Erosion and Sediment Control

Note: This page is currently under revision.

Overview

Effective ESC starts before topsoil stripping begins. This flow chart shows the ESC process from construction project start to finish. Scroll through the wiki to read about each step of the process.

Erosion and sediment controls (ESC) are technologies, practices and procedures that are applied to prevent the release of sediment from construction sites. Rapid urban expansion and associated construction activities are a significant source of stress to the natural environment. As construction processes involve the removal of vegetation and de-stabilization of soils, they can accelerate natural processes of erosion and sedimentation, mobilizing more sediment and associated contaminants that can ultimately end up in downstream receiving water systems. ESC measures are essential to help reduce these sediment loads from active construction sites and protect downstream aquatic habitats from becoming impaired.

Inadequate ESC during construction can cause:

• sediment-laden runoff to enter downstream and adjacent natural features, including streams, lakes, wetlands and woodlots;
• deposition of sediment on adjacent private property and roadways;
• clogging of onsite stormwater management systems and LIDs;
• expensive cleanup and restoration costs;
• delays or stop-work orders; and
• fines from regulatory agencies.

Implementing effective ESC practices throughout all stages of construction is essential to sustainable urban growth and ensuring regulatory compliance.

The Toronto and Region Conservation Authority, through STEP, published the Erosion and Sediment Control Guide for Urban Construction in 2019. This wiki page summarizes key content from the guide and provides additional resources; however, readers should consult the full guide for comprehensive information. Click on the image to access the guide.

Erosion risk assessments (ERA)

ERAs divide a project site into areas of low, medium, and high erosion risk to optimize ESC placement. Kawartha Conservation used drones to map erosion risk on this site, helping to protect Sucker Creek other local water bodies from construction-related sediment runoff. Click the image to learn more (Kawartha Conservation, 2025).

To manage the potential negative impacts of construction activities in the absence of effective ESC measures, Erosion Risk Assessments (ERAs) are conducted to guide the selection and placement of appropriate ESC practices on site.

ERAs are recommended when:

• the extent of land disturbance is greater than 10 ha and duration is longer than 30 days, or
• construction activities are planned in or near natural water features, or
• the site drains to species at risk habitat

The hybrid qualitative ERA approach is recommended in the above situations, with the exception of instances where local regulatory agencies require a different approach. The hybrid qualitative ERA approach estimates erosion risk by dividing a site into areas based on soil, slope, and ground cover, then rating each area as low, moderate, or high erosion risk to help choose the right erosion control practices for each stage of construction. Completing an ERA demonstrates due diligence, identifies high-risk areas early, informs effective BMP selection and placement, guides the use of enhanced controls, and provides context for decision-making.

ESC plan design

An ESC plan should be created based on a given site’s ERA, with more controls used in the higher risk areas.

An ESC plan should be designed for each stage of construction:

1. Topsoil stripping, grading, and stabilization
2. Servicing
3. Building construction
4. Final stabilization/rehabilitation and ESC decommissioning

Types of ESC

Erosion controls
• prevent exposed soils from being entrained by water or wind
• addresses sediment at its source

Sediment controls
• remove sediment suspended in stormwater through settling and filtration

The most effective application of ESC utilizes a multi-barrier approach, in which erosion controls and sediment controls are installed in sequence to form a resilient system that protects the natural environment from sediment-related impacts. A multi-barrier system incorporates built-in redundancy, ensuring that if one control fails, additional measures remain in place to safeguard downstream features. Selecting appropriate BMPs for each project stage requires an understanding of their function, intended use, expected performance, and maintenance needs. Note: Isolation measures are not covered on this page but are detailed in the 2019 Erosion and Sediment Control Guide for Urban Construction.

Table 1 and 2 provide an overview of common erosion and sediment controls. Click on the BMP name in the first column to read the detailed design requirements and installation, inspection, maintenance, and decommissioning guidance from the 2019 Erosion and Sediment Control Guide for Urban Construction. A description and common applications of each practice are listed in the second and third columns, respectively. The fourth column provides links to design drawings and other resources.

