Abstract
The dense highland field area in the upstream region of the Lake Soyang watershed is subject to excessive soil erosion during the wet season. In this study, stormwater runoff from the Lake Soyang watershed was monitored during four rainfall events at 10 locations throughout 2016. The maximum SS concentration at Naedongcheon, which is located in the upper part of the Soyang River, reached 4598 mg/L. The event mean concentration (EMC) of SS loads in Naedongcheon ranged from 82.2 mg/L to 926.3 mg/L. We found that, although the first flush events were usually concentrated in highly paved urban areas, a first flush occurred in the agricultural area of the dense highland field region. The first flush phenomenon was identified by a dimensionless cumulative runoff mass and volume curve (M(V) curve), and the intensity of the first flush was analyzed by the coefficient of the nonlinear regression model and the FF30 and FF25 values (the fraction of pollution load transported by the first 30% and 25% of runoff, respectively). Nonlinear regression models using the power function were applied to fit the M(V) curve, the FF30 values were inversely proportional to the coefficient a of the regression model. A long-term seasonal trend decomposition for monthly turbidity and precipitation was performed for the Lake Soyang. Long-term turbidity trend was approximately coincident with the trend in long-term precipitation. In addition, the present status of the best management practices (BMPs) in the upper part of the Soyang River basin was investigated, and a survey of the management and operation of the BMPs was conducted for selected farmers.
Highlights
Lake Soyang is located on the upper part of the Han River in South Korea
The first flush mostly In Naedongcheon and Jungjohangcheon, the first flush is indicated by the SS, total phosphorus (TP) and biochemical oxygen demand (BOD) values
A storm water runoff survey was conducted at 10 survey points in the Soyang River basin
Summary
Lake Soyang is located on the upper part of the Han River in South Korea. The human population is concentrated in the lower part of the Han River, including the capital Seoul. The highland fields in this area cause a large amount of suspended sediments to be discharged into the river, which increases the turbidity of Lake. A large amount of nonpoint source pollutants enter Lake Soyang and cause the turbid water phenomena [5]. Because of the rising turbidity of the lake after typhoon Ewiniar, the Ministry of Environment assigned the Lake Soyang watershed area, Yanggu-gun, Hongcheon-gu, and the surrounding areas as a nonpoint source pollution management area. The water quality characteristics of each rainfall event were evaluated via storm water flow and water quality measurements at 10 targeted points in the nonpoint source pollution management area. By exploring and analyzing the various research results from the nonpoint source pollution management area, effective alternatives for reducing sediment discharge in the Lake Soyang watershed area can be assessed
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