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[[File:Pdf image.png|100px|thumb|alt=pdf image|<font size=3>[https://stormwater.pca.state.mn.us/index.php?title=File:Overview_for_pretreatment_vegetated_filter_strips_-_Minnesota_Stormwater_Manual_June_2022.pdf Download pdf]</font size>]]
 
[[File:General information page image.png|right|100px|alt=image]]
 
[[File:General information page image.png|right|100px|alt=image]]
 
[[file:Filter strip for bioswale.jpg|thumb|300px|alt=image of filter strip|<font size=3>The vegetated filter strip in this photo is pretreatment for a bioswale. Photo courtesy of Alisha Goldstein, U.S. EPA.</font size>]]
 
[[file:Filter strip for bioswale.jpg|thumb|300px|alt=image of filter strip|<font size=3>The vegetated filter strip in this photo is pretreatment for a bioswale. Photo courtesy of Alisha Goldstein, U.S. EPA.</font size>]]
  
It is important to tailor a pretreatment practice to the specific site and type of receiving structural stormwater BMP. Many factors influence the choice of pretreatment practices, including but not limited to: (1) contributing area characteristics (drainage area, connected imperviousness, land uses, soils, slopes, dominant vegetation, source controls in place, and availability of public lands ); (2) existing infrastructure (above and below ground); and (3) type of structural stormwater BMP with infiltration/filtration BMPs having that have the greatest need for removal of solids prior to treatment areas. The following section describes the specific strengths, weaknesses, and applicability of pretreatment vegetated filter strips.  
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It is important to tailor a <span title="Pretreatment reduces maintenance and prolongs the lifespan of structural stormwater BMPs by removing trash, debris, organic materials, coarse sediments, and associated pollutants prior to entering structural stormwater BMPs. Implementing pretreatment devices also improves aesthetics by capturing debris in focused or hidden areas. Pretreatment practices include settling devices, screens, and pretreatment vegetated filter strips."> [https://stormwater.pca.state.mn.us/index.php?title=Pretreatment '''pretreatment''']</span> practice to the specific site and type of receiving structural stormwater <span title="One of many different structural or non–structural methods used to treat runoff"> '''best management practice'''</span> (BMP). Many factors influence the choice of pretreatment practices, including but not limited to: (1) contributing area characteristics (<span title="The total drainage area, including pervious and impervious surfaces, contributing to a BMP"> '''[https://stormwater.pca.state.mn.us/index.php?title=Contributing_drainage_area_to_stormwater_BMPs contributing drainage area]'''</span>, <span title="A subset of impervious cover, which is directly connected to a drainage system or a water body via continuous impervious surfaces."> '''connected imperviousness'''</span>, land uses, soils, slopes, dominant vegetation, source controls in place, and availability of public lands ); (2) existing infrastructure (above and below ground); and (3) type of structural stormwater BMP with <span title="Infiltration Best Management Practices (BMPs) treat urban stormwater runoff as it flows through a filtering medium and into underlying soil, where it may eventually percolate into groundwater. The filtering media is typically coarse-textured and may contain organic material, as in the case of bioinfiltration BMPs."> [https://stormwater.pca.state.mn.us/index.php?title=Stormwater_infiltration_Best_Management_Practices '''infiltration''']</span>/<span title="Filtration Best Management Practices (BMPs) treat urban stormwater runoff as it flows through a filtering medium, such as sand or an organic material. They are generally used on small drainage areas (5 acres or less) and are primarily designed for pollutant removal. They are effective at removing total suspended solids (TSS), particulate phosphorus, metals, and most organics. They are less effective for soluble pollutants such as dissolved phosphorus, chloride, and nitrate."> [https://stormwater.pca.state.mn.us/index.php?title=Filtration '''filtration''']</span> BMPs having that have the greatest need for removal of solids prior to treatment areas. The following section describes the specific strengths, weaknesses, and applicability of pretreatment <span title="Pretreatment vegetated filter strips are designed to provide sedimentation and screening (by vegetation) to treat stormwater runoff prior to entering a structural stormwater BMP. Pretreatment vegetated filter strips are especially effective at capturing excess sediment in stormwater runoff by settling solids. Pretreatment vegetated filter strips provide limited (due to size) volume reduction, peak flow reduction, infiltration, and biological treatment. Stormwater management processes not provided in pretreatment vegetated filter strips include filtration and sorption."> [https://stormwater.pca.state.mn.us/index.php?title=Overview_for_pretreatment_vegetated_filter_strips '''vegetated filter strips''']</span>.  
  
