| Title |
Development of a Pollutant Load Delivery Model for Stream Water Quality: A Case Study of the Kyeongan TMDL Subwatershed |
| DOI |
https://doi.org/10.15681/KSWE.2025.41.5.321 |
| Keywords |
Kyeongan stream; Pollutant load delivery model; Total maximum daily load; Water quality |
| Abstract |
This study introduces the Delivery Load?Flowrate?Discharge Load?Seasonality (LQLS) model, designed to assess pollutant dynamics in the Kyeongan Stream watershed, a key tributary of the Paldang Reservoir that supplies drinking water to Seoul. Utilizing monitoring data from 2021 to 2023 collected at two TMDL-designated terminal points, we categorized pollutant sources into discharges from sewage treatment plants (STPs), individual point sources, and non-point sources. The LQLS model, which integrates flow-dependent and seasonal functions, outperformed traditional L?Q and LQL models in predictive accuracy. The model performed well for BOD5 and total nitrogen across all statistical measures; however, it faced limitations in estimating total phosphorus, particularly in terms of Nash-Sutcliffe Efficiency (NSE) and RSR, despite showing acceptable bias and agreement metrics. Seasonal analysis indicated that BOD5 and phosphorus accumulated during the dry season, followed by gradual dilution during the monsoon, while total nitrogen exhibited a significant first-flush effect. The peak runoff depths for non-point source pollutant concentrations varied by parameter, with phosphorus showing sharp increases at high flow levels. Although non-point sources contributed the largest portion of total pollutant loads (BOD5: 63?74%, TN: 52?57%, TP: 61?68%), their impact on the annual mean delivered concentration was relatively low (BOD5: 13?20%, TN: 34?38%, TP: 18?26%). This discrepancy is attributed to the episodic nature of non-point source pollution and the exclusion of high-flow data from this study. Consequently, reductions in pollutant loads from STPs had the most significant effect on improving delivered concentrations, while reductions from non-point sources had the least impact. |