## 3 Results and Discussion  
### Model Calibration and Verification Results  
The parameter range was determined based on the SWMM user manual and relevant studies in the surrounding area [61; 62; 63]. Rainfall data from four events, 20170610, 20170803, 20170808, and 20170925, were included to perform model hydrological and hydraulic parameter calibration. The model was verified using 10 actual rainfall processes measured from June to October 2016. A comparison of the measured and simulated results is shown in Figure 5.  
Figure 5: _Cont._As can be seen from Figure 4 and Table 3, the measured and simulated values during the calibration period are in good agreement. The Nash coefficient ENS between the simulated and measured values during the calibration period and the verification period is 0.69-0.96, and the absolute value of the total runoff error coefficient EQW is less than 0.30. The relative error of the peak flow rate EPR is less than 15%, indicating that the SWMM simulation constructed has high accuracy and the model is suitable for Wujin District, Changzhou City.  
Figure 5: Results of periodic field measurement and simulation.  
These findings align with [PERSON] et al. (2023) and [PERSON] et al. (2021), who demonstrated the effectiveness of GA for optimizing urban drainage systems. However, our study extends these results by incorporating LID measures, achieving a dual benefit of enhanced drainage efficiency and ecological sustainability [26, 39].  
The reduction in peak flood flow by 25.38% is particularly noteworthy, as it demonstrates the capacity of LID measures, such as rain gardens and permeable pavements, to delay runoff and mitigate flooding risks. This result supports the findings of [PERSON] et al. (2023), who highlighted the importance of LID in reducing urban runoff volumes [36].  
Integrating LID measures not only reduced surface runoff but also increased groundwater recharge by 17.32% and soil moisture content by 15.98%. These improvements are consistent with the findings of [PERSON] et al. (2022) and [PERSON] et al. (2017), who reported similar benefits from LID implementations in urban areas [45, 61].  
The comprehensive solution presents a compelling case for addressing the drainage issues in Wujin District, Changzhou City, offering a comprehensive and practical approach to resolving these challenges. The solution can effectively reduce the frequency of internal flooding and the maximum water depth, significantly improving drainage efficiency, controlling peak flow rates, increasing groundwater recharge, and improving the utilization rate of rainwater resources. In practice, although the implementation cost of this solution is relatively high, it would be essential to consider the long-term benefits. In densely populated areas with frequent economic activities, such as the central business district and educational establishments in the south, internal flooding will significantly impact daily life and the regular operation of economic activities. Implementing a comprehensive package of measures will significantly reduce the frequency and severity of internal flooding, thereby ensuring the safety of residents and commercial activities in the area.  
Additionally, the package is beneficial for the environmental sustainability of the ecological protection area. Through measures such as permeable paving and rain gardens, the area's ecological balance can be maintained, and the negative impact of human activities on the natural environment can be reduced. From a maintenance and long-term benefits perspective, the comprehensive package can effectively extend the service life of the drainage system and reduce the additional costs associated with frequent maintenance and upgrades.