Investigation of changes in water quality parameters in Zayandehrood Dam basin

The fresh water resources are limited in the world and their distribution is heterogeneous. In the other hand industrial establishment and dam construction decrease the quality of these limited resources, so the monitoring of water quality is necessary and unavoidable. There are different methods for consideration of water quality changes (statistic tests, regression, time series, multivariate methods…). In this study, monthly time series of water quality parameters (Cl-, HCO3-, pH, EC, SAR, SO4) are used for study of Zayandehrud water quality. For this purpose, procedure presented by Box & Jenkins were used for modeling which contain three stages, including model recognition, parameter estimation and control of estimated parameters. For all parameters in six hydrometric stations, ARIMA, ARMA, AR, MA, multiplicative or seasonal models were obtained. After modeling pH, Cl- and HCO3- were forecasted from August 2005 up to August 2011 and the percentage of error was calculated. The lowest percentage of error was obtained for pH parameter (5%). In additional to modeling, the correlation between the river discharge and other parameters was calculated and it was distinguished that discharge has negative correlation with all parameters except pH in Eskandari station. The mean of discharge in twenty years’ period showed that Ghaleh Shahrokh station with 44.57 m3/s has the highest and Varzaneh station with 6.015 m3/s has the lowest mean of discharge.