Dyke Marsh Restoration

The National Park Service is working with the U.S. Army Corps of Engineers to restore Dyke Marsh Wildlife Preserve. Construction of a 1,500 foot breakwater started this July and is expected to take up to 18 months. The breakwater will help protect the marsh from erosion, shield the marsh from storms and encourage the accumulation of sediment, which is necessary for marsh regeneration. The first part of the breakwater construction will involve placement of rock baskets, known as marine mattresses, in the Potomac River to establish the base of the structure and provide stability for subsequent materials. The National Park Service and U.S. Army Corps of Engineers will restore portions of the marsh following the completion of the breakwater.

Located just a few miles south of Alexandria, Va., Dyke Marsh is one of the largest remaining freshwater tidal wetlands in the Washington metropolitan area. Dyke Marsh is viewed as a national treasure that holds extensive value not only for plants and animals, but for its recreational, educational and cultural purposes. It is estimated that the southern marsh has existed for 2,200 years, and the northern marsh has existed for 500 years.


Frequently Asked Questions

Why is it important to restore Dyke Marsh Wildlife Preserve?

Dyke Marsh provides a storm buffer for the George Washington Memorial Parkway, a natural filter for the Potomac River, and habitat for a variety of plants and wildlife, including six state-listed species of special concern (two bird species and four plant species).

It is critical to act now to protect and restore Dyke Marsh. Approximately 270 acres of marshland were damaged from the 1940s to the 1970s through the dredging of sand and gravel. In 2009, NPS partnered with USGS to investigate the state of Dyke Marsh. USGS found that the post-mined marsh is rapidly shrinking as a result of erosion caused primarily by storm waves driven northward up the Potomac River. Erosion in the marsh averages between 6 and 8 feet per year. USGS found that without intervention, this unique ecosystem would be entirely lost by 2035.

How is this work being funded?

In 2013, on the anniversary of superstorm Hurricane Sandy, the US Fish and Wildlife Service awarded $24.9 million to the National Park Service for Dyke Marsh Wildlife Preserve Restoration through the Hurricane Sandy Mitigation program. The project was the largest of 31 resiliency projects awarded to restore coastal marshes, wetlands and shoreline, create open connections to rivers and streams for fish passage and reduce the risk of flooding from future storms.

NPS in partnership with US Army Corps of Engineers worked to design and construct the restoration project through the Interagency and International Support program.

How will the project impact boating and recreational fishing?

Construction of the breakwater and restoration of marsh will not have significant impacts on boating and fishing. There will still be able plenty of areas to fish and boat in and around Dyke Marsh and other areas within the Potomac River. In addition, the breakwater will not impede boating in the existing navigation channel. NPS will mark the waterward end of the breakwater with lights and signs to caution boaters.

Will there be water quality impacts?

There will be temporary impacts to water quality due to the short-term disturbance/turbidity in the water from the construction efforts. Construction will be conducted to minimize these impacts as much as possible, such as careful placement of marine mattresses. After the project has been completed, it will assist in nutrient reduction in the Potomac River and positively impact long-term water quality in the area.

When is the project expected to start and end?

Construction of the breakwater started in July 2018 and is expected to take up to 18 months. The National Park Service and Army Corps of Engineers plan to begin restoration of the marsh following the completion of the breakwater. The NPS will monitor the site following construction completion.

How can I learn more about this project?

Project documents including the Dyke Marsh Restoration and Long-term Management Plan are available at: https://parkplanning.nps.gov/projectHome.cfm?projectID=20293

Last updated: October 10, 2018

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