All terms in this glossary are from The Living City Policies for Planning and Development in the Watersheds of the Toronto and Region Conservation Authority (LCP).


Accessory building or structure

A non-habitable building or structure that is subordinate and exclusively devoted to a main use, building, or structure, and is located on the same lot as the main use, building or structure to which it is subordinate.


Any action taken to minimize the adverse effects of climate change, or to take advantage of any beneficial effects of climate change. If mitigation measures are able to reduce the scale of change or extend the length of time over which it occurs, adaptation becomes much easier.

Adaptive management

An iterative approach to policy, planning, design, construction and monitoring that facilitates adaptation to changing environmental conditions over time.


Any works occurring on an existing building or structure that serve to increase the total area of that building or structure.

Adjacent lands

Those lands contiguous to a specific natural heritage feature or area where it is likely that development or site alteration would have a negative impact on the feature or areas. The extent of the adjacent lands may be recommended by the Province or based on municipal approaches which achieve the same objectives. (Provincial Policy Statement, 2014)


The distance from a hazard/feature prescribed in TRCA’s Regulation to delineate the regulated area.


Within the context of Section 8.0 of the LCP, straightening, changing, diverting an existing channel of a river, creek, stream or watercourse or changes to the Lake Ontario shoreline.

Approval Authority

In the land use and development context, this includes any public body (e.g., municipality, conservation authority, provincial ministry) that has the authority to regulate and approve development projects that fall under its mandate and jurisdiction (e.g., Planning Act, Environmental Assessment Act, Aggregate Resources Act, Conservation Authorities Act).


A saturated permeable geologic unit that can transmit significant quantities of groundwater under ordinary hydraulic gradients. They can be classified as confined or unconfined. In southern Ontario, aquifers are typically comprised of sand and/or gravel, or fractured limestone.


A geologic formation that is permeable enough to transmit groundwater in quantities that are significant in the study of regional groundwater flow, but not permeable enough to allow the completion of production wells within them. In southern Ontario, they are typically formed as the result of depositional processes from ancient shallow seas and lakes, and comprise silt, clay, and lower permeability limestone and shale.

Archaeological Assessment

For a defined project area or property, a survey undertaken by a licensed archaeologist within those areas determined to have archaeological potential in order to identify archaeological sites, followed by evaluation of their cultural heritage value or interest, and determination of their characteristics. Based on this information, recommendations are made regarding the need for mitigation of impacts (including long-term protection planning) and the appropriate means for mitigating those impacts.

Archaeological Resources

Includes artifacts, archaeological sites and marine archaeological sites as defined under the Ontario Heritage Act. The identification and evaluation of such resources are based upon archaeological fieldwork undertaken in accordance with the Ontario Heritage Act. (Provincial Policy Statement, 2014)

Archaeological Site

Defined in Ontario Regulation 170/04 as “any property that contains an artifact or any other physical evidence of past human use or activity that is of cultural heritage value or interest.”

Area of Interference

See Other Areas/Areas of Interference.

Areas of Natural and Scientific Interest (ANSIs)

Areas of land and water containing natural landscapes or features that have been identified (by the Province) as having science or earth science values related to protection, scientific study or education. (Provincial Policy Statement , 2014)


Bankfull Discharge

The formative flow of water that characterizes the morphology (shape) of a fluvial channel. In a single channel stream, bankfull is the discharge which just fills the channel without flowing onto the flood plain.


That portion of stream flow derived from groundwater storage to surface streams.


The variability among organisms from all sources including terrestrial, marine and other aquatic ecosystems and the ecological complexes of which they are part; this includes diversity within species and ecosystems.


A strip of permanent vegetation that helps alleviate the negative impacts of development on natural features and functions and can include a non-vegetated erosion access allowance (also see definition for erosion access allowance) required to manage a natural hazard.

Built Green Elements

In the context of green infrastructure, they are human-created systems and technologies that are designed to mimic ecological functions to reduce environmental impacts from human activities, such as stormwater management ponds, green roofs, green walls, permeable pavement, and rainwater harvesting.

Built Heritage Resources

A building, structure, monument, installation or any manufactured remnant that contributes to a property’s cultural heritage value or interest as identified by a community, including an Aboriginal community. (Provincial Policy Statement, 2014)


Class Environmental Assessment

An environmental assessment done for a group, or “class” of projects that are carried out routinely and have predictable and mitigable environmental effects.


In the context of conservation and land use planning, compensation is defined as the replacement of lost/altered ecosystem services or ecological function.

Comprehensive Environmental Study

A study or plan undertaken by, or under the direction of, a public agency at a landscape scale including watershed plans, subwatershed studies, environmental implementation reports, environmental management plans, or similar documents, that have been prepared to address and document various alternatives and are part of a joint and harmonized planning process, or community plans that include comprehensive environmental impact studies.

Conservation Easement

Legally binding instruments whereby the landowner transfers/relinquishes specific rights, such as the ability to create building lots or cut trees, to an easement holder (usually a nature conservation organization or agency). Depending on the terms of the conservation easement agreement, the easement holder has the right and responsibility to inspect the property and ensure the terms of the conservation easement are being respected.

Conservation of Land

The protection, management or restoration of lands within the watershed ecosystem for the purpose of maintaining or enhancing the natural features and ecological functions and hydrological functions, within the watershed. (Conservation Ontario, 2008) Conservation of land includes all aspects of the physical environment, be it terrestrial, aquatic, biological, botanic or air and the relationship between them (611428 Ontario Ltd. vs. Metropolitan Toronto and Region Conservation Authority).

