GEOSPATIAL TECHNOLOGY BASED SOIL LOSS ESTIMATION FOR SUSTAINABLE URBAN DEVELOPMENT OF BUTWAL SUBMETROPOLITAN CITY, NEPAL
Geo-spatial technology was attempted to estimate the potential and actual soil loss and its correlative interpretation with physiographic soil units and land use and cover types in Butwal sub-metropolitan city, Central Region of Nepal. Among several empirical and physically based soil erosion models, widely used RKLS and RKLSCP, Revised Universal Soil Loss Equation (RUSLE) were employed to estimate the potential and actual soil loss in the present investigation, respectively. Five years of rainfall, topographic contour-spot height and soil map were basically used as source of information for in-depth investigation. Butwal sub-metropolitan located at foothill of Chure/Siwalik range was found highly sensitive or prone to soil erosion. A total of 32.68 and 1.83 million tons soil was potentially and actually estimated annually being lost from the city. Erosion rates were found highly correlated with the slope of physiographic soil unit. 60.93% of the total potential soil loss was mainly contributed only by physiographic-soil unit 12 with the spatial extent of 34.10% of the city area. This unit was characterized by steeply to very steeply sloping mountainous terrain having dominant slope greater than 30° and loamy skeletal as dominant soil texture. Significant difference was found in the estimation of RKLS and RKLSCP indicating the substantial reduction contribution of soil loss by land use/cover types predominated by forest. after agriculture. Thus physiographic-soil unit 12 having soil loss highest must be given higher priorities for soil conservation and optimum urban land use planning required for sustainable urban development. Lower percentage of actual soil to the potential loss indicated the fact of contribution of cover management and erosional control practice factor in reducing soil erosion in existing situation.