Definition of Low Impact Development

This guide has been developed as a tool to help developers, consultants, municipalities and landowners understand and implement more sustainable stormwater management planning and design practices in their watersheds. Many jurisdictions have defined the term low impact development. For this document, the following definition, adapted from the United States Environmental Protection Agency will be used:

systems and practices that use or mimic natural processes that result in the infiltration, evapotranspiration or use of stormwater in order to protect water quality and associated aquatic habitat.

The field of stormwater management has undergone considerable evolution in the last 40-50 years, from underground drainage systems for rapid water disposal, to stormwater management ponds, to today’s myriad of near-to-nature practices and technologies. This paradigm shift could be explained by a change of perception about water from a waste to a resource. With this evolution comes the evolution of terminology to describe the latest visions, practices and technologies. There are various terms used in stormwater management related literature across the globe. Some terms differ only in their geography while others differ in their connotation.

Regional terminology use

Terminology	North America	New Zealand	Australia	United Kingdom	Europe
Green Infrastructure (GI)1	x1	-	-	-	-
Low Impact Development (LID)	x1	x2	-	-	-
Water Sensitive Urban Design (WSUD)	x	x2	-	-	-
Integrated Urban Water Management (IUWM)	-	-	-	-	x1
Best Management Practices (BMPs)	x1	-	-	-	-
Stormwater Control Measures (SCMs)	x1	-	-	-	-
Alternative Measures	-	-	-	-	x1
Source Control	x1	-	-	-	-

In many cases, the terms LID and GI are used interchangeably to describe an alternate management approach from the conventional ‘grey’ infrastructure approach. The inconsistent use of these two terms by different agencies and scholars across North America and other parts of the world contributes to the confusion already associated with these relatively new approaches to stormwater management. In this guide we make a distinction between LID and GI on the grounds of geographic and structural (engineered) scales of classification and implementation. Traditionally, the term infrastructure connotes a requirement that is necessary to keep an urban center functional, while green space connotes a want, putting it at the bottom of priority lists. The term GI emerged to put more emphasis on green space as a need rather than a want and elevate it within budget priority lists. As such, in addition to traditional water-related infrastructure, GI encompasses non-traditional infrastructure, such as:

• heritage features,
• parklands,
• street trees,
• natural channels, or

in other words any natural(ized) green space.

GI describes a strategically planned and delivered network of natural and semi-natural elements that collectively deliver a wide range of ecosystem, social and economic services to help reduce dependence on grey infrastructure and to address environmental resilience and climate change. The LID approach to stormwater management falls under the overarching umbrella of GI as a semi-natural element. LID comprises comprehensive, engineered site-design strategies and techniques that seek to mitigate the impacts of increased runoff and stormwater pollution by replicating or maintaining the site’s pre-development hydrological and ecological functions. This is achieved as close to the runoff source as possible through the processes of retention, filtration, infiltration and evapotranspiration. These practices can effectively remove nutrients, pathogens and metals from runoff, and they reduce the volume and intensity of stormwater flows.

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A stormwater management strategy that seeks to mitigate the impacts of increased urban runoff and stormwater pollution by managing it as close to its source as possible. It comprises a set of site design approaches and small scale stormwater management practices that promote the use of natural systems for infiltration and evapotranspiration, and rainwater harvesting.

The slow movement of water into or through a soil or drainage system.

Penetration of water through the ground surface.

The quantity of water transpired (given off). Retained in plant tissues, and evaporated from plant tissues and surrounding soil surfaces. Quantitatively it is usually expressed in terms of depth of water per unit area during a specified period. e.g. mm/day

The combined loss of water to the atmosphere from land and water surfaces by evaporation and from plants by transpiration.

Green infrastructure

Low impact development is a stormwater management and land development strategy applied at the parcel and subdivision scale that emphasizes conservation and use of on-site natural features integrated with engineered, small scale hydrologic controls to more closely mimic pre-development hydrologic functions.

A stormwater management strategy that seeks to mitigate the impacts of increased urban runoff and stormwater pollution by managing it as close to its source as possible. It comprises a set of site design approaches and small scale stormwater management practices that promote the use of natural systems for infiltration and evapotranspiration, and rainwater harvesting.

Low Impact Development. A stormwater management strategy that seeks to mitigate the impacts of increased urban runoff and stormwater pollution by managing it as close to its source as possible. It comprises a set of site design approaches and small scale stormwater management practices that promote the use of natural systems for infiltration and evapotranspiration, and rainwater harvesting.

State of the art methods or techniques used to manage the quantity and improve the quality of wet weather flow. BMPs include Source, Conveyance and End-Of-Pipe Controls.

A biological community, including humans and their natural environment.

The portion of water precipitated onto a catchment area, which then flows as surface discharge from the catchment area past a specified point.

Water from rain, snow melt, or irrigation that flows over the land surface.

refers to the characteristics and functions of a system prior to urban development.

Relating to the properties, distribution and effects of water on and below the earth’s surface, and in the atmosphere.

The technique of removing pollutants from runoff as it infiltrates through the soil.

Natural or artificial means of intercepting and removing surface or subsurface water (usually by gravity).