Glossary of Terms

A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, T, U, V, W, X, Y, Z

A

• Aggregate: A broad category of particulate material used in construction, including sand, gravel, crushed stone, slag, recycled concrete and geosynthetic aggregates, and available in various particulate size gradations.

B

• Berm: A compacted earthen wall that diverts runoff or creates shallow ponding of runoff. In some cases, runoff ponds behind the berm and gradually flows through it or is infiltrated.
• Biofilter: A bioretention stormwater best management practice featuring an impermeable liner and underdrain that prevents infiltration of runoff into the underlying native soil; provides sedimentation and filtration of urban runoff as it passes through the mulch layer, engineered filter media and vegetation root zone.
• Bioretention: A stormwater filtration and infiltration practice. The practice is a shallow excavated surface depression containing a prepared soil mix, mulch, and planted with specially selected vegetation. The system is engineered to temporarily store runoff in the depression and gradually filters it through the mulch, filter media, and root zone. They remove pollutants from runoff through filtration in the soil and uptake by plant roots and can help to reduce runoff volume through evapotranspiration and infiltration.

C

• Check dam: Structure constructed of a non-erosive material, such as suitably sized aggregate, wood, gabions, riprap, or concrete, used to slow runoff water to allow sedimentation, filtration, evapotranspiration, and infiltration into the underlying native soil. Can be employed in practices such as bioswales and enhanced grass swales.
• Cistern: Tank used to store rainwater (typically roof runoff) for later use.

D

• Depression Storage: A technique for incorporating shallow depressed areas into urban landscaped areas for storing and infiltrating runoff. Typically, depression storage areas are small and have limited capacity and limited duration of retention in order to address property owner concerns relating to insects, damage to structures and inconvenience of ponded water on their property.
• Detention: The temporary storage of stormwater to control discharge rates, and allow for sedimentation.
• Drawdown time: The period between the maximum water level and the minimum level (dry weather or antecedent level).
• Dry swale: 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.

E

• Evapotranspiration; The combined loss of water to the atmosphere from land and water surfaces by evaporation and from plants by transpiration.
• Enhanced grass swale: Vegetated open channels designed to convey, treat and attenuate stormwater runoff, also referred to as enhanced vegetated swales. Enhanced grass swales are not capable of providing the same water balance and water quality benefits as dry swales, as they lack the engineered soil media and storage capacity.
• Environmental Impact Report (EIR): The evaluation of the possible effects that may arise from a proposed project on the environment, together consisting of the natural, social and economic aspects.
• Exfiltration: Loss of water from a drainage system as a result of percolation or absorption into the surrounding medium (e.g., the infiltration of water into the native soil through a perforated pipe wall as it is conveyed).

F

• Filter media: The engineered soil bed component of bioretention cell or dry swale designs, typically composed of a sandy soil mixture containing a limited proportion of fine textured material, which provides a growing medium for vegetation, maintains a high rate of infiltration over the lifespan of the practice, and retains contaminants through filtration and adsorption to soil particles.
• Filtration: The technique of removing pollutants from runoff as it infiltrates through the soil.
• Fines: Soil materials with less than a 0.050 mm diameter particle size.
• First flush: Initial pulse of stormwater runoff which picks up the pollutants that have settled on surfaces during the dry period. The first flush contains the highest pollutant concentrations.
• Forebay: A pretreatment basin at the inlet of a practice that allow settling out of sediment and associated contaminants suspended in urban runoff.
• Flow path length: The minimum linear distance of water flow across a surface.
• Fluvial geomorphology: The study of the processes responsible for the shape and form, or morphology, of watercourses; describes the processes whereby sediment (e.g., silt, sand, gravel) and water are transported from the headwaters of a watershed to its mouth.
• Fused grid : A hybrid neighbourhood and district layout model that combines the geometries of inner city grid road patterns with the loop and cul-de-sac road patterns of conventional suburbs.

