Seite - 496 - in Book of Full Papers - Symposium Hydro Engineering

The monitoring of the seasonal development and changes of the vegetation forms an essential part in the scope of this research study. Although the impact of vegetation on slope stability in mountainous regions are understood and documented, it is difficult to predict how vegetation will impact mass movement processes, such as landslides and mudflows. Vegetation helps to stabilize slope materials by improving the resistance of slopes to both, surficial erosion and mass wasting. Vegetation survival environments are correlated with slope failure- formational environments. Thus, assessments of the spatial distribution of damaged vegetation and its recovery conditions are important for determining susceptible terrain and surface materials to mass movement processes. The assemblage of trees and other vegetation growing above hillslopes plays an important role in intercepting slope materials and protecting them from the actions of sunshine, wind and rain. Vegetation, including the plant litter (leaves), helps stabilize the slope materials (1) by extensively altering the soil hydrology by reducing water loss and transpiration, intercepting raindrops and dissipating erosive energy and (2) by altering the mechanical and hydrological properties of the soil by affecting the developing root systems. Thus, vegetation improves resistance on slopes to surficial erosion and mass wasting, whereas the removal of slope vegetation tends to accelerate or increase slope failure. Gravity, flowing water, and temperature changes are the main (geomorphic) forces behind mass movement processes. The primary force that acts on mass movement is gravity. However, the substrate, environmental terrain and several additional factors can induce mass movement processes. Among these causative factors, vegetation affects the accumulation of slope material. The thickness of the material strongly affects the relative slope stability by supporting vegetation with stronger roots and influencing the effect of the subsurface on the overland flow. Hence, interactions between vegetation and materials affect mass movement processes (Zhang et al.,2015). Vegetation requires water, sunshine, nutrients and specific air temperatures. All of these factors are controlled primarily by the local topographical environment and material properties. Elevation influences the air temperature, slope gradient affects the groundwater conditions, slope aspect controls the sunlight duration, and materials provide the nutrients. The topographical conditions influence mass movement processes, such as rockslides, creep and landslides, by affecting the force balance of the surface materials and providing potential energy. The vegetation in the study area is mainly characterized by a grass, bush and low tree vegetation (Fig.3), whereby the vegetation is concentrated on the river terraces and in those flatter upper parts of the hills smoothened by glacial erosion. In the lower parts of the valleys debris flow, gully erosion, rockfall and landslides are leading to the decrease of vegetation occurrence and density. 496