An Analysis of Soil-moisture Condition and Slope Vulnerability in Shiv-khola Watershed, Darjeeling, West Bengal

The slope instability of the Shiv-khola watershed, Kurseong Division, Darjiling is linked with periodical soil-moisture condition by estimating evapotranspiration following Penman, 1963 and Jensen, 1990 and surface run-off using SCS curve number (CN) technique of USDA, 1972. During May to October slope materials experience positive moisture balance. Maximum drying is experienced in early summer when soil becomes dry and the spring starts to be dormant. Easy and immediate drainage on slope makes the materials unstable and thus instability during monsoon becomes maximum when pore water pressure drives the saturated soil down slope through number of frequent landslides.