Research on hydrodynamic synergistic protection of biogeomorphological features in silty-sand coastal environments

This study aims to address the unclear synergistic mechanisms and lack of quantitative tools for multi-biogeomorphic unit systems in silty-sandy coast protection, focusing on the crab burrow-salt marsh vegetation-oyster reef system, to provide a theoretical basis for ecological protection design. By combining flume experiments and theoretical modeling, a "sea-land gradient bio-protection profile" framework incorporating parametric schemes (oyster reef arrangement coefficient ψ=0.85, vegetation stem-leaf correction factor φ=1.68, crab burrow morphology factor m=0.6) was developed. A cascade calculation model was used to quantify multi-element synergistic effects, validated with data from a typical cross-section in the Yellow River Delta. Multi-module coupling achieved a wave height attenuation rate of 73.2% (H_t/H_i=0.052/0.10) and a bed shear stress reduction of 30% (τ_b=0.186 Pa). The hexagonal oyster reef arrangement improved wave dissipation efficiency by 41% compared to the linear arrangement. The full-unit synergistic model (M3) reduced prediction errors to 8.3%, significantly outperforming the traditional model (85.4%). The three biogeomorphic units generate synergistic benefits through a "reef-sedimentation promotion — vegetation wave filtering — burrow substrate stabilization" cascade effect. Ignoring biotic synergy overestimates hydrodynamic risk by 38.5%. The result provide a quantitative design tool for Nature-based Solutions (NbS) in silty-sandy coasts.