Coastal, River, & Wetland Restoration
- Pope Branch and Lower Anacostia Park
the challenge The Pope Branch and Fort Dupont Creek tributaries of the Anacostia River in socio-economically challenged Northwest Washington, DC are heavily degraded urban streams partially buried in culverts. Urban development has caused substantial incision and habitat loss in the streams owing to flashy hydrology, deferred sewer maintenance, and contaminated storm water. Specific project objectives included daylighting the culverted streams and providing fish passage and in-stream habitat, improving circulation and providing pedestrian access to the park from the adjacent neighborhood (which lacked recreation areas), and improving the quality of water entering the Anacostia and Chesapeake Bay. Adding to these challenges was the fact that hydraulic analysis showed insufficient slope available to move water and sediment in an open channel across the park to the Anacostia River.
the interdisciplinary approach Working under contract to the US Army Corps of Engineers, we interfaced with multiple stakeholder groups, including the Metropolitan Washington Council of Governments, National Park Service, DC Department of Health, DC Watershed Protection, DC Parks, USGS, and the Anacostia Waterfront Initiative to develop plans for the restoration of the Fort Dupont and Pope Branches and the creation of a treatment wetland for water quality enhancement in Lower Anacostia Park. These plans were integrated with the Anacostia Waterfront Framework Plan through DC Office of Planning.
To overcome the problem of insufficient hydraulic gradient, Bioengineering Group staff devised a solution that involved flowing both creeks into a large constructed wetland in Lower Anacostia Park. The wetland was held just above the elevation of mean high water in the Anacostia to avoid diurnal tidal flushing that would reduce residence time needed for water quality improvement. A further obstacle was two existing 8 and 9 foot diameter trunk sanitary sewers running parallel to the river that intersected the grade line of the stream--overcome by shielding them with a protective concrete structure that created a sequence of pools and spillways leading to the main wetland complex, thus creating a fish-passable sculptural water feature for the park. Other park enhancements included creation of open fields for recreation, an upgrade of the path system, expansion of parking using porous pavement and augmentation of biodiversity and the environmental education component of the park.
the results In the end our designs demonstrated that properly designed treatment wetlands can be sited in a park not only to improve water quality to also be compatible with public access requirements and with meeting the recreational and conservation goals of the park. These plans balanced the need to restore streams that were impaired by leaking sewage and impervious surface development, treated stream flow through a treatment wetland adjacent to the river at the confluence of the two streams, and provided public access well received by stakeholders. All of these measures were integrated into the landscape of the park in a manner that upgraded the beauty, biodiversity, and functionality of the park, both for the recreating public and the ecological communities. And, finally, the result of this design is a reduction of 80% of the pollution entering the Anacostia River from the watersheds of these two streams.