The Pope Branch Stream Restoration project required the restoration of 4,770 linear feet of a tributary to the Anacostia River that is divided into three sections by culverts under Minnesota Avenue SE and Branch Avenue SE, Washington, DC. This project is the first stream restoration project for DC Water, which usually only undertakes water and sewer repairs. Due to DC Water’s inexperience with streams other than their use of it as receiving bodies for culverts and alignment for water and sewer pipes, a construction firm knowledgeable and skilled in aquatic resource restoration and management was imperative to successfully restoring the stream and associated aquatic and terrestrial resources, specifically wetlands and native plant communities. In addition, the complex and detailed specification requirements of DC Water construction projects also demanded a team that can skillfully conduct interdisciplinary coordination and communication, detailed management of administrative procedures and accurate scheduling and timely execution of construction activities per protocol.
U&A was selected for construction through a very competitive bidding process. The highly urbanized landscape is mostly impervious and, therefore, the stream has been subjected to highly erosive conditions. In tackling the eroded stream that begins in a narrow valley about 130 feet above sea level and ends at a wider, flatter area in the highly developed floodplain of the Anacostia at 8 feet above sea level before entering a roughly 1,500 linear foot culvert, U&A’s engineering and project management staff walked the site to identify existing site conditions to identify features to keep intact, e.g., native gravel soil and sandstone bedrock, and valuable landscape and hydrologic features to incorporate into the constructed project. The project presented varying degrees of opportunities for more fully reconnecting the floodplain, creating seepage conditions for habitat as well as water quality benefits and respecting and integrating native geology to ensure a robust hyporheic zone, all of which U&A methodically incorporated during construction through collaboration with the client, DC Water, and its design contractor and outside funding agencies with the goal to increase site specific restoration potential.
An example of the beneficial modification is the excavation of legacy sediment in the floodplain at the downstream end of the project, adding a pool in front of the culvert to allow sediment to settle and reducing the slope of a cascade. This modification achieved the following:
- greatly enhanced the floodplain connection, which allows stormflows to dissipate over a larger area, creates more riparian and floodplain habitat for native vegetation, and increases residence time to allow nutrient processing, sedimentation, and temperature reduction;
- significantly reduced future maintenance costs of removing sediment that would otherwise have continued to settle in the culvert without the extended floodplain and deep sedimentation pool; and
- gentle cascades and riffle weirs to allow fish passage, should the tidal gate be removed and/or remaining segment of the stream get daylighted in the future.
The stream also had multiple locations with exposed sewer lines, some encased and others not, that required careful planning and execution while filling in the incised channel, installing grade control structures, and excavating pools.
This design/build project is located in the Anacostia watershed on the South East Side of Washington D.C. Approximately 4,700 feet of stream was restored by an RSC system in addition to the construction of four storm sewer outfalls. The primary land uses of the 250-acre watershed are parkland and residential lands. Pope Branch is listed on the 303-D List for bacteria, organics, and metals. The primary sources of pollutants are stormwater runoff from yards, streets, and parking lots as well as an aging sanitary sewer that runs along the stream. This project has multiple components, all of which will work toward improving the water quality of Pope Branch. DDOE, DCWASA, and the District Department of Parks and Recreation have partnered on a stream restoration and sewer replacement project in the Pope Branch tributary of the Anacostia River. At three different locations DDOE installed regenerative stormwater conveyances to help catch and filter stormwater run-off from the streets that drain into the Pope Branch tributary of the Anacostia River. The project will reduce erosion and decrease pollutants reaching Pope Branch and the Anacostia River by slowing down and infiltrating stormwater runoff from streets along Pope Branch. This project was implemented using American Recovery and Reinvestment Act (ARRA) funding and was a partnership between DDOE and the District Department of Parks and Recreation (DPR).