Developing-site specific spatial and systems model of landslide susceptibility index (LSI): the case of Gen. Nakar-Infanta, Quezon [Philippines]
Abucay, E.R. | Magcale-Macandog, D.B. | Espaldon, M.V.O. | Monsalud, F.C., Philippines Univ. Los Banos, College, Laguna (Philippines)
Landslides are responsible for the considerable loss of agricultural production, infrastructure and lives in the entire world aggravated by increased urban development, landuse change and abnormal weather (rainfall). Successive typhoons hit Infanta-Gen. Nakar area form November 13, 2004 to December 03, 2004 causing floods and lanslides. This study attempted to develop a site-specific landslide susceptibility index (LSI) model using Geographic Information System (GIS) for spatial analysis and STELLA for dynamic systems modeling. Landslide prone areas were sampled and analyzed for soil texture, atterberg limits and Cation Exchange Capacity (CEC). Random household experiences and the possible causes of landslide in the area. Landuse maps were generated from 2002 and 2008 Terra Look satellite images. Modeling was done thru GIS and STELLA. Result of the soil survey and analysis showed that the soil in the study area is generally deep to very deep (lm), red clayey soils, low-medium clay activity (CEC=16.45 cmol (+)/kg) and increasing plasticity index (PI) with increasing clay. In the span of six years (2002-2008) drastic change in landuse of the case study site was observed resulting in 52.27% reduction in forest cover, increase in annual crops, coconut mixed with crops and shrubs and built-up areas, respectively. The spatial landslide susceptibility model showed that as 24-hr total rainfall reaches 150 mm, susceptible and highly susceptible areas increased by 37% and 110%, respectively. The site-specific LSI systems model also reveals that changes in vegetation accompanied by unusually high 24-hr total rainfall had high susceptibilities. Susceptibility to landslides is greatly affected by vegetation, geophysical characteristics and climatic conditions. On the other hand, human activities (e.g. charcoal making) indirectly affect landslide susceptibility thru removal and change in vegetation cover.
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