Erosion controls

Table 1. Erosion Controls

BMP (click for more information)	Description	Applicability	Additional Resources	Example Image
Minimized or Phased Land Clearing	Preservation of vegetated areas intercepts and infiltrates rainfall.	Areas not being immediately developed on larger sites (>10 ha)
Vegetated Filter Strips	Gently sloping, vegetated areas that slow and filter runoff.	Areas that may benefit from leaving vegetation in place	Vegetated filter strip design Wiki	Source: Trinkhaus Engineering
Slope Drains	Flexible pipe that conveys water down a disturbed slope to prevent erosion from concentrated runoff.	Exposed (and especially long or steep) slopes that convey concentrated flow
Interceptor Swales	Stabilized flow path that conveys runoff away from bare soil to sediment control measures.	Any unstabilized areas, but especially where: Upslope drainage area is greater than 2 ha Slope² × Length ≥ 0.75 m In conjunction with slope drains Perimeter of site or stabilized/restored areas Toe of slopes Adjacent to valley/stream corridors
Outlet Protection	Energy dissipation devices or surface hardening that prevents scour erosion at outlets.	Base of any outlet releasing concentrated flow	Baffle shapes and size analysis
Mulching	Layer of organic material (e.g., straw, bark, wood shavings, paper fibre, compost) that absorbs rainfall and acts as a physical barrier to erosion.	Short term on bare soil not subject to concentrated flows Dry mulch best where not seeded Only apply Hydro-mulch (with tackifier) alone for temporary erosion control In conjunction with a tackifier/seeding on slopes steeper than 2H:1V
Seeding	Application of seed to establish vegetation for soil stability.	Click to expand.
Surface Roughening	Creates uneven surfaces and depressions to reduce runoff velocity, trap sediment, keep seed in place, and improve vegetation establishment	*Inactive (<30 days) disturbed surfaces Exposed slopes, especially steeper than 3H:1V and H>1.5 m Where vegetation cannot be established In conjunction with mulching/seeding
Rolled Erosion Control Products	Netting, blankets, or turf reinforcement mats act as a physical barrier to erosion. Biodegradable options free of plastic netting prevent wildlife ensnaring.	*Bare areas that convey concentrated flows Slopes steeper than 2H:1V that have not been stabilized Within natural water features if permitted Temporarily on banks of sediment control traps or basins Newly seeded areas if seeding does not provide immediate stabilization Erosion scars
Chemical Soil Stabilization	Substances that bind soil particles to stabilize the soil surface.	Subject to CA approval within regulated area In conjunction with seeding in areas not accessed by vehicles Only applied on bare soil if: reapplied at recommended frequency, no concentrated flows, no vehicle traffic, short term use only	Anionic Polyacrylamide Application Guide for Urban Construction in Ontario (TRCA, 2013)

Sediment controls

Table 2. Sediment Controls

BMP (click for more information)	Description	Applicability	Other Resources	Example Image
Sediment Control Fence	Geotextile material supported by posts and trenched into the ground to support settling of sheet flows.	Site perimeter up-gradient side of sensitive areas/streams Around material stockpiles 1.5 m away from slope base Do not install perpendicular to concentrated flows Parallel to areas with sediment laden sheet flow
Filter Socks	Tubular mesh socks filled with wood chip or compost that dissipate flow velocities and pond water to promote sediment settling.	applied along contours on level and sloped areas, perpendicular to sheet flows 1.5 m from slope base site perimeter as check dams in swales and ditches around storm drain inlets and sediment bags base of topsoil stockpiles in place of sediment fence when frozen	Source to Stream Conference Presentation Compost Biofilters for Stormwater Management (TRCA, 2007)
Natural Fibre Logs	Similar to filter socks but made of biodegradable materials such as coir, straw, or wood.	applied along contours on level and sloped areas, perpendicular to sheet flows 1.5 m from slope base site perimeter as check dams in swales and ditches Around storm drain inlets and sediment bags base of topsoil stockpiles in place of sediment fence when frozen
Rock Check Dams	Weir constructed across channels from granular material and geotextile to reduce flow velocity.	Perpendicular to concentrated flow channels, especially in long/steep channels Do not use in natural features
Vehicle Tracking Controls	Measures such as mud mats, shaker racks, or wheel washers to prevent vehicles from tracking mud offsite.	Vehicle tracking controls: site >1 ha grading/filling close to entrances Weather/site conditions cause mud Wheel washing: Mud tracking ongoing issue and vehicle tracking controls not providing mitigation/cannot be constructed due to site constraints contaminated soils required by municipality
Sediment Dewatering Bags	Large geotextile bags used to filter sediment-laden water from pumped discharge.	anywhere dewatering necessary to create a dry work area, particularly where space limited where flow dispersion is needed to prevent erosion best used in treatment train
Storm Drain Inlet Protection	Blocks sediment entry to inlets while allowing water through.	all operational inlets at grade around or overtop the inlet below grade inside a storm drain treatment train required for drainage areas >1 ha
Sediment Traps	Runoff detention area created by an embankment or depression to allow sediment settling.	end of a treatment train before discharged offsite across drainage/conveyance features drainage areas ≤ 2 ha that do not drain to another detention feature
Sediment Ponds	Similar to sediment traps but larger. Excavated depression for permanent water retention.	Treatment of runoff from drainage areas > 2 ha end-of-pipe control	https://sustainabletechnologies.ca/home/erosion-and-sediment-control/construction-sediment-control-ponds/
Weir Tanks	Tanks that detain stormwater runoff to promote sediment settling.	Sediment removal for short-term pumping / dewatering activities when more stringent effluent water quality standards required Planned pumping rates are high and require large capacity
Polymer Flocculants	Chemical agents that bind suspended particles to enhance sediment removal.	Treatment for short-term pumping activities A high sediment removal rate is required but area too small for wet pond Water contains contaminants or a large proportion of fine sediments more stringent effluent water quality standards required Other conventional BMPs cannot achieve removal rates	https://sustainabletechnologies.ca/home/erosion-and-sediment-control/polymers/
Active Treatment Systems	Systems combining tanks, flocculants, and filters for precise and high-efficiency contaminant removal.	Treatment for short-term pumping activities A high sediment removal rate is required but area too small for wet pond Water contains contaminants more stringent effluent water quality standards required Other conventional BMPs cannot achieve removal rates

