Ecological and navigational impact of the construction and operation of the Qingyuan dam

Dam construction has important impact on the ecological environment and navigation conditions of a river. Therefore, evaluating the degree of impact of such engineering constructions and seeking the optimum management are vital. This study considered the example of the construction of the Qingyuan Dam on the Beijiang River (China). The flow condition was calculated using a two-dimensional hydrodynamic model, and a habitat suitability model and navigation risk indicators were used to conduct quantitative assessment of the impact of different scenarios. The spawning ground habitat of Megalobrama terminalis was taken as an ecological measurement index. The gray correlation analysis method was used to quantify the influence of four flow indexes (i.e., water surface slope, backflow, flow velocity, and water depth) on navigation safety. The simulation results showed that construction of the Qingyuan Dam had serious negative impact on the ecological environment in the dry season, but that dry season navigation conditions have been improved greatly. Following construction of the dam, with increase in the Feilaixia Hydro-junction discharge, the ecological and navigable usable area both first increased and then decreased. With comprehensive consideration of the usable area and the spatial distributions of habitat suitability and navigation risk, when the Feilaixia Hydro-junction discharge is 3000 m3/s and the water level in front of the Qingyuan Dam is 10 m, the ecological and navigation benefits of the studied river reach were determined to be optimal. These research results could provide guidance for the management of the Feilaixia–Qingyuan river section, and help deliver optimum ecological and navigational benefits.