Urbanization changes natural pervious surfaces to hard, impervious surfaces such as roads, buildings and roofs. These modifications significantly affect the natural hydrologic cycle by increasing stormwater runoff rates and volume. Under these circumstances, green roofs offer multiple benefits including on-site stormwater management that mimics the natural hydrologic conditions in an urban area. It can retain a large amount of rainwater for a longer time and delay the peak discharge. However, there is very limited research that has been carried out on the retrofitted green roof for stormwater management for South Korean conditions. This study has investigated the performance of retrofitted green roofs for stormwater management in a highly urbanized area of Seoul, the capital city of Korea. In this study, various storm events were monitored and the research results were analyzed to check the performance of the green roof with controlling the runoff in urban areas. Results also allowed us to conclude that the retention mainly depends on the intensity and duration of the rain events. From the analysis, average runoff retention on the green roof was 10% to 60% in different rain events. The application of an extensive green roof provides promising results for stormwater management in the highly urbanized area of Seoul.

Green blue roof has the potential to reduce the surface temperature of the building in the urban areas. Green blue roof is a new innovative low impact development (LID) practice that has exhibited an option to mitigate the heat island phenomena in urban area. This is the modified form of green roof that has ability to store rainwater in vegetation, soil layer and increases the evapotranspiration rate which decreases the temperature of an area. For this purpose, green blue roof is installed at the Cheong-un middle school building roof, Seoul, Korea. During the different time scenarios the surface temperature from the green blue roof and control roof were analyzed and their results were compared with each other. The results revealed that the surface temperature of green blue roof was much less as compared to control roof under same climatic conditions. From the results it is also concluded that surface temperature value of green blue roof was less than 5°C to 9°C as compared to control roof.

Low impact development (LID)/green infrastructure (GI) practices have been identified as the sustainable practices of managing the stormwater in urban areas. Due to the increasing population, most of the cities are more developing which results in the change of natural area into impervious areas (roads, buildings etc.). Moreover, urbanization and climate change are causing many water-related problems and making over cities unsafe and insecure. Under these circumstances, there is a need to introduce new stormwater management practices into developed cities to reduce the adverse impacts of urbanization. For this purpose, retrofitting low impact development practices demands more attention to reduce these water-related problems and trying to make our cities sustainable. In developed areas, there is a little space is available for the retrofitting of LID practices for the stormwater management. Therefore, the selection of an appropriate place to retrofitting LID practices needs more concern. This paper describes the successfully applied retrofitting LID practices around the globe. It also includes the process of applying retrofitting LID practices at the suitable place with the suitable combination. Optimal places for the retrofitting of different LID practices are also mentioned. This paper also highlights the barriers and potential solutions of retrofitting LID practices in urban areas.

For the past few decades, rapid urban development and climate change has caused many meteorological disasters (flooding, droughts, and heat waves) in South Korea. The current stormwater management system (gray infrastructure) is based on the pipe networks, which is not an effective method to control flash flooding problems during big rain events. Therefore, there is a need to find a more sustainable stormwater-management system that can have the ability to solve these water-related problems in urban areas. Low-impact development (LID)/green infrastructure (GI) practices are an effective approach to solving the adverse effects of urbanization and to addressing climate change. This paper reviews national water-management policies which were selected for flood and environmental protection from 1960 to 2017. Research results of applied LID practices in Korea also show that these practices are useful for stormwater management in urban areas. The dominating challenges identified are: lack of proper knowledge for implementing LID practices; uncertainties in the benefits of LID/GI practices; and lack of cooperation and collaboration between different agencies for the expansion of LID projects. Finally, some opportunities for LID/GI practices in Korea are also described.

This field study elaborates the role of grass swale in the management of stormwater in an urban parking lot. Grass swale was constructed by using different vegetations and local soil media in the parking lot of Mapu-gu Seoul, Korea. In this study, rainfall runoff was first retained in soil and the vegetation layers of the grass swale, and then infiltrated rainwater was collected with the help of underground perforated pipe, and passed to an underground storage trench. In this way, grass swale detained a large amount of rainwater for a longer period of time and delayed peak discharge. In this field study, various real storm events were monitored and the research results were analyzed to evaluate the performance of grass swale for managing rainfall runoff in an urban area. From the analysis of field experiments, grass swale showed the significant rainfall runoff retention in different rain events. Grass swale markedly reduced total rainfall runoff volume and peak flow during the small storm events of intensity about 30 mm/h. From the analysis, on average rainfall runoff retention from the grass swale was found around 40 to 75% during the various small rain events. From the results, we can say that grass swale is a stormwater mitigation practice which can help avoid flash flooding problems in urban areas.

Permeable pavement is an effective low impact development (LID) practice that can play an important role in reducing rainfall runoff amount in urban areas. Permeable interlocking concrete pavement (PICP) was retrofitted in a tremendously developed area of Seoul, Korea and the data was monitored to evaluate its effect on the hydrology and stormwater quality performance for four months. Rainfall runoff was first absorbed by different layers of the PICP system and then contributed to the sewage system. This not only helps to reduce the runoff volume, but also increase the time of concentration. In this experiment, different real rain events were observed and the field results were investigated to check the effectiveness of the PICP system for controlling the rainfall runoff in Songpa, Korea. From the analysis of data, results showed that the PCIP system was very effective in controlling rainfall runoff. Overall runoff reduction performance from the PCIP was found to be around 30–65% during various storm events. In addition, PICP significantly reduced peak flows in different storm events which is very helpful in reducing the chances of water-logging in an urbanized area. Research results also allow us to sum up that retrofitted PICP is a very effective approach for rainfall runoff management in urban areas.