Evaluation of Thermal Stratification and Eutrophication in Zayandeh Roud Dam Reservoir Using Two-Dimensional CE-QUAL-W2 Model

Abstract

The purpose of this study was to investigate thermal stratification and eutrophication in the Zayandeh Roud Dam reservoir located in the central part of Iran using the CE-QUAL-W2 two-dimensional model. The model was used to simulate the temperature and water quality parameters of the reservoir from 2013 to 2015. The selected water quality parameters, which are effective in eutrophication, included nitrate (NO3), phosphate (PO4), dissolved oxygen (DO), and total phosphorus (TP). Model calibration and validation were done from October 2013 to January 2015, and the results showed an appropriate convergence between the simulated and observed data. Based on the simulated data, summer stratification in the Zayandeh Roud reservoir caused changes in water quality and anaerobic conditions of the hypolimnion. The reservoir eutrophication condition was investigated based on Carlson’s index, which indicated that the reservoir was in the eutrophic condition in most months of the year. In addition, two management scenarios, reduction of nutrients loads and reaeration of the hypolimnion, were evaluated to mitigate the eutrophication. The former can produce a mesotrophic condition while the latter needs excessive reaeration in order to decrease trophic levels and phosphorus concentration in the hypolimnion.