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→Planning
Once runoff from an impervious surface becomes concentrated, a [[swales|swale]] design should be used instead of a vegetated filter strip <ref name="Barrett2004"/>.
Once runoff from an impervious surface becomes concentrated, a [[swales|swale]] design should be used instead of a vegetated filter strip <ref name="Barrett2004"/>.
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For a table summarizing information on planning considerations and site constraints see [[Site considerations]].
==Design==
==Design==
*The flow path length across the vegetated filter strip should exceed the maximum flow path length across the impervious surface draining to it.
*The flow path length across the vegetated filter strip should exceed the maximum flow path length across the impervious surface draining to it.
*The filter strip should have a flow path length of ≥ 5 m; however, some pollutant removal benefits are realized ≥ 3 m.
*The filter strip should have a flow path length of ≥ 5 m; however, some pollutant removal benefits are realized ≥ 3 m.
*Should be graded to provide a 75 to 150 mm elevation drop between pavement edge or flush curb and filter strip surface to dissipate energy, promote settling and allow for accumulation of sediment and debris between cleanings.
===Pretreatment===
===Pretreatment===
*A [[gravel diaphragm]] at the top of the slope is always recommended.
*A [[level spreader]] or [[gravel diaphragm]] at the top of the slope is always recommended.
*When filter strip slopes are greater than 5%, a series of [[level spreaders]], [[check dams]] or gravel diaphragms should be used to help maintain sheet flow.
*When filter strip slopes are greater than 5%, a series of [[level spreaders]], [[check dams]] or gravel diaphragms should be used to help maintain sheet flow.
*Filter strips should drain continuously as sheet flow until reaching a [[swales|swale]], [[bioretention]] facility, or other LID practice.
*Filter strips should drain continuously as sheet flow until reaching a [[swales|swale]], [[bioretention]] facility, or other LID practice.