Difference between revisions of "Sedimentation"

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=== Overview ===
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[[File:Screenshot 2025-07-09 145748.png|500px|thumb|right|Sedimentation is the process where particles suspended in a fluid settle to the bottom due to gravity.]]
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Sedimentation is a fundamental process used in stormwater treatment to remove pollutants from runoff. It relies on gravity to deposit suspended sediment and debris into a designated settling area for later removal. Many pollutants that adhere to solids, such as metals, phosphorus, and hydrocarbons, are also removed through this process.
+
== Overview ==
 +
 
 +
<imagemap>
 +
File:Screenshot 2025-07-11 113242.png|thumb|500px|This cross-section of a road from the Markham Municipal Green Road Pilot Project shows a primary inlet connected to a catchbasin sump with a hickenbottom-style riser, promoting sedimentation before water reaches the infiltration gallery. Sediment should be removed from the catchbasin regularly. Image adapted from Schollen & Company Inc (STEP, 2018). <ref>Sustainable Technologies Evaluation Program. 2018. The Markham Municipal Green Road Pilot Project. https://sustainabletechnologies.ca/app/uploads/2018/12/Markham-Green-Road-Case-Study_FINAL.pdf</ref> <span style="color:red">''Explore this image map with your cursor and click on highlighted labels to learn more on the Wiki.''</span>
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 +
rect 48 212 323 296 [[Overflow]]
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rect 778 436 1143 544 [[Infiltration trenches|Infiltration]]
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rect 367 523 699 641 [[Inlet sumps: Gallery|Inlet sump]]
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rect 388 261 557 439 [[Pretreatment]]
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rect 493 7 820 166 [[Inlets|Inlet]]
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rect 208 704 775 845 [[Aggregates|Granular bedding]]
 +
 
 +
</imagemap>
 +
 
 +
Sedimentation is a fundamental process used in stormwater treatment to remove suspended solids from runoff. It relies on gravity to deposit suspended sediment and debris into a designated settling area for later removal. Many pollutants that adhere to solids, such as metals, phosphorus, and hydrocarbons, are also removed through this process.
 
Stormwater treatment practices that primarily use sedimentation include:
 
Stormwater treatment practices that primarily use sedimentation include:
 
* Stormwater [[wet ponds]] and [[dry ponds]]
 
* Stormwater [[wet ponds]] and [[dry ponds]]
−
* Underground storage tanks and chambers
+
* Underground storage tanks and [[Rainwater harvesting#Cisterns|chambers]]
 
* [[Stormwater wetlands]]
 
* [[Stormwater wetlands]]
−
* [[Oil grit separators (OGS)]]
+
* [[Oil and grit separators (OGS)]]
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* [[Catch basins]] and pre-treatment sumps
+
* Catch basins and [[pre-treatment]] sumps
 
* [[Vegetated swales]]
 
* [[Vegetated swales]]
  
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=== Types of Settling ===
+
== Types of settling ==
−
Sedimentation occurs in two main forms:
+
Sedimentation occurs in two main forms (Minton, 2013)<ref>Minton, G. 2013. The Principles of Gravity Separation. https://www.stormwater.com/stormwater-bmps/article/13008476/the-principles-of-gravity-separation</ref>:
  
 
'''Dynamic Settling''' – Takes place during active storm flow conditions when runoff is moving through the system.
 
'''Dynamic Settling''' – Takes place during active storm flow conditions when runoff is moving through the system.
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Practices such as ponds and wetlands rely on quiescent settling, whereas systems like oil grit separators and catch basins rely more on dynamic settling. The effectiveness of sedimentation systems is largely governed by the surface loading rate (SLR), which is the rate at which water is introduced to the settling area. Higher SLRs generally result in lower pollutant removal efficiency.
 
Practices such as ponds and wetlands rely on quiescent settling, whereas systems like oil grit separators and catch basins rely more on dynamic settling. The effectiveness of sedimentation systems is largely governed by the surface loading rate (SLR), which is the rate at which water is introduced to the settling area. Higher SLRs generally result in lower pollutant removal efficiency.
  
