GIS APPLICATION IN DETERMINING BIOPHYSICAL FACTORS AFFECTING LANDSLIDE IN TAPL WATERSHED, NAKHON SI THAMMARAT

Abstract

Slope map, geology map, land-use map and drainage system map of two sub-watersheds, Klong Kratun and Klong Dindaeng in Tapi basin were, one at a time, overlayed on landslide map of the same area interpreted from Landsat taken on November 22, 1988 when devastated landslide and flood occurred in order to determine factors causing this natural hazard using GIS as a tool. Results reveal that of total slided area of 14.75 sq.km or about 6.19 % of study area, landslides were mostly occurred on slope 17° - 35° with granitic rock formation and covered by both forest and rubber plantation. Slided area increases with and increasing slope with maximum of 7.13 % of area having slope steeper than 35º. Granatic rock indicates the highest proportion of landslide with about 7.6 % of its formation followed by shale / slate and alluviam. Regarding vegetative cover, the largest proportion of slided area was found in rubber plantation (7.5 % of its area) followed by forest area (5.98 %). Gullies of stream orders seem to show less impact on landslide in this study area.