Algal Boom Characteristics of Yeongsan River Based on Weir and Estuary Dam Operating Conditions Using EFDC-NIER Model

Darae Kim,Changmin Shin

doi:10.3390/w13162295

Abstract

A number of hydraulic structures have been installed along the Yeongsan River, including an estuary dam and two weirs (Seungchon and Juksan). While these structures aid in regional water security and use and reduce flooding, they reduce water flow in the summer, thereby frequently causing algal blooms. This study simulated algal bloom and water quality characteristics of sections of the Yeongsan River in South Korea under different weir and estuary dam operating conditions using the Environmental Fluid Dynamics Code—National Institute of Environment Research (EFDC-NIER) model. Results showed that when the management levels of the Juksan Weir and estuary dam were maintained, simulated water levels were EL. 3.7 m in the weir section and EL. −1.2 m (below average water level of the Yellow Sea) in the dam section. When both the weir and dam were open, the water levels varied with the tide; in contrast, when the Juksan Weir alone was open, the water level was between EL. −1.2 and −0.9 m, in line with the management level of the estuary dam. Opening the weir alone reduced algal blooms by 72–84% in the weir region, and opening the estuary dam alone reduced the algal blooms by 83% in the dam region. This improvement was attributed to the reduced water retention time and dilution due to seawater inflows.

Highlights

Estuaries are transition areas between land and sea, and environmental changes in an estuary can have a significant influence on the adjacent ocean environment
This study aims to (1) construct a model that can simulate water flow and water quality in the mainstream section and estuary dam of the Yeongsan River using the Environmental Fluid Dynamics Code (EFDC)-National Institute of Environment Research (NIER) model and (2) use the model to assess water flow and water quality characteristics based on the operational conditions of the multifunctional weirs and estuary dam
The middle and downstream sections of the Yeongsan River show high phytoplankton concentrations attributed to the increase in retention time caused by the Seungchon and Juksan Weirs and the estuary dam, and the influence of point and non-point pollution sources scattered throughout the basin

Summary

Introduction

Estuaries are transition areas between land and sea, and environmental changes in an estuary can have a significant influence on the adjacent ocean environment. In the Des Moines River (Iowa, USA), algae decreased by 65–75% as they passed through two reservoirs, due to algal sedimentation and light limitation and, in both reservoirs, algal loss increased as the residence time and water temperature increased, which is opposite to the algal physiological characteristics in rivers [4]. In both lakes and nearshore coastal waters of Florida, phosphorus is the primary limiting factor for phytoplankton, but the chlorophyll to phosphorus ratios and chlorophyll to biovolume ratios were significantly lower in marine system than lakes [5]. Two large weirs (Seungchon and Juksan) and an estuary dam have been installed in the middle and downstream sections of the river, which reduce hydraulic flushing and cause frequent algal blooms during summer

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Results

Conclusion