LID FAQ’s and Resources

Site Factsheets


Design Challenges and Perceived Risks

Construction Issues

Maintenance and Operations of LID:


 General Answers

 What is LID?

  • Low Impact Development or LID is an innovative approach to land development that mimics the natural movement of water in order to manage stormwater (rainwater and urban runoff) close to where it falls
  • LID uses small, simple design techniques and cost-effective landscape features that allow water to infiltrate, filter, store, evaporate, and detain runoff located at the lot level
  • These techniques are based on the principle of using stormwater as a resource

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Why do we need LID in our Watershed?

  • Current Stormwater Management involves conveying, managing, and treating stormwater in large, costly end-of-pipe facilities such as stormwater ponds
  • Urbanization and traditional development practices lead to an increase in hard or impervious surfaces such as rooftops, parking lots and driveways
  • An increase in hard surfaces impacts the natural flow of water
  • When water flows down city streets, it picks up chemicals, trash and bacteria, and carries those pollutants into the storm drain system, where they are carried directly out to our creeks, the Credit River and eventually Lake Ontario
  • Pollutants enter our water system and impact ecosystems, wildlife and our drinking water supply
  • The impacts of rapid growth and urbanization can be relieved through implementation of LID best management practices

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What is the end goal of LID?

  • LID’s goal is to mimic a site’s per-development hydrology
  • The goal of LID is to prevent measurable harm to streams, lakes, wetlands and other natural aquatic systems from commercial, residential or industrial development sites
  • LID practices manage development and stormwater runoff more effectively than traditional stormwater practices and provides an innovative, simple, and cost effective approach

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How will LID help our community?

  • Enhance the recreational and aesthetic values of the community through increased green infrastructure and open space
  • Contribute to groundwater recharge through infiltration
  • Protect stream and lake water quality for safe, abundant, and clean drinking water now and into the future

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Where can LID be applied?

  • LID is a versatile approach that can be applied equally well to new development, urban retrofits, and redevelopment / revitalization projects
  • Link urban design tools (for now) can be applied on roofs, on lawns, in parking lots, streets, medians

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Who is going for LID Now?

  • Ontario Ministry of the Environment (MOE) – Water Opportunities Act
  • Places to Grow Act – Niagara Greenbelt growth
  • Mississauga Green Development Standards
  • Developers are using it regardless of government buy-in

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What are the (cost and environmental) benefits of using LID? Is LID the most cost-effective option for best stormwater management?

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What are examples of LID?

Best Management Practices (BMPs), are the building blocks of LID. Almost all components of the urban environment have the potential to serve as BMP. This includes not only open space, but also rooftops, streetscapes, parking lots, sidewalks, and medians.

  • Rain Garden – depressions that contain soil amendments and appropriate plants that promote both infiltration of stormwater and treatment of pollutants
  • Grassy Swale – vegetated channels that slow stormwater runoff and promote infiltration, trap sediment, and help treat pollutants
  • Downspout redirect – extension or bend in your existing gutter which redirects rain water to a grassy or permeable area
  • Rain Barrels – tanks that attach to the end of your downspouts to collect rain water from your roof
  • Porous Pavement – concrete or asphalt that allows rain to infiltrate, thereby reducing runoff and promoting groundwater recharge

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What other websites can I visit to learn about LID?

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Design Challenges and Perceived Risks Answers

Does LID work in Cold Climates?

There is a common misperception that LID is untested in cold weather climates.

  • LID in cold weather climates has been researched for the past 20 years. In fact, the development of LID began in a region with frequent winter freezes and thaws, Prince George’s County, Maryland.
  • Research institutions in cold weather climates, such as University of Guelph, Queens University, University of New Hampshire, University of Wisconsin, University of Minnesota, and the Villanova University (Pennsylvania), have been actively researching LID.
  • Cold climate adaptations to LID include:
    • extending filter beds or storage beds and underdrain pipes to below the frost line
    • over-sizing the underdrain to reduce the freezing potential
    • selecting salt-tolerant vegetation
  • Permeable pavement can provide better performance in the winter than conventional pavements, because it allows snow melt to drain before it can refreeze on the surface to form black ice.
  • There are no stormwater management techniques that capture road salts. The only way to limit road salt water pollution is through the use of alternative de-icers and improved application methods.

