Detecting Abrupt and Gradual Changes in Water Quality Parameters at the Downstream Stations of Gotvand-Olia Dam

In this study, the trend of changes in water quality parameters of Karoon River was investigated at three downstream stations of Gotvand-Olia Dam using Mann-Kendall test. In addition, Theil-Sen test was employed to determine the slope of the trend line. Furthermore, two change point tests including Pettit and Lombard tests were used to detect the abrupt and gradual change point of quality parameters time series. The results of Man-Kendall test showed that apart from pH, all of the parameters were of a positive trend in the studied period 1985 to 2016. Notably, that 80% of the parameters had a significant positive trend. The results of the slope test showed that water quality in Karoon River has been decreasing in all the three stations. The results of Lombard and Pettit tests respectively showed that 76% and 96% of the parameters had a chance point. Moreover, the Lombard test detected that 20% and 63% of the parameters experienced abrupt and gradual changes, respectively. Hydrological conditions such as the droughts happened in the late 70's and the mid-80's can be mentioned as one of the reasons identified for the cause of the change point in the time series of parameters.