Low impact development (LID) is a more sustainable land development approach (compared with conventional designs) that begins with a site planning process that identifies critical natural resource areas for preservation. LID mimics a site’s predevelopment hydrology by using design techniques that infiltrate, filter, store, evaporate, and detain runoff close to its source.
Development patterns based on conventional zoning codes often result in “sprawl” with its associated large impervious areas, loss of natural resources and habitat, increase in nonpoint source pollution, and alteration of hydrologic systems. Conventional developments often start with clearing and leveling of the entire parcel. Construction of wide, paved roads and over-designed large parking lots typically follows. These sprawling impervious areas eliminate vegetation and prevent water from infiltrating into the ground (see Figures 19.53.140-1 and 19.53.140-2). The result is the conveying of polluted runoff to water bodies. In order to deal with stormwater that runs off these sites, structural controls such as catch basins, pipes, and detention ponds are used. Instead of “greenscapes,” conventional landscaping of these developments brings additional concerns including the introduction of non-native plants, use of herbicides, pesticides and fertilizers, and excessive water consumption.
The LID approach provides opportunities to build homes while conserving natural areas and drainage patterns. LID is accomplished as a two-step process; first – thoughtful site planning and, second – incorporation of “natural” stormwater best management practices (BMPs).
Thoughtful site planning begins with the identification of critical site features such as wetlands, habitat areas, or drinking water protection areas that should be set aside as protected open space. Natural features, such as vegetated buffers and view sheds, will also play an integral role in any LID planning exercise. After the critical open space areas are identified and set aside, sustainable development areas are then identified as “building envelopes.”
Figure 19.53.140-1 Large, impervious surfaces eliminate vegetation and prevent water from infiltrating into the ground |
Figure 19.53.140-2 A clustered development with smaller setbacks and preserved natural areas (left) contrasts with a conventional subdivision where all the trees have been removed. |
Within the delineated building envelopes, a broad range of design techniques or BMPs, such as shared driveways, permeable pavers, and bioretention, are used to reduce the level of impervious cover and improve the quantity and quality of stormwater drainage. Other LID design techniques include green roofs, roof rainwater collection systems, rain gardens, grassed swales, stormwater infiltration systems, and alternative landscaping. Through these techniques, natural drainage pathways are conserved, open space is preserved, and the overall impact from development is significantly reduced.
Often LID techniques provide benefits beyond those related to water and drainage. For example, green roofs also muffle noise by reducing reflective sound, mitigate “urban heat island” effects by creating microclimates that cool and humidify air in their immediate area, absorb dust and smog as well as nitrates and other aerosol contaminants from air and rainfall, and generally provide natural habitat for wildlife including birds, butterflies, and insects.
LID techniques implement development practices that are sustainable and can result in: multi-functionality, lower construction costs, environmental and social benefits, reduced off-site costs, more functional use of open space land, better integration of the built environment with the natural environment, reduced energy costs and increased property values.
Design guidelines in Articles IV and V related to LID are identified with a ♠ symbol.
(Ord. 559 § 6 (Exh. A § 2(C)))
