Overview

Marsh Terracing is a coastal restoration tool that is commonly used to reestablish marshes in shallow, open water areas. They function by reducing wave energy and water velocities. In turn, the calmer water allows more sunlight to penetrate to the shallow bottom, promoting the growth of marsh and seagrass. This ultimately increases habitat quality for fish and wildlife.

The City of Virginia Beach is leading an effort to design and permit marsh terraces within Bonney Cove, located in the Back Bay National Wildlife Refuge. The project will restore valuable habitat for Back Bay fish and wildlife species, improve water quality, and reduce flood impacts by reducing wave heights and water velocities. The outcome will be a community-supported, shovel-ready project that demonstrates the efficacy of the first-ever application of marsh terraces in the Mid-Atlantic region.

Why is it needed?

Periods of sustained southerly winds push water from Currituck Sound into Back Bay, increasing water levels by several feet and flooding low-lying lands, homes, and critical roadways. Although such events used to be rare, more than five have been experienced in the last four years. Analysis has indicated that increased sea levels and marsh loss are significant contributing factors. The project site was strategically selected as it offers an opportunity to restore approximately 260 acres of marsh island habitat that has resulted in the opening of a secondary channel that allows increased flow of water to areas with high community exposure. Unmitigated, the continued degradation and loss of these marsh island systems will further increase the propagation of floodwaters through this critical pathway and also continue to increase fetch and wave heights into the north end of the bay.

This project is the first step in a more comprehensive vision of restoration in Back Bay, and the larger Albemarle-Pamlico estuary, to strategically close hydraulic pathways and advance restoration objectives. Through the export of proven expertise from successful marsh terracing projects, this project lays the foundation for future projects through the development of detailed cost estimates, identification of best sources for local/regional materials, and establishment of partnerships with permitting officials at various levels of government.

How will it work?

1. Stakeholder Workshop: A workshop with Back Bay stakeholders and regulatory agencies will provide a forum to gather input on permitting, design, and constructability considerations.
2. Initial Permitting: Required permits will be secured before initiating surveys and monitoring research within Back Bay National Wildlife Refuge.
3. Field Data Collection: Investigation of baseline field conditions requires a soil survey, water quality, water level, and flow measurements, a survey to determine depths and elevations of existing marshes, and a vegetation survey to establish the types of invasive and native marsh present at the site.
4. Alternative Development: Different design options for the marsh terraces will be evaluated. A numerical model will be used to determine the optimal width, configuration, and spacing of the terraces. The numerical model will also be used to evaluate the benefits and adverse impacts of the alternatives.
5. Environmental Assessments: As the project is located within a National Wildlife Refuge, it will be necessary for the City to coordinate with the U.S. Fish and Wildlife Service to prepare an Environmental Assessment in compliance with the National Environmental Policy Act (NEPA).
6. Engineering and Design Plans: Upon approval of the NEPA document, the project can advance past the preliminary design phase. Design plans, artistic renderings, technical specifications, construction schedule, and staging plan will be developed.
7. Stakeholder Engagement: The final designs and renderings will be presented at a public engagement meeting with Back Bay stakeholders to identify any barriers to implementation. Additionally, lessons learned from the project will be shared with other communities, planning entities, and academic institutions within the region and state.
8. A Joint Permit Application will be filed to coordinate permits required by the Norfolk District U.S. Army Corps of Engineers for work in waters of the United States (including wetlands), as well as corresponding permits from the Virginia Marine Resources Commission and the Virginia Department of Environmental Quality.

Current Updates

• The City hosted a virtual workshop on November 17, 2020, where the following agencies contributed feedback:
• Back Bay Restoration Foundation
• Albemarle-Pamlico National Estuary Partnership
• National Oceanic and Atmospheric Administration Fisheries Service
• U.S. Army Corps of Engineers
• U.S. Environmental Protection Agency (Region 3)
• U.S. Fish and Wildlife Service, Back Bay National Wildlife Refuge
• Virginia Beach wetlands Board
• Virginia Department of Conservation and Recreation
• Virginia Department of Environmental Quality
• Virginia Department of Wildlife Resources
• Virginia Marine Resources Commission
• A vegetation survey and bathymetric of existing conditions in Bonney Cove are complete. The surveys were both covered under a USFWS Special Use Permit (SUP). The vegetation survey mapped and documented the types of native and invasive vegetation present at the site which will be used to develop the planting design on the marsh terraces, focusing on restoring native vegetation. The bathymetric data establishes existing bottom elevations which will be used for numerical modeling of project alternatives, and to determine quantities of fill materials to build the proposed marsh terraces.
• A water quality survey of existing conditions in Bonney Cove is complete. The survey, also covered under a USFWS SUP, involved the collection of water samples and deployment/retrieval of hydrodynamic sensors (pressure sensors, acoustic Doppler current profilers, and optical backscatter sensors) at three sampling points in Bonney Cove. This data is required for the numerical modeling and designing of the proposed marsh terraces.
• A Geotechnical survey of Bonney Cove is complete. The survey, covered under Virginia Marine Resources Commission (VMRC) Permit No. 2020-2286, Department of Army Permit No. 2020-02439, and a USFWS SUP, included a collection of 10 soil borings in locations that avoided aquatic vegetation habitat. The soil samples were retrieved by drilling with a specialized airboat-mounted drill rig which was essential for drilling in shallow areas as it avoids disruption to the bottom habitat. The soil samples are being analyzed at a lab for analysis and will be used to provide information on soil profiles to estimate bearing capacity, acceptable side slopes, minimum berm width, and maximum crown elevation of the marsh terraces.
  
• The preliminary (30% design) of the marsh terraces is complete. The preliminary design includes both 15-foot wide and 30-foot wide marsh terraces that maximize native vegetation species diversity. Numerical modeling is underway to quantify flood risk reduction benefits including a reduction in wave heights and flow velocities through Bonney Cove.
  
• The Environmental Assessment (EA) is underway. The EA document will include a brief discussion of: