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Line 1: − <poem>+ − A choking layer of ≥ 100 mm is the recommended method to prevent migration of finer [[filter media]] into an underlying reservoir of [[Reservoir gravel|coarse aggregate]].+ + + + + + + − + − ;High performance bedding (HPB)+ − : + − </poem>
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[[File:Gravel.jpg|thumb|medium sized granular, free from fines]]
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 gravel|storage reservoir 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 pavements]].
Suitable materials include:
Suitable materials include:
;High performance bedding (HPB)
: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
:Is a clean, angular aggregate screened between 10 and 20 mm. Free from fines by definition.
;Pea Gravel
;Pea Gravel
:Pea gravel or crushed stone 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 has been associated with rapid decline and [[Clogging#Filter fabric|clogging]] in some circumstances.
[[category: materials]]
[[category: materials]]