A Modelling Approach for Flooding Effects on Water Quality of Zarjoob River Using HEC-RAS

Floods have direct impacts on the organisms of rivers and indirect impacts on ecosystems of rivers. In this study we perform a water quality model of the zarjoob river by Hydrologic Engineering Center-River Analysis System (HEC-RAS) model, specifically for Carbonaceous Biochemical Oxygen Demand (CBOD) , Dissolved oxygen ( DO ) and nitrite ( No2 ) based on the hydrodynamic simulation for normal and flood condition  to determine the extent of pollution loading in the river. Results showed that trend of dissolved oxygen in flood conditions was reversed compared to dry conditions and showed a slight increase along the river. Downstream of zarjoob river on flood condition, whenever the BOD decreased, DO concentrations increased from 5.5 mg/L to 6.2 mg/L, indicating that water quality was not as sensitive to variations of the BOD as expected. This study showed that rainy events were important environmental factors positively affecting aeration, which raised the dissolved oxygen content of the Zarjoob River except for nitrite. This paper is the first report of the innovative use of HEC-RAS model Without the help of accompanying qualitative analysis models such as Qual2K, WASP … to simulate water quality in an urban river.