G

• Grass swales: 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.
• Geotextile: A filter fabric that is installed to separate dissimilar soils and provide runoff filtration and contaminant removal benefits while maintaining a suitable rate of flow; may be used to prevent fine-textured soil from entering a coarse granular bed, or to prevent coarse granular from being compressed into underlying finer-textured soils.
• Granular: Gravel, or crushed stone of various size gradations (i.e., diameter), used in construction; void forming material used as bedding and runoff storage reservoirs and underdrains in stormwater infiltration practices.
• Gravel diaphragm: Is a level spreading device placed at a runoff discharge location, perpendicular to flow, to maintain sheet flow and distribute runoff as evenly as possible across a pervious area or stormwater infiltration practice. A gravel diaphragm acts as a pretreatment device, settling out suspended sediments before they reach the practice.
• Green roof: A thin layer of vegetation and growing medium installed on top of a conventional flat or sloped roof, also referred to as living roofs or rooftop gardens.
• Green infrastructure: Natural vegetation and vegetative technologies in urban settings such as: urban forests; green roofs; green walls; green spaces; rain gardens; bioswales; community gardens; natural and engineered wetlands and stormwater management ponds; and porous pavement systems. These systems are designed to provide multiple benefits, such as moderate temperatures, clean air and water, and improve aesthetics.
• Groundwater discharge: The outflow of groundwater to a well, spring, wetland or watercourse.
• Groundwater recharge: The inflow of surface water to a groundwater reservoir or aquifer.

H

Hydraulic Conductivity

A parameter that describes the capability of a medium to transmit water.

Hydrologic Cycle

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

Hydrologic Regime

The characteristic pattern of precipitation, runoff, infiltration and evaporation affecting the hydrology of a system.

Hydrologic Soil Groups

A soil classification system based on the ability to convey and store water; divided into four groups:

A – well drained sands and gravel, high infiltration capacity, high leaching potential and low runoff potential;

B – Moderately drained fine to coarse grained soils, moderate infiltration capacity, moderate leaching potential and moderate runoff potential;

C – Fine grained, low infiltration capacity, low leaching potential and high runoff potential;

D – Clay soils, very low infiltration capacity, very low leaching potential and very high runoff potential.

I

Impervious

A hard surface area (e.g., road, parking area or rooftop) that prevents or retards the infiltration of water into the soil.

Infiltration

Penetration of water through the ground surface.

Inline

Refers to a system that accepts all of the flow from a drainage area and conveys larger event flows through an overflow outlet.

L

Landform

The natural features of the landscape, dictates flow patterns, runoff velocities and discharge rates.

Landscape-based Approach

The principle that development form, servicing and stormwater management strategies should be defined by the biophysical, hydrological and ecological attributes of the landscape.

Lot Level

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.

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.

M

Master Environmental Servicing Plan (MESP)

Is a community-scale planning assessment of servicing and environmental considerations for a development project.

Mulch

Shredded woody material or leaf compost used as a top dressing over vegetation beds that provides a source of soil nutrients and helps retain soil moisture; in bioretention cells and dry swales the surface mulch layer provides pollutant removal and improves growing conditions for the selected plants; shredded hardwood bark has been found to work best as it is less likely to float.

N

Native Soil

The natural ground material characteristic of or existing by virtue of geographic origin.

O

Offline

Refers to a system that when full, stormwater will bypass the practice. Offline systems use flow splitters or bypass channels that only allow the water quality volume to enter the facility. This may be achieved with a pipe, weir, or curb opening sized for the target flow, but in conjunction, create a bypass channel so that higher flows do not pass over the surface of the filter bed.

P

Permeable Pavement

Is 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.

Physiography

The physical features of the land, including topography, morphology and geologic origin. The physical feature of the land has an influence on the surface water movement and the interactions between surface water and groundwater.

Pollution Hot Spot

areas where certain land uses or activities have the potential to generate highly contaminated runoff (e.g., vehicle fuelling, service or demolition areas, outdoor storage and handling areas for hazardous materials and some heavy industry sites).

Pollutant Load

The total mass of a pollutant entering a waterbody over a defined time period.

Predevelopment

refers to the characteristics and functions of a system prior to urban development.

Pretreatment

Initial capturing and removal of unwanted contaminants, such as debris, sediment, leaves and pollutants, from stormwater before reaching a best management practice; Examples include, settling forebays, vegetated filter strips and gravel diaphragms.

