## 1 Introduction  
Since the 1960s, the amount of pollutants introduced to streams has increased due to the increase in wastewater discharge caused by rapid urbanization and industrialization. In general, pollutants introduced into streams from watersheds can mainly be classified into point pollution sources, which constantly come from specific places, and nonpoint pollution sources, which normally exist over large areas and then discharged into streams along with surface runoff during rainfall. Nonpoint pollution sources are difficult to quantify because their discharge is different depending on topographical conditions, the characteristics of the watershed, land use type, and hydrological conditions [1, 2, 3, 4, 5, 6]. To address this problem, the Ministry of Environment (ME; Rep. of Korea) implemented the total maximum daily load (TMDL) program on the Nakdong River in 2004. Since the water quality and flow are measured simultaneously by the TMDL monitoring network, unlike the conventional water quality monitoring network, it is possible to quantify the pollutant load from the flow [7]. The TMDL program of South Korea is managing to achieve the target water quality at the reference flow, which involves specific flow conditions averaged over the past decade. Therefore, there is a limitation for managing the water quality using TMDL for the various flow conditions [7]. In recent years, the pollution of water bodies has been analyzed, and the effect of flow fluctuations on water quality has been investigated using the load duration curve (LDC), which considers various flow conditions for the entire stream [8]. Through analysis of the pollutant load, research on the water quality of urban streams has been conducted in various ways. Numerous studies have identified the sources of pollution in simple and indirect ways using the relationship between flow and pollutant load. [PERSON] et al. analyzed the changing characteristics of the water quality in the Gyeon-gan stream for ten years and investigated those characteristics using the flow-pollutant load relationship [9]. [PERSON] et al. evaluated the organic matter load contained in the streams flowing into Masan Bay using the flow-pollutant loading equation and thus classified the pollution sources of each stream [10]. [PERSON] et al. investigated the outflow characteristics of pollutants subjected to the TMDL program and the degree of water quality deterioration by section and season under flow conditions, using discharge and water quality data in the Seomjin River [7]. Studies have also been conducted using LDCs. [PERSON] et al. investigated the water pollution load according to discharge conditions using an LDC for the major tributaries of the Nakdong River; in addition, the location and period for water quality management were suggested [11]. [PERSON] et al. found regions that preferentially require the management of nonpoint pollution sources and proposed a method for setting management goals, mainly for the four major rivers in Korea, by creating an LDC and evaluating the water quality characteristics for each flow condition [12]. [PERSON] et al. calculated the TMDLs for ammonia to evaluate the water quality upstream of the Taoxi River in the Taihu Basin in China and conducted research on the analysis of water quality characteristics using LDCs to quantify monthly and seasonal variations in TMDLs [13]. [PERSON] et al. conducted research on the application of the LDC method for the management of water pollution in the Yuanhe River, a tributary of the Ganjiang River, which itself is a tributary of the Yangtze River [14]. [PERSON] et al. presented an alternative for estimating the coliform load reduction at various locations in the Piranga and Piracicaba basins using the LDC method [15]. As in the previous studies, LDC has been used in various ways to evaluate the water pollution load of rivers in space and time. In addition, it is suggested to be highly useful as a major analysis method for river water quality management.