Department of Public Works staff told the Envision Needham Center working group on Sept. 10 that federal and state stormwater mandates and local flood history will shape the design choices for the Great Plain Avenue corridor. Staff said the town must reduce phosphorus loading and that infiltration is the preferred treatment approach; they said the town has a target to remove roughly 2,100 pounds of phosphorus (as stated at the meeting) and that town projects must provide ways to capture and treat runoff as part of corridor work.
Staff described the downtown area as the summit of three drainage basins, with runoff draining toward several reservoirs and under the railroad toward neighborhoods that have experienced flooding in past storm events. That geography, staff said, means implementing infiltration and other stormwater best management practices (BMPs) is essential as the town reconstructs or rehabs streets and sidewalks in the project area.
Consultants and staff noted the two‑lane alternative creates more contiguous space behind the curb line for street trees, vegetated bump‑outs and similar surface BMPs that can treat stormwater and reduce phosphorus loading; the 4‑lane alternative, which largely preserves existing curb and pavement, offers fewer large surface BMP locations but still allows some bump‑out treatments. Staff added there are ongoing and completed dredging and maintenance actions at nearby reservoirs that factor into the town’s phosphorus‑reduction strategy.
The meeting did not adopt specific BMP designs, and staff said detailed stormwater engineering (including whether and where surface BMPs are feasible), utility conflicts and specific infiltration designs will be defined in later design phases. Participants asked about the feasibility of mixing underground treatment and surface BMPs and how those choices would interact with pedestrian and curb management decisions; staff said those tradeoffs will be evaluated as part of the design and cost estimates when a right‑of‑way option is selected.
The discussion distinguished two design steps: the committee’s present role of choosing how to allocate the right‑of‑way (how much curb and sidewalk area to create) and the later design phase when the engineering team will locate infiltration facilities, pipework and other underground treatment infrastructure. No binding engineering decision was taken at the Sept. 10 meeting.