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An analysis of the impact of a low impact development (LID) on runoff was performed using a Storm Water Management Model 5 (SWMM5)-LID model. The SWMM5 package has been developed to facilitate the analysis of the hydrologic impacts of LID facilities. Continuous simulation of urban stormwater runoff from the district which included the LID design was conducted. In order to examine the impact of runoff in the LID district the first, second and third highest ranked flood events over the past 38 years were analyzed. The assessment estimated that a LID system under historical storm conditions would reduce peak runoff by approximately 55-66% and runoff volume by approximately 25-121% in comparison with that before the LID design. The impact on runoff was also simulated under 50, 80 and 100 year return period conditions. Under these conditions, the runoff reductions within the district were estimated to be about 6-16% (peak runoff) and 33-37% (runoff volume) in comparison with conditions prior to the LID. It is concluded from these results that LID is worthy of consideration for urban flood control in future development and as part of sewer and stormwater management planning.

At present, the development in rainwater management approach is still insufficient due to the numerous adverse effects of urbanization. Storm water management is being developed to restore the natural state of water cycle undergoing several processes which were hindered such as infiltration and evapotranspiration. Low Impact Development (LID) was established in order to reduce the negative effects of urbanization to our environment. These developments can be used to respond to the effects of climate change such as heat island phenomenon. The effects of the development of new town in the district plan with application of LID facilities were studied and reported. Typically, LID facilities were applied in small scale development and were rarely used in large-scale development. Most of studies, however, did not assessment the effects of large-scale development projects with LID application to the natural water cycle. This study was conducted to simulate the urban hydrologic cycle simulation on Asan-Tangjeong in Korea. This study may be used in urban hydrologic cycle simulation and establishment of an urban water management plan in the future. Lastly, this study generated a model using the recently updated SWMM5 which determined the hydrologic cycle simulation after installation of LID facilities.

a b s t r a c tThe installation and maintenance costs, as well as non-point pollution reduction efficiency of LID facilities, should be reflected to design and apply LID facilities. In addition, when considering the characteristics of LID facilities installed in a spatially distributed way, efficiencies and costs associated with installation locations of LID facilities should also be reflected in the design. In this study, the optimal design method of multiple bioretention cells is proposed with a focus on considering both cost and non-point pollution (TP) reduction efficiency. EPA SWMM is applied to simulate bioretention cells in the target catchment, and an interaction module between MATLAB and EPA SWMM is constructed to optimize multiple objective functions. The target catchment is the Daeyeon Campus of Pukyong National University at Busan, South Korea, and a total of 140 bioretention cells design alternatives are searched to obtain optimal design solution. As a result of comparing the three design alternatives based on the cost, it is shown that the proposed method can find the optimal design layout for a total design capacity of bioretention cells and install locations in accordance with the given budget.

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