Parks, Open Spaces, & Greenways
- Cambridge Stormwater Wetland
Cambridge, Massachusetts
the challenge As part of a massive sewer segregation project designed to eliminate Combined Sewer Overflows (CSO’s) to the Alewife Brook as part of the Boston Harbor Cleanup, the City of Cambridge needed to construct a stormwater management basin. The most feasible alternative was to construct the basin on land owned by the state, an idea at first rejected by the owner agency. Located within the 100-year flood plain in the Alewife Brook Reservation, an urban wild, the site currently serves as habitat for a diverse wildlife population and as a recreational area laced with informal hiking and bike trails. The challenge was to design a constructed wetland and detention basin that met the technical requirements for detention and treatment while simultaneously meeting the habitat and recreational functions envisioned for the area in the Massachusetts Department of Conservation and Recreation (DCR) master plan for the Alewife Brook Reservation.
the interdisciplinary approach The Bioengineering Group was retained to design this stormwater management facility as a multi-functional wetland that serves the combined objectives of stormwater detention, water quality improvement, wildlife habitat enhancement, and recreation/education. Our scope of work included the formulation of alternatives, participation in public meetings and outreach, MEPA and other permitting support, the preparation of responses to comments, completion of a wildlife inventory, and the bioengineering design of the detention basin as a stormwater wetland park.
The stormwater wetland is designed to minimize flooding of the Alewife Brook by retaining up to 10.3 acre-feet of stormwater to shave peak flows to the Alewife Brook during major storm events. The stormwater wetland provides treatment of the stormwater “first flush” via sediment removal, biological filtration, and thermal regulation while providing recreational trails, enhanced wildlife habitat and wetlands, and an educational feature promoting stormwater management best practices.
Our landscape architects also designed a new entrance to the reservation to improve public access and the park’s amenities including an amphitheater/outdoor classroom, boardwalks, overlooks, benches, and interpretive signage highlighting the historical, ecological, and hydrological features of the site.
the resultsDescribed in the Boston Globe as “a far cry from the traditional treatment prescribed by engineers,” the stormwater wetland incorporates both conventional and bioengineered structures designed with a natural “look and feel” that won praise from stakeholder groups. The wetland increases base flows in the brook and enhances the health of adjacent natural wetlands via infiltration for groundwater recharge. In addition, the stormwater management park incorporates a site layout and plant species selected for synergistic relationships with existing ecological patterns and natural processes that provide a significant improvement over the existing degraded habitat. The City was delighted to save more than $15 million dollars compared to the alternatives, and the DCR was pleased to have a cost-sharing partner to implement elements of its Master Plan—a win for those parties as well as the natural systems and local communities.