Multi-objective optimization of sponge facility layout in built-up urban areas.

• A decision-making system of sponge facility allocation optimization is established; • The runoff coefficient grading of each sub-catchment area is analyzed; • The regression relationships between LID facilities and the control effects are built; • The layout of LID facilities is optimized and gray facilities are connected reasonably. In order to effectively cope with the destruction of natural hydrological cycle mechanism, frequent urban flood, serious water pollution and other problems, which are caused by the rapid urbanization process, the 'sponge city' concept has been widely used in China. This paper mainly focuses on how to rationally arrange the sponge grey and green facilities in built-up urban areas. With background analysis as the premise, model construction as the platform and swarm intelligence optimization as the method, the optimal proportion of sponge green facilities is determined. Furthermore, gray facilities are strengthened for the problem area, and the optimal allocation scenario of sponge facilities with the combination of gray and green is obtained through continuous circulation. The final results show that the optimal layout proportion of rain garden, sunken green space, permeable pavement and green roof are 3.88%, 7.95%, 2.01% and 0.99% respectively, which can meet the 80% runoff control rate and 40% pollution load control rate in the standard. Based on the simulation results of 50a rainfall, regulation and storage facilities are arranged near the severely overloaded node and the diameter of the overloaded pipes are increased. It can be proved that runoff and pollution can be effectively controlled and urban flood can be alleviated with grey facilities by model. The research results of this paper are expected to provide the overall idea and method of layout optimization of grey-green facilities for sponge city construction in built-up urban areas. [ABSTRACT FROM AUTHOR]