4. Surface Run-off, Soil Erosion and Slope Instability

The dynamic nature of a landscape results from the interaction of surface run-off with rocks and soil being guided by geo-hydrologic variables. The estimation of surface run-off and its better understanding reveals a clear idea about the degree and amount of surface erosion and slope vulnerability over the space. In this chapter Soil Conservation Service (SCS) Run-off Curve Number (CN) model proposed by United State Department of Agriculture (USDA 1972) is used to determine the surface run-off from six individual sub-watersheds for predicting the periodical spatial distribution of slope instability and soil erosion. The determined Curve Number (CN) under antecedent moisture condition-III (AMC-III) for sub-watershed I, II, III, IV, V and VI are 85.02, 73.52, 87.36, 87.76, 85.57 and 89.85 respectively. Sub-watershed I contributes maximum run-off from a rainfall of 90.5 mm (4,52,359.4 m³) which is followed by VI, III, IV, V and II. Landslide Potentiality Index Value (LPIV) is derived for each watershed which reveals that Sub-watershed I and VI is the significant landslide prone unit of the study area. Finally, considering both run-off and LPIV an instability scale has been made which reveals that Sub-watershed VI, I and III have to be paid more attention for a proper management of land, water and soil during the months of July, August and September. All the necessary constructions, plantation and related preparedness through raising awareness and making task forces during pre-monsoon dry period are of utmost importance for managing landslip and soil erosion at Shivkhola Watershed.