Protecting LID features during construction

LID practices that promote infiltration as their primary function for water quality & management of overland flows - such as bioretention areas, permeable pavements, and infiltration trenches (link pages) - are vulnerable to damage during construction activities that can compromise their ability to function as intended.

These features can become clogged with sediment, experience erosion at inlets and in planted areas, suffer compaction from heavy machinery, or be contaminated by pollutants in construction runoff.

To minimize these risks and maintain effective protection throughout all phases of construction, the following best practices should be implemented:

• Keep LID perimeter controls in working order throughout construction
• Protect LID inlets
• Avoid heavy equipment on infiltration areas (i.e., driving vehicles through filter beds, or over granular water storage and bedding layers
• Phase construction so that LID measures are constructed last. Underground LID features can be built early in the construction process, provided they are protected by a barrier such as a plug.
• Keep LID installations offline via flow diversion until construction is complete, the drainage area is stabilized, and vehicle mud tracking is stopped.
• Avoid using LID areas as temporary detention basins, but in cases where flow cannot be routed around LID areas, protection should be used to prevent accumulated sediment from migrating into the subgrade.
• Be mindful of stockpile locations relative to LID areas
• Inspect LID areas during ESC site inspections
• Identify and mark LID areas to increase awareness

Spill Response

Creating a spill response, control, and reporting plan is a key part of erosion and sediment control (ESC) for construction projects. Although spills are not common, their environmental impact can be significant. A well-developed plan allows for quick, effective action that reduces environmental harm and cleanup needs. It also shows due diligence in protecting natural features.

At a minimum, the plan should include:

• Emergency contact numbers;
• A list of on-site spill control materials; and
• Clear steps for responding to different types of spills.

Prevention is equally important and involves:

• Identifying potential pollutants;
• Assessing risks; and,
• Safely storing materials away from storm drains and water bodies.

When spills occur, immediate action is required. Minor spills must be contained, cleaned up, and documented. Significant spills, such as those that may affect nearby or downstream water features, must be reported right away to the contract administrator, Ontario Spills Action Centre, and other relevant contacts. Response efforts should begin immediately, including monitoring and recording spill details and cleanup steps. Strong planning, prevention, and response protocols help minimize environmental damage during construction.

An example spill response/reporting plan by the City of Mississauga for small, medium, and large spills is available for download (downward facing arrow on the top righthand side) and printing (Printer emoticon on top right hand side) on the right.

Plan Submission and Approval

The submission requirements for erosion and sediment control strategies are organized based on three planning stages: early, intermediate, and late, which align with both the land-use and infrastructure planning processes. Each stage builds on the previous one, helping to gradually refine ESC strategies as more project details become available.

• In the early stage, the focus is on high-level planning, identifying potential impacts, and committing to appropriate ESC approaches.
• During the intermediate stage, ESC planning becomes more site-specific, using detailed information about layout, grading, and servicing.
• In the late stage, a comprehensive ESC report and drawings are submitted.

This progressive approach ensures that ESC strategies evolve alongside the project’s design and that regulatory requirements are addressed at each stage. The permits and approvals required for an urban construction project are dictated by relevant legislation as well as project and site-specific circumstances. Early consultation with regulatory agencies is encouraged in order to allow time for any necessary permits and approvals to be issued. Refer to Chapters 8 and 9 in the 2019 guide for full details on requirements for each planning stage and the approvals process.

