Low Impact Development

Why bother?
Rainwater fails to recharge the groundwater supply when it encounters impermeable surfaces and drains directly into surface waters, storm drains or sewer lines. The Metropolitan Boston area near Rte. 495 is being developed rapidly, with high growth rates translating into new homes, malls, roads, businesses and parking areas. These developments normally consist mostly of impermeable areas--rooftops, parking lotw and roads--connected to a storm drain system. But today methods exist which can allow water to recharge even with this new construction. The key is finding ways to allow clean water to soak into the ground as close as possible to where it falls. This has the added benefit of reducing the high costs of capturing and transporting water through drains and pipes and attempting to remove pollutants at the end of the pipe. These pollutants (salt, oil and grease, petrochemicals, nutrients and sand) usually end up in the Assabet River and its tributaries.

Roofs:
Buildings can be designed so that rainwater falling on a sloped roof is captured by gutters and delivered to drywells near the building (Floral Street School/Shrewsbury; DPW/Westborough). Rainwater can also be retained on a flat "Green Roof" which insulates, cools and evaporates stormwater, despite being only 2-3 inches thick. Heavy storms may generate some runoff, but green roofs and drywells can accommodate runoff from most storms. Rainbarrels or larger rain collection cisterns collect roof water to be used for irrigation and infiltration. Even roof color makes a difference: white roofs don't heat rainwater as much as dark roofs.

Parking Lots:
Parking lot size can be reduced through design specifications requiring spaces for compact cars (Bedford requires 30%). Parking "islands" can be turned into vegetated depressions, such as bioretention areas, raingardens or vegetated swales, that capture the runoff, filter and infiltrate it. These are attractive and low maintenance, supporting healthy vegetation. Seasonal parking areas, such as at outdoor recreation areas and overflow parking, can be made of permeable pavement, as can emergency access roads. The greatly reduced runoff from these parking lots can be directed to infiltration basins (either open or sub-surface), as in the Cherry Street project in Hudson, or vegetated swales that clean the water prior to discharging to surface waters.

Roads:
Roads designed to be narrower and built without curbs greatly reduce the runoff generated in residential and commercial areas. Water will naturally run off the roadsides into grassed swales or raingardens, creating attractive landscape features with low maintenance needs.

Wastewater:
Much of local groundwater is drained from the watershed through the sewer system--by seeping through joints in sewer pipes ("infiltration", draining through the gravel trenches in which the pipes lie, or simply by being drinking water which is used and then flushed away to the local treatment plant. Until recently, Massachusetts regulations require one to hook up to the local sewer if one was available, but as of 2006 (?) septic, advanced, and ecological on-site systems may be used even in sewered areas. In addition, developments may provide their own small wastewater treatment facilities which discharge to groundwater (e.g., Weston Village center, see www.ecological-engineering.com/services.html).

Links to additional LID information:
Discovery Museums in Acton: Low Impact Development Brochure (pdf) (High-res 3 MB) (Low-res 245 KB)
University of New Hampshire Stormwater Center:
Innovative Stormwater BMP Inventory for New England: Searchable by state and town, the UNHSC-NEMO Innovative Stormwater Management Inventory is a database of New England sites where innovative stormwater BMPs have been implemented. Database users are welcome to add new examples of innovative BMP implementation and provide suggestions of how to improve this regional resource.You can access the database here
Low Impact Development at the EPA
Low Impact Development at the Mystic River Watershed Association
Low Impact Development Center
Massachusetts Low Impact Development Toolkit (contains 9 factsheets on LID techniques)
Nashua NH's Alternative Stormwater Management Methods Manual
School Projects using LID (for teachers and students)
Stormwater Manager's Resource Center
Green roofs
www.greenroofs.com
Permeable paving Uni Eco-stone
Grasspave
Gravelpave
Rain barrels and cisterns New England Rain Barrel
SmartStorm Rainwater Recovery Systems
Rain gardens