−
=== Key Design Parameters ===
+
== Key design parameters ==
 
The performance of sedimentation systems depends on several factors:
 
The performance of sedimentation systems depends on several factors:
  
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'''Particle Size Distribution''' – Determines the settling velocity of solids in runoff.
 
'''Particle Size Distribution''' – Determines the settling velocity of solids in runoff.
  
−
'''Inlet and Outlet Design''' – Properly designed structures reduce resuspension and short-circuiting of flow.
+
'''[[Inlet]] and Outlet Design''' – Properly designed structures reduce resuspension and short-circuiting of flow.
  
−
===table===
+
<br>
  
 
{| class="wikitable"  
 
{| class="wikitable"  
 +
|+Permanent pool storage, surface loading rates and detention times for sedimentation practices.  Calculations are based on a one hectare drainage area with 85% imperviousness, peak flow rate for 4 hour Chicago distribution for 25 mm event and runoff coefficient of 0.81.<ref>References include: MOE, 2003; City of Toronto catch basin standard (T 705.010); OGS vendor technical manuals, TRCA OGS sizing review tool.</ref>
 
|-
 
|-
 
! Practice
 
! Practice
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| colspan="6" | '''Pre-treatment Practices (approx. 30-50% TSS removal)'''
 
| colspan="6" | '''Pre-treatment Practices (approx. 30-50% TSS removal)'''
 
|-
 
|-
−
| Oil Grit Seperator
+
| Oil Grit Separator
 
| 12
 
| 12
 
| 4.7
 
| 4.7
Line 75: Line 90:
 
|}
 
|}
  
−
=== Particle Settling and Particle Size Distribution ===
+
== Particle settling and particle size distribution ==
  
 
Settling velocity is influenced by particle size, shape, specific gravity, and water temperature. Coarser particles settle faster, whereas fine silts and organic matter take longer. Temperature affects viscosity, meaning lower temperatures reduce settling efficiency. Understanding particle size distributions at a site is critical for designing effective sedimentation systems.
 
Settling velocity is influenced by particle size, shape, specific gravity, and water temperature. Coarser particles settle faster, whereas fine silts and organic matter take longer. Temperature affects viscosity, meaning lower temperatures reduce settling efficiency. Understanding particle size distributions at a site is critical for designing effective sedimentation systems.
  
−
Research has shown wide variations in particle sizes in urban runoff, influenced by factors such as native soil texture, tree canopy cover, traffic levels, and road maintenance practices. While laboratory analyses help determine particle size, field studies provide more practical insights into sedimentation system performance.
+
Research has shown wide variations in particle sizes in urban runoff, influenced by factors such as native soil texture, tree canopy cover, traffic levels, and road maintenance practices. While laboratory analyses help determine particle size, field studies provide more practical insights into sedimentation system performance. The studies cited in the table below show a range of values found in literature. D10 is the diameter at which 10% of the particle size distribution falls below, D50 is the diameter at
−
 
+
which 50% of the particle size distribution falls below, and D90 is the diameter at which 90% of the particle size distribution falls below.
−
=== Best Practices for Sedimentation-Based Stormwater Treatment ===
 
−
 
 
−
'''Design for Adequate Surface Area''' – Systems should have sufficient area to slow down flow and enhance settling.
 
−
 
 
−
'''Maintain Low Surface Loading Rates''' – Lower SLRs improve treatment performance.
 
−
 
 
−
'''Use Pre-Treatment Systems''' – Oil grit separators and catch basins can extend the life of downstream sedimentation systems.
 
  
−
'''Incorporate Periodic Maintenance''' – Regular sediment removal prevents resuspension and system clogging.
 
−
 
−
'''Account for Seasonal Variability''' – Adjust design parameters based on temperature effects on settling velocity.
 