Conservation Project

Activities, buildings or structures for conservation and hazard management purposes on publicly-owned lands such as, but not limited to: flood and erosion control works, habitat creation and enhancement, tree and shrub planting, environmental education, trails and low intensity recreation activities, cultural heritage and archaeological preservation and interpretation and conservation parks.

Conservation-Related Accessory Uses

A use of land, buildings or structures and associated activities that is incidental or subordinate to the principal conservation project use, building, structure or activity located on the same lot, and may include activities such as, but not limited to: farmers markets, demonstration or pilot projects and facility rentals for environmentally-themed meetings, conferences and social events.

Cultural Heritage Landscapes

A defined geographical area that may have been modified by human activity and is identified as having cultural heritage value or interest by a community, including an Aboriginal community. The area may involve features such as structures, spaces, archaeological sites or natural elements that are valued together for their interrelationship, meaning or association. (Provincial Policy Statement, 2014)

Cultural Heritage Value or Interest

For the purposes of the Ontario Heritage Act and its regulations, archaeological resources that possess cultural heritage value or interest are protected as archaeological sites under Section 48 of the act. Where analysis of documented artifacts and physical features at a given location meets the criteria stated in the Standards and Guidelines, that location is protected as an archaeological site and further archaeological assessment may be required.

Cumulative Impacts

A number of individual impacts viewed in combination on a regional, watershed, subwatershed or reach basis.



A barrier constructed to hold back, forward, or divert water.

Debris Jams

Occur where debris (both trash from destroyed structures and natural materials like fallen trees) builds up to create a temporary dam. While the damming lasts, there can be flooding upstream. When the pressure of the water eventually breaks the jam, there can be flash flooding downstream. These conditions can also result from ice jams.

Designated Greenfield Area

The area within a settlement area that is not built up area. Where a settlement area does not have a built boundary, the entire settlement area is considered designated greenfield area. (Growth Plan for the Greater Golden Horseshoe, 2006)

Designated Vulnerable Areas

Areas defined as vulnerable, in accordance with provincial standards, by virtue of their importance as a drinking water source. (Provincial Policy Statement, 2014) In the context of source water protection pursuant to the Clean Water Act, they are vulnerable areas are areas containing a significant groundwater recharge area, a highly vulnerable aquifer, a surface water intake protection zone, or a wellhead protection area. (Clean Water Act, 2006 - O. Reg 28/07)

Development (in LCP Section 7.0 – Planning)

As defined in the Provincial Policy Statement, 2014 - The creation of a new lot, a change in land use, or the construction of buildings and structures, requiring approval under the Planning Act, but does not include: a) activities that create or maintain infrastructure authorized under an environmental assessment process; b) works subject to the Drainage Act; or c) for the purposes of policy 2.1.3(b), underground or surface mining of minerals or advanced exploration of mining lands in significant areas of mineral potential in Ecoregion 5E, where advanced exploration has the same meaning as under the Mining Act. Instead, those matters shall be subject to policy 2.1.4(a). (Also see the definitions of site alteration and infrastructure)

Development (in LCP Section 8.0 – Permitting)

As defined in the Conservation Authorities Act - (a) the construction, reconstruction, erection or placing of a building or structure of any kind, (b) any change to a building or structure that would have the effect of altering the use or potential use of the building or structure, increasing the size of the building or structure or increasing the number of dwelling units in the building or structure, (c) site grading, or (d) the temporary or permanent placing, dumping or removal of any material, originating on the site or elsewhere.

Development Limit

The point to which development can extend, defined by the greater extent of natural hazards and natural features plus any applicable potential natural cover, buffer, freeboard, or erosion access allowance.

Dewatering and Dewatering Discharge

Extraction of water from the ground, for the purposes of controlling groundwater, and expelling that water after it is extracted.


The downward vertical projection of the outer most extent of tree branches.

Dynamic Beach Hazard

Areas of inherently unstable accumulations of shoreline sediments along Lake Ontario, as identified by provincial standards. The dynamic beach hazard limit consists of the flood hazard limit plus a dynamic beach allowance. (Provincial Policy Statement, 2014).


Ecological Function

The natural processes, products or services that living and non-living environments provide or perform within or between species, ecosystems, and landscapes. These may include biological, physical, and socio-economic interactions (Provincial Policy Statement)

Ecological Integrity

In the context of the Oak Ridges Moraine Conservation Plan, including hydrological integrity, the condition of ecosystems in which, (a) the structure, composition and function of the ecosystems are unimpaired by stresses from human activity, (b) natural ecological processes are intact and selfsustaining, and (c) the ecosystems evolve naturally.

Ecological Land Classification

The Canadian classification of lands from an ecological perspective; an approach that attempts to identify ecologically similar areas.

Ecosystem Services

The benefits provided by ecosystems that are critical to the environment’s life support systems and that contribute to human welfare both directly and indirectly and therefore represent social and economic value.


A right to, interest in, or legal liability on real property that does not prohibit passing title to the property but that diminishes its value.

Endangered Species

A species that is listed or categorized as an “Endangered Species” on the Ontario Ministry of Natural Resources and Forestry official species at risk list, as updated and amended from time to time. (Provincial Policy Statement, 2014)

Environmental Assessment

A study that is completed by the proponent to assess the potential environmental effects (positive or negative) of an individual project, pursuant to the Environmental Assessment Act. Key components of an environmental assessment include: consultation with government agencies and the public; consideration and evaluation of alternatives; the management of potential environmental effects. Proponents can include the provincial government, municipal governments, and public organizations such as conservation authorities. The environmental assessment program generally does not apply to the private sector. However, sometimes private firms are required by a regulation or may voluntarily go through an environmental assessment process.

Environmental Flow Threshold

The minimum in-stream flow necessary to maintain the ecological function of a watercourse.

Environmentally Significant Areas

Areas identified by a municipality or by a (previous) TRCA program based on specific criteria.

Erosion (as a natural process)

The process of gradual washing away of soil by water movement or seepage (at the ground surface), commonly occurring in one of the following manners: a) rainfall or snowmelt and surface runoff (sheet, rill, or gully erosion); b) internal seepage and piping; c) water flow (banks or base of river, creek, channel); and d) wave action (shorelines of ponds, lakes, bays) The erosion process affects the soil at the particle level by dislodging and removing (transporting) the soil particles from the parent mass (with water movement as the agent). Other processes such as wind and frost may assist in the weathering or dislodging and transport of soil particles.

Erosion Access Allowance

The setback needed to ensure there is a large enough safety zone for people and vehicles to enter and exit an area during an emergency, such as a slope failure or flooding, and to provide sufficient area to access and maintain protection works along valley and stream corridors and the Lake Ontario shoreline.

Erosion Allowance

Where there is no reliable recession information, the province recommends a setback distance (30 metres) to allow for erosion along the Great Lakes St. Lawrence River system (including the Lake Ontario Shoreline). Along the Lake Ontario Shoreline, TRCA requires a 30-metre erosion allowance based on 0.3 metres average erosion rate per year extended over a 100-year time period.

Erosion Hazard

The loss of land, due to human or natural processes, that poses a threat to life and property. The erosion hazard limit is determined using considerations that include the 100-year erosion rate (the average annual rate of recession extended over a one hundred year time span), an allowance for slope stability, and an erosion/erosion access allowance. (Provincial Policy Statement, 2014) To fulfill TRCA’s Regulatory responsibilities, the erosion hazard limit shall be established in accordance with the text of TRCA’s Regulation (refer to Appendix C).

Essential Emergency Service

Services that would be impaired during an emergency as a result of flooding, the failure of floodproofing measures and/or protection works, and/or erosion.


The combined loss of water to the atmosphere from land and water surfaces by evaporation and from plants by transpiration.

Existing natural cover

That portion of natural cover of the target terrestrial natural heritage system that is existing.

Existing Vacant Lot of Record

A parcel or tract of land described in a deed or other legal document that is capable of being legally conveyed, containing no preexisting buildings or structures.


Fee Simple (ownership)

Ownership of a property that entails the full bundle of rights associated with owning a property.


Includes (a) parts of fish, (b) shellfish, crustaceans, marine animals and any parts of shellfish, crustaceans or marine animals and (c) the eggs, sperm, spawn, larvae, spat and juvenile stages of fish, shellfish, crustaceans and marine animals (Fisheries Act, section 2).

Fish Habitat

Spawning grounds and any other areas, including nursery, rearing, food supply and migration areas on which fish depend directly or indirectly in order to carry out their life processes (Fisheries Act, section 2(1).

Fisheries Timing Window

As established by the Ministry of Natural Resources and Forestry and applied by TRCA staff, that window of time when construction around or in-water is permitted, given that critical life stages of fish take place outside of this window; there are both cold water and warm water fisheries timing windows.

Five Tests (of a permit application under TRCA’s section 28 Regulation)

The control of flooding, erosion, dynamic beaches, pollution, and conservation of land.


TRCA's watersheds are "flashy", meaning that when rain falls on the ground it travels overland and reaches the rivers quite quickly. Flash floods occur after a rain event, dam failure, or after water held back by an ice or debris jam is released. In a flash flood situation you may have little or no warning, nor time to prepare, as water levels within the rivers can rise quickly.


A flood is an overflow or inundation that comes from a river or other body of water and causes or threatens damage. It occurs as the result of relatively high streamflow overtopping the natural or artificial banks in any reach of a stream (measured by either gauge height or discharge quantity).

Flood Fringe

For river, stream and small inland lake systems, means the outer portion of the flood plain between the floodway and the flooding hazard limit. Depths and velocities of flooding are generally less severe in the flood fringe than those experienced in the floodway. (Provincial Policy Statement, 2014)

Flood Hazard

Means the inundation, under the conditions specified below, of areas adjacent to a shoreline or a watercourse and not ordinarily covered by water (note: high points of land not subject to flooding but surrounded by floodplain or flooded land are considered to be within the flood hazard) Lake Ontario Flood Hazard Limit - the one hundred year flood, plus an allowance for wave uprush and other waterrelated hazards. Riverine Flood Hazard Limit – the flood produced by the Hurricane Hazel storm event or the one hundred year flood, whichever is greater.

Flood Plain

The area, usually low lands adjoining a watercourse, which has been or may be subject to flood hazards. (Provincial Policy Statement, 2014)

Flood Plain Spill Area

Where flood waters are not physically contained within the valley or stream corridor and exit to surrounding lands. As a consequence, the limit and depth of flooding are difficult to determine. Flood spill areas occur naturally, or can occur as a result of downstream barriers to the passage of flood flows, such as undersized bridges or culverts.

Flood Vulnerable Area

Sub-area within the Regulatory Storm Flood Plain containing multiple existing structures and/or roads for which a single, comprehensive flood remediation approach may be viable.


The combination of measures incorporated into the basic design and/or construction of buildings and structures or properties to reduce or eliminate flood hazards, wave uprush and other water-related hazards along the shoreline of Lake Ontario, and flood hazards along watercourses. (Provincial Policy Statement, 2014) There are three different types of floodproofing: Dry Passive floodproofing – includes the use of fill, columns, or design modifications to elevate openings in the building or structure at, or above, the level of the flood hazard. These measures do not require flood warning or any other action to put the flood protection into effect. Dry Active floodproofing – includes techniques such as installing water tight doors, seals or floodwalls to prevent water from entering openings below the level of the flood hazard. Advance warning is almost always required to make the flood protection operational (i.e. closing of water tight doors, installation of waterproof protective coverings or windows etc.). Wet floodproofing – involves designing a building or structure using materials, methods and design measures that maintain structural integrity by avoiding external unbalanced forces from acting on buildings or structures during and after a flood, to reduce flood damage to contents, and to reduce the cost of post flood clean up. Buildings and structures are designed so as to intentionally allow flood waters to enter and exit, ensuring the interior space below the level of the flood hazard remains unfinished, nonhabitable, and free of service units and panels.


