Low Impact Development

Issue

Conventional development can have a detrimental effect on water quality, natural hydrology, the integrity and function of streams and wetlands, natural habitat and biodiversity, and maintaining the water balance of an area. The conversion of natural land to impervious surfaces, especially those that are directly connected to waterways, are of particular concern due to increases in the amount, timing and velocity of flow, which can degrade streams and increase pollutant loads from urban runoff.

Part of the Solution

Low Impact Development (LID) is a storm water management approach that actually integrates older techniques with new innovative methods that strive to manage urban runoff as close to the source as possible. LID uses a decentralized system of detention and treatment solutions to fit the needs of a particular site. This is accomplished by mimicking or recreating a site's predevelopment hydrologic conditions by using design techniques that infiltrate, filter, store, evaporate and detain runoff on-site as much as possible.

LID relies on landscape and engineering features, known as site specific Best Management Practices (BMPs)¹. Site based BMPs can address water quality and hydrology concerns, protect natural resources and biodiversity, and cut costs of storm water management by reducing the size or need for large detention basins, pipes and pumping facilities.

LID is a versatile approach applicable to a variety of development types. It can be applied equally well to new development and redevelopment/revitalization and lower density as well as higher density projects. LID techniques have been successfully used in areas of various soil types, including soils with low percolation rates (note: in these cases special soil engineering or supplemental drainage may be needed). It can also be used in a variety of settings from residential to commercial and from small development to large. The techniques can be applied at site specific neighborhood, or regional levels, and take advantage of "natural" infrastructure to address drainage and reduce the impacts of the built environment.

Pollutants from urban areas (see Table 1) can have serious impacts on aquatic ecosystems. For example, excessive amounts of nutrients such as nitrogen or phosphorous can lead to algal blooms or the proliferation of undesirable plant species that can seriously disrupt the ecology of wetlands or other aquatic environments. Sediment resulting from inappropriate construction practices, poorly degraded development or other activities in a watershed can clog stream bottoms and cause damage to the aquatic ecosystem. Changes in the hydrology resulting from urban development can cause major changes to stream channel dynamics, often creating further impacts and erosion downstream. LID techniques can greatly reduce these non-point source pollution risks by slowing runoff, increasing the sorption of pollutants in soils and organic matter, and through the uptake of pollutants in vegetation (phytoremediation).

¹ These BMPs may also be referred to as Intgrated Management Practices (IMPs).