## 4 Conclusions  
In this study, water quality and flow status were identified for the Gul-po stream, a stream subjected to the total maximum daily load (TMDL) program in the Han River system, using water quality concentrations and daily flow data as measured by the TMDL monitoring network. The outflow characteristics of the pollutants that flow into the Gul-po stream were analyzed by deriving the flow-pollutant load relationship and determining whether the target water quality was exceeded under various flow conditions through the load duration curve (LDC) to propose appropriate management measures for the pollutants introduced into the stream. The conclusions are thus as follows:  
1. When the water quality and flow status were analyzed for each year, it was found that the flow increased and the water quality improved in the upper and middle parts of the stream after 2018, under the influence of the ozone-treated reclaimed water supply project implemented in April 2019. T-N, however, increased rapidly after 2018, since the concentration in the treated water was higher than that of the stream water. In the middle part of the stream, the overall water quality was poor compared to the upper and lower parts. This appears to be due to the high population density and the untreated water discharged from livestock/agricultural farms and industrial complexes affected the water quality at the middle point in the Gul-po stream. 2. When the flow-pollutant loading equation was derived for each point, the flow index (b) values of BOD, T-P, COD, TOC, and SS were lower than 1 in the upper part, except for T-N, indicating that their concentrations decreased as the flow increased. The flow index value of T-N, however, was greater than 1. This appears to be due to the influence of ozone-treated reclaimed water with a higher T-N concentration than the stream water. In the middle and lower parts of the stream, the flow index values of the water quality characteristics, except for T-N, were greater than 1, indicating that their concentrations increased as the flow increased. In the lower part of the stream, in particular, the flow index values were higher than those in the middle part, showing that the influence of nonpoint pollution sources was large, since the water quality concentration increased rapidly along with the increase in flow. 3. The results of this study revealed that the upper part of the Gul-po stream is significantly affected by point pollution sources, while the middle and lower parts are affected by nonpoint pollution sources in nearby areas, even though the overall target water quality is satisfied. This indicates that different water quality management measures are required for each distinct part of the Gul-po stream. A comparison with the target water quality by basin under the implementation of phase 2 of the TMDL program (2021 to 2030) revealed that the total overage rate in the Gul-po stream increased, and that the overage rate was higher than 50% (depending on the flow section for each point), indicating the occurrence of sections that could not satisfy the target water quality. Therefore, it is necessary to supplement the current management plan by reflecting the pollution source characteristics for each point of the Gul-po stream, to ensure that phase 2 water quality targets can be achieved. This study conducted quantitative analysis of water pollution on nonpoint and point sources by applying LDC and flow-pollutant loading equations to urban rivers with highly polluted condition. In the future, if this research method is applied to more diverse urban rivers and comparatively evaluated, it is expected that it will be helpful in the management of river water quality. Conceptualization, J.-Y.J. and D.-W.J. ; methodology, J.-Y.J. and D.-W.J. ; formal analysis, J.-Y.J. ; investigation, J.-Y.J., D.-W.K., and Y.-J.C.; writing--original draft preparation, J.-Y.J. ; writing--review and editing, J.-Y.J. and D.-W.J. ; visualization, J.-Y.J., D.-W.K., and Y.-J.C.; supervision, D.-W.J.