Water Quality Evaluation of Tigris River by using Canadian and Horton Water Quality Index

Water quality index (WQI) is a simplified and explicable number calcuated from data on tested prameters in water. In this study, two methods for calculating water quality index (WQI) were used to assess the water quality of Tigris River using monthly data from 2011 to 2013. The data were collected at four different gauging stations. Two gauing stations are located on Tigris River at upstream in Mosul city while the other two downstream gauging stations are located on Tigris River at downstream in Al-Amarah city. The Canadian Council of Ministers of the Environment’s (CCME WQI) and Horton (Horton’s WQI) methods were applied to assess the water quality of Tigris River at the selected stations. The data used in the assessment included several parameters such as calcium (Ca), magnesium (Mg), sodium (Na), potassium (K), chloride (Cl), sulfate (SO4), bicarbonate (HCO3), nitrate (NO3), total dissolved solid (TDS), biochemical oxygen demand (BOD5) and electric conductivity (EC). According to the values of CCME WQI mehod, the quality of Tigris River in Mosul city was at a good level (the values of WQI were varied from 83 to 94) while it and falls under the marginal category in Al-Amarah city (the values were varied from varied from 52 to 59). However, the application of Horton’s WQI method showed that the quality of Tigris River in Mosul city was fluctuated from excellent to good (values of WQI varied from 24 to 80 per month) while it was poor in  Al-Amarah city (values of WQI varied from 74 to 160 per month).  In conclusion, the Horton’s WQI method was found more relastic when used to  assess the water quality of Tigris River compared with CCME WQI method.