Scenario optimization of water supplement and outflow management in Yilong Lake based on the EFDC model

To address the problem of poor hydrodynamic conditions in Yilong Lake and to meet the water quality standards, the EFDC model was applied to propose an optimization plan for water supplement and outflow management of Yilong Lake. The model explores the impact of wind forcing, water supplement from external watersheds, outflow management and setting up an enclosure in the lake on the hydrodynamics in Yilong Lake. The results show that (1) the overall velocity of the water body of Yilong Lake is relatively slow, 90% of the area is lower than 0.01 m s−1, the central and eastern areas are faster and the western is slower. During the dry period and the wet periods of the year, improves the flow velocity of the water body in 90% of the area is increased by 80% compared to no wind velocity; (2) the increase in the amount of water supplement is significant for the improvement of the hydrodynamic conditions of water body; the water supplement volume at the two water supplement points of Mafangwan is conducive to improving the hydrodynamic conditions. If the total water supplement volume is increased by 10 million cubic meters per year which corresponds to water supplement volume increases at the Pubu and the Mafangwan by 33 and 35%, respectively, then water area with flow velocity greater than 0.007 m can be increased to 70%; (3) based on the demand for water quality, the water level management curves for different seasons are designed. It should be dominated by the eastern outflow, during the spring, coordinated by the southern and eastern outflows during the summer, and should be dominated by the southern outflow during the autumn and winter period.