For river, stream and small inland lake systems, the portion of the flood plain where development and site alteration would cause a danger to public health and safety or property damage. Where the One-Zone concept is applied, the floodway is the entire contiguous flood plain. Where the Two-Zone concept is applied, the floodway is the contiguous inner portion of the flood plain, representing that area required for the safe passage of flood flow and/or that area where flood depths and/or velocities are considered to be such that they pose a potential threat to life and/or property damage. Where the two zone concept applies, the outer portion of the flood plain is called the flood fringe. (Provincial Policy Statement, 2014)


A safeguard of separation in either length (linear - a specified distance) or height (vertical - a specified elevation) from the Regulatory Flood Plain or other specified flood level.


Green Infrastructure

Natural vegetation, vegetative systems, soil in volumes and qualities adequate to sustain vegetation and absorb water, and supportive green technologies that replicate ecosystem functions. (Also see natural green elements and built green elements)

Greenfield Development

Development taking place on formerly vacant/agricultural land usually situated within the outer reaches of an urban envelope, usually on a block-wide scale.

Groundwater Discharge

The removal of water from the saturated zone across the water-table surface, together with the associated flow toward the water table within the saturated zone.

Groundwater Feature

Water related features in the earth’s subsurface, including recharge/discharge areas, water tables, aquifers and unsaturated zones that can be defined by surface and subsurface hydrogeological investigations. (Provincial Policy Statement, 2014)

Groundwater Recharge

The entry into the saturated zone of water made available at the water-table surface, together with the associated fl ow away from the water table within the saturated zone.

Groundwater Reservoir

An aquifer or aquifer system in which groundwater is stored. The water may be placed in the aquifer by artificial or natural means.



That portion of a building or structure containing rooms or spaces required and intended for overnight occupancy and associated living space, and includes those portions which contain facilities for storage (not including garages), heating, airconditioning, electrical, hot water supplies, etc., which are necessary to maintain the habitable condition.

Habitat of Endangered and Threatened Species

Habitat of endangered species and threatened species: means a) with respect to a species listed on the Species at Risk in Ontario List as an endangered or threatened species for which a regulation made under clause 55(1)(a) of the Endangered Species Act, 2007 is in force, the area prescribed by that regulation as the habitat of the species; or b) with respect to any other species listed on the Species at Risk in Ontario List as an endangered or threatened species, an area on which the species depends, directly or indirectly, to carry on its life processes, including life processes such as reproduction, rearing, hibernation, migration or feeding, as approved by the Ontario Ministry of Natural Resources and Forestry; and places in the areas described in clause (a) or (b), whichever is applicable, that are used by members of the species as dens, nests, hibernacula or other residences. (Provincial Policy Statement, 2014)

Hazardous Lands (in Section 7 – planning)

Property or lands that could be unsafe for development due to naturally occurring processes. Along the shorelines of the Great Lakes - St. Lawrence River System, this means the land, including that covered by water, between the international boundary, where applicable, and the furthest landward limit of the flooding hazard, erosion hazard or dynamic beach hazard limits. Along the shorelines of large inland lakes, this means the land, including that covered by water, between a defined offshore distance or depth and the furthest landward limit of the flooding hazard, erosion hazard or dynamic beach hazard limits. Along river, stream and small inland lake systems, this means the land, including that covered by water, to the furthest landward limit of the flooding hazard or erosion hazard limits. (Provincial Policy Statement, 2014)

Hazardous Lands (in Section 8 – permitting)

Land that could be unsafe for development because of naturally occurring processes associated with flooding, erosion, dynamic beaches or unstable soil or bedrock. (Conservation Authorities Act, 1990)

Hazardous Sites

Property or lands that could be unsafe for development and site alteration due to naturally occurring hazards. These may include unstable soils (sensitive marine clays [leda], organic soils) or unstable bedrock (karst topography). (Provincial Policy Statement, 2014)

Headwater Drainage Feature (HDFs)

Ill-defined, non-permanently fl owing drainage features that may not have defined bed or banks; they are zero-order intermittent and ephemeral channels, swales and rivulets, but do not include rills or furrows (also see watercourse). HDFs that have been assessed through TRCA’s Evaluation, Classification and Management of Headwater Drainage Features Guideline, as “protection” and “conservation” are subject to TRCA’s Regulation; those assessed as “mitigation” may be subject to TRCA’s Regulation.

Highly Vulnerable Aquifer

An aquifer on which external sources have or are likely to have a significant adverse effect, and includes the land above the aquifer. (Clean Water Act, 2006 – O. Reg. 28/07)

Hydraulic Floodway

In Section 8.0 of The Living City Policies, the inner portion of the flood plain where flood depths and velocities are generally higher and faster flowing than those experienced in the outer or fringe portion of the overall flood plain. The hydraulic floodway represents that area required for the safe passage of flood flow and/or that area where flood depths and/or velocities are considered to be such that they pose a significant threat to life and/or property damages.


The study of how surface water moves through various pathways in terms of water depth, velocity, and pressures acting on hydraulic structures and systems.


