Studying the Effects of Point Source Pollution on Water Quality in River-basin Scale based on Hydrological and Water Quality Model, SWAT; Seymareh River-Basin as a Case Study

The abundance of phosphorus, nitrogen and sediment loads in the watershed affected by point and non-point pollution sources due to agricultural activities, animal breeding, urban and industrial development have led to increasing threats to surface water resources in the country. In this research, the spatiotemporal hydrological, sediment and nutrients modelling of water resources has been developed in SWAT environment for the Seymareh River-basin. The SWAT model performances in simulating the flow rate, sediment, and nutrients in different hydrometric and water quality monitoring stations have been evaluated using statistical indicators R2 (correlation coefficient) and NS (Nash-Sutcliffe). The SWAT model calibration and validation was accomplished by SWAT-CUP tool and SUFI2 technique. According to SWAT model results, the NS coefficients in various hydrometric/monitoring stations for calibration stage are more than 0.51, 0.53, 0.52, and 0.47 respectively for flow rate, sediment, total nitrogen (TN), and total phosphorus (TP). The results demonstrated that the complete removal of the phosphorus loads in 5 important point contaminant sources will reduce the average phosphorus concentration from 1.34 mg/L to 1.14 mg/L in the monitoring point (river basin outlet). Furthermore, the effects of Kermanshah City sewage on water quality degradations in the Seymareh control point are dominant in comparison to other pollution point sources. Non-point pollution sources (agriculture drainage, animal breeding, and soil erosions) have significant contribution in water quality deteriorations in the Seymareh River-basin compared to point sources