## 1 Introduction  
Uncertainty in rainfall patterns due to climate change, urbanization, and industrialization, water security in the urban area has been continuously and globally considered as an important issue. In modern urban pavement, bituminous materials such as asphalt and impervious materials, such as concrete, are used, and a continuous increase in the runoff coefficient was expected. Numerous studies have analyzed the increase of surface runoff and various problems resulting from it with statistical analysis results using water level, rainfall distribution, and population density known to increase the risk [1, 2, 3]. In particular, changes in urban runoff characteristics cause a decrease in the efficiency of existing rainwater drainage systems, which are known to be a representative cause of various urban water circulation problems due to a decrease in the groundwater level. Global warming due to the climate change can bring the anomalies in the precipitation in the world [4]. In particular, the annual change in rainfall in terms of rainfall intensity in South Korea from 1961 to 2003 was studied by [PERSON] et al. (2005). It was found that the rainfall intensity exceeding 20 mm/h gradually increases and the possibility of developing into a heavy rain further increases [5]. In addition, if the climate change and the increase of rainfall intensity continue, the total rainfall on the Korean Peninsula will continue to increase by the end of the 21 st century and it was predicted to increase by about 25% ([PERSON], 2018). The impervious land area in Korea has continuously increased over the past four decades, and it is now about 8.0%. Further, in Seoul, the biggest city in Korea, more than 54% of the area was impervious, so rainwater drainage efficiency was very low (Figure 1). Based on the statistical data for the last 7 years, it was also found that the impermeable area ratio of major cities has increased, except for some island areas (Figures 2 and 3). Figure 1: Increase of Impermeable Area in South Korea ([PERSON], 2018). Figure 2: Ratio of impermeable area and its changes for 7 years. (from 2013 to 2019) in major cities and provinces. Therefore, [PERSON] and [PERSON] (2014) conducted a research that the maximum outflow reduction effect of 15% of the total outflow volume and 18% of the peak flow could be expected by controlling the impervious pavement of application site [PERSON] and [PERSON] (2014). A rainwater drainage system must have the ability to respond to hydraulic, hydrological, and environmental issues, and problems that are compounded by continuous urban development and climate change. The currently installed conventional rainwater drainage system is a method of draining the surface runoff flowing along the ground surface through grating-type rainwater harvesting on the outside of sidewalks and roads. However, its efficiency was rapidly reduced, due to the illegal dumping of garbage, the inflow of floating debris, and the installation of illegal covers in commercial facilities, which is a structural disadvantage (Figure 4). Figure 4: Performance degradation of rainwater collecting trenches. (**left**: unexpected cover installation; **right**: cigarette butts in the grating chamber). Figure 3: Location of major cities and provinces in South Korea. In order to overcome the disadvantages of the conventional rainwater drainage system, an Infiltration Rainwater Drainage (IRD) system was developed, and various studies of evaluation and improvement were conducted. The IRD system was one which installed p IRD system was more efficient than the existing runoff reduction facilities because of its increasing infiltration rate. Such a result was a guaranteed application of IRD as part of runoff-reducing facilities. Therefore, the IRD system was expected to be viable for practical application with subsequent research for improvements [18; 19; 20; 21; 22; 23; 24]. [PERSON] et al.