What is LID?

  • Low Impact Development (LID) or green infrastucture is a stormwater management philosophy that attempts to mimic and work with nature by capturing surface water over a small area as close to its source as possible and facilitating its infiltration into the ground. “Green infrastructure ” encompasses approaches and technologies to infiltrate, evapotranspire, capture, and reuse stormwater to maintain or restore natural hydrologies.  In doing so, the impact of development is reduced and the natural movement of water is promoted. When applied on a wide scale it can maintain or restore a watershed’s hydrologic and ecological functions.  LID is in contrast to the current prevalent stormwater management practice of capturing surface water over a large area and directing it into large detention ponds and vaults where it is retained and released into a stormwater conveyance system (either pipes or streams) in a controlled manner.
  • LID Benefits
    • Improved water quality: pollutants such as oil, bacteria, sediments, metals, hydrocarbons and some nutrients in stormwater are reduced before water reaches streams and Puget Sound.
    • Reduced number of costly erosion events: volume of water that enters streams is reduced thus decreasing amount of erosion in the gulches
    • Restored aquatic habitat: less erosion means less damage to fish habitats
    • Improved groundwater recharge: water that goes into detention facilities and discharged into pipes goes straight into Puget Sound and never has a chance to soak into the ground.
    • Enhanced neighborhood beauty: traditional stormwater management infrastructures are typically concrete and fenced. LID facilities are neither of these.
  • LID Best Management Practices (BMPs) or techniques include:
    • Permeable/Pervious pavement: allows water to flow through pavement into the ground; typically not a do-it-yourself project because it requires an engineer to design and a contractor to install; homeowners can do small scale projects using pervious pavers
    • Rain gardens (bioretention facilities): landscaped depression areas that allow rainwater to be absorbed into the ground.
      • Materials: Native vegetation and soil amendments
      • Installers: Landscapers
      • Designers: Landscape architects/engineers
    • Vegetated swales: gently sloped depressions planted with dense vegetation which slows flows to facilitate infiltration and filters water to improve water quality
    • Rain barrels: captures rainwater that falls on roofs to be used later for irrigation needs; many nurseries and garden centers sell them as do some public agencies
    • Vegetated rooftops:  roofs covered with plants and dirt; they absorb rainwater and provide insulation and create habitat; typically not a do it yourself project because they need to be engineered to ensure the structure can bear the additional weight and won’t leak

The United States Environmental Protection Agency (EPA) has created “fact sheets” explaining the benefits of LID or green infrastructure: