Difference between revisions of "Bioretention: Sizing and modeling"

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The exceptions are the depth (''d'') and Permeable area (''P''), as only one of these is required to find the other.  
The exceptions are the depth (''d'') and Permeable area (''P''), as only one of these is required to find the other.  
Note that some of these parameters are limited:
Note that some of these parameters are limited:
*The ''maximum'' total depth will be limited by construction practices i.e. not usually > 2 m.
#The ''maximum'' total depth will be limited by construction practices i.e. not usually > 2 m.
*The ''maximum'' total depth may be limited by the [[Infiltration| conditions underground]] e.g. the groundwater or underlying geology/infrastructure.
#The ''maximum'' total depth may be limited by the [[Infiltration| conditions underground]] e.g. the groundwater or underlying geology/infrastructure.
*The minimum total depth may be limited by the need to support vegetation i.e. not < 0.6 m.
#The minimum total depth may be limited by the need to support vegetation i.e. not < 0.6 m.
 
#The area P for a [[green roofs]], [[absorbent landscapes]] and [[permeable paving]] may be very similar or equal to the catchment area, so that the I/P ratio is close to 1.
 
#[[Infiltration trenches]], [[Infiltration chambers| chambers]] and [[bioretention cells]] have a maximum recommended I/P ratio of 20.
*The area P for a [[green roofs]], [[absorbent landscapes]] and [[permeable paving]] may be very similar or equal to the catchment area, so that the I/P ratio is close to 1.
*[[Infiltration trenches]], [[Infiltration chambers| chambers]] and [[bioretention cells]] have a maximum recommended I/P ratio of 20.


{|class="wikitable"
{|class="wikitable"
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<math>P=\frac{IiD}{nd+qD}</math>
<math>P=\frac{IiD}{nd+qD}</math>


This spreadsheet has been set up to perform either of the above calculations.
<strong>[[Media:Infiltration Sizing.xlsx|Download .xlsx calculation tool]]</strong>
<strong>[[Media:Infiltration Sizing.xlsx|Download .xlsx calculation tool]]</strong>


[[category: modeling]]
[[category: modeling]]
[[category: infiltration]]
[[category: infiltration]]

Revision as of 20:11, 18 August 2017

Before beginning the sizing calculations most of the following parameters must be known or estimated. The exceptions are the depth (d) and Permeable area (P), as only one of these is required to find the other. Note that some of these parameters are limited:

  1. The maximum total depth will be limited by construction practices i.e. not usually > 2 m.
  2. The maximum total depth may be limited by the conditions underground e.g. the groundwater or underlying geology/infrastructure.
  3. The minimum total depth may be limited by the need to support vegetation i.e. not < 0.6 m.
  4. The area P for a green roofs, absorbent landscapes and permeable paving may be very similar or equal to the catchment area, so that the I/P ratio is close to 1.
  5. Infiltration trenches, chambers and bioretention cells have a maximum recommended I/P ratio of 20.
Inputs
Symbol Units Parameter
D hrs Duration of design storm (for MOECC volume based caclulations set to 1)
i mm/hr Intensity of design storm (for MOECC volume based calculations use whole storm depth (link to map))
q mm/hr Infiltration coefficient, calculated from measured infiltration rate and applied safety factor
n - Porosity, as measured (or default to 0.35)
I m2 Impermeable area i.e. catchment
d m depth of Infiltration facility or BMP
P m2 Permeable area i.e. area of the facility or BMP

To calculate the required depth, where the area of the facility is constrained:

To calculate the require facility area or footprint where the depth is constrained:

This spreadsheet has been set up to perform either of the above calculations. Download .xlsx calculation tool