Evaluation of Water Quality Changes in Zayandehroud River Using IRWQISC Quality Index

The examination of the quality of surface water, which is crucial for water supply, has attracted the interest of numerous researchers for a long time. Various indicators are employed to evaluate the quality of water in rivers, and among these indices is the Iran Surface Water Quality Index (IRWQISC).

In this study, water quality changes of Zayandehroud River located in Chaharmahal va Bakhtiari and Isfahan provinces were evaluated using IRWQISC yearly. Physicochemical parameters including BOD5, COD, DO, pH, EC, nitrate, phosphate, ammonium, temperature and total hardness were used to calculate the IRWQISC index in 7 selected stations for 12 years (2004-2015).

 Comparison electrical (EC) values in the stations showed that, EC increased from the upstream to the downstream of Zayandehroud River, and the concentration of parameters in the first station (Kouhrang tunnel) was much lower than the other stations in most years. The results of IRWQISC index showed that values was relatively good in all stations. The best and lowest water quality according to this index were good and moderate in 2006 and 2010 with the values of 73.2 and 49.6, respectively.

Overall, based on the twelve-year average of IRWQISC index, in the selected stations water quality was moderately good in Gharaghush, Cham-nar, Zamankhan Bridge, Kouhrang tunnel, Sudegan and Horeh stations, and was medium in Azadegan station. Identification of pollution sources and controlling inputted pollutants is necessary to protect and prevent the water quality decreasing of the Zayandehroud River.