Comparison of hydrogeochemistry and hydrogeology of Asmari and Sarvak Formations as a reservoir of large karst springs of Zagros in the northeast of Khuzestan

Zagros Mountain, southwest Iran, includes karst springs with high discharge, so that the large springs in Iran are discharged from the limestone (Sarvak and Asmari formations) of this mountain. The hydrochemistry and hydrogeology of eight large springs located in the northeast of Khuzestan province, with an average discharge more than 1.5 m3/s  have been investigated from April 2018 to November 2019. Initially, the location of large karst springs in Iran has been determined based on the available data. The location of these springs in relation to distribution of karstic formations and digital elevation model (DEM) as well as the relationship between the average discharge, altitude and electrical conductivity have been investigated. Piper diagram has been used to determine the type of the spring water. The ion ratios and saturation indices were used to identify the dissolution intensity of carbonate rocks as well as water residence time in the karst system. The results show the relationship between the springs altitude and the electrical conductivity with the discharge is inverse. The predominant type of the spring’s water is HCO3-Ca and in some springs discharge frome Asmari  limestone is Ca-SO4 and Na-Cl due to recharge via Gachsaran Formation.The lack of significant change in the Mg2+/Ca2+ concentration in Sarvak springs indicates a long residence time in the karst system. The large springs of Sarvak and Asmari with high discharge (including Brahim Mardun, Chalshah Sarbazar, Sabzab, and Bibi Tarkhun) have large catchment area, the base flow is more than quick flow in most of the springs. The Keynow anticline is the richest aquifer with high dynamic reservoir in Zagros Mountain.