Low Impact Development (LID)

Definitions & Purpose

LID refers to engineered systems, either structural or natural, that use or mimic natural processes to promote infiltration, evapotranspiration, and/or reuse of storm water as close to its source as possible to protect water quality and aquatic habitat. LID practices at the regional and site-specific level preserve, restore, and create green space using soils, vegetation, and rainwater harvesting techniques. These systems and practices are referred to as Best Management Practices (BMPs). 

Green infrastructure (GI) includes LID practices but is a broader practice that also includes ecological services and approaches such as "filtering air pollutants, reducing energy demands, mitigating urban heat islands, sequestering and storing carbon, enhancing aesthetics and property values, and preserving and creating natural habitat functions.

Urban development has historically resulted in increased impervious surfaces, vehicle use, and other human activities that introduce pollutants and create adverse hydrologic conditions detrimental to water quality. In the past, the goal of traditional storm water management was to convey these flows offsite as directly as possible, giving little to no consideration to preserving open spaces or creating pervious areas where rainfall could be managed on-site. Flood control infrastructure such as storm drains have been used to convey runoff and discharge it to a receiving surface water. Polluted runoff degrades the quality of the receiving water, impacting aquatic life and dependent ecosystems. Incorporating LID practices reduces the impact of development on natural waterways and watersheds and provides practical as well as aesthetic benefits. Other benefits include reduced construction costs by conveying runoff through vegetated swales instead of through pipes. Pavers or other pervious surfaces can reduce the size of an on-site basin by retaining runoff within a subsurface storage layer and bioretention areas can provide retention and treatment to improve water quality before discharging. These types of designs also enhance the aesthetics of the development and are viewed favorably by the public. 

LIDs can:

• Help improve water quality
• Recharge groundwater aquifers
• Restore habitats
• Reduce the chances of flooding 
• Look beautiful
• Be cost effective