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Welcome to the Low Impact Development Planning and Design Guide.

This document – the Low Impact Development Stormwater Management Planning and Design 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 sustainable stormwater planning and practices in the CVC and TRCA watersheds. The use of sustainable stormwater planning and practices will help ensure the continued health of the streams, rivers, lakes, fisheries and terrestrial habitats in our watersheds. The guide is intended to provide engineers, ecologists and planners with up-to-date information and direction on landscape-based stormwater management planning and low impact development stormwater management practices such as rainwater harvesting, green roofs, bioretention, permeable pavement, soakaways and swales. The information contained in the guide will help practitioners adopt landscape-based stormwater management approaches, and will help select, design, construct and monitor more sustainable stormwater management practices.

Preface

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.

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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.

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 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.

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.

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

Referring to the source of a stream or river.