R

Rain garden

A lot level bioretention cell designed to receive and detain, infiltrate and filter runoff, typically used for discharge from downspouts.

Rainwater harvesting

Is the practice of intercepting, conveying and storing rainwater for future use. The captured rainwater is typically used for outdoor non-potable water uses such as irrigation and pressure washing, or in the building to flush toilets or urinals or other uses that do not require potable water.

Recharge

The infiltration and movement of surface water into the soil, past the vegetation root zone, to the zone of saturation or water table.

Riparian

A vegetated ecosystem alongside a waterbody, characteristically have a high water table and are subject to periodic flooding.

Runoff

Water from rain, snow melt, or irrigation that flows over the land surface.

S

Sedimentation

Settling-out or deposition of particulate matter suspended in runoff.

Soakaway

An excavated area lined with geotextile filter cloth and filled with clean granular stone or other void forming material, that receives runoff and allow it to infiltrate into the native soil; can also be referred to as infiltration galleries, French drains, dry wells or soakaway pits.

Soil Amendment

The practice of adding organic material, such as mulch or compost to topsoil to improve fertility, and tilling of the native soils to reverse compaction and restore its water retaining capacity.

Standing Water

Water ponded on the ground surface.

Stone Reservoir

An underlying aggregate material bed that temporarily stores stormwater before infiltrating into the native soil or being conveyed by an underdrain pipe.

Stormwater Planer

A bioretention cell that features an imperveable liner that collects and treats stormwater through sedimentation and filtration only (i.e., no infiltration).

Stream Channel

A natural waterway, formed by fluvial processes, that conveys running water.

T

Treatment Train Approach

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

U

Underdrain

A perforated pipe used to assist the draining of soils.

Urbanization

The changing of land cover and land uses from rural to urban; the growth of urban settlements.

V

Vegetated Filter Strip

Are gently sloping, densely vegetated areas that treat runoff as sheet flow from adjacent impervious areas. They function by slowing runoff velocity and filtering out suspended sediment and associated pollutants, and by providing some infiltration into underlying soils. Also known as buffer strips and grassed filter strips.

W

Water Balance

The accounting of inflow and outflow of water in a system according to the components of the hydrologic cycle.

Water Cycle

The continuous movement of water from the oceans to the atmosphere (by evaporation), from the atmosphere to the land by condensation and precipitation, and from the land back to the sea (via groundwater and stream flow); also referred to as hydrologic cycle.

Water Budget

The mathematical expression of the water balance.

Water Quality Volume

The amount of stormwater runoff from a given area required to be retained by stormwater management practices to reduce pollutant load to an acceptable level.

Water Table

Subsurface water level which is defined by the level below which all the spaces in the soil are filled with water; The entire region below the water table is called the saturated zone.

Watershed

An area of land that drains into a river or a lake. The boundary of a watershed is based on the elevation (natural contours) of a landscape.

A broad category of particulate material used in construction, including sand, gravel, crushed stone, slag, recycled concrete and geosynthetic aggregates, and available in various particulate size gradations.

Mineral particles which are smaller than 2 mm, and which are free of appreciable quantities of clay and silt. Coarse sand usually designates sand grains with particle size between 0.2 and 0.02 mm.

A broad category of particulate material used in construction, including sand, gravel, crushed stone, slag, recycled concrete and geosynthetic aggregates, and available in various particulate size gradations.

A compacted earthen wall that diverts runoff or creates shallow ponding of runoff. In some cases, runoff ponds behind the berm and gradually flows through it or is infiltrated.

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.

A compacted earthen wall that diverts runoff or creates shallow ponding of runoff. In some cases, runoff ponds behind the berm and gradually flows through it or is infiltrated.

A bioretention BMP featuring an impermeable liner and underdrain that prevents infiltration of runoff into the underlying native soil; provides sedimentation and filtration of urban runoff as it passes through the mulch layer, engineered filter media and vegetation root zone.

A bioretention cell that features an impermeable liner that collects and treats stormwater through sedimentation and filtration only (i.e., no infiltration).

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

A perforated pipe used to assist the draining of soils.

