Definition of Low Impact Development
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 (Fletcher et al., 2014). 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. Table __ presents the various terminologies used in different parts of the world and where each term originated (highlighted in yellow). For detailed descriptions of each term, please refer to Fletcher et al. (2014).
Table 1. Regional terminology use.
| Terminology | New Zealand | Australia | United Kingdom | Europe |
|---|---|---|---|---|
| Green Infrastructure | Guelph, Ontario | 89% | Farahbakhsh et al. (2009) | |
| Dual Use Cisterns1 | Toronto, Ontario | 23 to 46% | TRCA (2010) | |
| Dual Use Cisterns1 | Australia | 60 to 90% | Hardy et al. (2004) | |
| Dual Use Cisterns1 | Australia | 40 to 45% | Coombes and Kuczera (2003) | |
| Dual Use Cisterns1 | New Zealand | 35 to 40% | Kettle et al. (2004) | |
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 Low Impact Development (LID) Planning and Design guidance document 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.