistic and strongly-related set of parameters for each defined calibration region; secondly, multi-scenario criteria was applied in order to test different hypothetical sliding depths, with particular attention to root distribution profiles obtained from field surveys. A quantitative index (the Weighted Modified Success Rate) was used to test the results obtained by the stability model (both standard calibration and multiple scenario). The results showed that using forest categories to set up multiple calibration regions is very effective in standard calibration procedure. Moreover, potential sliding depth in each region was effectively identified at the depth where Root Area Ratio values fall below 0.1 % and the maximum available rooted soil cohesion is less than 5 kPa. In this way the multiple region calibration approach becomes feasible also when data on observed landslides are scarce and it can be used just to calibrate the hydrologic factor range.