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Numerical Study on Hydro-sedimentary Responses to Morphological Interventions in a Choked Coastal Lagoon: A Case Study of Pinqing Lagoon, China
Enjin Zhao, Chaohui Nie, Yang Wang, Zhao Lu, Hongchao Lu, Fengyuan Jiang and Xiuyun Huang

Choked coastal lagoons are prone to hydrodynamic degradation and sediment deposition because of their limited exchange with the open sea. To evaluate the effectiveness of targeted morphological interventions, a high-resolution FVCOM model was established for Pinqing Lagoon, China. Four scenarios were systematically evaluated: removing internal groynes (Case I), modifying the tidal inlet (Case II), artificially diverting freshwater (Case III), and a comprehensive application of the above measures (Case IV). Results indicated that widening the tidal inlet (Case II) accelerated local water flow, but paradoxically decreased the global tidal prism by 1.02% due to altered internal tidal resonance and choking effects. Conversely, removing internal flow obstructions (Case I) minimized tidal energy dissipation, maximizing the tidal prism (+2.64%) and triggering a local velocity increase of up to 133%. Although the integrated scheme (Case IV) achieved optimal environmental benefits by shortening the water half-exchange time to 114.1 hours and mitigating localized sedimentation, Case I emerged as the most cost-effective strategy. This study reveals the morphodynamic resilience of large-scale choked lagoons, emphasizing that smoothing internal tidal propagation paths can be more effective than merely widening external inlets, thereby providing crucial scientific references for sustainable coastal management.

Keywords: coastal lagoon, hydro-sedimentary dynamics, morphological intervention, tidal prism, water half-exchange time, Pinqing Lagoon