Numerical simulation of Dissolved Oxygen as a water quality indicator in artificial lagoons—Case​ study El Gouna, Egypt

Abstract

Dissolved oxygen (DO) is one of the most significant environmental indicators of water quality. Preservation of reasonable DO concentrations is essential for a healthy aquatic life. In this research, numerical simulations of DO concentrations were discussed using TELEMAC-WAQTEL-O2 model. Firstly, the model was verified by comparing its results to analytical solutions in different 1D and 2D cases considering pulse and constant DO injections. Based on the very good agreement between the model and analytical results in different simulation scenarios, the TELEMAC-WAQTEL-O2 model has proven its ability to be applied to more complex cases. Consequently, this model was applied to investigate El Gouna artificial lagoons in Egypt under the effect of different weather conditions including tide, mean and maximum wind and different water temperatures. Investigating the water quality of El Gouna lagoons is important to monitor negative anthropogenic impacts to protect the lagoons and the nearby Red Sea coast. Negative effects of effluents from a nearby desalination plant on DO concentration were discussed considering different brine discharges, DO concentrations of brine discharge, injection times and weather conditions. This study presents one of the few systematic DO studies on artificial lagoons considering hydrodynamics and water quality issues. The results show a decrease in DO concentrations affected by high water temperatures. Further, the lagoons’ hydrodynamic has a relevant impact on DO concentrations, e.g., tide wave induced DO concentrations to increase and decrease following a sinusoidal wave. Also, winds affect the DO propagation as low DO concentrations are obtained near the inflow boundaries. The outcomes demonstrate that DO concentrations depend on the lagoons’ hydrodynamics, DO’s production and consumption rate and tracer transport. The polluted water with low DO concentrations flowing from the desalination plant followed the wind direction. Besides, different quantities of binary and different injection times have minor effects on DO concentrations in the lagoons.