Vegetation effects on slope stability modeling in Cunha river watershed, Santa Catarina

Abstract

Landslides are natural processes that can cause environmental, social, and economic impacts. The identification and mapping of landslide prone areas are important procedures to watershed management. In this regard, slope stability models can help on these procedures. However, these models frequently neglect the effect of vegetation. This study presents a methodology that considers effects of vegetation in the factor of safety (FS) equation. To this end, parameters related to vegetation effect in slope stability were inserted in SHALSTAB model to verify its influence over landslides occurred in the Cunha River basin. The mechanical effects caused by vegetation added to the FS equation are root cohesion (cr), overload generated by vegetation weight (Sw) and shear stress caused by wind effects on tree canopy (Ve). Subsequently, we did a sensitivity analysis to identify which parameters have higher influence on the FS, adding the relevant ones to SHALSTAB formulation. We observed that crheightens slope stability and its influence is the most significant among the analyzed parameters, being higher in shallow soils and lower as soil depth increases. Sw reduces slope stability and wields more influence in shallow soils. Ve presented low influence on FS and was not added to SHALSTAB formulation. The FS equation proved to be sensitive on the slope to a minimum point, after this point the FS tends to vary little with the increase in the slope. The sensitivity of SHALSTAB to vegetation parameters was like the FS sensitivity. Thus, the vegetation influence on slope stability analysis proved to be relevant. Therefore, the modified SHALSTAB formulation proposed in this study can be useful to slope stability assessment in vegetated areas.