University of New Hampshire Stormwater Center has various LID studies focused on cold climate issues:

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Do infiltration LID practices contaminate soils and groundwater?

  • Unlike conventional stormwater management which seeks to combine, centralize, and treat stormwater, LID treats stormwater near the source in decentralized practices spread across the site.
  • Treating and infiltrating stormwater close to the source prevents contamination of relatively clean runoff which can be infiltrated with dirty runoff.
  • Decentralized stormwater management avoids creating areas of high pollutant concentrations that the soils and vegetation cannot incorporate.
  • Most pollutants (sediment, nutrients, metals, bacteria, oil & grease) are filtered out and captured in bioretention media or the upper layers of native soil in an infiltration practice.
  • A 2008 TRCA study of 12 stormwater practices in the GTA found that small distributed stormwater infiltration practices do not contaminate underlying soils, even after more than 10 years of operation.

Evaluation of Permeable Pavement and Bioswale, Seneca College (includes results of soil contamination analysis for stormwater practices) –

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Are LID practices hazards or dangers to public safety?

  • The small distributed practices of LID are often safer for the public than centralized systems which may have large storage volumes of water.
  • Potential hazards to public safety must be carefully considered in any stormwater management design. Below are examples of guidance provided in the CVC/TRCA LID Planning and Design Guide to protect the public.
    • The maximum allowable surface ponding in LID practices is 15 to 25 cm, which must drain down within 24 hours. The 24 hour maximum surface ponding time is less than the time required for one mosquito breeding cycle.
    • Any depressions for stormwater capture in pedestrian areas, like a bioretention planter in a street sidewalk, needs to be surrounded by curb, railing or fencing to protect the public from trips and falls and the practice from compaction. Where space is available, slopes of 1V:3H are recommended.
    • The Ontario Building Code requires that rainwater harvesting systems used for indoor non-potable uses must have backflow preventer valves to prevent mixing and possible contamination of municipal drinking water supplies.
    • Most permeable pavers on the market meet design standards for the disabled.

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Can LID work in low infiltration soils (clays) or in areas with high groundwater?

  • The goal of LID is to mimic the natural hydrology or the post-development infiltration volumes with pre-development infiltration volumes. If there is little stormwater being infiltrated in the pre-development condition, then the post-development design will be less reliance on infiltration.
  • Infiltration practices over clay soils can be designed with underdrains to provide a factor of safety and avoid prolonged storage of stormwater. The underdrains can be raised above the bottom of the facility to allow for a minimum volume to be infiltrated.
  • Considerable infiltration can still be achieved in clay soils. Studies of infiltration practices with underdrains and in clay soils have shown annual stormwater volume reductions in the range of 20 – 80%.
  • Tight or compacted soils can be amended with compost to increase stormwater retention and infiltration.
  • LID is not just infiltration practices. There are many LID tools and design variations that can be used to reduce runoff volumes and treat stormwater that do not rely on infiltration.
    • Practices like bioretention or dry swales can be lined in areas of high groundwater or contaminated soils. This design variation will slow and filter stormwater.
    • Green roofs and rainwater harvesting systems can also be used in areas where infiltration is inappropriate.

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Will LID practices damage building and road foundations or utilities?

  • A four (4) metre setback is recommended for any infiltration practice located near buildings.
  • For infiltration practices within the right-of-way, a separation barrier might be needed to prevent saturation of the road’s subbase.
  • Utilities need to be consulted for appropriate horizontal and vertical clearance distances. It is feasible for certain utilities to cross infiltration practices like linear bioretention, but special protection might be necessary.

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Where can I get specifications, standards, and details for LID?

  • The CVC/TRCA LID Stormwater Management Planning and Design Guide provides specifications for most materials associated with LID practices.
  • Many LID tools, like soakaways, infiltration trenches, and enhanced swales, are already in common use and have accepted standard details. Newer practices like bioretention and permeable pavement may require non-standard details to be used until municipalities formally accept a standard detail.
  • Non-standard LID design details can be created based on details in the 2003 MOE and the CVC/TRCA LID Planning and Design Guide.

