Analysis of the Pollution Load Contribution Rate of Inflowing Tributaries for the Sustainable Management of the Seomjin River (Seombon D)

The total maximum daily load (TMDL) system divides the watershed into unit basins for implementation and evaluates water quality by assessing whether targets have been achieved based on investigated data through continuous monitoring. River water quality is influenced by the amount and type of pollutants entering the river, making continuous monitoring, along with analysis and evaluation, essential for the ongoing development of policies and systems aimed at improving water quality. In this study, basic data for water quality management were gathered by analyzing the pollution contributions of the main river (the Seomjin River) and its tributaries, identifying major pollutant sources, and conducting trend analyses. The delivery pollution load of the Seombon D unit basin, one of the main watersheds of the Seomjin River in South Korea, shows a rapid increasing trend (BOD, 1.2–2.4, 2020), which is different from the trend in the B unit watershed of the Boseong River, also a tributary. The rapid increase is presumed to be due to the characteristics of Seombon D, including the inflow of pollution sources of Seombon C, an upstream point. The D unit basin of Seombon is located in the middle of the unit watersheds that divide the main stream of the Seomjin River in Korea into A, B, C, D, E, and F. This increase is thought to be due to the inflow of pollutants specific to Seombon D’s characteristics and the influence of the upstream Seombon C unit basin. In the pollution load contribution rate analysis of Seombon D, it was found that the contribution rate from Seombon C, the upstream area (BOD, 38.42–120.08%), was higher than that of the Boseong B unit basin tributary. The self-purification capacity of Seombon D is believed to have contributed to the improvement in its water quality. It is essential to manage the upstream Seombon C unit basin to sustainably improve the water quality of the Seombon D unit basin. Therefore, managing Seombon C is deemed necessary to further enhance the water quality of Seombon D.