Spatial Modeling of Rain-Triggered Landslides

Almost all preparatory and triggering causal factors are well set in place in the case of Philippines to make its sloping terrains vulnerable to landslides; the history of landslide occurrences stands as foolproof evidence. A review of the past events however indicates that rainfall has, inter alia, been offering the triggering effect to cause most of the devastating landslides. A number of such landslides have occurred in the Southern Leyte province of Philippines causing considerable loss of life and damage to properties. Facilitating towards managing the associated landslide risk in Southern Leyte it was aimed at delineating the areas that are prone to rain-triggered landslides. The SINMAP model which combines a mechanistic slope stability model with a steady-state hydrology model was employed in way accomplishing this, much needed, task. Elevation data in the form of a raster GIS layer was the main input for the model. Mapping of past landslide initiation points was also completed with the aid of satellite based remotely sensed data and a GPS survey.The SINMAP model, with a careful attribution of the requisite geotechnical and hydraulic parameters, delineated 47% of the study area which is about 850 km2 to be unstable and quasi-stable under extreme rainfall events recorded in the past. This zonation of landslide hazard was considered to be very satisfactory as 82% of the total recorded landslides were found to fall in the unstable regions.