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[[File:Vegetated_filter_strip_1.jpg|thumb|Hey Dean, What's the caption for this photo?]]

[[File:Vegetated_filter_strip_1.jpg|thumb|Grass filter strip draining to vegetated swale.  Source: Trinkhaus Engineering]]

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While filter strips are a simple technology, proper design requires attention to detail because small problems, such as concentration of inflowing runoff or improper grading, can decrease effectiveness and create nuisance soil erosion or ponding of water conditions.

While filter strips are a simple technology, proper design requires attention to detail because small problems, such as concentration of inflowing runoff or improper [[grading]], can decrease effectiveness and create nuisance soil erosion or ponding of water conditions.

*The maximum contributing flow path length across adjacent impervious surfaces must < 25 m.  

*The maximum contributing flow path length across adjacent impervious surfaces must < 25 m.  

*The impervious surfaces draining to a filter strip must have slopes < 3%.

*The impervious surfaces draining to a filter strip must have slopes < 3 %.

*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.

===Pretreatment===

===Pretreatment===

*A [[gravel diaphragm]] at the top of the slope is always recommended.  

*A [[gravel diaphragm]] at the top of the slope is always recommended.  

*When filter strip slopes are greater than 5%, a series of [[level spreaders]] 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.

===Berms===

===Berms===

*When designed as a stand alone water quality BMP (i.e., not pretreatment to another BMP) the vegetated filter strip should be designed with a pervious berm at the toe of the slope for shallow ponding of runoff.

*When designed as a stand alone water quality BMP (i.e., not pretreatment to another BMP) the vegetated filter strip should be designed with a pervious [[berm]] at the toe of the slope for shallow ponding of runoff.

*Media for the berm should consist of 40% excavated [[topsoil]], 40% [[sand]], and 20% [[choking layer|fine gravel]].   

*Media for the berm should consist of 40 % excavated [[topsoil]], 40 % [[sand]], and 20 % [[choking layer|fine gravel]].   

*The berm should be 150 to 300 mm in height above the bottom of the depression and should contain a perforated pipe [[underdrain]] connected to the storm sewer,  

*The berm should be 150 to 300 mm in height above the bottom of the depression and should contain a perforated pipe [[underdrain]] connected to the storm sewer,  

*Runoff ponds behind the berm and gradually flows through it, into the underdrain connected to the storm sewer system. The volume ponded behind the berm should be equal to the water quality storage requirement. During larger storms, runoff will overtop the berm and flow directly into a storm sewer inlet. <ref>Cappiella, K., T. Schueler, and T. Wright. 2006. Urban Watershed Forestry Manual, Part 2. Conserving and Planting Trees at Development Sites. Center for Watershed Protection. Prepared for United States Department of Agriculture, Forest Service.</ref>.

*Runoff ponds behind the berm and gradually flows through it, into the underdrain connected to the storm sewer system. The volume ponded behind the berm should be equal to the water quality storage requirement. During larger storms, runoff will overtop the berm and flow directly into a storm sewer inlet. <ref>Cappiella, K., T. Schueler, and T. Wright. 2006. Urban Watershed Forestry Manual, Part 2. Conserving and Planting Trees at Development Sites. Center for Watershed Protection. Prepared for United States Department of Agriculture, Forest Service.</ref>.

===Soil Amendments===

===Soil Amendments===

If native soils on the filter strip site are highly compacted, or of such low fertility that vegetation cannot become established, they should be tilled to a depth of 300 mm and amended with [[compost]] to achieve an [[organic matter]] content of 8 - 15 %.

If native soils on the filter strip site are highly compacted, or of such low fertility that vegetation cannot become established, they should be tilled to a depth of 300 mm and amended with [[compost]] to achieve an [[organic matter]] content of 5 - 15 %.

==Landscaping==

==Landscaping==

Filter strip vegetation can consist of [[Turf|turf grasses]], meadow [[Graminoids: List|grasses]], [[Perennials: List|wildflowers]], shrubs, and [[trees]]. Trees and shrubs with deep rooting capabilities are recommended for planting to maximize soil infiltration capacity <ref>Philadelphia Water Department (PWD). 2007. Philadelphia Stormwater Management Guidance Manual. Philadelphia, PA.</ref>.

The context of filter strips is often natural, informal and somewhat informal. Filter strip vegetation can consist of [[Turf|turf grasses]], meadow [[Graminoids: List|grasses]], [[Perennials: List|wildflowers]], shrubs, and [[trees]]. Trees and shrubs with deep rooting capabilities are recommended for planting to maximize soil infiltration capacity <ref>Philadelphia Water Department (PWD). 2007. Philadelphia Stormwater Management Guidance Manual. Philadelphia, PA.</ref>.

   

   

*Filter strips used for snow storage and treatment should be planted with non-woody vegetation. Designers should choose vegetation that stabilizes the soil and is salt tolerant where the filter strip will be used for snow storage or to treat road runoff.

*Filter strips used for snow storage and treatment should be planted with non-woody vegetation. Designers should choose vegetation that stabilizes the soil and is salt tolerant where the filter strip will be used for snow storage or to treat road runoff.

*Vegetation at the toe of the slope (where ponding may occur) should be able to withstand both wet and dry soil conditions.  

*Vegetation at the toe of the slope (where ponding may occur) should be able to withstand both wet and dry soil conditions.

*Whatever the type of vegetation used, it must be densely planted to slow runoff, collect sediment, and allow for infiltration.  

Although filter strips are often grassed, alternatives include forested filter strips or multi-zone filter strips, which feature several vegetation zones providing a gradual transition from turf to meadow to shrub and forest. The multi-zone filter strip design can be effective as a buffer zone to an existing natural heritage feature.

Although filter strips are often grassed, alternatives include forested filter strips or multi-zone filter strips, which feature several vegetation zones providing a gradual transition from turf to meadow to shrub and forest. The multi-zone filter strip design can be effective as a buffer zone to an existing natural heritage feature.

{{:turf}}

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{{:Filter strips: Performance}}

{{:Filter strips: Performance}}

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[[Category: Pretreatment]]

[[Category: Pretreatment]]