## 3 Results and Discussion
### LID Scenario Analysis and Benefit Evaluation  
#### 3.4.1 Simulation Effects of the LID Plans Under Different Structural Parameters  
According to the above analysis results, due to the highly comprehensive parameter sensitivity of the aquifer, the thickness and slope of the planting soil are significantly smaller, and the aquifer itself does not belong to the solid structural layer and the influence effect is similar to that of planting soil thickness, so the comparison and optimization design of runoff control benefits for the concave green space mainly focus on the latter two. Figure 4 shows the runoff characteristics of the green space and the hardened surface under the initial parameters (parameter disturbance rate 0) and the control hardened surface with disturbance rate of \(-10\%\) and \(10\%\) compared to the planted soil thickness and the planted soil slope of \(-10\%\) and \(10\%\) structural parameters under the precipitation scenario of the 1a recurrence period. As can be seen from Figure 4b,d, after the implementation of LID facilities, the real-time runoff of the overflow drainage outlet is significantly reduced, and  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Disturbance Ratio** & \begin{tabular}{c} **Positive Ideal Solution** \\ **Distance D+** \\ \end{tabular}  & \begin{tabular}{c} **Negative Ideal Solution** \\ **Distance D–** \\ \end{tabular}  & \ \begin{tabular}{c} **Relative Proximity C** \\ \end{tabular}  & \begin{tabular}{c} **Sort Result** \\ \end{tabular}  \\ \hline \(-30\%\) & 0.200 & 0.397 & 0.665 & 1 \\ \(-20\%\) & 0.381 & 0.234 & 0.381 & 7 \\ \(-10\%\) & 0.235 & 0.320 & 0.577 & 4 \\ \(0\%\) & 0.321 & 0.335 & 0.511 & 5 \\ \(10\%\) & 0.243 & 0.352 & 0.592 & 3 \\ \(20\%\) &the peak value is less obvious than that of the hardened surface. Moreover, the control effect of peak runoff when the planting soil thickness increases by 10% is better than when the planting soil thickness decreases by 10%, mainly because planting soil with greater thickness can absorb and store more runoff. The effect of runoff control is more obvious. For the disturbance of planting soil slope (Figure 4c,e), when the slope decreases by 10%, the effect of runoff flow control under LID is worse than that under the condition of 10% increase. However, by comparing the real-time flow characteristics under the conditions of the two hardened surfaces, it can be found that the average flow rate of the hardened surface under the mild slope is significantly lower than that under the condition of a steep slope. This is because, when the slope is slower, the runoff velocity of the surface of the planting soil (or hardened surface) is slower, and the flow into the overflow well and drainage pipe is also smaller. Due to the smaller flow rate, the runoff control benefits are not significant. Compared with Figure 4a, the concave green space under the default parameter structure shows the best benefit in terms of peak runoff reduction or peak delay, which is consistent with the TOPSIS analysis results. Figure 5 shows the cumulative rule of total runoff over time in the above five schemes. It is not difficult to see that, in terms of the total overflow, there is no significant difference in the runoff control benefits between the planted soil thickness of \(\pm\)10% and the planted soil slope of \(\pm\)10% (Figure 5b-e). However, the overflow value after the change of planting soil thickness is significantly greater than that after the change of default parameters and slope. The reason for this may be that the change in the thickness of planting soil (including the corresponding hardened surface) leads to the change in the hydraulic process of rainwater flowing into the overflow well, which leads to the increase in rainwater runoff speed and a significant increase in discharge.