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[[File:Gravel.jpg|thumb|medium sized granular, free from fines]]
[[File:Gravel.jpg|thumb|medium sized granular, free from fines]]
In [[bioretention]] systems a choking layer of ≥ 100 mm depth is the recommended method to prevent migration of finer [[filter media]] into an underlying reservoir of [[Reservoir gravel|coarse aggregate]].
In [[bioretention]] systems a choker layer of ≥ 100 mm depth is the recommended method to prevent migration of finer [[filter media]] into the underlying reservoir of [[Reservoir gravel|coarse aggregate]].
These same mid sized granular materials are recommended for use in [[Stormwater planter]] underdrains and may be useful in the fine grading of foundations courses for [[permeable paving]].
These same mid sized granular materials are recommended for use in [[Stormwater planter]] underdrains and may be useful in the fine grading of foundations courses for [[permeable paving]].
Suitable materials include:
Suitable materials include:
;High performance bedding (HPB)
;High performance bedding (HPB)
:Clean, angular aggregate screened to between 6 - 10 mm. Widely available and designed specifically for drainage applications. Free from fines by definition.
:Clean, angular aggregate screened to between 6 and 10 mm. Widely available and designed specifically for drainage applications. Free from fines by definition.
;HL 6
;HL 6
:Is a clean, angular aggregate screened between 10 - 20 mm. Free from fines by definition.
:Is a clean, angular aggregate screened between 10 and 20 mm. Free from fines by definition.
;Pea Gravel
;Pea Gravel
:Rounded natural aggregate, screened between 5 - 15 mm, and washed free from fines.
:Rounded natural aggregate, screened between 5 and 15 mm, and washed free from fines.
In most scenarios, a [[geotextiles|geotextile]] layer is unnecessary and have been associated with rapid decline and [[Clogging#Filter fabric|clogging]] in some circumstances.
In most scenarios, a [[geotextiles|geotextile]] layer is unnecessary and has been associated with rapid decline and [[Clogging#Filter fabric|clogging]] in some circumstances.
[[category: materials]]
[[category: materials]]