## 4 Conclusions  
In this research, urban flood experiments were conducted using the rainfall simulator. The rainfall simulator was designed to demonstrate rainfall intensity in range of 80-200 mm/h, and the full cone nozzle was adopted to spray uniform raindrops. The uniformity of rainfall distribution was tested by measuring the volume of rainwater for a single nozzle and entire nozzles. The single nozzle test results showed that the rainfall intensity was identically reproduced in all nozzles, and the rainfall intensity decreased by distance from the center point in a Gaussian-like distribution. In the case of the entire nozzle tests, even though the spatial distribution of rainfall intensity shows some irregularities, the uniformity coefficient shows 89.2%, which was satisfied highly recommended standard.  
Using the rainfall simulator, flood experiments were conducted in the 1/200 scale model of the Sadang station by changing the rainfall intensity. The model has limitations that the sewer systems were neglected, and small buildings were grouped as a block. Thus, the measured inundation depth in the model tended to be overestimated compared to the real flood that occurred in 2011. The experimental results show that the rainwater mainly accumulated in the eastern part of the crossroad in which the entrances to the subway station are located. The flooded water in the crossroad flowed to two main roads that connect the crossroad and the relatively small road across the residential area. The flow velocity and inundation depth noticeably increased until the rainfall intensity reached to 160 mm/h and then slowly increased in the higher rainfall intensity.  
The quantitative analysis according to change of rainfall intensity was conducted by comparing inundation depth and runoff velocity at representative points. The runoff velocity at Roads A and B significantly rose between 80-160 mm/h, while the inundation depth slowly increased. In the case of the subway station entrance, the inundation depth at the entrance No. 1 shows the highest values, and the results indicate that a cut-off wall is necessary to prevent rainwater flowing into the underground space. Furthermore, the vulnerabilities of human activities during flood events were evaluated using the moment and the friction instabilities. The analysis results show that human activities at point 1 located on Road B are the most vulnerable compared to other areas because the inundation depth and the runoff velocity exceeded the instability boundary of 160 mm/h. From these results, the Sadang area is required to prepare the sewer systems or underground storages to endure a flood exceeding 160 mm/h rainfall intensity. Furthermore, city development strategies need to pursue a decrease in impermeable areas.  
Conceptualization, D.S.R.; experiments and analysis, H.S. and I.P.; writing--original draft preparation, H.S.; writing--review and editing, I.P.; supervision, D.S.R.; project administration, D.S.R. All authors have read and agree to the published version of the manuscript.  
This research was funded by the Korea Institute of Civil Engineering and Building Technology.  
Figure 10: Plots of the instability boundary against to inundation depth and runoff velocity.  
**Acknowledgments:** This research was funded by the project \"Effects of and solutions for the sophisticated urban geometric characteristics on the increased urban flooding damages\" of the Korea Institute of Civil Engineering and Building Technology.  
**Conflicts of Interest:** The authors declare no conflict of interest.