Response of water exchange characteristics to replenishment patterns in multi-island annular lagoons

Water replenishment is an effective strategy for improving lacustrine environments, particularly in complex multi-island lagoons that face challenges such as weak hydrodynamics in distal areas, inefficient flow partitioning, and unstable flow paths. Using Xinglin Lagoon in Xiamen as a case study, this research establishes a two-dimensional coupled hydrodynamic-water exchange numerical model to systematically investigate the response of water exchange capacity to replenishment layouts and proposes an optimized scheme. Results indicate that concentrated replenishment in the island complex achieves optimal effectiveness, leveraging the plum blossom-shaped island configuration to facilitate uniform flow distribution. For the main lake body, distributed replenishment effectively addresses hydrodynamic deficiencies in sheltered areas. Based on current operational capacities, the recommended optimized layout allocates 80,000 m³/day to Jiutianhu, 40,000 m³/day to Houxi, and two coastal replenishment points along the eastern shoreline at 30,000 m³/day each. These findings provide theoretical support and practical guidance for water replenishment projects in lakes with similar morphological complexities. The findings provide theoretical support and practical experience for water replenishment projects in lakes with similar challenges.