Low-impact development (LID) is a green building process that utilizes nature in order to direct storm water closer to its source. LID methods include:

• Creating appealing and functional site drainage
• Preserving and restoring natural scenery
• Using rain gardens, permeable pavements, vegetated rooftops and bioretention facilities

LID can be used in existing or new developments and can be adjusted to suit a wide range of land uses and settings. LID principles can help promote the natural movement of water and reduce the impact of already constructed areas. For example, a green roof (made of plants and shrubbery) may be added in the midst of dense urbanization as a way to reduce rainfall runoff. Other places where green landscaping can be used to reduce runoff are on impermeable surfaces such as parking lots.

So why is runoff bad? Runoff is comprised of dirt, pollutants, rain, and other matter it collects in storm drains and streams. Polluted runoff can degrade wildlife and even threaten public health. In urbanized areas, the movement of runoff is determined by sidewalks and buildings. Many cities use rooftop gardens and planters to capture the rainwater and keep it from additionally polluting runoff.