In 2003, Norfolk designed a four lot subdivision in the Forestdale section of Sandwich, Massachusetts. Due to the need to maintain existing site run-off characteristics, Norfolk utilized Low Impact Development (LID) techniques to treat and recharge stormwater from the 825-foot long subdivision road that ended in a cul-de-sac.
LID techniques utilized at the site included
- Vegetated swales
- Bioretention
- Minimization of paved impermeable surfaces (reduced roadway width and sidewalk on one side of road)
- Minimum disruption of area due to careful placement of site features, thus retaining natural ability of landscape to adsorb and treat stormwater runoff.
A 625-foot long vegetated swale intercepts the run-off from the off-site contributory watershed area, and stores and infiltrates the entire 100-year design storm volume. Two bioretention basins collect all of the on-site run-off from the 100-year design storm. The first bioretention basin in located at the entrace to the subdivision, while the second vehicle access to the cul-de-sac, minimizes impermeable paved surface (reduced pavement area by 1,320 square feet), and treats and infiltrates all roadway run-off up to the 100-year storm event.
The roadway width was reduced from the Town standard of 24 feet to a 20 foot width, resulting in a further reduction of 3,330 square feet of impermeable roadway surfaces. The overall reduction in impermeable roadway surface was 23%.
The roadway itself was strategically located to minimize disturbance to the site. The roadway was located on the uphill side of the site, promoting stormwater management on the individual lots, thereby reducing the required size of the stromwater handling facilities, and minimizing the impact of non-point source pollutants such as excess nutrients from improperly applied fertilizers and herbicides / pesticides.