Suspended material retention in riverine reservoirs: Role of hydropeaking, density currents, and settling velocity

Study Region: Paldang Lake (PL), a riverine reservoir in South Korea, located at the confluence of three major rivers. Study Focus: This study evaluates the retention and transport mechanisms of suspended materials within PL. We employed calibrated hydrodynamic and temperature models integrated with a Lagrangian particle tracking framework to simulate the behavior of fine and coarse particles under three distinct flow regimes: hydropeaking, non-hydropeaking, and flood events. The analysis highlights the role of hydropeaking operation, density currents, and particle settling in modulating particle pathways and residence times. New Hydrological Insights for the Region: Our simulations reveal that hydropeaking flows significantly enhance lateral mixing and extend the residence times of fine particles, while coarse particles remain less mobile due to interactions with bed roughness. Stratified flow at confluences inhibits mixing between tributary inflows, leading to bimodal residence time distributions that highlight the importance of weak-flow zones as retention hotspots. During flood events, strong advective forces dominate, resulting in uniform particle transport regardless of settling velocity. These findings provide a deeper understanding of how hydrodynamic forces, stratification, and particle properties influence suspended material retention in PL, offering practical insights for optimizing dam operations and reservoir management to improve water quality and ensure long-term sustainability.