Evaluating hydrodynamics and implications to sediment transport for tidal restoration at Swan Cove Pool, Virginia

Coastal restoration projects are significantly important in coastal ecosystems as wetland losses accelerate. This study investigates tidal hydrodynamics and the potential impacts of a waterway opening on an existing roadway to restore and revitalise salt marshes in a small estuarine system in Virginia, USA. A depth-integrated, discontinuous Galerkin shallow-water equations model (DG-SWEM) is applied for astronomic tide simulation. The model employs a high-resolution unstructured mesh with a minimum element size of less than one meter and resolves complex tidal flows in the entire barrier island system, including the existing culvert gate and canal system. Compared to the existing system, the water exchange increased dramatically (flushing time also dramatically decreased) under the opened scenarios regardless of the opening width (22.9-, 30.5-, and 38.1-m width). By increasing the opening width, peak velocity through the proposed opening decreased 30–40%, and the maximum shear stress was reduced by more than half. The high-resolution model represented complex tidal flows, including eddies, and assisted in striking a balance of water-exchange capability, opening stability, and minimising their potential erosions for the opening design. Besides, erosion and sediment transport potentials for suspended sediments were estimated using bed shear stress and a Lagrangian particle tracking module. Such proxy modelling approach allows for the impact assessment of civil engineering and ecological waterworks in complex and highly damped tidal flow areas and is readily transferrable to other like systems (e.g. causeway construction, causeway cutting, biota passageways, and inlet modification).

随着湿地流失速率加快，海岸修复项目在海岸生态系统中具有至关重要的意义。本研究针对美国弗吉尼亚州一处小型河口系统，探究了潮汐水动力学过程，以及在现有道路上开设航道开口以恢复并复壮盐沼的潜在影响。本研究采用深度积分型间断伽辽金浅水方程模型（discontinuous Galerkin shallow-water equations model, DG-SWEM）开展天文潮汐模拟。该模型采用最小单元尺寸小于1米的高分辨率非结构化网格，能够解析整个障壁岛系统内的复杂潮汐流场，包括现有涵闸与渠系。与现有系统相比，无论开口宽度为22.9米、30.5米还是38.1米，开设航道开口后的情景下水体交换量均显著提升，纳潮冲刷时间也同步大幅缩短。随着开口宽度增加，拟建航道开口处的峰值流速降低30%~40%，最大剪切应力则削减过半。该高分辨率模型能够复现包括涡旋在内的复杂潮汐流场，有助于在水体交换能力、开口稳定性以及降低开口潜在侵蚀风险之间达成最优平衡，为开口设计提供支撑。此外，研究通过底床剪切应力与拉格朗日粒子追踪模块，估算了悬浮泥沙的侵蚀与输运潜力。此类替代建模方法可用于复杂强阻尼潮汐流区域的土木工程与生态水利工程影响评估，且可便捷推广至其他类似场景，如堤道修建、堤道开挖、生物通行通道建设与口门改造等。