Thesis (M.Sc.)--Chulalongkorn University, 2000

QUAL2E-UNCAS was used to study Nakhon Nayok river water quality. Five simulated water quality parameters consist of Dissolved Oxygen (DO), Biochemical Oxygen Demand (BOD), ammonia nitrogen (NH3_N), nitrite nitrogen (NO2_N), nitrate nitrogen (NO3_N), dissolved phosphorous (Dis_P), and temperature. In order to get critical area of Nakhon Nayok river, water quality parameters were simulated during dry season, i.e. October-April. DO, BOD, Nitrogen Cycle, Phosphorous Cycle, and Temperature calibration results between water quality data of years 1993-1999 which are obtained from PCD and field survey data taken on December 8, 2000, It was found that all simulated water quality parameters show the good agreement with measured values, while water level and flow from simulation agree with measured ones only at upstream. In addition, GIS was used to visualize critical area. Study on uncertainty analysis makes one realize the respond of output to input. It can beused to plan the using of model to further study on water quality.