Low-impact development (LID) has been defined as “development which through its low negative environmental impact either enhances or does not significantly diminish environmental quality”.
The interplay between would-be developers and the UK planning authorities since the 1980s has led to a diversity of unique, locally adapted developments, often making use of natural, local and reclaimed materials in delivering highly affordable, low or zero carbon housing. These LIDs often strive to be self-sufficient in terms of waste management, energy, water and other needs.
There are numerous examples of LIDs throughout the UK, and local and national authorities have come to recognise the need for the concept to be incorporated into planning strategies.
Low-impact development (LID), in the UK sense of the term, was described by Simon Fairlie, a former editor of The Ecologist magazine, in 1996 as: “development that through its low impact either enhances or does not significantly diminish environmental quality.” Fairlie later wrote:
“Neither the term nor the concept was new. People have been living low impact lifestyles in low impact buildings for centuries; indeed until very recently the majority of people in the world lived that way.”
In 2009 Fairlie revised his definition of a LID as: “development which, by virtue of its low or benign environmental impact, may be allowed in locations where conventional development is not permitted.” He explained:
“I prefer this revised definition because wrapped up in it is the main argument; that low impact buildings need not be bound by the restrictions necessary to protect the countryside from ‘conventional’ high impact development – a.k.a. suburban sprawl. There are two other principle arguments in favour of LID: (i) that some form of exception policy is necessary because conventional housing in a countryside protected from sprawl becomes too expensive for the people who work there; and (ii) soon we will all have to live more sustainable low impact lifestyles, so pioneers should be encouraged.”
Others have expanded on the definition. A study by the University of West England acknowledged that: “LID is usually integrally connected with land management and as much as describing physical development, LID also describes a form of livelihood.” However, it also states that as LID is a “multi featured and intrinsically integrated form of development,” a simple definition cannot capture the meaning of LID and goes on to develop “a detailed themed definition with detailed criteria.”
Dr Larch Maxey in 2013 held the main features of LID to be:
locally adapted, diverse and unique
based on renewable resources
of an appropriate scale
increases public access to open space
generates little traffic
linked to sustainable livelihoods
co-ordinated by a management plan
English LID examples include the Hockerton Housing Project (Nottinghamshire), Michael Buck’s cob house in Oxfordshire, Landmatters (Devon) and Tinker’s Bubble (Somerset).
Transition Homes, currently under development in Transition Town Totnes, Devon, is an attempt to scale-up and mainstream LID by providing around 25 low cost, low carbon homes designed along permaculture principles. Residents will be allocated from the local housing needs register. Similarly, LILAC built in 2013 a ‘Low Impact Living Affordable Community’ of 20 homes and a common house in Bramley, Leeds, which was visited by Kevin McCloud and Mark Prisk, Minister of State for Housing and Local Government.
BedZED (London) is another example of a larger scale LID, which was built in 2000–2002 and has 82 homes, however it is not as affordable as many of the above examples as it was partly designed to attract urban professionals.
Findhorn Ecovillage has won a number of international awards. Steve James’s Straw House, Dumfries was built for £4,000.
The House of the Future, Cardiff, completed in 2000, was originally a showcase of the latest green building technologies, and later transformed into an education centre. In West Wales, Lammas Ecovillage (near Crymych, Pembrokeshire) is a community of independent, off-grid households begun in 2009. Nearby Pwll Broga roundhouse is a development that was built without planning permission in 2012, refused retrospective planning permission in 2014, but granted permission in July 2015, having met the requirements of the Welsh government’s One Planet Development policy. That Roundhouse (Brithdir Mawr, Newport, Pembrokeshire) was granted planning permission in 2008 with a review in 3 years.
Substantial research has concluded that LID represents some of the most innovative and sustainable development in the UK.
LIDs have innovated and demonstrated sustainable solutions including low/zero carbon housing design, rainwater harvesting, renewable energy generation, waste minimisation and innovative forms of land management, including No/low-till farming, permaculture and agroforestry.
