Effect of environmental flow management on river water quality: a case study at Yeongsan River, Korea

摘要

This paper describes a management scheme to control river water quality using additional waterndischarges from upstream dams, which results in an increase environmental flow (EF) followed bynan enhancement of water quality in a target river. To suggest a creditable management plan amongna suite of ideal scenarios, the monthly averaged water quality monitoring data from 2001 to 2006 atnthe Yeongsan (YS) River, Korea were investigated with respect to seasonal variation and spatialndistribution. From the analysis, it was found that while biochemical oxygen demand (BOD5) level innthe YS River was extremely high during the dry/drought season (April, May, and June; AMJ), the levelnwas subsequently decreased during the monsoon season (July, August, and September; JAS) duenmainly to the dilution effect of rainfall. To improve the water quality in AMJ, we here suggested anscenario of increasing EF using surplus water discharges from upstream dams, which wasnexamined by one dimensional riverine water quality model, QUAL2E model. Simulation resultnshowed that additional discharge from the upstream dams could lead, on average, to a 36% ofnwater quality improvement in mainstream with respect to BOD5. Model coefficients were validatednby comparing the six year monitoring data to minimize a sum of squares error, and showed a goodnagreement with the observed data. Overall, the methodology developed in this paper appears to benquite clear and straightforward, and thus, can be applied to a wide range of the flow managementsnor water quality controls in a stream with artificial structures.