A science that describes the movement of groundwater (water beneath the ground surface), and its interaction with water that moves on the ground surface in rivers, lakes, streams, and over land. Groundwater seeps into the ground to varying depths and collects in aquifers. Groundwater can remain stored underground for periods ranging from a few days to thousands of years.

Hydrologic Cycle

See water balance and water budget.

Hydrologic Features

In the Greenbelt, as designated under the Greenbelt Plan, and on the Oak Ridges Moraine (hydrologically sensitive features), as designated under the Oak Ridges Moraine Conservation Plan.

Hydrologic Function

The functions of the hydrological cycle that include the occurrence, circulation, distribution, and chemical and physical properties of water on the surface of the land, in the soil and underlying rocks, and in the atmosphere, and water’s interaction with the environment including its relation to living things. (Provincial Policy Statement, 2014)


Is the engineering science that analyzes the different components of the hydrologic cycle, and takes into account that the natural cycle can be altered by human and natural activities.


The seasonal pattern of surface and groundwater level fluctuations within a natural feature.


Infill Lot

An existing vacant lot of record and situated between existing urbanized/developed lots fronting onto a public road.


The downward entry of water through the soil surface into the soil. (MNR Water Resources Glossary)


Physical structures (facilities and corridors) that form the foundation for development. Infrastructure includes: sewage and water systems, septage treatment systems, stormwater management systems, waste management systems, electricity generation facilities, electricity transmission and distribution systems transportation corridors and facilities, oil and gas pipelines and associated facilities. (Provincial Policy Statement, 2014)


The development of a property, site, or area at a higher density than currently exists through: a) redevelopment, including the reuse of brownfield sites; b) the development of vacant and/ or underutilized lots within previously developed areas; c) infill development; and, d) the expansion or conversion of existing buildings. (PPS, 2014)

Interference (or Interfering in any way)

Any anthropogenic act or instance which hinders, disrupts, degrades or impedes in any way the natural features or hydrologic and ecologic functions of a wetland or watercourse. (Conservation Ontario, 2008)


Kettle Lakes

Depressions created by partially-buried glacial ice blocks as they melted. The depressions that filled with water became kettle lakes. Kettle lakes are not connected to a watercourse. An example of a Kettle Lake in TRCA’s jurisdiction is Preston Lake in Whitchurch- Stouffville.

Key Natural Heritage Features

In the Greenbelt, as designated under the Greenbelt Plan, and on the Oak Ridges Moraine, as designated under the Oak Ridges Moraine Conservation Plan.


Lake Iroquois Shoreline

A post-glacial landform that represents a major rise in elevation extending from west to east across TRCA’s jurisdiction, inland from Lake Ontario.

Lake Ontario Shoreline Reach

Segments of shoreline usually having relatively uniform physical characteristics. The extent/length of shoreline reach to be considered in the application of The Living City Policies to be determined by TRCA.

Lake Ontario Shoreline Sector

There are four sectors of Lake Ontario shoreline in TRCA’s jurisdiction: Etobicoke, Central, Scarborough, Pickering/Ajax.

Low Impact Development

A storm water management strategy that seeks to mitigate the impacts of increased runoff and stormwater pollution by managing runoff 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, evapotranspiration, and reuse of rainwater.


Major Recreational Use

Recreational facilities that require large scale modification of terrain, vegetation or both and usually also require large scale buildings or structures, and extensive parking areas, including but not limited to: golf courses, serviced playing fields, serviced campgrounds and ski hills.

Matrix Influence

The surrounding land-use of a habitat patch is known as “matrix”; In TRCA’s Terrestrial Natural Heritage System Strategy (2007), the influence the surrounding land-use has on a habitat patch is scored based on whether the area (2 km from a patch’s edge) is urban, agricultural or natural, and the score is known as the matrix influence.

Meander Belt Allowance

The area of land in which a watercourse channel moves or is likely to move over a period of time. The extent of the meander belt allowance is determined by a technical report using accepted scientific and engineering principles and includes considerations for meander amplitudes, erosion setbacks and factors of safety.

Minor Expansions (to major or minor recreational uses)

Require very little modification of terrain or vegetation and few if any, buildings, structures and limited parking. Proper site planning, scoped environmental studies and the incorporation of best management practices for site construction and future maintenance can generally minimize impacts to negligible levels.

Minor Recreational Use

Recreational facilities that require very little modification of terrain or vegetation and few if any, buildings, structures and limited parking or other impervious surfaces. They are of low intensity and a non-intrusive nature. They can include but are not limited to: non-motorized trails, boardwalks, picnic facilities, unserviced playing fields, natural heritage appreciation, unserviced camping on public and institutional land and accessory uses.


The prevention, modification or alleviation of impacts on the environment. It also includes any action with the intent to enhance beneficial effects.


The use of measures that seek to avoid, reduce or delay detrimental effects to the environment. In the context of climate change, it is actions to reduce greenhouse gas emissions.


Natural Cover

Land occupied by naturally and culturally occurring native or non-native vegetation that is not characterized as agricultural or urban land uses.

Natural Green Elements

In the context of green infrastructure, they are traditional natural features such as trees, wetlands, riparian areas, and buffers that should be protected and restored in a natural heritage system, as well as open space agricultural lands and soils that provide water retention benefits.

Natural System

Comprised of water resources, natural features and areas, natural hazards, and restoration areas of potential natural cover and buffers.

Navigable Water

Includes a canal and any other body of water created or altered as a result of the construction of any work. (Navigation Protection Act, 1985)


One Hundred Year Erosion Rate

The average annual rate of recession over a hundred year time span.