LID has also shown a capacity to enhance local biodiversity and public access to local space, and to produce traffic movements far below the national average. This has been attributed to lift-sharing, to residents’ greater use of public transport, walking and cycling and to the integration of local land based employment with other household activities. As the Welsh Assembly Government has noted, such “…Development therefore is not just describing a physical development. It is describing a way of living differently where there is a symbiotic relationship between people and land, making a reduction in environmental impacts possible”.
Over the years, there have been various struggles with planning authorities over LID in the UK. Tony Wrench spent over a decade fighting the planning authorities until he was granted planning permission for That Roundhouse. As Lisa Lewinsohn points out in her MSc thesis on LID, Tony Wrench and his partner Jane Faith have been “enforced against, fined, refused planning permission several times” while Lammas has “probably spent about £50,000 on the application process.” Similarly, since 1986 Tir Penrhos Isaf has tried several times to get planning permission and only succeeded in December 2006, twenty years after their first planning application was submitted.
The residents of Tir Penrhos Isaf consider:
“that current planning and building legislation represent some of the greatest obstacles to developing sustainable systems in Britain. The legislation favours those who already have land and property, actively encourages the squandering of resources and environmental degradation and actively discourages movements towards low impact, sustainable development.”
The extensive research interest in LID, backed up by the practical examples of the existing LIDs, has led to a growing number of planning policies in the UK designed to allow for LIDs. and the Welsh Assembly Government’s One Planet Development policy (OPD) which is supported by the independent One Planet Council. The first development to receive permanent planning permission under the One Planet scheme was Nant-y-Cwm, near Caerphilly. The criteria for OPD in Wales include the requirement that 65% of all subsistence, or 30% of food and 35% of livelihood, come from the land.
U.S. and Canada
Low-impact development (LID) is a term used in Canada and the United States to describe a land planning and engineering design approach to manage stormwater runoff as part of green infrastructure. LID emphasizes conservation and use of on-site natural features to protect water quality. This approach implements engineered small-scale hydrologic controls to replicate the pre-development hydrologic regime of watersheds through infiltrating, filtering, storing, evaporating, and detaining runoff close to its source. Green infrastructure investments are one approach that often yields multiple benefits and builds city resilience.
Broadly equivalent terms used elsewhere include Sustainable drainage systems (SuDS) in the United Kingdom (where LID has a different meaning), water-sensitive urban design (WSUD) in Australia, natural drainage systems in Seattle, Washington and “Onsite Stormwater Management”, as used by the Washington State Department of Ecology.
Alternative to conventional stormwater management practices
A concept that began in Prince George’s County, Maryland in 1990, LID began as an alternative to traditional stormwater best management practices (BMPs) installed at construction projects. Officials found that the traditional practices such as detention ponds and retention basins were not cost-effective and the results did not meet water quality goals. The Low Impact Development Center, Inc., a non-profit water resources research organization, was formed in 1998 to work with government agencies and institutions to further the science, understanding,and implementation of LID and other sustainable environmental planning and design approaches, such as Green Infrastructure and the Green Highways Partnership.
The LID design approach has received support from the U.S. Environmental Protection Agency (EPA) and is being promoted as a method to help meet goals of the Clean Water Act. Various local, state, and federal agency programs have adopted LID requirements in land development codes and implemented them in public works projects. LID techniques can also play an important role in Smart Growth and Green infrastructure land use planning.
Designing for low-impact development
The basic principle of LID to use nature as a model and manage rainfall at the source is accomplished through sequenced implementation of runoff prevention strategies, runoff mitigation strategies, and finally, treatment controls to remove pollutants. Although Integrated Management Practices (IMPs) — decentralized, microscale controls that infiltrate, store, evaporate, and detain runoff close to the source — get most of the attention by engineers, it is crucial to understand that LID is more than just implementing a new list of practices and products. It is a strategic design process to create a sustainable site that mimics the undeveloped hydrologic properties of the site. It requires a prescriptive approach that is appropriate for the proposed land use.
Design using LID principles follows four simple steps.
Determine pre-developed conditions and identify the hydrologic goal (some jurisdictions suggest going to wooded conditions).
Assess treatment goals, which depend on site use and local keystone pollutants.
Identify a process that addresses the specific needs of the site.
