Low Impact Development Techniques (LID)
What Is It
Low Impact Development is a comprehensive land planning and engineering design approach with the goal of maintaining and enhancing storm water runoff of developing watersheds. LID systems utilize practices that create or mimic natural processes that result in infiltration, evapotranspiration or use of storm water in order to protect water quality and associated watersheds.
Principles of LID
- Preserve and recreate natural landscape features
- Minimize effect of development to site hydrology (imperviousness)
- Scatter integrated management practices throughout site development
- Maintain runoff rate and duration from a developed site
- Implement pollution prevention, proper maintenance, and public education
Common LID Techniques
A garden that takes advantage of rainfall and storm water runoff in its design and plant selection. Two basic types include underdrained and self-contained. Both are designed to improve water quality, reduce runoff volumes and facilitate infiltration of clean water. Water in a rain garden should fully drain within four hours of a one inch rain event.
Designed to provide an element of water quality control while also allowing quantity control by infiltrating and temporarily storing water runoff. Often used in development sites, the main goal is to minimize, detain and retain post construction runoff uniformly and mimic pre-development hydrology. In a swale design, water is often spread along a shallow lengthy graded ditch to maximize stormwater duration in the swale to allow for greater infiltration and trapping of contaminants and silt.
Rain Barrel or Cistern
A waterproof container for holding liquids, built to catch and store rainwater. Distinguished from wells by their waterproof lining; rain barrels are often used to capture rainwater from rooftop gutters. The captured water can be utilized to irrigate the surrounding landscape and reduce stormwater runoff of developed property.
Vegetated Roof (Green Roof)
A roof of a building designed to be partially or completely covered in vegetation. Plant materials are layered over a waterproof membrane and aid in the absorption of rainwater. Green Roofs also provide insulation, mitigate a heat island effect in urban areas, provide a pleasing aesthetic and create wildlife habitat.
Specifically designed materials in conjunction with a base and subbase that allow the movement of storm water through the surface. Permeable pavers or pavement designs can reduce runoff, trap suspended solids and filter pollutants. The porous surface may require specific clean out maintenance based on design; but can be utilized for parking areas, sidewalks, paths, lawns, bikelanes and driveways.