Water-exchange Capacity Induced by River Discharge and Bay Mouth Archipelago in a Macro-tidal Embayment

As a critical interface between terrestrial and marine environments, bays experience significant land-sea interactions, with complex hydrodynamic processes playing a role in their water-exchange capacity. This study investigates how medium-sized rivers and the archipelago near the mouth of Yueqing Bay influence its water-exchange capacity. Half-exchange time, combined with a validated three-dimensional hydrodynamic model based on the Finite Volume Community Ocean Model, was used to assess the bay's water-exchange capacity. The results show that the half-exchange time in Yueqing Bay decreases from the bay head to the mouth, ranging from up to 30 days at the head to less than 1.5 days at the mouth, with an overall average of 8–9 days. Seasonal variations in river discharge, particularly from the Oujiang River, lead to changes in water-exchange capacity, with summer rates being 13.6% higher than those in winter. Additionally, a flood event increases water-exchange capacity near the mouth by 6.5%. The surrounding islands enhance tidal energy within the bay, resulting in an 11.6% increase in water-exchange capacity. This study provides valuable insights into the roles of river discharge and nearby islands in controlling water renewal processes, thereby enhancing understanding of the key mechanisms involved.