Evaluating vulnerable zones and spatiotemporal dynamics in Saemangeum lake under sluice gate operation

This study investigates the spatiotemporal dynamics of water quality and hydrodynamics in Saemangeum Lake, an artificial brackish coastal lake shaped by sluice gate operations and the interaction of freshwater and seawater inflows. The Delft3D model examines four critical factors affecting water quality: flow velocity, stratification intensity, pollutant retention, and hypoxia occurrence. Seasonal simulations reveal significant stratification and hypoxia during the summer, caused by vertical density differences and the counterflow between surface and bottom layers. In contrast, winter conditions exhibit stronger circulation and reduced stratification. A vulnerability index is introduced to identify critical zones requiring targeted management. Key findings indicate that Zones M1 (northern Mankyeong section) and D1 (Dongjin section) are highly vulnerable due to stagnant hydrodynamics, prolonged residence times, and frequent hypoxia events exacerbated by salinity stratification. This study emphasizes the importance of optimizing sluice gate operations, particularly increasing seawater inflow frequency during periods of intensified stratification and adopting zone-targeted management interventions to mitigate hypoxia and improve water quality. These findings will provide valuable insights into reducing stratification and hypoxia periods in brackish waters like Saemangeum Lake and will raise awareness of the importance of hydraulic flow and aquatic environment management.