For projects requiring a TRCA permit, information on the TRCA permitting process can be found here.

ESC report contents and drawings checklists, created by TRCA in 2019, are available for download here.

Routine inspection

ESC inspection programs regularly assess the effectiveness of BMPs, identify maintenance and repair needs, and identify areas where BMPs should be replaced or augmented. Consult the appendices linked in the first column of table 1 and 2 (above) for BMP-specific inspection points.

Inspections should be conducted:

• Before there is any activity to see the natural landscape, drainage, and sensitive features
• During the initial installation of ESC measures
• On a weekly basis during active construction
• Before and after significant rainfall and snowmelt events
• After any extreme weather which could result in damage to ESC measures
• Daily during extended rain or snowmelt periods
• Monthly during inactive periods (> 30 days)
• During or immediately following any spill event
• Before construction is shut down for the winter to ensure the site is ready for freezing conditions and thaws
• At the end of construction to confirm that the site has achieved at least 80% stabilization (CSA, 2018) and that permanent vegetation areas are well-established and effectively preventing erosion

Where applicable, inspections of ESC measures should be integrated with inspections of LID features. Construction and assumption inspections (https://wiki.sustainabletechnologies.ca/wiki/Inspections_and_maintenance#Inspection_.26_Maintenance_Terminology) for LID features are often required on the same schedule as ESC measures - for example, weekly, after major storm events, or at key construction milestones.

Ponding in front of this catchbasin indicates that this ESC inlet control is working. Ponding water allows for suspended sediments to settle. (Photo source: CISEC)

This inlet control has worked well, but the sediment should be removed as soon as possible. (Photo source: CISEC)

Performance Monitoring

An in-water turbidity monitoring station.

It is important to evaluate the cumulative effectiveness of all the controls installed on a construction site. Turbidity (a proxy for TSS) of the site discharges or the receiving water system is typically measured to assess ESC effectiveness. Turbidity targets vary based on duration of exposure, as the extent of potential harm to receiving aquatic ecosystems is dictated by both concentration and duration:

Table 3: Maximum allowable construction-based turbidity increases in the receiving water system at different durations

Construction-based turbidity increase (NTU)	Duration (h)
≤ 25	Any duration
761	0.5
324	1
138	2
84	3
59	4
45	5
36	6
29	7

The extent of turbidity monitoring and methods used on a given construction project should be based on erosion risk, receiving water flows, presence of species at risk, and type and location of discharge points. The monitoring program for sites applying the receiving water target should include the following components:

• One continuous online turbidity monitoring station 5 to 15 m downstream of the last site discharge point.
• At least one continuous online turbidity monitoring station immediately upstream of the site.

Map showing an example construction site with two pond discharges and an upstream and downstream monitoring site.

Each turbidity monitoring station should be equipped with a turbidity sonde, data logger, power supply, protective enclosure, and, where Species at Risk (SAR) are present, telemetry capabilities. Continuous turbidity monitoring should be maintained until the site has reached at least 80% effective permanent stabilization. Where continuous monitoring is not feasible, grab samples should be collected. To support interpretation of turbidity exceedances, precipitation data should be obtained from a rain gauge located within 5 km of the site. Clear protocols for responding to and reporting turbidity exceedances should be established for all sites with continuous monitoring.

Maintenance of ESC

Timely maintenance of ESC practices is essential for demonstrating due diligence on construction sites. Repairs or replacements should be completed promptly - within 48 h, or sooner if there is imminent environmental risk. Where feasible, backup materials should be stored on-site to expedite maintenance. Maintenance tasks vary depending on the ESC practice and a list of maintenance tasks can be found for each BMP by clicking on the first column of table 1 and 2 (above). General ESC maintenance tasks are listed in Table 4.

