Application of Shannon entropy in determining the most effective chemical parameter in surface water quality (Case study: Sofi Chay watershed)

Because of scarcity of surface water, consideration of water quality is a very important issue in Iran. Surface water quality monitoring and assessment is very expensive and time consuming; Therefore, finding a cheap, simple, and relatively exact method which can predict water quality would be very useful. In this study, Water Quality Index was used for measuring water quality. In order to monitor surface water quality and calculating the water quality, the data of six quality survey stations in SofiChay watershed during the period 1972-2012 were used. To determine the influencing parameter on the surface water quality within the watershed, the Shannon weight entropy method was used. Based on the amount of Shanon entropy and the calculated entropy weight, the effective parameter was evaluated in six stations: Tazekand, khormazard, Esfestanaj, Kahlikdarasi, Maragheh, and Khekan. The results indicated influencing parameters at the stations studied are pH, Mg, TDS, EC, and HCO3 respectively. Calculating the water quality index through using Shannon entropy indicated excellent quality of surface waters of the study area.