−
 
−
===table===
 
 
{| class="wikitable"  
 
{| class="wikitable"  
 +
|+Comparison of particle size distributions from previous studies in cold climates (STEP, 2012)<ref name = "STEP2012">Sustainable Technologies Evaluation Program. 2012. Characterization of Particle Size Distributions of
 +
Runoff from High Impervious Urban Catchments in the Greater Toronto Area. https://sustainabletechnologies.ca/app/uploads/2013/03/PSD-2012-final.pdf</ref>
 
|-
 
|-
 
! Land use
 
! Land use
 
! Number of <br />observations
 
! Number of <br />observations
 
! Location
 
! Location
−
! Sample<br />location
+
! Sampling<br />location
−
! Sample<br />method
+
! Sampling<br />method
 
! Analytical<br />method
 
! Analytical<br />method
−
! d<sub>10</sub><br />/µm
+
! D<sub>10</sub><br />/µm
−
! d<sub>50</sub><br />/µm
+
! D<sub>50</sub><br />/µm
−
! d<sub>90</sub><br />/µm
+
! D<sub>90</sub><br />/µm
 
! Source
 
! Source
 
|-
 
|-
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| 5.9
 
| 5.9
 
| 44
 
| 44
−
| SWAMP<ref>Once overheard on the subway</ref>
+
| (SWAMP, 2005)<ref name="SWAMP">SWAMP. 2005. Synthesis of Monitoring Studies Conducted Under the Stormwater Assessment Monitoring and Performance Program. https://sustainabletechnologies.ca/app/uploads/2013/01/Final_SWAMP_Synthesis.pdf</ref>
 
|-
 
|-
 
| Parking<br />lot
 
| Parking<br />lot
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| 9.0
 
| 9.0
 
| 92
 
| 92
−
| SWAMP
+
| (SWAMP, 2005)<ref name="SWAMP"/>
 
|-
 
|-
 
| Commercial<br />parking lot
 
| Commercial<br />parking lot
Line 138: Line 143:
 
| 8.5
 
| 8.5
 
| 25.9
 
| 25.9
−
|  
+
| Lab report, 2010
 
|-
 
|-
 
| Public bus<br />yard
 
| Public bus<br />yard
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| 19.2
 
| 19.2
 
| 154.1
 
| 154.1
−
|  
+
| (Stantec, 2008)
 
|-
 
|-
 
| Commerical<br />parking lot
 
| Commerical<br />parking lot
Line 160: Line 165:
 
| 55
 
| 55
 
| 500<br />
 
| 500<br />
−
|  
+
| (Horwatich & Bannerman, 2010)<ref>Horwatich, J.A. and Bannerman, R.T., 2010, Parking lot runoff quality and treatment efficiency of a
 +
stormwater-filtration device, Madison, Wisconsin, 2005–07: U.S. Geological Survey Scientific
 +
Investigations Report 2009–5196, 50 p</ref>
 
|-
 
|-
 
| Mixed use
 
| Mixed use
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| 42
 
| 42
 
| 200
 
| 200
−
|  
+
| (Selbig & Bannerman, 2011)<ref name="Selbig">Selbig , W. R., & Bannerman, R. T., 2011. Characterizing the Size Distribution of Particles in Urban
 +
Stormwater by Use of Fixed-Point Sample-Collection Methods. Open-File Report 2011–1052,
 +
U.S. Department of the Interior and U.S. Geological Survey, Reston.</ref>
 
|-
 
|-
 
| Parking lot
 
| Parking lot
Line 182: Line 191:
 
| 54
 
| 54
 
| 350
 
| 350
−
|  
+
| (Selbig & Bannerman, 2011)<ref name="Selbig"/>
 
|-
 
|-
 
| Parking lot
 
| Parking lot
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| 46
 
| 46
 
| -
 
| -
−
|  
+
| (Fowler et al, 2009)<ref>Fowler, G.D.; Roseen, R.M.; Ballestero, T.P.; Guo, Qizhong; and Houle, James, 2009, Sediment
 +
monitoring bias by autosampler in comparison with whole volume sampling for parking lot runoff,
 +
in Proceedings of the World Environmental and Water Resources Congress 2009—Great Rivers,
 +
Kansas City, Mo., May 17–21, 2009: p. 1514-1522</ref>
 