The natural ground material characteristic of or existing by virtue of geographic origin.

Deposition of material of varying size, both mineral and organic away from its site of origin by the action of water, wind, gravity or ice.

Settling-out or deposition of particulate matter suspended in runoff.

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

a top dressing over vegetation beds that provides suppresses weeds and helps retain soil moisture in bioretention cells, stormwater planters and dry swales.

The engineered soil component of bioretention cell or dry swale designs, typically with a high rate of infiltration and designed to retain contaminants through filtration and adsorption to particles.

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

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 slow movement of water into or through a soil or drainage system.

Penetration of water through the ground surface.

Structures constructed of a non-erosive material, such as suitably sized aggregate, wood, gabions, riprap, or concrete; used to slow runoff water. Can be employed in practices such as bioswales and enhanced grass swales.

A broad category of particulate material used in construction, including sand, gravel, crushed stone, slag, recycled concrete and geosynthetic aggregates, and available in various particulate size gradations.

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.

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.

Tank used to store rainwater (typically roof runoff) for later use.

A technique for incorporating shallow depressed areas into urban landscaped areas for storing and infiltrating runoff. Depression storage areas are small and have limited capacity and limited duration of retention in order to address property owner concerns relating to insects, damage to structures and inconvenience of ponded water on their property.

A technique for incorporating shallow depressed areas into urban landscaped areas for storing and infiltrating runoff. Depression storage areas are small and have limited capacity and limited duration of retention in order to address property owner concerns relating to insects, damage to structures and inconvenience of ponded water on their property.

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

The period between the maximum water level and the minimum level (dry weather or antecedent level).

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 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.

Abiotic transfer of water vapour to the atmosphere.

Vegetated open channel, with check dams; designed to convey, treat and attenuate stormwater runoff.

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.

The accounting of inflow and outflow of water in a system according to the components of the hydrologic cycle.

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 evaluation of the possible effects that may arise from a proposed project on the environment, together consisting of the natural, social and economic aspects.

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 downward movement of water through the soil, the downward flow of runoff from the bottom of an infiltration BMP into the soil.

Loss of water from a drainage system as a result of percolation or absorption into the surrounding medium (e.g., the infiltration of water into the native soil through a perforated pipe wall as it is conveyed).

A system flow of gully inlets, pipes, overland flow paths, open channels, culverts and detention basins used to convey runoff to its receiving waters. City of Toronto 45 Wet Weather Flow Management November 2006

The engineered soil component of bioretention cell or dry swale designs, typically with a high rate of infiltration and designed to retain contaminants through filtration and adsorption to particles.

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 attachment of gas, vapour or dissolved matter onto the surface of solid materials.

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

Soil particles with a diameter less than 0.050 mm.

The delivery of a disproportionately large load of pollutants during the early part of storms due to the rapid runoff of accumulated pollutants. The first flush of runoff has been defined several ways (e.g., 10 mm per impervious area).

Initial pulse of stormwater runoff which picks up the pollutants that have settled on surfaces during the dry period. The first flush contains the highest pollutant concentrations.

The delivery of a disproportionately large load of pollutants during the early part of storms due to the rapid runoff of accumulated pollutants. The first flush of runoff has been defined several ways (e.g., 10 mm per impervious area).

Initial pulse of stormwater runoff which picks up the pollutants that have settled on surfaces during the dry period. The first flush contains the highest pollutant concentrations.

A pretreatment basin at the inlet of a practice that allow settling out of sediment and associated contaminants suspended in urban runoff.

Initial capturing and removal of unwanted contaminants, such as debris, sediment, leaves and pollutants, from stormwater before reaching a best management practice; Examples include, settling forebays, vegetated filter strips and gravel diaphragms.

Ground depression acting as a flow control and water treatment structure, that is normally dry.

Soil, sand and minerals washed from land into water, usually after rain. They pile up in reservoirs, rivers and harbors, destroying fish-nesting areas and holes of water animals and cloud the water so that needed sunlight might not reach aquatic plans. Careless farming, mining and building activities will expose sediment materials, allowing them to be washed off the land after rainfalls.