 
==Processes==
 
==Processes==
Pretreatment vegetated filter strips are designed to provide sedimentation and screening (by vegetation) to treat stormwater runoff prior to entering a structural stormwater BMP. Pretreatment vegetated filter strips are especially effective at capturing excess sediment in stormwater runoff by settling solids. Pretreatment vegetated filter strips provide limited (due to size) volume reduction, peak flow reduction, infiltration, and biological treatment. Stormwater management processes not provided in pretreatment vegetated filter strips include filtration and sorption.
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Pretreatment vegetated filter strips are designed to provide <span title="Sedimentation is the process by which solids are removed from the water column by settling. Sedimentation practices include dry ponds, wet ponds, wet vaults, and other devices."> [https://stormwater.pca.state.mn.us/index.php?title=Stormwater_sedimentation_Best_Management_Practices '''sedimentation''']</span> and screening (by vegetation) to treat stormwater runoff prior to entering a structural stormwater BMP. Pretreatment vegetated filter strips are especially effective at capturing excess sediment in stormwater runoff by settling solids. Pretreatment vegetated filter strips provide limited (due to size) volume reduction, peak flow reduction, infiltration, and biological treatment. Stormwater management processes not provided in pretreatment vegetated filter strips include filtration and sorption.
  
 
==Applicability and suitability==
 
==Applicability and suitability==
Pretreatment practices are NOT stand-alone treatment practices and should only be installed in conjunction with a treatment practice immediately downstream. The applicability of pretreatment vegetated filter strips with regard to the cold climate, retrofits, ultra-urban settings and other considerations is presented below.
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Pretreatment practices are NOT stand-alone treatment practices and should only be installed in conjunction with a treatment practice immediately downstream. The applicability of pretreatment vegetated filter strips with regard to the cold climate, retrofits, <span title="Highly urban and ultra-urban settings have a large percentage of impermeable surface and typically have limited space to install surface BMPs. An example would be a downtown area."> '''highly urban and ultra-urban environments'''</span> and other considerations is presented below.
  
 
===Cold Climate Suitability===
 
===Cold Climate Suitability===
During winter months, pretreatment vegetated filter strips will become frozen and covered by ice and snow to some extent. This will diminish the effectiveness of the practice if flows become channelized, resulting in reduced trapping of sediments. Once the snow and ice melts, sheet flow is re-established, and vegetation actively removes sediment, pretreatment filter strips will provide some snowmelt treatment. Pretreatment vegetated filter strips are often less effective during cold climate conditions due to reduced biological activity (dormant vegetation) and reduced settling velocities. Storing snow on pretreatment vegetated filter strips is not recommended because it will extend the duration of ineffective treatment due to increased snowpack. In rare instances, some types of invasive annual vegetation reduce perennial cover which results in periods of unestablished vegetation during periods of runoff (e.g., winter thaws and spring snowmelt events) and less pretreatment.
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During winter months, pretreatment vegetated filter strips will become frozen and covered by ice and snow to some extent. This will diminish the effectiveness of the practice if flows become <span title="Water flow focused into individual straight pathways rather than across a broad area (sheet flow)"> '''channelized'''</span>, resulting in reduced trapping of sediments. Once the snow and ice melts, <span title="Water, usually storm runoff, flowing in a thin layer over the ground surface. A synonym is overland flow."> '''sheet flow'''</span> is re-established, and vegetation actively removes sediment, pretreatment filter strips will provide some snowmelt treatment. Pretreatment vegetated filter strips are often less effective during cold climate conditions due to reduced biological activity (dormant vegetation) and reduced settling velocities. Storing snow on pretreatment vegetated filter strips is not recommended because it will extend the duration of ineffective treatment due to increased snowpack. In rare instances, some types of invasive annual vegetation reduce <span title="A perennial plant or simply perennial is a plant that lives more than two years"> '''perennial'''</span> cover which results in periods of unestablished vegetation during periods of runoff (e.g., winter thaws and spring snowmelt events) and less pretreatment.
  
 
===Retrofit Suitability===
 
===Retrofit Suitability===
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==Applicability to MPCA stormwater permits==
 
==Applicability to MPCA stormwater permits==
If designed properly, this practice meets the intent of the stormwater permit, as identified in [https://stormwater.pca.state.mn.us/index.php?title=2018_Minnesota_Construction_Stormwater_Permit sections 16 and 17], as pretreatment for an infiltration or filtration system.
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If designed properly, this practice meets the intent of the [https://stormwater.pca.state.mn.us/index.php?title=Construction_stormwater_program Construction stormwater permit], as pretreatment for an infiltration or filtration system.
  
 
==Advantages and limitations==
 
==Advantages and limitations==
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===Advantages===
 
