Modelling the effect of Nature Based Solutions on slope instability

In the framework of the OPERANDUM (OPEn-air laboRAtories for Nature baseD solUtions to Manage environmental risks) project, modelling the effect of the Nature Based Solutions (NBS) on selected open-air laboratories plays a determinant role. In this work, we focus the attention on the Vögelsberg (Tyrol, Austria) landslide case study, located in the municipality of Wattens. The 0.25 km² active part of the slope shows annual movement rates in the order of 3.5-6 cm/a. Recent studies provided evidence that the motion is mainly driven by variations of the groundwater level. The latter are related to prolonged moist periods during which excessive rainfall or snow melt water can infiltrate and act on the geo-hydrological system. With the aim of enhancing the slope stability employing NBS, a detailed analysis of the hydrogeology and the slope characteristics have been carried out, obtaining the required technical parameters describing the involved soil material. Furthermore, a slope stability analysis by means of different numerical models has been performed. Results prove that variations of the groundwater level in the range of 1-2 m can strongly affect the stability of the slope. Thus, specific NBS should aim at reducing the amount of infiltrating water. Examples of such NBS include the adaptation of forest management and land use planning, the introduction and re-activation of drainage channels and the sealing of leaky streams and channels. Beside the effects of the variation of the groundwater level, results have proved that the slope could fail under the action of a moderate seismic load. In this scenario, it is likely that the effects of the NBS would be insufficient to maintain the slope intact.