Application of mathematical model for the dilution of waste water from land utilization in the upper tha chin watershed, Thailand

The objective of this study was tomathematicalmodeling development for generating the water storage capacity necessary to dilute waste water from land utilization in the Upper Tha Chin Watershed (UTCW) within three scenarios: existing land use condition, expected land use change in the year 2020, and regulating water storage to dilute Biochemical Oxygen Demand (BOD). The Soil and Water Assessment Tool (SWAT) model was applied in order to estimate the amount of the streamflowand BOD based on the observed land use and water release data from the reservoir, from January, 2013 to December, 2014 as presented in Scenario 1. The reliability of the model was calibrated with the observed data by adjusting the coefficient of the key parameters through SWAT calibration uncertainty procedures (SWAT-CUP) and validating the observed data from seven hydrologic stations. The simulating the impact of land utilization in the year 2020 in Scenario 2, and the drainage simulation of the Krasiao reservoir on BOD in Scenario 3. The results obtained from the SWAT model found that in Scenario 1 indicated that the streamflow was 374.74 million cubic meter (MCM) and BOD was 2.70 mg/L. The simulation of Scenario 2, forecasting the expected land use change in year 2020, showed that the amount of the streamflow decreased to 65.09 MCMand BOD was 2.70 mg/L; when compared with Scenario 1. The simulation of Scenario 3, regulating water storage for diluting waste water, found that BOD during the dry season of December, January, February, and March was 3.08, 3.24, 1.52, and 2.70 mg/L, respectively; and a decrease to 1.50 mg/L with an increased drainage of the Krasiao reservoir. This study shows that the SWAT model successfully stimulated and assessed the effects of land use activities on streamflow, sediment, and BOD; including the successful drainage of the Krasiao reservoir in both watershed and sub-watershed areas.