Topographic Wetness Index and Terrain Ruggedness Index in geomorphic characterisation of landslide terrains, on examples from the Sudetes, SW Poland

Topographic Wetness Index (TWI) and Terrain Ruggedness Index (TRI) are secondary geomorphometric parameters used to describe and quantify local relief. In this paper their usefulness in geomorphological studies of landslides is explored. Using a sample of twelve objects from the Sudetes, SW Poland, spatial and statistical distributions of TWI and TRI values are presented and discussed. Both TWI and TRI prove capable of differentiating landslide population into smaller groups, consistent with their variable origin and mechanism of displacement. Considerable disruption of original slope surface during movement results in high TWI range values and low TRI values, whereas for translational rock slides and slumps the relationship is opposite. Spatial patterns of high TWI values help to identify lines of preferential drainage of a landslide body. Directional analysis shows that different types of displacement have their specific morphological signatures. Both TWI and TRI provide new information about landslide morphology and are recommended for use, especially to characterize depositional parts of landslides. The study is based on high resolution digital elevation model derived from airborne laser scanning (LiDAR) which proved useful in detailed characterization of landslide morphology.