## 2 Materials and Methods
### Prototype Simulation
#### 3.3.2 Results of Prototype Simulation
Based on the maximum surface runoff and rainfall duration, the runoff of each model was shown in dimensionless form (Figure 20). As a result of the dimensionless comparison, it was possible to prevent the performance degradation of drainage facilities due to rapid surface runoff by applying the IRD system. In addition, it was found that the penetration pattern varies greatly depending on the design factor. The infiltration rate and surface runoff rate of each drainage system for total rainfall were calculated as shown in Table 10. Up to 71% of the precipitation applied to the design catchment area can be drained through infiltration with the IRD system. The detailed runoff, internal storage, and retention rates of each drainage system are compared as summarized in Table 11. In the case of Pr-PE1S10 designed with a simple drainage layer structure, the retention rate was simulated as 94.23%. The single drainage layer design was a relatively unfavorable condition for rainwater drainage compared to the complex structure design. As a result of simulation according to the permeability of the pavement when designing multiple structures, the highest total amount of infiltration was calculated as 1.11 m\({}^{3}\) for Pr-Pe2S10 due to the high permeability of the pavement. As a result of simulation of Pr-Pe4S10, Pr-Pe4S13, and Pr-Pe4S15, the infiltration amount decreased with the increase of the transverse slope. As shown in Table 9, this was identified as a phenomenon caused by an increase in the surface runoff with an increase of the cross-slope. Figure 19: Results with various permeability: (**a**) infiltration; (**b**) surface runoff. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Case No.**} & \multicolumn{2}{c}{**Maximum Infiltration**} & \multicolumn{3}{c}{**Maximum Surface Runoff**} \\ \cline{2-6}  & \(Q\) **(m\({}^{3}\)/s)** & \(t\) **(s)** & \(Q\) **(m\({}^{3}\)/s)** & \(t\) **(s)** & **Reduction Ratio (\%)** \\ \hline Pr-Pe2S10 & 0.0019 & 80 & 0.000567 & 587 & 78.4 \\ \hline Pr-Pe3S10 & 0.0018 & 101 & 0.000720 & 600 & 72.2 \\ \hline Pr-Pe4S10 & 0.0021 & 112 & 0.000393 & 600 & 81.2 \\ \hline \hline \end{tabular}
\end{table} 
Table 9: Results of permeability variation. As a result of the overall simulation, the displacement was plotted with respect to time. As a result of the simulation, it was found that the outflow characteristics changes according to the design factors of the IRD system. The maximum inflow rate reduction effect of more than 50% was found when the IRD system was applied (Figure 21). The maximum peak flow reduction rate was compared to the existing drainage system. The deviation of peak flow according to the design factor was 13% according to the structure, 10% according to the permeability, and 12% according to the slope. In other words, the deviation due to the structure of the drainage system was the most significant. The IRD system with a single structure drainage layer stores 99.4% of the total rainfall inside due to the permeability of the drainage layer. The reduction rate of peak discharge was shown in Figure 22. Compared to the case of Pr-PE0 Sl0 (impervious pavement case), all the cases of the IRD reduce peak flow. The desirable reduction of the peak can be achieved combining cross section slope and permeability. \begin{table}
\begin{tabular}{c c c c c c c c} \hline
**Case No.** & **Infiltration** & **Drainage Block** & **Drainage Hole** & **Drainage Soil** & **Storage** & **Storage Ratio** \\  & **(m\({}^{3}\))** & **(m\({}^{3}\))** & **(m\({}^{3}\))** & **(m\({}^{3}\))** & **(m\({}^{3}\))** & **(\%)** \\ \hline Pr-Pe1 Sl0 & 0.52 & 0 & 0.013 & 0.0170 & 0.490 & 94.23 \\ Pr-Pe2 Sl0 & 1.11 & 0.097 & 0.018 & 0.0170 & 0.980 & 88.29 \\ Pr-Pe3 Sl0 & 0.988 & 0.067 & 0.030 & 0.0260 & 0.310 & 31.37 \\ Pr-Pe4 Sl0 & 0.92 & 0.011 & 0.022 & 0.0190 & 0.872 & 94.78 \\ Pr-Pe4 Sl3 & 0.755 & 0.010 & 0.019 & 0.0159 & 0.697 & 92.31 \\ Pr-Pe4 Sl5 & 0.756 & 0.010 & 0.019 & 0.0157 & 0.711 & 94.04 \\ \hline \end{tabular}
\end{table} 
Table 11: Comparison of storage capacity.