Difference between revisions of "Runoff volume control targets"

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[[File:90th percentile.png|thumb|Recommended regional 90th percentile volume targets for Ontario<ref> Aquafor Beech, EarthFX. Runoff Volume Control Targets for Ontario Final Report. 2016:125. http://www.downloads.ene.gov.on.ca/envision/env_reg/er/documents/2017/012-9080_Runoff.pdf. Accessed September 11, 2017.</ref>]]
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[[File:Screenshot 2025-09-12 113952.png|500px|thumb|right|Recommended regional 90th percentile volume targets for Ontario (MECP, 2022) <ref>MECP. 2022. Low Impact Development Stormwater
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[[File:Pearson_Graph.png|thumb|Typically designed to handle the smaller, most frequent storm events, LID practices in Southern Ontario are usually sized according to the 90th percentile event]]
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Management Guidance Manual Draft. https://ero.ontario.ca/public/2022-01/Draft%20LID%20Stormwater%20Management%20Guidance%20Manual%202022.pdf</ref>]]
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Typically designed to handle the smaller, most frequent storm events, LID practices in Ontario are usually sized according to the 90th percentile event. In many areas this translates into events that are < 30 mm in depth. Note that 25 mm is considered to be a suitable representation of the ‘first flush’ volume, and that controlling this amount of runoff may provide stormwater engineers with control over 90 % of the mean annual pollutant load <ref>Pitt, R. 1999.  Small Storm Hydrology and Why it is Important for the Design of Stormwater Control Practices. In: Advances in Modeling the Management of Stormwater Impacts, Volume 7. Computational Hydraulics International, Guelph, Ontario and Lewis Publishers/CRC Press. 1999</ref>.
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Typically designed to handle the smaller, most frequent storm events, LID practices in Ontario are usually sized according to the 90th percentile event. The rainfall depth of the 90th percentile event varies geographically. Use the map on the right to determine the typical 90th percentile event based on the site location. Controlling this amount of runoff may provide stormwater engineers with control of over 90 % of the mean annual pollutant load <ref>Pitt, R. 1999.  Small Storm Hydrology and Why it is Important for the Design of Stormwater Control Practices. In: Advances in Modeling the Management of Stormwater Impacts, Volume 7. Computational Hydraulics International, Guelph, Ontario and Lewis Publishers/CRC Press. 1999</ref>.
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See [[Understanding rainfall statistics]] to learn how to calculate the 90th percentile event using rainfall observations for a specific site.
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See [[Climate change]] to learn about adjusting runoff volume control targets to account for future precipitation trends.
  
 
===Runoff Volume Control Target (RVC<sub>T</sub>)===  
 
===Runoff Volume Control Target (RVC<sub>T</sub>)===  
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'''Volume capture and treatment''' - Also referred to as `treatment and release`, where the volume capture and treatment directly aims at reducing surface water impairment through treatment of the specified volume, often referred to as a “water quality volume”.<ref>MOECC (2018)</ref>}}
 
'''Volume capture and treatment''' - Also referred to as `treatment and release`, where the volume capture and treatment directly aims at reducing surface water impairment through treatment of the specified volume, often referred to as a “water quality volume”.<ref>MOECC (2018)</ref>}}
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==See also==
 
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*[[Understanding_rainfall_statistics]]
 

Latest revision as of 15:54, 12 September 2025

Recommended regional 90th percentile volume targets for Ontario (MECP, 2022) [1]

Typically designed to handle the smaller, most frequent storm events, LID practices in Ontario are usually sized according to the 90th percentile event. The rainfall depth of the 90th percentile event varies geographically. Use the map on the right to determine the typical 90th percentile event based on the site location. Controlling this amount of runoff may provide stormwater engineers with control of over 90 % of the mean annual pollutant load [2].

See Understanding rainfall statistics to learn how to calculate the 90th percentile event using rainfall observations for a specific site.

See Climate change to learn about adjusting runoff volume control targets to account for future precipitation trends.

Runoff Volume Control Target (RVCT)[edit]

"The means to achieve the RVCT includes:
Retention - where the captured volume shall be ultimately infiltrated, evapotranspired or re-used and the specified volume will not later be discharged to sewer networks (with the exception of internal water re-use activities) or surface waters and does not therefore become runoff, and

Volume capture and treatment - Also referred to as `treatment and release`, where the volume capture and treatment directly aims at reducing surface water impairment through treatment of the specified volume, often referred to as a “water quality volume”.[3]

  1. ↑ MECP. 2022. Low Impact Development Stormwater Management Guidance Manual Draft. https://ero.ontario.ca/public/2022-01/Draft%20LID%20Stormwater%20Management%20Guidance%20Manual%202022.pdf
  2. ↑ Pitt, R. 1999. Small Storm Hydrology and Why it is Important for the Design of Stormwater Control Practices. In: Advances in Modeling the Management of Stormwater Impacts, Volume 7. Computational Hydraulics International, Guelph, Ontario and Lewis Publishers/CRC Press. 1999
  3. ↑ MOECC (2018)

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.

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

Any form of rain or snow.

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

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.

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

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