Seasonal contributions and efficiency analysis of green-gray-blue coupled infrastructures system for the improvement of water quality in urban lakes

Rapid urbanization changes the water cycle in urban areas, which exacerbates pollution and ecological degradation in water bodies. This problem can be effectively addressed by green-gray-blue infrastructures system, of which water transfer project and sponge city project are two key strategies, but have never been placed together as a system. Therefore, taking Dong-Sha Lake basin in Wuhan, China as an example, this research aims to investigate the potential of green-gray-blue infrastructures system composed of water transfer project and sponge city project to improve urban lake water quality, in which their seasonal performance and efficiency are innovatively discovered, and the annually efficient operation schemes are proposed. The SWMM model and MIKE 21 model are utilized for simulation. The results indicate that the green-gray-blue solution can reduce the total nitrogen (TN) concentration in urban lakes by 40 %–60 % annually, with water transfer project functioning in dry season and sponge city project functioning in flood season; the inlet-outlet arrangement and diversion discharge are primary factors influencing the performance of water transfer with the closer distance to inlet or outlet and the larger discharge contributing to the higher pollutants removal rate but perhaps less efficiency; the green infrastructures (GIs) paving area is the main index of sponge city projects; when its portion reaches 50 %, the TN concentration in urban lakes can be reduced over 50 % annually. The research provides an excellent example of green-gray-blue system to address urban water quality issues, with a particular focus on the combination of water transfer and sponge city projects.