Alger Park Stream Restoration

Habitat, water quality, and stability are restored on one of the most highly eroded stream gullies in the District within Alger Park, a popular neighborhood stream valley park nestled in Southeast Washington, DC.

Biohabitats helped the District restore stability, habitat, and water quality to a headwater stream located in the steep, forested slopes of Alger Park. Stormwater runoff from the 35-acre, highly impervious surrounding sewershed had degraded the stream, causing severe erosion and channel instability. A combination of excessive unmanaged stormwater flows from outfalls and overland flow pathways, along with steep topography, highly erodible soils, and invasive vegetation, contributed to stream and park impairments.

Biohabitats began by assessing the watershed hydrology, stream geomorphology, natural resources, biological community, streambank erosion (BEHI), and stream stressors in the valley. The team then created a design to restore a natural, self-sustaining stream able to resist storm flows. The approach aimed to improve ecological function to the extent practicable based on site constraints, such as the steep slopes and confined valley. Establishing a floodplain connection was the most critical target. The upstream approached increased interaction between stream and potential floodplain areas. The design raised the channel bed elevation to provide a reconnection with geomorphic surfaces that had been suspended above and along the existing channel. Raising the stream invert restored a subterranean reservoir of the riparian area without the need for forest removal. The additional stored groundwater is likely to increase and sustain baseflows during dry summer months. This is an essential parameter for sustaining aquatic biota. An increased hydroperiod will allow native riparian vegetative to more rapidly establish while suppressing non-native species. Restoration of the downstream reach focused on modifying and enhancing wetland conditions, removing invasive species, increasing habitat complexity, and improving connections to stormwater outfalls. The design included a multi-threaded channel with naturalized valley-spanning wetland grade controls and integrated existing storm sewer outfalls by eliminating large drops creating “bubbler” outlets.

Given the park’s popularity and residential surroundings, communication and community engagement were essential. Biohabitats participated in community site walks and meetings during each phase of the design to help ensure that residents understood the purpose of the project.

TAGS

• Assessment+Monitoring
• Design
• Ecological Restoration