Spatial monitoring and zoning water quality of Sistan River in the wet and dry years using GIS and geostatistics

Water quality and quantity is considered as one of the main pillars of sustainable development. On the other hand, rivers are regarded as one of the main and accessible resources that provide the human needs, that in addition to the water quantity, water quality is also one of the important determinative parameters. This study deals with spatial monitoring of chemical parameters of Sistan River water in the dry and wet years in order to follow the variations in the water chemical quality, determine the most suitable sites to extract potable water and irrigation, and optimize management of water resources in Sistan Plain. For this purpose, climate variables including monthly precipitations (1981–2010) were used to determine the index years of dry and wet together with the results of chemical decomposition of Sistan River water. First, mapping of the parameters of TDS, SAR, EC, Na, Ca, Mg, Cl, SO4 and HCO3 was done in GIS using Geostatistical methods, and then maps were classified according to international standards Wilcox and Schoeller. Finally, using the overlapping method, the river's water quality was determined to extract potable water and irrigation during the wet and dry years. The Wilcox standard results indicated that the quality of the Sistan River's water for irrigation during the drought period lies within the five classes of C3S2, C4S1, C2S2, C3S1and C4S2, and in the wet year period, it lies in the classes of C2S1 and C1S1. The Schoeller diagram results revealed that in the wet year period, the river's water quality is in the range of good and acceptable for drinking purposes. On the other hand, during the drought period, it is in the status of acceptable, moderate, unfavorable, and absolutely unfavorable, acceptable status, the highest percentage is allocated.