Evaluate the effect Geo Hydrological drought on groundwater quality for agricultural purposes (Case Study: Marand plain)

Abstract Groundwater quality assessment is important for the management of the agricultural industry with the aim of using these resources in agriculture. Purpose of this research is studying the effect of decline the water table on groundwater quality of Marand plain using geographical information system (GIS) for water needed of Agriculture. In this research, successive periods of Hydrogeological drought were detected using SWI index in 6 periods (6, 9, 12, 18, 24 and 48 months) in Marand plain in West Azerbaijan. For this purpose, water quality data of 70 wells and monthly water levels data in 23 wells in the period of 2001-2011 was used. The maps were produced by kriging in Arc GIS software. Results showed that groundwater drought has not happened a in studied area randomly and its focus in the West of aquifer is more than the East. Results of study based on electrical conductivity (EC), Sodium Absorption Ratio (SAR) and Chlorine showed that water quality decreases from the center of aquifer toward its outlet so that at the end of aquifer , water quality become too salty. This situation is intensified in periods that are increased water withdrawal. Evaluation of water quality for agricultural purposes based on Wilcox diagram showed that in the drought 2010- 2011 of Marand plain about 44 percent of groundwater had more salty.