ANALYSIS OF TOPOGRAPHIC CONTROL OF SHALLOW LANDSLIDING USING A PHYSICALLY-BASED MODEL

M. Borga, G. Dalla Fontana (DTeSAF, University of Padova, AGRIPOLIS, via Romea, 35020 Legnaro, Padova, Italy), L. Marchi (CNR-IRPI, C.so Stati Uniti 4, 35020 Camin, Padova, Italy)

A model for the topographic influence on shallow landslide initiation, previously proposed by Montgomery and Dietrich (1994), is applied on a mountainous study basin where high-resolution digital elevation data are available: the 5 km2 wide Cordon catchment, located in North-eastern Italy. The model is composed of two parts: a steady-state model for shallow subsurface runoff and an infinite-slope, Coulomb failure model which assumes that the soil is cohesionless at failure. Subsurface runoff increases pore pressures in the soil, reducing the effective normal stress and consequently the strength of the soil. The model is intended to be simple and delineates those areas most prone to shallow landsliding due to surface topographic effects on hydrologic response. An inventory of a number of landslide scars is used to document sites of instability and to provide a test of model performance by comparing observed landslide locations with model predictions. Furthermore, in this communication we assess how grid size affects derived topographic attributes and model results and the effects of introducing a multiple-direction flow partitioning algorithm instead of a single direction algorithm.