LAUSR

Abstract Study region The karst system of the Syemareh Dam site with the reservoir capacity of 3.2 b m 3 , located in the Zagros fold belt, southwestern of Iran, was studied under two conditions: before and after the reservoir impoundment as pre-reservoir and post-reservoir conditions, respectively. Study focus Despite a mixing of several water resources including the dam reservoir contributed to the flow rate of the downstream springs, the number of end-members was still unknown and their mixing ratio was unquantified. In this study, firstly a statistical approach (e.g. loading plot and matrix plot) was utilized to identify possible chemical reactions. Then, End Member Mixing Analysis (EMMA) was used to determine the number of end members. Lastly, the MIX code was utilized to quantify the mixing ratios. Three scenarios (i.e. assuming three, four and five end members) were compared to find a reliable mixing model based on the best match between the observed and estimated values of species concentration. In order to improve the calibration of the reliable mixing model, the species concentrations were corrected by deduction of the effect of plausible chemical reactions. New hydrological insights for the region The five end-members mixing model consisted of three aquifers, deep groundwater, and the reservoir was suggested as the dominant mixing process. Leakage from the reservoir as an end member was quantified by calculating the mixing ratio of the reservoir through mixing modeling for the first time.