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Line 27: − 2016 guide to copy sizing from:<ref>http://www.dnrec.delaware.gov/swc/Drainage/Documents/Sediment%20and%20Stormwater%20Program/Functional%20Equivalents/3.06.2.9.%20Sheet%20Flow_FEQ%20JUL%202016.pdf</ref>+ − + + + + + + + + + + + + +
→Design
A limiting design factor is that the maximum flow path length across the impermeable surface should be less than 25 metres. This is because runoff flowing as sheet flow over an impermeable surface tends to concentrate after 25 metres <ref>Claytor, R. and T. Schueler. 1996. Design of Stormwater Filtering Systems. Center for Watershed Protection. Ellicott City, MD.</ref>. Once runoff from an impervious surface becomes concentrated, a [[swales|swale]] design should be used instead of a vegetated filter strip <ref name="Barrett2004"/>.
A limiting design factor is that the maximum flow path length across the impermeable surface should be less than 25 metres. This is because runoff flowing as sheet flow over an impermeable surface tends to concentrate after 25 metres <ref>Claytor, R. and T. Schueler. 1996. Design of Stormwater Filtering Systems. Center for Watershed Protection. Ellicott City, MD.</ref>. Once runoff from an impervious surface becomes concentrated, a [[swales|swale]] design should be used instead of a vegetated filter strip <ref name="Barrett2004"/>.
==Design==
==Design==
{|
|+Minimum length of filter strips<ref>http://www.dnrec.delaware.gov/swc/Drainage/Documents/Sediment%20and%20Stormwater%20Program/Functional%20Equivalents/3.06.2.9.%20Sheet%20Flow_FEQ%20JUL%202016.pdf</ref>
|-
|The first 3 m of filter must be ≤ 2% in all cases.
|-
!Slope of filter strip
!Minimum length (m)
|-
|< 3 %
|7.5
|-
|3 - 8 %
|15
|}
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.