Hydrological modeling of the Mun River basin in Thailand

Sources of pollution in river basins are increasing due to rapid changes in land uses and excessive nutrient application to crops which lead to degraded instream water quality. In this connection, the Mun River basin, one of the important and largest river basins in Thailand, has been studied. Comparative figures of nutrients in the Mun’s water over a decade showed an increased total nitrogen (TN) and phosphorus (TP) ratio in the Lower Mun region (TN:TP > 14). Laboratory analysis of weekly water samples showed a realistic nutrient response when daily rainfall was compared to the seasonal water quality data collected by the Pollution Control Department (PCD). The Hydrologic Simulation Program – FORTRAN (HSPF) was calibrated and used to assess the effects of different land uses on river water quality. Model parameters related to hydrology and sediment were calibrated and validated using relevant measurements by the Royal Irrigation Department (RID). With a reasonable and acceptable model performance (r2 = 0.62), the highest simulated runoff was observed in urban areas. The trend of agricultural land (as a percentage of total area) – total nitrogen showed a linear relationship of a good correlation (i.e. r2 = 0.85). Based on the findings, it can be concluded that this model is expected to provide vital information for developing suitable land management policies and strategies to improve river water quality.