Shrestha, Sangam creator Babel, Mukand Singh Chairperson Gupta, Ashim Das Examination Committee Clemente, Roberto S. Examination Committee Zoebisch, Michael A. Examination Committee Danish International Development Agency (DANIDA) Scholarship donor The Government of Denmark Scholarship donor text series technical report th Pathum Thani, Thailand Asian Institute of Technology 2004 continuing eng 135 leaves Agricultural non-point source pollutants especially sediment and plant nutrients pose a significant threat to water resources and management. Best Management Practices (BMPs) can be used to reduce the impact of these pollutants, however this requires full understanding and analysis of effectiveness of the alternative practices. Watershed quality models are the most cost-effective tools to aid in decision making process of selecting the BMPs that is most effective in reducing the pollutant loads. The main objective of this study is to apply the Annualized Agricultural Non-Point Source Pollution (AnnAGNPS) model to assess the watershed quality and evaluate the effectiveness of BMPs for sediment and nutrients loading reduction in the Masrang Kho la Watershed in the Siwalik Hills of Nepal. AnnAGNPS simulations are compared with two years of field observations from the study watershed. The model underestimates the runoff volume by 15% during calibration phase and 22% during validation phase whereas the peak flow is overestimated by 2.5 times more during calibration phase and 4 times more during validation phase. However, the relationships between simulated and observed runoff volume and peak flows are highly correlated. Runoff underestimation is attributed to the method of land cover discretization. The comparison of simulated and observed sediment yields demonstrate that the model is not best suited for short-term individual event sediment production. This is due to the use of Revised Universal Soil Loss equation (RUSLE) within AnnAGNPS, and parameters associated with determining soil loss are derived from the long-term average annual soil loss estimates. The simulation results indicate the croplands are the most critical areas for soil erosion as well as nutrient loading. Among the four BMPs (Mulch tillage, 2-year crop rotation of Maize-Soybean-Maize-Soybean, Mulch tillage with 2-year crop rotation of Maize-Soybean- Maize-Rice, and 2-year crop rotation of maize-Soybean-Maize-Millet) analyzed, the results indicate that the 2-year crop rotation of Maize-Soybean-Maize-Millet is most promising in reducing sediment and nutrients loading. A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science Thesis (M.Sc.) - Asian Institute of Technology, 2004 Watersheds Nepal Asian Institute of Technology. http://203.159.5.9/ait-thesis/detail.php?q=B09121 http://203.159.5.9/ait-thesis/detail.php?q=B09121 041006 20260817162951.0