a b s t r a c tThis study used the United States Environmental Protection Agency's (US EPA) stormwater management model (SWMM) to quantify nonpoint source (NPS) pollutant load from the combined sewer in the Nakdong River basin, Korea. In the simulation using SWMM, the river basin consisted of 39 subwatersheds with 48 sanitation districts. For each sanitation district, combined sewer overflow (CSO) and bypass flow of the sewer treatment plant (STP) were estimated as NPS discharge. In the simulation, it assumed that a STP can receive up to three times the design peak flow rate of the STP and bypass the remainder of the intercepted stormwater during a storm event. The model was calibrated and validated with the observed water quantity and quality data in 2006 and 2007, respectively. As a result of the simulation, the estimated average load of biochemical oxygen demand (BOD) was 409.5 kg/ha/yr and 62.8 kg/ha/yr for the sanitation coverage (proportion of the area covered by the sewer system in a sanitation district) of above 40% and below 10%. The results showed that different unit loads of NPS can be estimated from each sanitation district depending on the degree of urbanization.

Recently, in urban areas, watershed management paradigms have changed the water cycle and water quality. This study explored the implementation of multiple low impact development (LID) facilities to improve the water cycle and water quality according to the paradigms. The study area was the Daeyeon campus of Pukyong National University, Busan. In this area, permeable pavement is installed in various LID facilities. In this study, a total of 35 optimal implementation plans of permeable pavement are presented. The suggested optimal designs confirm that the installation of a permeable pavement considering one purpose alone (for example, water quality improvement) does not satisfy the other purposes (for example, runoff reduction); in other words, such an installation is uneconomical. Therefore, this study proposes optimal installation designs for permeable pavements that can achieve multiple purposes (in this case, water quality improvement and runoff reduction) with a limited budget using the methodology suggested herein.