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

Thesis (M.Eng.) - Asian Institute of Technology, 2006

This study was conducted to evaluate soil and water quality in a particular sub basin of Ping River Basin. The selection of a pilot sub basin in Ping watershed was done based on a number of criteria such as scoring approaches. It was found that Mae Rim sub basin has the highest soil erosion score and this was the main basis for selecting the basin for this study. After selecting Mae Rim sub basin, data on watershed, land use, soil, climate, topography, and crop were collected from relevant sources. These data were used as inputs to run the AnnAGNPS (Annualized AGricultural Non point Source) model in order to simulate soil and water quality in the selected sub basin. In evaluating soil and water quality using AnnAGNPS (a continuous simulation and distributed pollution model), a number of procedures which include identification, extraction, and processing of critical area data using an AreView Geographic Information System (GIS) was used. The 2 years of synthetic climate data were used to generate event and source accounting predictions for a multi-use 522 square kilometer watershed in Mae Rim pilot sub basin. Results show very high erosion in high slope areas in northern part of Mae Rim. Water quality parameters such as Nitrogen, Phosphorus, and Organic Carbon, on the other hand, were found to have concentration within acceptable limits. These results reflect that the quality of water is not a major concern at the site, at this time. However, in this study area, a great number of observed data are required for calibration and validation before using the model as a tool for development planning and management. So if further testing can be undertaken, the approach adopted in this pilot sub basin can be applied to other watersheds in Thailand