|-
 
|-
 
| Mixed use<br />(roads)
 
| Mixed use<br />(roads)
Line 204: Line 216:
 
| 52.5
 
| 52.5
 
| 145
 
| 145
−
|  
+
| (Winston & Witter, 2019)<ref>Winston, R. J., & Witter, J. D. 2019. Evaluating the particle size distribution and gross solids contribution of stormwater runoff from Ohio’s roads (Final Report, State Job Number 135258). Ohio Department of Transportation, Office of Statewide Planning & Research.</ref>
 
|-
 
|-
 
| Mixed use
 
| Mixed use
Line 215: Line 227:
 
| 16.4
 
| 16.4
 
| 55.1
 
| 55.1
−
|  
+
| (STEP, 2012)<ref name = "STEP2012"/>
 
|-
 
|-
 
| Parking lot
 
| Parking lot
Line 226: Line 238:
 
| 12.4
 
| 12.4
 
| 55.2
 
| 55.2
−
|  
+
| (STEP, 2012)<ref name = "STEP2012"/>
 
|}
 
|}
 +
 +
== Best practices for sedimentation-based stormwater treatment ==
 +
 +
'''Design for Adequate Surface Area''' – Systems should have sufficient area to slow down flow and enhance settling.
 +
 +
'''Maintain Low Surface Loading Rates''' – Lower SLRs improve treatment performance.
 +
 +
'''Use Pre-Treatment Systems''' – Oil grit separators and catch basins can extend the life of downstream sedimentation systems.
 +
 +
'''Incorporate Periodic Maintenance''' – Regular sediment removal prevents resuspension and system clogging.
 +
 +
'''Account for Seasonal Variability''' – Adjust design parameters based on temperature effects on settling velocity.
 +
 +
==References==

Latest revision as of 18:34, 18 July 2025

Sedimentation is the process where particles suspended in a fluid settle to the bottom due to gravity.

Overview[edit]

OverflowInfiltrationInlet sumpPretreatmentInletGranular bedding
This cross-section of a road from the Markham Municipal Green Road Pilot Project shows a primary inlet connected to a catchbasin sump with a hickenbottom-style riser, promoting sedimentation before water reaches the infiltration gallery. Sediment should be removed from the catchbasin regularly. Image adapted from Schollen & Company Inc (STEP, 2018). [1] Explore this image map with your cursor and click on highlighted labels to learn more on the Wiki.

Sedimentation is a fundamental process used in stormwater treatment to remove suspended solids from runoff. It relies on gravity to deposit suspended sediment and debris into a designated settling area for later removal. Many pollutants that adhere to solids, such as metals, phosphorus, and hydrocarbons, are also removed through this process. Stormwater treatment practices that primarily use sedimentation include:

Types of settling[edit]

Sedimentation occurs in two main forms (Minton, 2013)[2]:

Dynamic Settling – Takes place during active storm flow conditions when runoff is moving through the system.

Quiescent Settling – Occurs between storm events when water is retained in a storage system, allowing suspended particles to settle under still conditions.

Practices such as ponds and wetlands rely on quiescent settling, whereas systems like oil grit separators and catch basins rely more on dynamic settling. The effectiveness of sedimentation systems is largely governed by the surface loading rate (SLR), which is the rate at which water is introduced to the settling area. Higher SLRs generally result in lower pollutant removal efficiency.

Key design parameters[edit]

The performance of sedimentation systems depends on several factors:

Permanent Pool Volume – The volume of water permanently stored in a system, aiding quiescent settling.

Surface Loading Rate – The volume of water per unit surface area per unit time.

Detention Time – The length of time water remains in the system before discharge.

Particle Size Distribution – Determines the settling velocity of solids in runoff.

Inlet and Outlet Design – Properly designed structures reduce resuspension and short-circuiting of flow.


