What Is Low Impact Development And Why Should You Consider It?

Low Impact Development (LID) is a land planning and engineering approach that reduces the impacts of urbanization on the environment. It integrates soils, biology, and hydrology into the plan development stage, involves methods for decreasing runoff volume, and promotes the use of natural processes like swales, wetlands, and natural vegetation to decrease flow and increase infiltration. The goal of LID is to create an environmental design that mimics natural watershed functions by limiting the impacts on waterflow and absorption within the watershed.

Urban development causes changes in how water moves through watersheds. Sidewalks, parking lots, rooftops, and other impervious surfaces do not allow water to enter the ground. Instead, it runs down these surfaces and into streams and other waterbodies such as Lake Whatcom. These hydrological changes contribute to two things: less ground water resources and a potential impairment to surface water if the runoff is not treated.

Factors that go into Low Impact Developments

Design lots so that they reduce the amount of clearing needed for the buildings. Utilize existing natural vegetation such as swales and stands of trees for controlling storm water. This not only helps reduce flooding and pollution concerns, but may save in the overall costs for infrastructure and maintenance of stormwater systems.

• Use porous pavement rather than conventional pavement like concrete. Porous pavement is permeable and allows water to be absorbed (infiltrate) rather than contribute to storm water runoff.         
• Route water from rooftops to vegetated areas or on-site infiltration systems.
  
• Integrate architectural designs into site plan that reduce the actual footprint of the building, thus reducing impervious surfaces on the total land area of the property. For example, instead of building a single story home, build “up” to reduce the volume of storm water runoff and increase open space.
  

Scenario 1- A Conventional Site Design

Site Design Concerns:

• Structures close to steep slopes, streams, and wetlands may result in disturbances to fish and wildlife habitat as well as property loss or damage.
  
• Multiple rooftops increase the amount of impervious surface covering the lot, which increases the amount of storm water runoff from the site.
  
• Paved walkways, patio, and driveway contribute to the amount of impervious surface covering the site.
  
• The large percentage of impervious surface on this lot creates challenges for managing the large volume of storm water runoff that will be generated.
  

Scenario 2- A Low Impact Site Design

Site Design Benefits:

• Tailoring the project to the site reduces disturbance of natural features such as steep slopes, wetlands, and streams, which helps protect fish and wildlife habitat.
  
• Minimizing the number of structures on the site reduces rooftop surfaces, which in turn reduces the amount of impervious surface on your site.
  
• Driveways, walkways, and patios made of surfaces such as gravel, lattice paving blocks, and wood reduce the amount of storm water runoff from the site.