## 3 Results and Discussion
### Analysis of Model Optimization Results
#### 3.3.1 Optimized Drainage Network Layout and LID Measures  
(1) New Rainwater Main  
The drainage system in Wujin District is currently experiencing congestion in specific locations, particularly in the densely populated and economically active central residential zone and around the southern educational institutions. A new high-capacity stormwater trunk pipe is planned in these areas to enhance the drainage system's efficiency. The trunk pipe will be constructed along the main roads and connected to multiple branch pipes, thereby ensuring the rapid drainage of water during periods of heavy rainfall. The diameter of the trunk pipe will be 2 m, with a length of approximately 5 km. It will cover major waterlogging points and low-lying areas. An increase in the capacity of the main pipe will result in a notable enhancement of the drainage capacity of the area, which will, in turn, lead to a reduction in the frequency and severity of flooding. (2) Additional Branch Drainage  
Several additional drainage branch lines are intended to be incorporated into the existing drainage system, particularly in the eastern mountainous region and the western village area, where flooding is a recurrent phenomenon. The new drainage branch lines will be connected to the main pipe and extend to various low-lying areas, ensuring rainwater's rapid collection and discharge. The branch lines are designed with a diameter of 0.8 m and will span approximately 8 km. The rationalization of the layout of the branch pipes allows for the dispersion and direction of runoff more effectively, thereby reducing the pressure on the main pipes and improving the overall efficiency and reliability of the drainage system. (3) Construction of Rainwater Storage Ponds  
Two substantial stormwater storage tanks are scheduled for construction in the southwest lake and central park areas to store excess runoff during peak rainfall. The storage tanks will be connected to the surrounding drainage network and have capacities of 3000 and 2000 cubic meters. The construction of these storage tanks can effectively alleviate the drainage pressure caused by instantaneous rainfall, reduce the peak flow rate, and provide conditions for reusing rainwater resources. A filtering system and a plant purification zone will be installed in the storage tanks to ensure that the stored rainwater can gradually infiltrate and be purified, thereby reducing the impact on the natural environment. (4) Rain Garden  
In areas with high pedestrian traffic, such as educational establishments and business districts in the south, the installation of multiple rain gardens serves to mitigate the risk of internal flooding and enhance the aesthetic quality of the environment. Rain gardens effectively absorb and treat pollutants in runoff, utilizing the natural filtering effect of plants and soil while reducing surface runoff's quantity and velocity. The dimensions of each rain garden are approximately 200 square meters, and they are situated in the school playground, commercial district green space, and along the roads. The construction of rain gardens has the dual benefit of enhancing the area's aesthetic appeal while markedly reducing the rainwater collection rate, thereby mitigating the risk of internal flooding. The maintenance of rain gardens primarily involves routine tasks such as plant trimming, removal of debris and sediment, replenishment of much layers, and inspection of drainage systems. Over the long term, properly maintained rain gardens can function effectively for over 20 years. They reduce municipal stormwater management costs by mitigating runoff, enhance biodiversity through the creation of microhabitats, and contribute to the reduction of urban heat island effects by increasing green cover. However, without consistent maintenance, their infiltration capacity could decrease due to sediment clogging and their visual appeal could diminish. Permeable paving techniques are encouraged in roads and squares in the eastern mountainous region and the western village area.