# Research on Ecological Lawn Regulation and Storage System in Flight Area Based on Sponge Airport
## 2 Modeling of Rainwater System in Research Area
### Generalization of Rainwater System  
The SWMM is used to generalize the rainwater system in the airport flight area based on the rainwater pipe network data provided by the airport and fieldwork on the rainwater pipe network. The airport flight area is divided into two runways, east and west, and currently mainly operates on the west runway. This paper mainly focuses on the simulation and analysis of the west runway. The study area has a relatively small catchment area, and the changes in land type before and after construction are straightforward. Additionally, comprehensive data on the region's drainage network and topography are available, which allows for the use of manual delineation methods to divide the sub-catchments. Using the airport flight area construction blueprints, the area and width of each sub-catchment were determined. Elevation data, satellite maps and land use type information were utilized to establish the Manning's coefficient, depression storage, impervious area ratio and slope of each sub-catchment. Furthermore, the rainwater drainage network diagrams and corresponding data provided necessary parameters such as the length, dimensions, starting and ending depths and slopes of the drainage pipes. After manually delineating [12] the sub-catchments accurately, the processed data were imported into the SWMM (stormwater management model) for modeling. This approach ensures that the model reflects the physical characteristics and hydrological dynamics of the airport flight area accurately, allowing for the precise simulation of stormwater runoff and management. In the model, the ponding collection points in the catchment area are generalized as nodes, and the drainage open ditches and covered blind ditches are generalized as pipelines. The drainage outlets, pump stations and reservoirs are consistent with their actual locations in the airport flight area. A total of 161 sub-catchment areas, 74 nodes, eight drainage outlets, 81 sections of sewers and two reservoirs are generalized (Figure 2).  
This paper adopts the method of calibrating the model parameters using the runoff coefficient [13; 14] and verifying the calibration parameters based on the measured rainfall and waterlogging statistics of a certain scene [15]. Referring to the relevant literature, the following value ranges of the parameters are set: the roughness coefficient of the impermeable area is 0.011-0.024 [16], the roughness coefficient of the permeable area is 0.060-0.240 [17] and the roughness coefficient of the pipe is 0.009-0.0150 [18]; the storage capacity of the impermeable area and depression are 1.50-3.50 mm and 2.54-7.62 mm, respectively [14]; and the maximum and minimum infiltration rates are 72.00-78.00 mm/h and 3.18-3.82 mm/h, respectively [19], with an attenuation constant within 2-7 /h. By calibrating the parameters, two rainfall processes with return periods of 3 years and 5 years are simulated, with the simulated runoff coefficients of 0.66 and 0.70, respectively. According to the GB 50014-2021 [20], the numerical simulation values meet the comprehensive runoff coefficients of the research area within the range of 0.6-0.7. The SWMM of the research area is stable and has the required accuracy.  
Figure 1: Present situation and problems in the airport flight area.