A thesis submitted in partial fulfillment of the requirements for the degree of Master of Engineering.

Thesis (M.Eng.) - Asian Institute of Technology, 2000

Erosion Productivity Impact Calculator (EPIC) was applied in a rainfed agricultural terraced watershed in Nepal. Performance of EPIC in simulating runoff, soil loss, nutrient loss and crop growth was evaluated. EPIC could predict daily runoff within 35 % of observed values for rainfalls greater than 30 mm. For smaller rainfalls, variations in predicted results were more. There was also wide variation in observed and predicted peak runoffs by more than 50%. Based upon size and intensity, rainfall events were divided into three categories to predict soil losses. Those were small (less than l 5mm), moderate (15 - 30mrn) and high (more than 30 mm). USLE could predict erosion loss from moderate rainfalls within 25 % of observed values. However, for higher rainfall events, USLE underpredicted soil losses. Based upon average annual soil loss from the watershed, the model was calibrated and soil losses were predicted for different scenarios of management practices. For simulation of nutrient loss, information on annual losses of Nitrogen and Phosphorus was taken from a research study carried out in the area. Predictions were made on N and P losses by runoff, and effects of applying organic residues and chemical fertilizer (Urea) on Maize yield. Longterm simulations were carried out for 50 years to assess the effects of erosion on crop productivity. It was found that there would be gradual decline in productivity and relative productivity will reach to 0.90 after 50 years.