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→Design
{{plainlist| 1=Where:
{{plainlist| 1=Where:
*''A<sub>c</sub>'' = The area of the catchment (m²),
*''A<sub>c</sub>'' = The area of the catchment (m²),
*''R'' = The capture efficiency (suggest 0.8),
*''R'' = The capture efficiency (default to 0.8),
*''L<sub>o</sub>'' = The sediment loading rate (m³/Ha/yr), and
*''L<sub>o</sub>'' = The sediment loading rate (m³/Ha/yr), and
*''F<sub>c</sub>'' = The cleanout frequency (yrs)
*''F<sub>c</sub>'' = The cleanout frequency (yrs)
Sediment loading rates from impervious surfaces studied by STEP were between 0.3 - 0.6 m³/ha/yr <ref>Goncalves, C., & Van Seters, T. (2012). Characterization of Particle Size Distributions of Runoff from High Impervious Urban Catchments in the Greater Toronto Area. Retrieved from https://sustainabletechnologies.ca/app/uploads/2013/03/PSD-2012-final.pdf</ref>. In Brisbane a value of 0.6 m³/ha/yr is the default value used to size small forebays <ref name ="HW">Healthy Waterways Ltd. (2014). Bioretention Technical Design Guidelines. Retrieved from https://hlw.org.au/u/lib/mob/20150715140823_de4e60ebc5526e263/wbd_2014_bioretentiontdg_mq_online.pdf</ref>.
Sediment loading rates from impervious surfaces studied by STEP were between 0.3 - 0.6 m³/ha/yr <ref>Goncalves, C., & Van Seters, T. (2012). Characterization of Particle Size Distributions of Runoff from High Impervious Urban Catchments in the Greater Toronto Area. Retrieved from https://sustainabletechnologies.ca/app/uploads/2013/03/PSD-2012-final.pdf</ref>. In Brisbane a value of 0.6 m³/ha/yr is the default value used to size small forebays <ref name ="HW">Healthy Waterways Ltd. (2014). Bioretention Technical Design Guidelines. Retrieved from https://hlw.org.au/u/lib/mob/20150715140823_de4e60ebc5526e263/wbd_2014_bioretentiontdg_mq_online.pdf</ref>.
2. a) To size a forebay for (''A<sub>f</sub>'') 80 % capture efficiency of particles ≥ 1 mm may be estimated<ref name="HW"/> as:
2. a) The area of a forebay with (''A<sub>f</sub>'') 80 % capture efficiency of particles ≥ 1 mm may be estimated<ref name="HW"/> as:
:<math>A_{f}=120\times Q</math>
:<math>A_{f}=120\times Q</math>
: <math>A_{f}=\frac{V_{f}}{d_{f}}</math>
: <math>A_{f}=\frac{V_{f}}{d_{f}}</math>
It is recommended that both sizing calculations be made and the forebay be designed to meet both targets.
It is recommended that both sizing calculations be made and the forebay be designed to meet both targets. In some cases the additional storage required to meet both targets will reduce the expected frequency of maintenance. See below.
===Example calculation===
===Example calculation===
A parking lot catchment of 1.7 Ha is being routed through a small forebay into a bioretention cell. The system should be designed to require cleaning no more often than once per year.
The volume is calcualted as:
:<math>V_{f}=1.7\times 0.8\times 0.6\times 1=</math>
==Gallery==
==Gallery==