One Hundred Year Flood

That flood, based on an analysis of precipitation, snow melt, or a combination thereof, having a return period of 100 years on average, or having a 1% chance of occurring or being exceeded in any given year. (Provincial Policy Statement, 2014)

One Hundred Year Flood (Lake Ontario)

The peak instantaneous still water level, plus an allowance for wave uprush and other water-related hazards for Lake Ontario in the Great Lakes-St. Lawrence River System that has a probability of occurrence of one per cent during any given year.

One Zone Concept

See Floodway.

Original Ground Floor Area

The total area of the main floor of a building, (excluding decks, patios, garages and other accessory structures), as existed as existed at the time of the original construction date of the building.

Original Habitable Ground Floor Area

The total area of the main floor of a building containing rooms or spaces required and intended for overnight occupancy and associated living space, and includes those portions which contain facilities for storage (not including garages), heating, air-conditioning, electrical, hot water supplies, etc., which are necessary to maintain the habitable condition, as existed at the time of the original construction date of the building.

Other Areas/Area of Interference

Areas where development could interfere with the hydrologic function of a wetland including areas within 120 metres of all provincially significant wetlands or wetlands on the Oak Ridges Moraine and areas within 30 metres of all other wetlands.

Other Inland Lakes

Lakes that are not kettle lakes and are not connected a watercourse.

Other Wetlands

In the context of TRCA’s Regulation, any wetland that is not a provincially significant wetland and not on the Oak Ridges Moraine.



Any deleterious physical substance or other contaminant that has the potential to be generated by development in an area to which a regulation made under clause (1) (c) applies (Conservation Authorities Act, section 28(25)).

Potential Natural Cover

Land that is not existing natural cover, but has the potential to be restored.

Provincial Standards

The most recently approved legislation, regulations, policies, manuals and technical guidelines administered or prepared by the Province, as amended from time to time.



The restoration, repair, or replacement of a building or structure within its original footprint, not to exceed its original ground floor area, gross floor area or height, and without any change to its original use.

Recreational Use

See definitions for major and minor recreational use.


The creation of new units, uses or lots on previously developed land in existing communities, including brownfield sites. (Provincial Policy Statement, 2014)

Regional Flood Control

Stormwater management control of flood flows from the regional storm event (Hurricane Hazel) to mitigate increases in flood risk associated with development (urbanization).

Regional Flood Control Facility

A flood control facility designed to control the Regional Storm.

Regional Storm

The rainfall event and soil conditions existing during Hurricane Hazel that occurred within the Humber River watershed in Toronto in 1954, transposed over a specific watershed and combined with local conditions.

Regional Storm Flood Line

Measured in metres above sea level, the level to which the Regional Storm Flood Plain rises.

Regulated Area

The land described in, and subject to, TRCA’s Section 28 Regulation under the Conservation Authorities Act.


TRCA’s Regulation under Section 28 of the Conservation Authorities Act for Development, Interference with Wetlands, and Alterations to Shorelines and Watercourses.

Regulation Limit

The greatest extent of all regulated areas that defines an area of interest; the regulation limit does not represent a development limit.

Regulatory Flood

The more severe of the Regional Storm and the 100-Year Storm.

Regulatory Flood Plain

The area adjacent to a watercourse that would be inundated by a flood resulting from the most severe of the Hurricane Hazel Flood Event Standard (Regional Storm) or the 100 Year Flood Event Standard, whichever is greater.


To restore the ecosystem to a higher functioning condition.


The construction or modification of infrastructure for the purpose of reducing or eliminating risk due to natural hazards.

Renewable Energy

Energy obtained from sources that are essentially inexhaustible (unlike, for example, fossil fuels, of which there is a finite supply). Renewable sources of energy include conventional hydroelectric power, wood, waste, geothermal, wind, photovoltaic, and solar thermal energy.


See reconstruction.


To repair or re-establish functioning ecosystems; the process of altering a site to establish a defined, native, historic ecosystem; the goal is to emulate the structure, function, diversity and dynamics of a specified ecosystem.

River or Stream Valley (Apparent or Confined)/Valley Corridor

Depressional features associated with a river or stream, whether or not they contain a watercourse, with defined slopes extending from the long term stable slope projected from the predicted stable toe of slope, plus a 15-metre allowance (in the context of defining the Regulated Area), or, an applicable buffer (in the context of defining the Natural System).

River or Stream Valley (Not Apparent or Unconfined)/ Stream Corridor

Depressional features associated with a river or stream, whether or not they contain a watercourse, with ill-defined slopes extending from the maximum extent of the predicted meander belt allowance of the river or stream; plus a 15-metre allowance (in the context of defining the Regulated Area), or, an applicable buffer (in the context of defining the Natural System).


Safe Access (Safe Ingress/Egress)

Vehicular and pedestrian access to and from a site is safe, for the nature of the development, from the risks due to flooding or erosion hazards consistent with Provincial and TRCA standards.


Soils or other surface materials transported by wind or water as a result of erosion.

Sedimentation (water)

Sedimentation is an increase in the amount of solid particles suspended in water, caused primarily by soil erosion. The main human causes of sedimentation are forestry, farming, and construction. When sediment settles, it can smother the feeding and spawning grounds of fish and kill aquatic organisms.

Shoreline Protection Works

Engineered methods for shorelines located within hazards that reduce hazard losses by modifying the hazards at the shoreline. Protection approaches can be classified as either structural or non-structural.

