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About the Low Impact Development Planning and Design Wiki Guide

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About the Contents of this Guide

The Low Impact Development Stormwater Management Planning and Design Guide (LID SWM Guide) has been developed by Credit Valley Conservation (CVC) and Toronto and Region Conservation Authority (TRCA) 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 (U.S. EPA, 2007) will be used:

Low impact development (LID) is a stormwater management strategy that seeks to mitigate the impacts of increased runoff and stormwater pollution by managing runoff as close to its source as possible. LID comprises a set of site design strategies that minimize runoff and distributed, small scale structural practices that mimic natural or predevelopment hydrology through the processes of infiltration, evapotranspiration, harvesting, filtration and detention of stormwater. These practices can effectively remove nutrients, pathogens and metals from runoff, and they reduce the volume and intensity of stormwater flows.

The LID SWM Guide provides information and direction to assist engineers, ecologists and planners with landscape-based stormwater management planning and the selection, design, construction and monitoring of sustainable stormwater management practices. The focus of this guide is on guidance regarding the planning and design of structural low impact development practices for stormwater management.

The practice of managing stormwater is continuing to evolve as the science of watershed management and understanding of our watersheds grow. Effective management of stormwater is critical to the continued health of our streams, rivers, lakes, fisheries and terrestrial habitats. CVC and TRCA believe that an improved understanding of the municipal and environmental planning process and the requirements for stormwater management will lead to improvements in management practices and an increasingly standardized and streamlined approach to addressing stormwater throughout the CVC and TRCA watersheds.

The LID SWM Guide is intended to augment the Ontario Ministry of the Environment (OMOE) Stormwater Management Planning and Design Manual (2003). The OMOE manual provides design criteria for “conventional” end-of-pipe stormwater management practices such as wet ponds and constructed wetlands but provides only limited information about lot level and conveyance controls. The OMOE manual does, however, emphasize the use of a “treatment train” approach to reduce the impacts of stormwater runoff. A treatment train approach – a combination of lot level, conveyance, and end-ofpipe stormwater management practices – is usually required to meet the multiple objectives of stormwater management, which include maintaining the hydrologic cycle, protecting water quality, and preventing increased erosion and flooding.

This LID SWM Guide focuses on a number of lot level and conveyance stormwater management practices that have been used extensively in Europe, the United States, British Columbia and at demonstration sites in Ontario. These practices have only recently been considered for broad application in Ontario as part of the treatment train approach. These low impact development practices include green roofs, bioretention, permeable pavement, soakaways, perforated pipe systems, enhanced grass swales, dry swales and rainwater harvesting. The LID SWM Guide recommends and supports the use of the treatment train approach for stormwater management. Accordingly, the reader is urged to refer to the OMOE manual (OMOE, 2003), as a guide for incorporating more traditional practices such as wet ponds and wetlands into the overall stormwater management planning and design process.

The LID SWM Guide is not intended to limit innovation or restrict the use of creative solutions for stormwater management. Indeed, the OMOE, CVC, TRCA and partner municipalities encourage the development of innovative designs and technologies.

Related Documents

This manual is not a stand-alone document. It is intended to augment the Ontario Ministry of the Environment’s 2003 Stormwater Management Planning and Design Manual, which provides design criteria for “conventional” end-of-pipe stormwater management practices such as wet ponds and constructed wetlands. It is also a companion document to other stormwater related guidance documents prepared by CVC and TRCA. Amongst others, these include:

CVC

• Credit River Water Management Guidelines (CRWMG) (2007);

• Credit River Stormwater Management Criteria (currently under development; will be an appendix to the CRWMG;

• Geomorphic and Meander Belt Guidelines (an appendix to the CRWMG); • Floodline Mapping Guidelines (an appendix to the CRWMG);

• Environmental Impact Report Terms of Reference (an appendix to the CRWMG);

• Technical Guidelines for Floodproofing, 1994 (an appendix to the CRWMG);

• Hydrologic/Hydraulic Modeling (an appendix to the CRWMG Guidelines);

• Guidelines for Hydrogeologic Studies (an appendix to the CRWMG);

• Headwater Assessment Guidelines (an appendix to the CRWMG).

TRCA

• Planning and Development Procedural Manual (2007);

• Stormwater Management Criteria (currently under development);

• Floodplain Management Guideline; and

• Stream Crossing Guidelines.

Notice

The contents of this report do not necessarily represent the policies of the supporting agencies. Although every reasonable effort has been made to ensure the integrity of the report, the supporting agencies do not make any warranty or representation, expressed or implied, with respect to the accuracy or completeness of the information contained herein. Mention of trade names or commercial products does not constitute endorsement or recommendation of those products.

Acknowledgements

Project Team:

• Toronto and Region Conservation Authority

• Credit Valley Conservation Authority

• Sustainable Technologies Evaluation Program

• Aquafor Beech Limited

• Schollen & Company

• Dougan and Associates

• Kidd Consulting

• Center for Watershed Protection

• Chesapeake Stormwater Network

Funding support for this document was generously provided by:

• Region of Peel

• City of Toronto

• Region of York

• Fisheries and Oceans Canada

• Ontario Ministry of the Environment

• Environment Canada’s Great Lakes Sustainability Fund

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.

Stormwater Management

Credit Valley Conservation

Toronto and Region Conservation Authority

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.

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 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.

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.

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

The temporary storage of stormwater to control discharge rates, and allow for sedimentation.

Surface runoff from at-grade surfaces, resulting from rain or snowmelt events.

Refers to the conditions in which an organism lives and survives or the conditions in which an organism resides. These conditions can be described as aspects of a “physical”, “social” or an “economic” environment, depending on the perspective perceived by the observer.

The treatment of urban runoff as close to the source area as possible through application of small scale stormwater management practices on individual properties that are linked to downstream conveyance and end-of-pipe practices.

Stormwater management following the hierarchical approach: Source Control measures, Conveyance Control measure and End of Pipe treatment to achieve the water quality and water balance target for lot level development of the preferred strategy.

A combination of lot level, conveyance, and end-of-pipe stormwater management practices.

Movement of water from one location to another.

The circulation of water from the atmosphere to the earth and back, through precipitation, runoff, infiltration, groundwater flow and evapotranspiration.

A shallow excavated surface depression containing prepared filter media, mulch, and planted with selected vegetation.

An alternative practice to traditional impervious pavement, prevents the generation of runoff by allowing precipitation falling on the surface to infiltrate through the surface course into an underlying stone reservoir and, where suitable conditions exist, into the native soil.

A shallow constructed channel, often grass-lined, which is used as an alternative to curb and channel, or as a pretreatment to other measures. Swales are generally characterized by a broad top width to depth ratio and gentle grades.

Vegetated, open channels designed to convey, treat and attenuate runoff. Design variations range from simple grass channels, which are designed primarily for conveyance to more complex treatment and volume reduction designs like enhanced grass swales, and dry swales or bioswales.

Linear bioretention cell designed to convey, treat and attenuate stormwater runoff. The engineered filter media soil mixture and vegetation slows the runoff water to allow sedimentation, filtration through the root zone, evapotranspiration, and infiltration into the underlying native soil.

The practice of intercepting, conveying and storing rainwater for future use. Captured rainwater is typically used for outdoor non-potable water uses such as irrigation, or in the building to flush toilets.

Referring to the source of a stream or river.