9. Shallow Landslide Hazard Mapping for Davao Oriental, Philippines, Using a Deterministic GIS Model

Davao Oriental located at 7°30′N and 126°50′E is one of the many landslide-prone provinces in the Philippines experiencing severe rainfall throughout the year. With the increase in population and other infrastructural developments, it is necessary to map the landslide potential of the area, to assure the safety of the people and delineate suitable land for development. In order to produce rainfall-induced shallow landslide hazard maps, Stability Index Mapping (SINMAP) was used over a 5-m interferometric synthetic aperture radar (IFSAR)-derived digital terrain model (DTM). SINMAP is based on the infinite slope stability model. Topographic, soil geotechnical, and hydrologic parameters (cohesion, angle of friction, bulk density, infiltration rate, and hydraulic transmissivity) were assigned to each pixel of the DTM with the total area of 5,164.5 km² to compute for the corresponding factor of safety. The landslide hazard maps generated using SINMAP are found to be accurate when compared to the landslide inventory from 2003 to 2013. The landslide susceptibility classification was translated to zoning maps indicating areas that are safe from shallow landslides, areas that can be built upon with slope intervention and monitoring, and the no-build areas. These maps complement the structurally controlled landslide, debris flow, and other natural hazard maps that are being prepared to aid proper zoning for residential and infrastructural developments.