HR: 0800h
AN: H51C-0377    [Abstracts]
TI: A New Method for Determination of Most Likely Initiation Points and the Evaluation of Digital Terrain Model Scale in Terrain Stability Mapping
AU: * Tarolli, P
EM: paolo.tarolli@unipd.it
AF: Dipartimento Territorio e Sistemi Agro Forestali, University of Padova, Agripolis - Viale dell' Universita, 16, Legnaro, PD 35020 Italy
AU: Tarboton, D G
EM: dtarb@cc.usu.edu
AF: Utah Water Research Laboratory, Utah State University, 4110 Old Main Hill, Logan, UT 84321 United States
AB: Physically-based models have been used previously to model and map the spatial distribution of shallow debris slides, and areas of potential instability. Here we use the SINMAP stability index (SI) defined as the probability that the factor of safety is greater than 1. We introduce a new approach for determining the most likely initiation point (MLIP) by identifying the grid cell with critical (lowest) stability index on each downslope path from ridge to valley. 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. The accuracy of models depends on the quality of input variables, in particular the digital terrain model (DTM) from which many of the input variables for terrain stability models are derived. In this paper we use airborne laser altimetry (LIDAR) derived elevation data for testing the effect of different DTM grid cell size resolution on the modeling of shallow landslides in a small basin located in the Northeastern Region of Italy. Physically based models quantify the potential instability at each location. Because in our study area the mapped landslides included landslide runout zones 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. 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. 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 the highest ratio of MLIP between within to outside mapped landslide areas for a grid cell size of 10 m. This 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 processes that become resolved.
DE: 1810 Debris flow and landslides
DE: 1815 Erosion
DE: 1819 Geographic Information Systems (GIS)
DE: 1826 Geomorphology: hillslope (1625)
SC: Hydrology [H]
MN: Fall Meeting 2005