Development and redevelopment within the City has contributed greatly to the pollution of our creeks and ocean. As previously undeveloped land is paved over and built upon, the amount of storm water running off roofs, streets, and other impervious surfaces into our waterways via the storm drain system increases.
The increased volume of storm water runoff and the pollutants carried with it continue to degrade water quality. As development increases, nature’s ability to maintain a water balance is lost to a changing landscape and new impervious surfaces.
Low Impact Development (LID) is an innovative storm water management approach with a basic principle that is modeled after natural processes: to manage rainfall at the source using decentralized, micro-scale controls. LID’s goal is to mimic a site’s predevelopment hydrology by using design techniques that infiltrate, filter, store, evaporate, and detain runoff close to its source.
Techniques are based on the premise that storm water management should not be viewed as storm water disposal. Instead of conveying, managing and treating storm water in large, costly end-of-pipe facilities located at the bottom of drainage areas, LID addresses storm water through small, cost-effective landscape features located at the lot level. These landscape features are the building blocks of LID.
Almost all components of the urban environment have the potential to support LID designs. This includes not only open space, but also rooftops, streetscapes, parking lots, sidewalks, and medians. LID is a versatile approach that can be applied equally well to new development, urban retrofits, and redevelopment/revitalization projects.
Development of LID principles began with the introduction of bioretention technology in the mid-1980s. LID was pioneered to help to help areas address the growing economic and environmental limitations of conventional storm water management practices. LID allows for development with less environmental impacts through the use of smarter designs and advanced technologies that achieve a better balance between conservation, growth, ecosystem protection, and public health/quality of life.
Today, bioretention is just one of the LID techniques available to users. Other techniques, such as permable pavers, tree box planters, and disconnected downspouts, are all LID designs engineered to control pollutants, reduce runoff volume, manage runoff timing, and address a number of other ecological concerns.
Depending on site constraints and project goals, LID designs can be simple, flexible, and effective. It works in highly urbanized constrained areas, as well as open regions and environmentally sensitive sites. LID allows for the integration of treatment and management measures into urban site features, and the result is a hydrologically functional landscape that generates less surface runoff, less pollution, less erosion, and less overall impacts to water quality.
Furthermore, it is being proven that LID costs less than conventional storm water management systems to construct and maintain, in part because of fewer pipes, fewer below-ground infrastructure requirements, and less imperviousness. Other benefits include enhanced property values and redevelopment potential, greater marketability, improved wildlife habitat, thermal pollution reduction, energy savings, and decreased flooding.
Challenges for LID designs are site specific. They include impermeable (clay) soils, steep slopes, and high ground water tables, all of which can make infiltration designs more difficult. LID also represents a change from the status quo, which can result in resistance and conflicts with existing design policies. Lastly, maintaining the designs once they are implemented is another challenge, which can be addressed through proper design and maintenance agreements.