Application of CE-QUAL-W2 model for simulation of water quality and ecological conditions in Doroudzan dam reservoir

This study presents the application of the CE-QUAL-W2 model to simulate the temperature, water quality, and ecological conditions of the Doroudzan dam reservoir, the primary drinking water source for Shiraz, Iran. Physicochemical and ecological water quality variables were collected from July 2019 to September 2020 with monthly and seasonal frequencies, respectively. The reservoir geometry was divided into 29 segments and 52 layers to reflect the hydrodynamic and water quality conditions of the reservoir within the simulation model. Key calibrated parameters are temperature and dissolved oxygen, with calibration performance quantified by mean absolute error and root mean square error values of respectively 0.73 and 0.84 °C for temperature, 1.21 and 1.37 mg/l for DO, and close agreement for phytoplankton and macrophytes. Results demonstrated a significant thermal stratification in the reservoir of the Doroudzan dam, characterized by a temperature difference of 15 °C within the water column. Comparative statistical analyses between the simulated and field observations revealed that the model accurately captured both spatial and temporal dynamics of water quality indicators within the deep reservoir. Additionally, the influence of nutrient loading on the reservoir eutrophication status was assessed using the tropic state index, which is equal to 56.1, demonstrating a eutrophic condition in the reservoir. Sustaining the reservoir’s ecological integrity and water quality requires proactive management to mitigate potential stressors and ensure the reservoir’s long-term functional stability.