Role of Sub-Basins in Water Quality of Chehelchay River

Temporal and spatial routing of water quality is necessary for planning water resource management. The aim of this study was to determine the quality of water resources of Chehelchay River using NSFWQI index. Sampling of water was done monthly during a rainy year from October 2015 to September 2016 from five stations in the outlet of the sub-basins. Dissolved oxygen, total solids, nitrate, phosphate, temperature, biochemical oxygen demand, pH, turbidity, fecal coliform parameters were tested based on standard methods. The NSFWQI index was calculated based on the data obtained from the sampling procedure. Then, the water quality was spatially classified into five classes (from very bad to excellent) using ArcGIS software. The effect of each sub-basin on rate of water quality index was determined and sub-basins were prioritized according to the percentage of effectiveness. The results showed that water quality was varied from bad to good in different months according to NSFWQI. In different seasons of the year, the river was placed in the middle class in terms of water quality. The reasons of being located in the middle class in this category might be due to factors such as decreasing river flow in the summer, increasing recreational and leisure activities in the river boundaries, agricultural wastes and unprincipled cultivation in sloping lands, drainage of rural sewage, wastewater from fish breeding pool, and high density of livestock trapped in the region. Therefore, the issue of water quality in this river, according to the results of the present research, should be considered by managers and planners of water resources management in the State.