Permanent pool storage, surface loading rates and detention times for sedimentation practices. Calculations are based on a one hectare drainage area with 85% imperviousness, peak flow rate for 4 hour Chicago distribution for 25 mm event and runoff coefficient of 0.81.[3]
Practice Permanent Pool
/m3/Ha 		Surface Area
/m2/Ha 		Surface Loading Rate
/L/min/m2 		Detention Time
/hrs 		Assumptions
Enhanced Treatment Practices (80% TSS removal)
Wet ponds/ Underground Tanks 250 167 33 >24 Underground tanks sized like ponds, average permanent pool depth =1.5m
Stormwater Wetland 140 622 8.8 >24 Average depth =0.225m
Pre-treatment Practices (approx. 30-50% TSS removal)
Oil Grit Separator 12 4.7 1177 Negligible Varies by manufacturer. 2.44m (8ft) diameter unit with permanent pool depth of 2.6m. 60% removal objective.
Catch Basin 1.6 1.8 3054 Negligible 5 catch basins (0.6 x 0.6m) per Hectare. Permanent pool depth of 0.9m.

Particle settling and particle size distribution[edit]

Settling velocity is influenced by particle size, shape, specific gravity, and water temperature. Coarser particles settle faster, whereas fine silts and organic matter take longer. Temperature affects viscosity, meaning lower temperatures reduce settling efficiency. Understanding particle size distributions at a site is critical for designing effective sedimentation systems.

Research has shown wide variations in particle sizes in urban runoff, influenced by factors such as native soil texture, tree canopy cover, traffic levels, and road maintenance practices. While laboratory analyses help determine particle size, field studies provide more practical insights into sedimentation system performance. The studies cited in the table below show a range of values found in literature. D10 is the diameter at which 10% of the particle size distribution falls below, D50 is the diameter at which 50% of the particle size distribution falls below, and D90 is the diameter at which 90% of the particle size distribution falls below.

Comparison of particle size distributions from previous studies in cold climates (STEP, 2012)[4]
Land use Number of
observations 		Location Sampling
location 		Sampling
method 		Analytical
method 		D10
/µm 		D50
/µm 		D90
/µm 		Source
Mixed
residential 		66 GTA Storm
sewer 		Auto-
sampler 		Coulter counter
particle analyzer 		0.9 5.9 44 (SWAMP, 2005)[5]
Parking
lot 		44 Markham Storm
sewer 		Auto-
sampler 		Coulter counter
particle analyzer 		2.0 9.0 92 (SWAMP, 2005)[5]
Commercial
parking lot 		1 Calgary Storm
sewer 		NA Coulter counter
particle analyzer 		2.1 8.5 25.9 Lab report, 2010
Public bus
yard 		11 Toronto Storm
sewer 		Auto-
sampler 		Micro-imaging 4.0 19.2 154.1 (Stantec, 2008)
Commerical
parking lot 		45 Madison,
WI 		Storm
sewer 		Auto-
sampler 		Wet sieve (>32um);
particle analyzer (<32um) 		<2 55 500
 (Horwatich & Bannerman, 2010)[6]
Mixed use 20 Madison,
WI 		Storm
sewer 		Auto-
sampler 		Wet sieve (>32um);
particle analyzer (<32um) 		<2 42 200 (Selbig & Bannerman, 2011)[7]
Parking lot 94 Madison,
WI 		Storm
sewer 		Auto-
sampler 		Wet sieve (>32 um);
particle analyzer (<32um) 		2 54 350 (Selbig & Bannerman, 2011)[7]
Parking lot 18 New
Hampshire 		Storm
sewer 		Auto-
sampler 		Particle analyzer - 46 - (Fowler et al, 2009)[8]
Mixed use
(roads) 		176 Ohio Catch
basin 		Auto-
sampler 		Coulter counter
particle analyzer 		11 52.5 145 (Winston & Witter, 2019)[9]
Mixed use 7 Toronto
 Storm
outfall 		Grab Coulter counter
particle analyzer 		4.0 16.4 55.1 (STEP, 2012)[4]
Parking lot 12 Toronto,
Vaughan,
Brampton 		Direct
runoff,
man hole 		Grab Coulter counter
particle analyzer 		2.6 12.4 55.2 (STEP, 2012)[4]

Best practices for sedimentation-based stormwater treatment[edit]

Design for Adequate Surface Area – Systems should have sufficient area to slow down flow and enhance settling.

