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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.

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.

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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.

a b s t r a c tGreen storm water infrastructure (GSI) or low impact development (LID) is an alternative land development approach for managing storm water close to the source that has been recommended instead of the traditional storm water design. The main purpose of LID is to reduce the impact of development on water-related problems through the use of GSI practices such as bioretention, green roofs, grass swales, and permeable pavements that infiltrate, evaporate, or harvest and use stormwater on the site where it falls. In recent years, more research has been carried out on GSI practices and the use of these practices has shown magnificent benefits in stormwater management. LID techniques have been successfully used to manage stormwater runoff, improve water quality, and protect environmental and hydrological aspects of the developed areas. Bioretention cells have been effectively used in retaining large volumes of runoff and capturing pollutants on site. Pervious pavements have been extremely effective and efficient at infiltrating stormwater on site and storing large quantities of rainwater. Sand ditches are a new water harvesting technique that is being used to significantly reduce runoff, soil loss and sediment loss and to increase infiltration. This paper highlights evidence in the literature regarding the beneficial uses of LID practices and encourages adopting these practices for environmental friendly construction and sustainable development in the world. In the end, some of recommendations for the implementation of LID practices to achieve multiple benefits are given.

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