Stopping Sediment Pollution from Flowing into Dyke Marsh

Sediment pollution

Huge amounts of orangey-brown sediment pollution are flowing into the western part of the Dyke Marsh Wildlife Preserve, especially during storm events.

This June 27, 2015 picture taken by Laura Sebastianelli and this video capture the serious degradation underway.

The U.S. Environmental Protection Agency says that sediment "degrades the quality of water for drinking, wildlife and the land . . . prevents animals from seeing food . . . prevents natural vegetation from growing . . . disrupts the natural food chain by destroying the habitat where the smallest stream organisms live and causing massive declines in fish populations. . . and can clog fish gills, affect fish egg and larvae development . . . . ," among other harms.

The Friends of Dyke Marsh contacted Fairfax County and National Park Service officials in 2014 and urged them to determine the cause and solution. 

County officials found that the major sources of the sediment are two highly degraded and unstable stormwater outfalls uphill from Dyke Marsh West in Mount Vernon District Park, near the intersection of Dartmouth and Swarthmore Drives in the Mount Vernon area.

Fairfax County’s stormwater office contracted with Wetlands Studies and Solutions to develop a design for an outfall and stream restoration and with Angler Environmental to do the construction.  As the sediment deposition and bank erosion became increasingly exacerbated and after some delays, FODM urged that the project be accelerated.  The county prioritized the project and started construction in August 2016. 

The county’s website explains the project’s goals:  “This project will protect surface waters, private property and county infrastructure, restore native vegetation and stop substantial sediment loss that is threatening Dyke Marsh.

quander outfallStorms are severely gouging out streambanks and sending sediment into Dyke Marsh. Photo by Glenda Booth“This project will stabilize a massive erosion gulley that is 20 feet deep, more than 50 feet wide and 200 feet long.  A total of 930 feet of outfall channel will be restored to prevent erosion, convey stormwater, and elevate the surrounding groundwater table to improve soils and support native vegetation.  Surveys were done to ensure that the endangered Small Whorled Pogonia (not found) and archeological sites (none found) would not be impacted by the project.  Surveys also determined the condition of the stream channel and soils, and documented the plant species and the condition of the plant communities that are on site.

“The project will include construction of three trail crossings of outfall channels and extensive native plantings to stabilize and restore habitat.

“This project will also remove some of the invasive vegetation within and adjacent to the restoration site in order to improve habitat in Mount Vernon District Park and ensure the success of restoration plantings.”

Project officials predict it to be completed in April 2017 and monitored through 2020.  The project’s website is at https://www.fairfaxcounty.gov/dpwes/stormwater/projects/quander_road.htm

The Mount Vernon Gazette (Connection Newspapers) published an article by Tim Peterson on July 28, 2016, about the project.  The article is here:   https://www.connectionnewspapers.com/news/2016/jul/28/mount-vernon-quander-road-stream-reconstruction-co/