Implement a practice that utilizes the chosen process and that fits within the site’s constraints.
The basic processes used to manage stormwater include pretreatment, filtration, infiltration, and storage and reuse.
Pre-treatment is recommended to remove pollutants such as trash, debris, and larger sediments. Incorporation of a pretreatment system, such as a hydrodynamic separator, can prolong the longevity of the entire system by preventing the primary treatment practice from becoming prematurely clogged.
When stormwater is passed through a filter media, solids and other pollutants are removed. Most media remove solids by mechanical processes. The gradation of the media, irregularity of shape, porosity, and surface roughness characteristics all influence solids removal. Many other pollutants such as nutrients and metals can be removed through chemical and/or biological processes. Filtration is a key component to LID sites, especially when infiltration is not feasible. Filter systems can be designed to remove the primary pollutants of concern from runoff and can be configured in decentralized small-scale inlets. This allows for runoff to be treated close to its source without additional collection or conveyance infrastructure.
Infiltration reclaims stormwater runoff and allows for groundwater recharge. Runoff enters the soil and percolates through to the subsurface. The rate of infiltration is affected by soil compaction and storage capacity, and will decrease as the soil becomes saturated. The soil texture and structure, vegetation types and cover, water content of the soil, soil temperature, and rainfall intensity all play a role in controlling infiltration rate and capacity. Infiltration plays a critical role in LID site design. Some of the benefits of infiltration include improved water quality (as water is filtered through the soil) and reduction in runoff. When distributed throughout a site, infiltration can significantly help maintain the site’s natural hydrology.
Storage and reuse
Capturing and reusing stormwater as a resource helps maintain a site’s predevelopment hydrology while creating an additional supply of water for irrigation or other purposes. Rainwater harvesting is an LID practice that facilitates the reuse of stormwater.
Five principles of low-impact development
There are 5 core requirements when it comes to designing for LID.
Conserve natural areas wherever possible (don’t pave over the whole site if you don’t need to).
Minimize the development impact on hydrology.
Maintain runoff rate and duration from the site (don’t let the water leave the site).
Scatter integrated management practices (IMPs) throughout your site – IMPs are decentralized, microscale controls that infiltrate, store, evaporate, and/or detain runoff close to the source.
Implement pollution prevention, proper maintenance and public education programs.
Typical practices and controls
Planning practices include several related approaches that were developed independently by various practitioners. These differently named approaches include similar concepts and share similar goals in protecting water quality.
Conservation design, also called Conservation Development
Better Site Design
Planners select structural LID practices for an individual site in consideration of the site’s land use, hydrology, soil type, climate and rainfall patterns. There are many variations on these LID practices, and some practices may not be suitable for a given site. Many are practical for retrofit or site renovation projects, as well as for new construction. Optimal places for retrofitting LID are single houses, school/university areas, and parks. Frequently used practices include:
Bioretention cells, also known as rain gardens
Cisterns and rain barrels
Pervious concrete, also called “porous pavement”, similar to Permeable paving
Grassed swales, also known as bioswales.
Commercially manufactured stormwater management devices that capture pollutants (e.g., media filters) and/or aid in on-site infiltration.
Limitations for LID progress
Urban areas are especially prone to create barriers for LID practices. The most common limits are:
lack of suitable places for LID facilities in existing complex infrastructure of urban areas
lack of design standards that can be applicable around the world
lack of knowledge about LID technology among local governments and residents
false belief that LID practices are difficult to maintain and/or the maintenance cost is high.
LID has multiple benefits, such as protecting animal habitats, improving management of runoff and flooding, and reducing impervious surfaces. For example, Dr. Allen Davis from the University of Maryland, College Park conducted research on the runoff management from LID rain gardens. His data indicated that LID rain gardens can hold up to 90% of water after a major rain event and release this water over a time scale of up to two weeks. LID also improves groundwater quality and increases its quantity, which increases aesthetics, therefore raising community value.
LID can also be used to eliminate the need for stormwater ponds, which occupy expensive land. Incorporating LID into designs enables developers to build more homes on the same plot of land and maximize their profits.
Source from Wikipedia