No abstract

Spatiotemporal water quality tendencies before and after total maximum daily load (TMDL) implementation in the Hangang basin were analyzed to determine the water quality improvement resulting from the TMDL policy. The periodicities of water quality indicators were also analyzed and water quality characteristics corresponding to different unit watershed units were identified in terms of pollution source. Considering five water quality indicators, including biochemical oxygen demand and total phosphorus, it was observed that water quality indicator concentrations were low in the upstream areas of the Bukhangang and Namhangang watersheds. However, they were high between the downstream areas of the Namhangang watershed and the Imjingang watershed and in the Hangang downstream and Jinwicheon watersheds. Additionally, the concentrations of water quality indicators in most of the unit watersheds where TMDL had been implemented decreased after TMDL implementation. However, increasing tendencies in the concentrations of water quality indicators continued to be observed in some of the watershed units in the upstream areas of the Bukhangang and Namhangang watersheds, possibly because these watersheds are affected by nonpoint source pollution owing to rainfall. Therefore, in the future, it would be necessary to implement policies that take these findings into consideration.

Objective: The objective of this study was to suggest a method through which load duration curve was used to assess the achievement of water quality targets in accordance with the criteria for pollutant load depending on flow rate variation. Methods: The stage-discharge curve and flow duration curve of Jungnang Stream were deduced. Using water quality targets and measurement of the stream, the flow duration curve was also drawn. Based on these, the feasibility of achievement of water quality targets in respect to flow rate was assessed. Results: In terms of the load duration curve of the stream, it was observed that excess of criteria for concentrations of BOD 5 , COD Mn and SS frequently occurred. On the other hand, when the flow rate was low, the concentrations of T-N and T-P exceeded the criteria. Conclusions: Through the load duration curve, the overall water quality of Jungnang Stream was understood. When the flow rate is high, management of point source of BOD 5 , COD Mn and SS is needed to achieve water quality targets for Jungnang Stream. On the other hand, when the flow rate is low, the management of non-point source T-N and T-P is necessary to attain the water quality goal.