Runoff volume control targets

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Recommended regional 90th percentile volume targets for Ontario
Typically designed to handle the smaller, most frequent storm events, LIDLow 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. practices in Southern Ontario are usually sized according to the 90th percentile event

Typically designed to handle the smaller, most frequent storm events, LIDLow 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. 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 flushThe 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.’ volume, and that controlling this amount of runoffThat potion of the water precipitated onto a catchment area, which 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. may provide stormwater engineers with control over 90 % of the mean annual pollutant loadThe total mass of a pollutant entering a waterbody over a defined time period. [1].

RunoffThat potion of the water precipitated onto a catchment area, which 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. Volume Control Target (RVCT)

"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 runoffThat potion of the water precipitated onto a catchment area, which 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., 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 volumeThe amount of stormwater runoff from a given area required to be retained by stormwater management practices to reduce pollutant load to an acceptable level.”.[2]

  1. 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
  2. MOECC (2018)