Significant (Provincially)

a) in regard to wetlands, coastal wetlands and areas of natural and scientific interest, an area identified as provincially significant by the Ontario Ministry of Natural Resources and Forestry using evaluation procedures established by the Province, as amended from time to time; b) in regard to woodlands; an area which is ecologically important in terms of features such as species composition to the broader landscape because of its location, size or due to the amount of forest cover in the planning area; or economically important due to site quality, species composition, or past management history. These are to be identified using criteria established by the Ontario Ministry of Natural Resources and Forestry; and c) in regard to other features and areas in policy 2.1 (of the PPS), ecologically important in terms of features, functions, representation or amount, and contributing to the quality and diversity of an identifiable geographic area or natural heritage system. d) in regard to mineral potential, an area identified as provincially significant through evaluation procedures developed by the Province, as amended from time to time, such as the Provincially Significant Mineral Potential Index; and e) in regard to cultural heritage and archaeology, resources that have been determined to have cultural heritage value or interest for the important contribution they make to our understanding of the history of a place, an event, or a people. Criteria for determining significance for the resources identified in sections (c)-(e) are recommended by the Province, but municipal approaches that achieve or exceed the same objective may also be used. While some significant resources may already be identified and inventoried by official sources, the significance of others can only be determined after evaluation. (Provincial Policy Statement, 2014)

Significant Groundwater Recharge Area

In the context of source water protection pursuant to the Clean Water Act, it is an area within which it is desirable to regulate or monitor drinking water threats that may affect the recharge of an aquifer. (Clean Water Act, 2006 – O. Reg. 28/07)

Site Alteration

Means activities such as grading, excavation, and the placement of fill that would change the landform and natural vegetative characteristics of a site. (Provincial Policy Statement, 2014)

Special Policy Area

Means an area within a community that has historically existed in the flood plain and where site-specific policies, approved by both the the Ministers of Natural Resources and Forestry and Municipal Affairs and Housing, are intended to provide for the continued viability of existing uses (which are generally on a small scale) and address the significant social and economic hardships to the community that would result from strict adherence to provincial policies concerning development. The criteria and procedures for approval are established by the Province. A Special Policy Area is not intended to allow for new or intensified development and site alteration, if a community has feasible opportunities for development outside the flood plain. (Provincial Policy Statement, 2014)

Species of (Conservation) Concern

According to the TRCA methodology, any species with a local rank of L1 to L3, and those L4 species found within the Built-up Area. Generally species that are disappearing in the regional landscape, primarily as a result of land use changes. Species of Concern can also be used as indicators – a surrogate measure - of ecosystem function. Improvements in their distribution may indicate an improving trend in ecosystem or regional health.

Spring Runoff

Also known as a ‘freshet’, spring runoff is the rise in water levels caused by melting snow.

Stable Slope Allowance – Defined Valleylands

The setback that ensures safety if the slumping or slope failure occur. It refers to a horizontal allowance measured landward from the toe erosion allowance equivalent to three times the height of the slope or through valid study; and - Lake Ontario Shoreline - the predicted long term stable slope projected from the stable toe of slope as may be shifted as a result of erosion over a hundred year period.

Stable Toe of Slope

As determined through a geotechnical study: a) the physical toe of slope where the existing toe is stable and not impacted by erosion; or b) the landward limit of the toe erosion allowance where the existing slope is unstable and/or impacted by erosion.

Stable Top of Slope/Bank (long term stable slope line)

As determined through a geotechnical study: a) the physical top of slope where the existing slope is stable and not impacted by toe erosion; or b) the landward limit of the toe erosion allowance plus the stable slope allowance where the existing slope is unstable and/or impacted by erosion.


Precipitation that accumulates in natural and/or constructed storage and stormwater systems during and immediately following a storm.

Stormwater Management

Functions associated with planning, designing, constructing, maintaining, financing and regulating the facilities (both constructed and natural) that collect, store, control and/or convey stormwater.

Stream Corridor

See River or Stream Valley (Not Apparent or Unconfined).


The discharge that occurs in a natural channel.


A subdivision of a watershed based on hydrology, generally corresponding to the area drained by a small tributary, as opposed to a major river.

Subwatershed Drainage Diversion

Diverting stormwater from one subwatershed to another.

Surface water feature

Water-related features on the earth’s surface, including headwaters, rivers, stream channels, inland lakes, seepage areas, recharge/discharge areas, springs, wetlands, and associated riparian lands that can be defined by their soil moisture, soil type, vegetation or topographic characteristics. (Provincial Policy Statement, 2014)

Surface water intake protection zone

in the context of source water protection pursuant to the Clean Water Act, it is an area that is related to a surface water intake and within which it is desirable to regulate or monitor drinking water threats. (Clean Water Act, 2006 – O. Reg. 28/07)

Sustainable Energy

Includes but is not limited to renewable energy sources such as hydroelectricity, solar energy (photovoltaic and heat), wind energy, wave power, geoexchange, bio-fuels and improvements in energy efficiency, distributed generation and district energy systems.

Sustainable Near-Urban Agriculture

The practice of growing food and production of livestock in a way that preserves and enhances the environment, provides economic opportunity and good health for individuals and communities, and connects people to the land around them. It generally avoids long-distance travel, striving instead to create fresh, healthy produce for local consumption. It focuses on both processes and produce. It is as much about the systems that create our food (i.e., who grows it, where, and how much) as it is about the food itself.


Target Terrestrial Natural Heritage System

The existing terrestrial natural heritage system and potential natural cover, as identified in TRCA’s Terrestrial Natural Heritage System Strategy, 2007.

Technical Reports

Means reports, studies or plans, typically prepared to support and implement the recommendations of a comprehensive environmental study, that provide detailed information regarding one or more aspects of the natural or physical sciences. For the purposes of this document, technical reports may include, but are not limited to, hydraulic analyses, stormwater management reports, functional servicing reports, hydrogeology reports, geomorphology studies, geotechnical reports and environmental impact studies, or similar documents. Technical reports must be prepared by a qualified professional in the relevant field.

