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

Abstract

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).

Keywords:

• Tidal exchange
• gate opening
• wetland restoration
• shallow-water equation
• sediment transport

Acknowledgements and funding

This paper is dedicated to Scott C. Hagen, who has continuously inspired and encouraged us (R.I.P. July 24, 2021). Also the authors sincerely thank the Chincoteague National Wildlife Refuge for providing collected data, anecdotal information, site visit and meeting space, and three anonymous reviewers for their time and insightful comments that improved the clarity of the manuscript.

Disclosure statement

The authors declare that they have no conflict of interest.

Additional information

Funding

Funding was provided by the U.S. Fish and Wildlife Service, Swan Cove Restoration Project (award: U.S. Department of the Interior’s (DOI’s) Hurricane Sandy Coastal Resilience Program Funding) and the Louisiana Sea Grant Laborde Chair Endowment. Internal research funding from the Center for Computation and Technology and the College of Engineering at Louisiana State University also partially supported this work. This work utilised high-performance computing services provided by Louisiana State University and the Louisiana Optical Network Initiative.