The Green Streets page on the Portland Bureau of Environmental Services website has many LID standard details in pdf and CAD format:

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Construction Issues Answers

Is LID more difficult to install than traditional stormwater management?

  • Most of the same contractors that install traditional stormwater management are capable of installing LID. The construction process is very similar to traditional stormwater management. The design is where LID differs greatly from traditional stormwater management.
  • The CVC/TRCA LID Planning and Design Guide is an excellent resource to contractors as it provides them with specifications regarding LID practices.

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Do I have to install LID in a particular season?

  • No, it is a common misconception that LID needs to be installed in the warmer months. LID can actually be installed without trouble in cold weather climates. Some LID technologies could be revisited in order to plant vegetation.
  • For example, a grassy swale can be excavated in the early winter, and revisited in the early spring in order to be vegetated.

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How can I ensure that the LID practice gets installed according to design?

  • An on-site inspector that has a comprehensive understanding of the project is crucial to the installation of the LID practice. The inspector should be on-site during the entire construction process.
  • It is especially important when the contractor has not typically installed LID designs as some details of the design may be overlooked.
  • For example, installing a 4” perforated pipe where the design calls for a 6” perforated pipe could result in clogging or longer drawdown times. It would be difficult to determine where the mistake occurred once everything is installed.

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How can I protect the infiltration areas during construction?

  • Wrapping the areas under construction in a filter fabric would help with fines entering the infiltration areas.
  • A silt fence would prevent runoff from entering the infiltration areas.
  • Digging small trenches beside the infiltration areas would direct flow away from the infiltration areas.

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What can I do to promote the establishment of vegetation?

  • Measures can be put in place to prevent soil compaction from heavy machinery during construction.
  • Ensure the selected vegetation has appropriate soil type and conditions.

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Maintenance and Operations of LID Answers

Is LID difficult to maintain?

  • LID, like all, SWM controls requires maintenance to maintain optimal performance. With proper training, education and monitoring, LID is not difficult to maintain.

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Does LID have higher rates of failure than traditional stormwater management?

  • Like any SWM control, failure can take place if proper construction and maintenance of the facility is not taking place. However, if failure does take place, its impact is much less significant than a single centralized end of pipe of control. LID places emphasis upon multiple source water controls, thus redundancy in design is built within its framework to handle possible failure of a LID feature as there are multiple sites to compensate.
  • Please Refer to Section 2.7

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How is LID maintained on private property

  • For LID constructed on a private property by a municipality or developer, it will usually be the responsibility of the property owner to maintain the LID feature. Maintenance requirements and responsibility of the property owner can be incorporated into the deed of the property. To assist property owners and ensure performance, municipalities can offer training to property owners, technical assistance and additional information. In other cases, there are examples of where the municipality establishes an easement to enter the private property to complete maintenance on the LID feature.

Additional Info:

  • Section 2.9.2 – Opportunities at the Neighborhood Scale – LID Stormwater Management Planning and Design Guide

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How can LID be maintained properly when there is a lack of knowledge among municipal staff?

  • Implementation of LID needs to be coordinated with the training of municipal staff. In recent years, CVC has put forward a LID planning and design guide to answer questions that municipal staff may have. Additional resources are available online, however working in coordination with your local conservation authorities, LID research centers and experienced water resource consultant can provide beneficial oversight and training for municipal staff.

Additional Information:

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How do you maintain LID sites in the winter time?

  • As many LID practices are situated within or adjacent to parking lots, consideration should be given on how winter maintenance practices impact LID features. Design and the placement of LID should account for the location of snow storage. The burying of a LID feature due to snow clearing may impact its function in the spring and summer.
  • As the snow melts, LID infiltration practices are susceptible to residual chloride due to winter salt application. Chloride is highly soluble in water and there are no natural removal mechanisms for chloride. As a result, plants within infiltration practices could be impacted by salt burn and scorch. Switching to a deicer application with a low chloride concentration or a deicer with no chloride may be beneficial in maintaining the success of the plantings.
  • Consideration should be also taken when winter sand is applied. LID practices like permeable pavement or pavers require liquid based deicer rather than sand due to the fact that sand can clog infiltration practices preventing water from properly draining.

Additional Information:

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