Table 4. ESC Maintenance and Repair Activities

Category	Key Actions and Considerations
Surface Repair	Regrade and fill eroded areas Upgrade stabilization where existing measures are inadequate Ensure discharge points are not causing erosion and apply stabilization if needed Restore disturbed or compacted areas caused by vehicle or equipment access
Sediment Removal	Remove and dispose of accumulated sediment before capacity is exceeded or when clogged Rake or replace overloaded granular materials
Structural Repair	Repair or replace damaged components such as filter socks and silt fences Reposition or resecure devices that have shifted Reinforce access restrictions to protected or stabilized areas
Vegetation Restoration	Re-seed areas where vegetation has failed Repair or replace damaged tree protection fencing or buffer zones
Flow Control Adjustments	Modify or reinforce swales, slope drains, and energy dissipators where flows are causing erosion or bypass Add or upgrade flow interruption devices if current setups are overwhelmed Regrade swales or adjust flow paths to reduce velocity and erosion risk
Corrective Actions	Implement fixes for recurring failures Replace underperforming ESC measures with more effective alternatives where necessary Prioritize and complete urgent repairs

Decommissioning of ESC

Decommissioning practices vary depending on the ESC and specific considerations can be found for each BMP by clicking on the first column of table 1 and 2 (above). General ESC decommissioning considerations are listed in Table 5.

Table 5. ESC Decommissioning

Category	Key Actions and Considerations
Timing & Prerequisites	Follow construction drawing sequencing, typically working upstream to downstream Only decommission ESC measures once areas receiving runoff are fully stabilized (i.e., vegetation well-established, slopes stabilized) Ensure runoff has been re-routed appropriately before removing conveyance features
Sediment and Material Removal	Remove accumulated sediment from ESC and dispose of in accordance with sediment quality and applicable legislation Treat water from dewatering activities using suitable sediment removal BMPs (e.g., sediment bags, weir tanks) Ensure flocculants and chemically treated sediment are disposed of properly Prevent thermal impacts by releasing water gradually to vegetated areas instead of directly into watercourses
ESC Feature Removal	Remove temporary ESC structures with minimal disturbance to stabilized areas and natural features Reusable materials (e.g., stakes, fence fabric) may be salvaged; others should be disposed of at appropriate facilities Biodegradable materials may be left in place if allowed and seeded appropriately for long-term restoration Some ESC practices may be retained or transitioned to permanent controls to manage long-term erosion and prevent sediment transport
Site Stabilization & Restoration	All disturbed areas must be graded and stabilized per final design Use native, weed-free vegetation for site restoration Stabilize areas before flow is returned to newly constructed or natural channels
Regulatory Compliance	Ensure removal follows manufacturer recommendations Coordinate with regulatory authorities where required Ensure stranded wildlife are safely relocated in accordance with permits

Additional Resources

• Course on Introduction to Erosion and Sediment Control & Best Practices for LID Implementation
• ESC guide for urban construction workshop (To access, enter password ESCGUCwebinar20
• Introduction to Erosion Sediment Control E-Learning Course
• Erosion Control Infrastructure – Asset Operation and Management Plans Presentation
• Low Impact Development Stormwater Management Guidance Manual (2022) Chapter 7: Erosion and Sediment Control during Construction
• B-6 Guidelines for Evaluating Construction Activities Impacting on Water Resources (Government of Ontario)
• B-6 Guidelines for Evaluating Construction Activities Impacting on Water Resources (Government of Ontario)
• Certified Inspector of Sediment and Erosion Control Training Manual (2014) CISEC
• ESC 2019 guide presentation
• Erosion and Sediment Control Practices Evaluation – Vaughan, Ontario
• CAN/CSA-W202-18: Erosion and sediment control inspection and monitoring
• Town of Milton, Erosion and Sediment Control Plan Terms of Reference

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.

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.

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 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.

Land owned by private individuals or companies.

Soil particles with a diameter less than 0.050 mm.

Sustainable Technologies Evaluation Program

Includes the protection of soil from dislocation by water, wind or other agents.

Best management practice. State of the art methods or techniques used to manage the quantity and improve the quality of wet weather flow. BMPs include: source, conveyance and end-of-pipe controls.

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 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.

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.

(1) The wearing away of the land surface by moving water, wind, ice or other geological agents, including such processes as gravitation creep; (2) Detachment and movement of soil or rock fragments by water, wind, ice or gravity (i.e. Accelerated, geological, gully, natural, rill, sheet, splash, or impact, etc).

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

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

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.

A body of water smaller than a lake, often artificially formed.

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 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.

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.

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.

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

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

The portion of water precipitated onto a catchment area, which then flows as surface discharge from the catchment area past a specified point.

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

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

Natural or artificial means of intercepting and removing surface or subsurface water (usually by gravity).

A structural best management practice that is located at the end of a flow conveyance route. End-of-Pipe Controls on surface and below ground but are not limited to wet ponds, constructed wetlands and other similar systems.

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.

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.

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

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.

Toronto and Region Conservation Authority

Box like underground concrete structure with openings in curb and gutter designed to collect runoff from streets and pavement.

Total suspended solids

Any form of rain or snow.

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