Drought effects on surface water quality in Golestan province for Irrigation Purposes, Case study: Gorganroud River

In this study, a part of the Gorganroud basin was selected to evaluate of the drought effect on 13 water physicochemical parameters. After collecting meteorological and hydrometric stations data in a period of 43-year (1350-1393), a 5-year drought index was determined using the standard precipitation index and moving average method. Then, the water quality parameters were obtained for a long-term and a drought period using the available hydrometric stations data. The average concentration of most of anions and cations, electrical conductivity, and sodium adsorption ratio have increased from upstream to downstream, so that, this increase in the downstream station is about seven times higher than its upstream station in the drought period. The average of anions, cations, electrical conductivity, and sodium absorption ratios were increase during the drought period compared to the long-term period. Using the Wilcox diagram, agricultural water quality is decreases in the direction of river flow, so that the water category changes from C2S1 (suitable for agriculture) in the upstream to C4S3 (harmful to agriculture) in the downstream. Therefore, it can be concluded that the occurrence of drought periods has a significant effect on the water quality factors in comparison with the long-term period, so that, the agricultural water quality drastically has reduced by a decrease in rainfall and subsequently decrease in river discharge within the drought period.