Threatened Species

Means a species that is listed or categorized as a “Threatened Species” on the Ontario Ministry of Natural Resources and Forestry’s official species at risk list, as updated and amended from time to time. (Provincial Policy Statement, 2014)

Three-Hundred and Fifty (350-Year) Storm Flood Plain

The area adjacent to a watercourse that would be inundated by a flood resulting from a 350-Year Storm.

Toe erosion allowance

The setback that ensures safety if the toe of the slope adjacent to the river or stream erodes and weakens the bank, increasing the risk of slumping.

Top of (valley) Bank (staked or physical)

The physical top of the valley bank is that point where there is a break in slope or grade which distinguishes the valley corridor landform from its surrounding landscape.

TRCA Standards

The most recently approved technical guidelines and checklists in TRCA’s Planning and Development Procedural Manual, as amended from time to time.

Treatment Train Approach

Providing stormwater treatment first, at the lot level, then in conveyance, followed by “end-of-pipe” (where stormwater gets discharged). A treatment train is required to meet the multiple objectives of water balance, water quality, erosion control and flood control in an overall stormwater management strategy.

Two Zone Concept

See Floodway.


Urban Flood

Street flooding, basement flooding, and flooding of other low lying urban areas due to lack of major overland flow routes or the limited capacity of existing drainage systems (e.g., undersized storm sewers). Urban Flooding is the responsibility of municipalities.

Urban Forest

All trees, shrubs and understorey plants, as well as the soils that sustain them, on public and private property within an urban setting.

Urban heat island effect

A “dome” of elevated temperatures over an urban area caused by structural and pavement heat fluxes, and pollutant emissions.


Valley Corridor

See River or Stream Valley (Apparent or Confined)

Valley Wall

The valley slope, from the stable toe of slope to its stable top of bank.


Land that has depressional features associated with a river or stream whether or not it contains a watercourse (Ontario Regulation 166/06 as amended) or a natural area that occurs in a valley or other landform depression that has water flowing through or standing for some period of the year. (Provincial Policy Statement, 2014) (also see Valley Corridor)


Water Balance

The hydrologic cycle of precipitation, groundwater infiltration, evapotranspiration (into the atmosphere and by plant interception), and surface runoff.

Water Budget

The mathematical expression of the water balance.

Water Taking

Extracting water, either from the ground, or from the surface of a water body.


An identifiable depression in the ground in which a flow of water regularly or continuously occurs (Conservation Authorities Act) - also see headwater drainage feature.


The entire area of land whose runoff water, sediments and dissolved materials (nutrients and contaminants) drain into a lake, river, creek, or estuary. Its boundary can be located on the ground by connecting all the highest points of the area around the river, stream or creek, where water starts to flow when there is rain. It is not man-made and it does not respect political boundaries.

Wave Uprush

The rush of water up onto a shoreline or structure following the breaking of a wave; the limit of wave uprush is the point of furthest landward rush of water onto the shoreline.

Wellhead Protection Area

An area that is related to a wellhead and within which it is desirable to regulate or monitor drinking water threats. (Clean Water Act, 2006 – O. Reg. 28/07)


- As it pertains to the Planning Act and the Provincial Policy Statement, wetland means lands that are seasonally or permanently covered by shallow water, as well as lands where the water table is close to or at the surface. In either case the presence of abundant water has caused the formation of hydric soils and has favoured the dominance of either hydrophytic plants or water tolerant plants (Provincial Policy Statement, 2014) - As it pertains to the Conservation Authorities Act, wetland means land that, (a) is seasonally or permanently covered by shallow water or has a water table close to or at its surface, (b) directly contributes to the hydrological function of a watershed through connection with a surface watercourse, (c) has hydric soils, the formation of which has been caused by the presence of abundant water, and (d) has vegetation dominated by hydrophytic plants or water tolerant plants, the dominance of which has been favoured by the presence of abundant water, but does not include periodically soaked or wet land that is used for agricultural purposes and no longer exhibits a wetland characteristic referred to in clause (c) or (d) (source: Conservation Authorities Act) – An area of land that is saturated with water long enough to promote hydric soils or aquatic processes as indicated by poorly drained soils, hydrophytic vegetation and various kinds of biological activity that are adapted to wet environments. This includes shallow waters generally < 2 metres deep (source: ELC for Southern Ontario – First Approximation and Its Application, Sept. 1998) – wetland hydrological functions may include flood attenuation, groundwater recharge, and baseflow maintenance during dry periods (by storing precipitation and/or floodwater and releasing it slowly over time). Water purification and erosion control are other broader examples of wetland functions.

Wildlife habitat

Where plants, animals and other organisms live, and find adequate amounts of food, water, shelter and space needed to sustain their populations. Specific wildlife habitats of concern may include areas where species concentrate at a vulnerable point in their annual or life cycle; and areas which are important to migratory or non- migratory species. (Provincial Policy Statement, 2014)


Treed areas that provide environmental and economic benefi ts to both the private landowner and the general public, such as erosion prevention, hydrological and nutrient cycling, provision of clean air and the longterm storage of carbon, provision of wildlife habitat, outdoor recreational opportunities, and the sustainable harvest of a wide range of woodland products. Woodlands include treed areas, woodlots or forested areas and vary in their level of significance at the local, regional, and provincial levels. (Provincial Policy Statement, 2014)


Zone of Influence (ZOI)

The geographic area affected by a particular groundwater withdrawal; where groundwater is being withdrawn, the water level in the aquifer being pumped decreases, with the greatest effect closest to the well. In three dimensions, this area of effect is shaped like an inverted cone, with the well in the centre. The shape of this cone is dependent on the nature of the aquifer being pumped, and the rate at which groundwater is being withdrawn.