A multi-scale approach for deterministic analysis of landslide triggering and mass flow mechanism at Kaliasaur (Rudraprayag)

Landslides are multi-phase mass flows often triggered by incessant rainfall and pose a severe threat to infrastructure and human lives in mountainous regions. A high-quality landslide assessment for a vast geographic expanse is economically unviable. Therefore, this study proposes a multi-scale approach to identify potential shallow landslide zones for a large area using the Transient Rainfall Infiltration Grid-Based Regional Slope Stability (TRIGRS) model, followed by targeted landslide assessment of the resulting vulnerable area and subsequent mass flow using a multi-phase mass flow framework. Finally, a preliminary design of a protective structure implemented as a rigid barrier is carried out based on obstacle flow interaction. A recurring landslide site in Kaliasaur, Uttarakhand, India, is analyzed using a 12.5 m resolution Digital Terrain Model (DTM) from the public domain and resampled DTM of 1 m resolution obtained from the aerial survey using an unmanned aerial vehicle (UAV). Based on the analysis of a 3-day rainfall event, 25.43% of the total area was unstable, and the percentage of landslide ratio class (LRclass) for validation of TRIGRS model parameters was 65.62% which can be referred to as a moderate success rate. The failed mass flow from the unstable zones in Kaliasaur has a maximum height and velocity of 6.93 m and 27.1 m/s, respectively. A rigid barrier of height 10 m adjacent to a national highway (NH-7) reduced the flow velocity by 17.73% and stopped the mass flow satisfactorily. This research advocates a multi-scale approach landslide hazard assessment to build a resilient infrastructure against landslides.