The minimum linear distance of water flow across a surface.

The study of the processes responsible for the shape and form, or morphology, of watercourses; describes the processes whereby sediment (e.g., silt, sand, gravel) and water are transported from the headwaters of a watershed to its mouth.

Soil or media particles smaller than sand and larger than clay (3 to 60 m)

A hybrid neighbourhood and district layout model that combines the geometries of inner city grid road patterns with the loop and cul-de-sac road patterns of conventional suburbs.

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.

Filter fabric that is installed to separate dissimilar soils and provide runoff filtration and contaminant removal benefits while maintaining a suitable rate of flow; may be used to prevent fine-textured soil from entering a coarse granular bed, or to prevent coarse granular from being compressed into underlying finer-textured soils.

Gravel, or crushed stone of various size gradations (i.e., diameter), used in construction; void forming material used as bedding and runoff storage reservoirs and underdrains in stormwater infiltration practices.

Gravel, or crushed stone of various size gradations (i.e., diameter), used in construction; void forming material used as bedding and runoff storage reservoirs and underdrains in stormwater infiltration practices.

A level spreading device placed at a runoff discharge location, perpendicular to flow, to maintain sheet flow and distribute runoff as evenly as possible across a pervious area or stormwater infiltration practice. A gravel diaphragm acts as a pretreatment device, settling out suspended sediments before they reach the practice.

A level spreading device placed at a runoff discharge location, perpendicular to flow, to maintain sheet flow and distribute runoff as evenly as possible across a pervious area or stormwater infiltration practice. A gravel diaphragm acts as a pretreatment device, settling out suspended sediments before they reach the practice.

Soil, sand and minerals washed from land into water, usually after rain. They pile up in reservoirs, rivers and harbors, destroying fish-nesting areas and holes of water animals and cloud the water so that needed sunlight might not reach aquatic plans. Careless farming, mining and building activities will expose sediment materials, allowing them to be washed off the land after rainfalls.

A thin layer of vegetation and growing medium installed on top of a conventional flat or sloped roof, also referred to as living roofs or rooftop gardens.

Natural vegetation and vegetative technologies in urban settings such as: urban forests; green roofs; green walls; green spaces; rain gardens; bioswales; community gardens; natural and engineered wetlands and stormwater management ponds; and porous pavement systems. These systems are designed to provide multiple benefits, such as moderate temperatures, clean air and water, and improve aesthetics.

The outflow of groundwater to a well, spring, wetland or watercourse.

A vegetated area such as a bog, fen, marsh, or swamp, where the soil or root zone is saturated for part of the year.

(a) A natural well-defined channel produced wholly or in part by a definite flow of water and through which water flows continuously or intermittently. Also, a ditch, canal, aqueduct, or other artificial channel for the conveyance of water to or away from a given place, as for the draining of a swamp.

(b) A stream or current of water. Legally, a natural stream arising in a given drainage basin but not wholly dependent for its flow on surface drainage in its immediate area, flowing in a channel with a well-defined bed between visible banks or through a definite depression (as a ravine or swamp) in the surrounding land, having a definite and permanent periodic supply of water (the stream may be intermittent), and usually, but not necessarily having a perceptible current in a particular direction and discharging at affixed point into another body of water.

(c) A legal right permitting the use of a flow of a stream (especially of one flowing through one’s land) or the receipt of water discharged upon land belonging to another.

Increases in groundwater storage by natural conditions or by human activity. See also artificial recharge

The inflow of surface water to a groundwater reservoir or aquifer.

Layer of rock or soil that holds or transmits water.

Any form of rain or snow.

1. A mineral soil separate consisting of particles less than 0.002 millimeter in equivalent diameter. 2. A soil texture class. 3. (Engineering) A fine-grained soil (more than 50 percent passing the No. 200 Sieve) that has a high plasticity index in relation to the liquid limit. (Unified Soil Classification System).

A hard surface area (e.g., road, parking area or rooftop) that prevents or retards the infiltration of water into the soil.

The slow movement of water into or through a soil or drainage system.

Penetration of water through the ground surface.

Refers to a system that accepts all of the flow from a drainage area and conveys larger event flows through an overflow outlet.

