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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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In [[bioretention]] systems 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]].
Suitable materials include:
Suitable materials include:
;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.
;HL 6
:Is a clean, angular aggregate screened between 10 - 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 - 15 mm, and washed free from fines.
In most scenarios, a [[geotextile]] layer is unnecessary and have been associated with rapid decline and clogging in some circumstances.
[[category: materials]]
[[category: materials]]