GIS-aided Biophysical Characterization of Southern Leyte Landscape in Relation to Landslide Occurrences

This study was conducted in Southern Leyte to characterize its biophysical attributes, identify factors influencing landslide occurrences, develop a landslide database, and present recommendations for suitable land use. The major attributes of the province that were mapped using geospatial technologies (geographic information system, global positioning system, and remote sensing) were rock formations and fault lines, seismic occurrences, slope characteristics, elevation, soil series, vegetation/land use, and rainfall characteristics. Some soil properties of the landslide areas were also determined. The highest frequency (21%) of landslide occurrences in Southern Leyte was observed in Miocene–andesitic, basaltic, dacitic flows, and breccia geologic formation which is associated with the Leyte segment of the Philippine Fault. It occurred at angles greater than 18° and was at the highest frequency (54%) at angles greater than 50° in both concave and convex slope curvatures. Forest cover in Southern Leyte decreased from 53 percent in 1954 to 38 percent in 1992—a 15 percent drop in almost four decades. This further decreased to 14 percent in 2010, a 24 percent decline in approximately two decades since 1992. Current vegetation is dominated by cultivated crops, coconut, and abaca.

The province is mapped as slightly suitable (36%) to moderately suitable (51%), to suitable (13%) for coconut and abaca production. Slightly suitable areas are those found at higher elevation (> 600 meters above sea level) and steep slopes (> 50°), while those suitable are found at lower elevations and gentle slopes. Landslide inventory revealed a total of 52 landslide points. The highest number of occurrences was observed in San Francisco, Liloan, and San Ricardo, Southern Leyte. Landslides generally occurred at the ridges near the fault line. It is strongly recommended that the unsuitable zones be planted with trees and forest cover should be restored, if possible to 1954 level to enhance stability. Human settlement is strongly discouraged in the unsuitable zones and its immediate vicinity (approximately within the 8-kilometer run-out distance).