Application of SWAT Model for Hydrologic and Water Quality Modeling in Thachin River Basin, Thailand

The Soil and Water Assessment Tool (SWAT) model was examined for its applicability in modeling flow, sediments and water quality parameters in upper Thachin River Basin, Thailand covering an area of 5,693 km2. The calibration of flow, sediments, and water quality parameter have shown satisfactory results with R2=0.77 and ENS coefficient = 0.78 for monthly flow calibration. The monthly flow validation values for R2 and ENS were 0.8 and 0.79, respectively. Calibration of sediments and water quality parameter were poor due to the non-availability of time series data. Sensitivity analysis showed that curve number is the most sensitive parameter to surface runoff, evapotranspiration and sediment yield and consequently to total water yield. Soil evaporation compensation factor and average slope length (SLSUBBSN) were most sensitive to evapotranspiration and sediment routing, respectively. Muskingum routing factors (MSK_X, MSK_CO1 and MSK_CO2) were also found sensitive to average monthly flows. The study concluded that SWAT model has huge potential in studying hydrology of watersheds even under data scarcity. An adequately calibrated model can be employed for studying land use change scenarios and probable climate change impacts on basin hydrology depending on availability of data.