The total surface area upstream of a point on a stream that drains toward that point. Not to be confused with watershed. The drainage area may include one or more watersheds.

The natural features of the landscape, dictates flow patterns, runoff velocities and discharge rates.

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

Relating to the properties, distribution and effects of water on and below the earth’s surface, and in the atmosphere.

The land draining to a single reference point (usually a structural BMP); similar to a subwatershed, but on a smaller scale.

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.

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.

Is a community-scale planning assessment of servicing and environmental considerations for a development project.

Is a community-scale planning assessment of servicing and environmental considerations for a development project.

a top dressing over vegetation beds that provides suppresses weeds and helps retain soil moisture in bioretention cells, stormwater planters and dry swales.

Decayed organic material used as a plant fertilizer. Compost helps to support healthy plant growth through the slow release of nutrients and the retention of moisture in the soil.

Refers to a system that when full, stormwater will bypass the practice. Offline systems use flow splitters or bypass channels that only allow the water quality volume to enter the facility. This may be achieved with a pipe, weir, or curb opening sized for the target flow, but in conjunction, create a bypass channel so that higher flows do not pass over the surface of the filter bed.

The amount of stormwater runoff from a given area required to be retained by stormwater management practices to reduce pollutant load to an acceptable level.

A hard surface area (e.g., road, parking area or rooftop) that prevents or retards the infiltration of water into the soil.

An underlying bed filled with aggregate or other void-forming fill material that temporarily stores stormwater before infiltrating into the native soil or being conveyed by an underdrain pipe.

The physical features of the land, including topography, morphology and geologic origin. The physical feature of the land has an influence on the surface water movement and the interactions between surface water and groundwater.

The water below the surface, and typically below the groundwater table.

Initial capturing and removal of unwanted contaminants, such as debris, sediment, leaves and pollutants, from stormwater before reaching a best management practice; Examples include, settling forebays, vegetated filter strips and gravel diaphragms.

A lot level bioretention cell designed to receive and detain, infiltrate and filter runoff, typically used for discharge from downspouts.

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.

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.

Human application of water to agricultural or recreational land for watering purposes. City of Toronto Wet Weather Flow Management November 2006 47

The addition of water to ground water by natural or artificial processes.

The infiltration and movement of surface water into the soil, past the vegetation root zone, to the zone of saturation or water table.

The upper surface of the zone of saturation, except where the surface is formed by an impermeable body.

Subsurface water level which is defined by the level below which all the spaces in the soil are filled with water; The entire region below the water table is called the saturated zone.

A vegetated ecosystem alongside a waterbody, characteristically have a high water table and are subject to periodic flooding.

A biological community, including humans and their natural environment.

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.

Deposition of material of varying size, both mineral and organic away from its site of origin by the action of water, wind, gravity or ice.

Settling-out or deposition of particulate matter suspended in runoff.

An underground water storage reservoir into which stormwater is directed and allowed to percolate into the underlying native subsoil.

An excavated area lined with geotextile filter cloth and filled with clean granular stone or other void forming material, that receives runoff and allow it to infiltrate into the native soil; can also be referred to as infiltration galleries, French drains, dry wells or soakaway pits.

Filter fabric that is installed to separate dissimilar soils and provide runoff filtration and contaminant removal benefits while maintaining a suitable rate of flow; may be used to prevent fine-textured soil from entering a coarse granular bed, or to prevent coarse granular from being compressed into underlying finer-textured soils.

An underground water storage reservoir into which stormwater is directed and allowed to percolate into the underlying native subsoil.

An excavated area lined with geotextile filter cloth and filled with clean granular stone or other void forming material, that receives runoff and allow it to infiltrate into the native soil; can also be referred to as infiltration galleries, French drains, dry wells or soakaway pits.

Movement of water from one location to another.

A perforated pipe used to assist the draining of soils.

The changing of land cover and land uses from rural to urban; the growth of urban settlements.

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

The total mass of a pollutant entering a waterbody over a defined time period.

The drainage area of a river.

An area of land that drains into a river or a lake. The boundary of a watershed is based on the elevation (natural contours) of a landscape.