A new method for determination of Most Likely Initiation Points and the evaluation of Digital Terrain Model scale in terrain stability mapping

P. Tarolli (1) , D. G. Tarboton (2)

1 Department of Land and Agroforest Environments
2 Department of Civil and Environmental Engineering

Physically-based models have been used previously to map areas of potential instability where shallow landslides may initiate. Here we introduce a new approach for determining the Most Likely Initiation Points (MLIP) for landslides. We identify the location with critical (lowest) stability index from a terrain stability model on each downslope path from ridge to valley. The SINMAP Stability Index (SI) was applied with this method. Only potential initiation points less than a threshold are considered to avoid identification of stable locations on downslope paths that do not contain any unstable locations. Mapped or observed landslides are often used to evaluate the effectiveness of model derived terrain stability maps, but a problem with these observations is that they may demarcate the entire landslide scar, including run out zones, rather than just initiation locations. Comparing such observations to SI does not provide a meaningful way to assess the effectiveness of the SI map because the demarcated area may include considerable area with stable SI values. In this paper we suggest using the relative density of MLIP locations within and outside demarcated landslide areas to assess the discriminating capability of a SI map. This approach was tested using landslides mapped from aerial photographs and airborne laser altimetry (LIDAR) derived elevation data for a small basin located in the Northeastern Region of Italy. Digital Terrain Models (DTMs) were derived from the LIDAR data for a range of grid cell sizes (from 2 to 50 m) and SI and MLIP evaluated for each. We found that the direct comparison of SI within and outside of landslides was not effective. However when MLIP was used we found appreciable differences between the density of MLIP points within and outside mapped landslides with ratios as large as three or more with the highest ratios for a DTM grid cell size of 10 m. This demonstrated the utility of the MLIP approach to quantifying the effectiveness of a terrain stability map when comparisons are to mapped landslides that include runout zones. This also suggests that in this study area, where landslides occurred in complexes that were sometimes more than 100 m wide, a DTM scale of 10 m is optimal. DTM scales larger than 10 m result in loss of resolution, while for DTM scales smaller than 10 m the physical processes responsible for triggering landslides are obscured by smaller scale DTM variability that is resolved.

Domaines: Interfaces continentales, environnement; Océan, Atmosphère; Sciences de la Terre

P. Tarolli, D. G. Tarboton. A new method for determination of Most Likely Initiation Points and the evaluation of Digital Terrain Model scale in terrain stability mapping. Hydrology and Earth System Sciences Discussions, 2006, 3 (2), pp.395-425. ⟨hal-00298671⟩