GIS-aided biophysical characterization and assessment of a landscape in relation to landslide occurrences

This study was conducted in the watersheds of St. Bernard, Southern Leyte to determine and identify the major factors influencing landslide occurrences and make recommendations for suitable land use. The major attributes of the watersheds that were mapped using geospatial (Geographical Information System)(GIS), Global Positioning System (GPS) and remote sensing (RS) technologies were: rock formation and fault lines, seismic occurrences, slope, Digital Elevation Model (DEM), and vegetation and land use. Slope Stability Index Mapping (SINMAP)in GIS environment was used to locate areas in the watershed that are prone to landslides. The data inputs to run the model are DEM, location of actual landslide initiation points (7 points; identified using SPOT image-5 m resolution taken in 2008, and ASTER image-10 m resolution taken in 2006 which were used as reference in the model) and geotechnical parameters (ex. soil density). Important output from SINMAP is a digital slope stability index (SI) map showing areas that are less prone to landslides (SI values 1) and areas that are less prone to landslides (SI values 1) or the unstable zones. The unstable zones constitute 33% of the total land area of the watersheds. These are found at the ridges near the fault line and at high elevation with slope angles 50 deg. It is strongly recommended that the unstable zones of the watershed should remain as protected zone and should be planted with trees to enhance slope stability. This research site is mapped as having moderately suitable (38%) to suitable (50%) for abaca and moderately suitable (44%) to suitable (53%) for coconut production. Moderately suitable areas are found at higher elevation ( 600 m asl) and slope angle 30 deg while suitable areas are found to lower elevations and gentle slopes. Human settlement is strongly discouraged in the unstable zones and its immediate surrounding vicinity (approximately than the 4 km run-out distance).