Maintain Low Surface Loading Rates – Lower SLRs improve treatment performance.

Use Pre-Treatment Systems – Oil grit separators and catch basins can extend the life of downstream sedimentation systems.

Incorporate Periodic Maintenance – Regular sediment removal prevents resuspension and system clogging.

Account for Seasonal Variability – Adjust design parameters based on temperature effects on settling velocity.

References[edit]

  1. ↑ Sustainable Technologies Evaluation Program. 2018. The Markham Municipal Green Road Pilot Project. https://sustainabletechnologies.ca/app/uploads/2018/12/Markham-Green-Road-Case-Study_FINAL.pdf
  2. ↑ Minton, G. 2013. The Principles of Gravity Separation. https://www.stormwater.com/stormwater-bmps/article/13008476/the-principles-of-gravity-separation
  3. ↑ References include: MOE, 2003; City of Toronto catch basin standard (T 705.010); OGS vendor technical manuals, TRCA OGS sizing review tool.
  4. ↑ 4.0 4.1 4.2 Sustainable Technologies Evaluation Program. 2012. Characterization of Particle Size Distributions of Runoff from High Impervious Urban Catchments in the Greater Toronto Area. https://sustainabletechnologies.ca/app/uploads/2013/03/PSD-2012-final.pdf
  5. ↑ 5.0 5.1 SWAMP. 2005. Synthesis of Monitoring Studies Conducted Under the Stormwater Assessment Monitoring and Performance Program. https://sustainabletechnologies.ca/app/uploads/2013/01/Final_SWAMP_Synthesis.pdf
  6. ↑ Horwatich, J.A. and Bannerman, R.T., 2010, Parking lot runoff quality and treatment efficiency of a stormwater-filtration device, Madison, Wisconsin, 2005–07: U.S. Geological Survey Scientific Investigations Report 2009–5196, 50 p
  7. ↑ 7.0 7.1 Selbig , W. R., & Bannerman, R. T., 2011. Characterizing the Size Distribution of Particles in Urban Stormwater by Use of Fixed-Point Sample-Collection Methods. Open-File Report 2011–1052, U.S. Department of the Interior and U.S. Geological Survey, Reston.
  8. ↑ Fowler, G.D.; Roseen, R.M.; Ballestero, T.P.; Guo, Qizhong; and Houle, James, 2009, Sediment monitoring bias by autosampler in comparison with whole volume sampling for parking lot runoff, in Proceedings of the World Environmental and Water Resources Congress 2009—Great Rivers, Kansas City, Mo., May 17–21, 2009: p. 1514-1522
  9. ↑ Winston, R. J., & Witter, J. D. 2019. Evaluating the particle size distribution and gross solids contribution of stormwater runoff from Ohio’s roads (Final Report, State Job Number 135258). Ohio Department of Transportation, Office of Statewide Planning & Research.

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.

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

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.

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.

Sustainable Technologies Evaluation Program

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.

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.

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

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

The net amount of something (e.g. chemical, such as phosphorus), calculated as the product of concentration and volume in a given time. Some BMPs significantly reduce loading of pollutants to the environment by reducing volume more so than concentration.

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

The net amount of something (e.g. chemical, such as phosphorus), calculated as the product of concentration and volume in a given time. Some BMPs significantly reduce loading of pollutants to the environment by reducing volume more so than concentration.

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

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

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 maximum flow rate occurring during a flood event measured at a given point in a river, street, or pipe system.

Total suspended solids

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

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

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

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

The point, location, or structure where wastewater or drainage discharges from a sewer pipe, ditch or other conveyance to a receiving body of water.

Systems designed to remove trash, debris and some amount of sediment, oil and grease from stormwater runoff based on the principles of sedimentation for the grit and phase separation for the oil.

Toronto and Region Conservation Authority

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

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

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

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