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*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===
*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 (e.g. gravel diaphragms) should be used to help maintain sheet flow.
*Filter strips should drain continuously as sheet flow until reaching a [[swale]], [[bioretention]] facility, or other LID practice.
===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 of [[sand]] and gravel at the toe of the slope for shallow ponding of runoff.
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>.
===Soil Amendments===
If 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 content of 8 to 15% by weight or 30 to 40% by volume.
==Landscaping==
Filter strip vegetation can consist of turf grasses, meadow grasses, wildflowers and herbs, shrubs, and trees. 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. Vegetation at the toe of the slope, where ponding will occur, should be able to withstand both wet and dry soil conditions. The planting areas can be divided into zones to account for differences in moisture conditions and slope.
==Gallery==
==Gallery==