DESIGN DETAIL: STORMWATER MANAGEMENT

Cutting gaps into curbs compensates for the lack of irrigation capacity by allowing runoff from impervious surfaces to flow into bioretention beds. Bioretention is described by MassDEP as "a technique that uses soils, plants, and microbes to treat stormwater before it is infiltrated and/or discharged" into ground or surface water resources.¹ Stormwater curb cuts thus help water reach new vegetation on the site and divert untreated rainwater from flowing directly into storm drains.

According to the MassDEP's Structural Best Management Practices Specifications for the Massachusetts Stormwater Handbook, bioretention areas and rain gardens are more effective than conventional infiltration structures. With proper design, including the grading of the impervious drainage area, layering of soil substrates, and plant selection, bioretention areas can remove up to 90% of total suspended solids and reduce phosphorus, nitrogen, metals, and bacteria.¹

Bioretention basins can reduce the rate of stormwater runoff leaving a site during precipitation events, preventing flooding and erosion, while also sinking filtered water down to recharge groundwater resources.

Because of B. Everett Hall Field's location partially within the Aquifer Recharge Zone and upstream from streams, rivers, and wetlands, bioretention areas can help mitigate the park's impacts on water quality while also adding visual interest and increasing habitat for birds and pollinators without requiring irrigation.

Incorporating "pretreatment" mechanisms to catch sediment and litter before entering bioretention areas is required, and routine maintenance of these elements is crucial to ensuring the optimal, longterm functionality of the vegetation. However, planting bunch grasses and sedges has proven a successful method for preventing sediment from entering the basin, allowing for easy maintenance and long-term plant health.² Precedents using plants as sediment traps only required sediment removal from forebays twice a year, a process that maintenance staff did with shovels and that took approximately 30-minutes per forebay. Little weeding was required because selected plants grew vigorously and filled the space.² asphalt drive and parking lot graded at a 2 to 5% slope toward cuts in the curb

5' sidewalk with a 2% cross-slope toward vegetation

5' pretreatment strip planted with low- or no-mow fesccues

3" mulch

3-4' planting media

2" choker course

2" drainage stone around perforated pipe