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--- filter_strip [2022/05/12 12:18] – admin
+++ filter_strip [2025/10/30 16:15] (current) – [Method to Determine Practice Efficiency] theresa_nelson
@@ Line 29: / Line 29: @@
 ====Level Spreader====
-If the required contributing area run-on lengths cannot be met or flow is concentrated, a level spreader may be constructed at the top of the filter strip. These devices disperse flows over a wide area, dissipating the energy of the runoff and creating sheet flow.  Level spreaders constructed with level, durable surfaces (such as concrete) are required to ensure sheet flow into the filter. The figure below illustrates a swale that fills up before flowing over the level spreader, onto a 1 foot (or larger) gravel diaphragm, then into the filter strip. Incoming flow should enter the swale parallel to the swale length. The designer should calculate the peak rate for the 1-yr storm and multiple that result by 10 feet per cfs to determine the required length of the level spreader, with a maximum length of 100 ft. This length requirement is based on releasing water into the level spreader at a non-erosive velocity. If soil conditions warrant, an underdrain should be installed to assist the swale drainage after a storm.
+If the required contributing area run-on lengths cannot be met or flow is concentrated, a level spreader may be constructed at the top of the filter strip. These devices disperse flows over a wide area, dissipating the energy of the runoff and creating sheet flow.  Level spreaders constructed with level, durable surfaces (such as concrete) are required to ensure sheet flow into the filter. The figure below illustrates a swale that fills up before flowing over the level spreader, onto a 1 foot (or larger) gravel diaphragm, then into the filter strip. Incoming flow should enter the swale parallel to the swale length. The designer should calculate the peak rate for the 1-yr storm and multiple that result by 10 feet per cfs to determine the required width of the level spreader, with a maximum width of 100 ft. This requirement helps ensure water is released into the filter strip at a non-erosive velocity. If soil conditions warrant, an underdrain should be installed to assist the swale drainage after a storm.
-[[File:/Images/Filter Strip.png]]
+{{ :wiki:images:filter_strip.png?600 |}}
-====Figure 1: Level spreader diagram====
 =====Vegetation=====
@@ Line 62: / Line 61: @@
 WinSLAMM must be used to calculate the efficiency of filter strips. The impervious area must be modeled as "directly connected". A dynamic infiltration rate of 0.01 in/hr can be assumed unless a soil texture evaluation or infiltration test indicates a higher infiltration rate is appropriate. Compost may be amended into the soil to improve the infiltration rate to the next soil type (as listed in WinSLAMM). The selected vegetation height and retardance class should be consistent with the expected land use and maintenance.
-:!: WinSLAMM will reduce the efficiency of a filter strip if the ratio of contributing area to filter strip area is greater than 5:1. WinSLAMM also reduces the modeled filter strip flow length based on the longitudinal slope of the filter strip. See the [[http://www.winslamm.com/docs/WinSLAMM%20Model%20Algorithms%20v7.pdf|WinSLAMM Model Algorithms document]] for additional information.
+:!: WinSLAMM will reduce the efficiency of a filter strip if the ratio of contributing area to filter strip area is greater than 5:1. WinSLAMM also reduces the modeled filter strip flow length based on the longitudinal slope of the filter strip. See the [[https://www.winslamm.net/docs/WinSLAMM%20Model%20Algorithms%20v11.pdf|WinSLAMM Model Algorithms document]] for additional information.
 ==References==
+  * {{ :wiki:flyers:filter_strip_flyer.pdf | Filter Strip Guidance for Owners}}
   *[[https://files.nc.gov/ncdeq/Energy%20Mineral%20and%20Land%20Resources/Stormwater/BMP%20Manual/C-9--Level-Spreader-Filter-Strips-11-20-2020.pdf|North Caroline Department of Environmental Quality Stormwater Manual: Level Spreader-Filter Strip]]