===Advantages===
Pretreatment vegetated filter strips provide many advantages as a pretreatment practice. They effectively remove sediments from stormwater runoff. The construction of this practice is often relatively simple compared to other pretreatment practices, though it does require a level spreader along with establishment of vegetative cover including periodic vegetation maintenance. Pretreatment vegetated filter strips are often easily accessible which makes maintenance more manageable and often have less non-routine maintenance costs (e.g. do not require the use of heavy equipment). Pretreatment vegetated filter strips offer aesthetic aspects enhancing stormwater designs desired in green infrastructure settings.
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Pretreatment vegetated filter strips provide many advantages as a pretreatment practice. They effectively remove sediments from stormwater runoff. The construction of this practice is often relatively simple compared to other pretreatment practices, though it does require a <span title="Level Spreaders are measures that reduce the erosive energy of concentrated flows by distributing runoff as sheet flow to stabilized vegetative surfaces."> '''level spreader'''</span> along with establishment of vegetative cover including periodic vegetation maintenance. Pretreatment vegetated filter strips are often easily accessible which makes maintenance more manageable and often have less non-routine maintenance costs (e.g. do not require the use of heavy equipment). Pretreatment vegetated filter strips offer aesthetic aspects enhancing stormwater designs desired in <span title="Green Infrastructure refers to ecological systems, both natural and engineered, that act as living infrastructure. Green Infrastructure elements are planned and managed primarily for stormwater control, but also exhibit social, economic and environmental benefits (Syracuse University)."> '''Green infrastructure'''</span> settings.
  
 
===Limitations===
 
===Limitations===
Pretreatment vegetated filter strips require runoff to be conveyed in shallow, distributed sheet flow. To maintain their effectiveness, pretreatment vegetated filter strips require regular routine inspection and maintenance to remove accumulated sediment and debris. Sediment and debris that is not removed often results in flow bypass or channelization of erosive flows through the pretreatment vegetated filter strip. Sites requiring re-sloping/grading and imported specification soils often incur additional construction costs due to the use of heavy equipment and associated labor. High loadings of pollutants might damage the vegetation (e.g., vegetation adjacent to a roadway or parking lot with high application rates of deicers). Proper siting and design will improve long-term performance and reduce maintenance expenses. Although pretreatment vegetated filter strips are suitable for many receiving structural stormwater BMPs, space and site requirements (e.g., slope, flow distribution) are the most common limits for the applicability of this practice.
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Pretreatment vegetated filter strips require runoff to be conveyed in shallow, distributed sheet flow. To maintain their effectiveness, pretreatment vegetated filter strips require regular routine inspection and maintenance to remove accumulated sediment and debris. Sediment and debris that is not removed often results in <span title="Stormwater runoff in excess of the design flow, which is diverted around a stormwater structure"> '''bypass flow'''</span> or channelization of erosive flows through the pretreatment vegetated filter strip. Sites requiring re-sloping/grading and imported specification soils often incur additional construction costs due to the use of heavy equipment and associated labor. High loadings of pollutants might damage the vegetation (e.g., vegetation adjacent to a roadway or parking lot with high application rates of deicers). Proper siting and design will improve long-term performance and reduce maintenance expenses. Although pretreatment vegetated filter strips are suitable for many receiving structural stormwater BMPs, space and site requirements (e.g., slope, flow distribution) are the most common limits for the applicability of this practice.
  
 
==Water quantity treatment==
 
==Water quantity treatment==
Pretreatment vegetated filter strips are designed to ease maintenance and prolong the lifespan of the downstream structural stormwater BMP, and thus provide limited volume reduction (due to size). Pretreatment vegetated filter strips are not to be confused with the structural stormwater BMP treatment vegetated filter strips, which are designed and used as a stand-alone structural stormwater BMP to reduce stormwater runoff volumes.
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Pretreatment vegetated filter strips are designed to ease maintenance and prolong the lifespan of the downstream <span title="A stationary and permanent BMP that is designed, constructed and operated to prevent or reduce the discharge of pollutants in stormwater"> '''structural stormwater BMP'''</span>, and thus provide limited volume reduction (due to size). Pretreatment vegetated filter strips are not to be confused with the structural stormwater BMP treatment vegetated filter strips, which are designed and used as a stand-alone structural stormwater BMP to reduce stormwater runoff volumes.
  
 
==Water quality treatment==
 
==Water quality treatment==
 
[[file:Vegetated filter strip 4.png|300px|thumb|alt=image of vegetated filter strip|<font size=3>Vegetated filter strips filter solids and debris from stormwater runoff before the runoff enters the treatment practice. In this image, the filter strip is treating runoff prior to the runoff entering a detention pond. Source: [http://www.stormwaterpartners.com/facilities/detention.html StormwaterPartners]</font size>]]
 
[[file:Vegetated filter strip 4.png|300px|thumb|alt=image of vegetated filter strip|<font size=3>Vegetated filter strips filter solids and debris from stormwater runoff before the runoff enters the treatment practice. In this image, the filter strip is treating runoff prior to the runoff entering a detention pond. Source: [http://www.stormwaterpartners.com/facilities/detention.html StormwaterPartners]</font size>]]
  
Properly designed pretreatment vegetated filter strips slow runoff velocities and allow sediment to settle. Pretreatment vegetated filter strips can also remove portions of other pollutants in runoff, including small particulates, hydrocarbons, heavy metals and nutrients such as phosphorus and nitrogen. Filter strips remove pollutant load through sedimentation, filtration, infiltration, biological uptake, and microbial activity.
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Properly designed pretreatment vegetated filter strips slow runoff velocities and allow sediment to settle. Pretreatment vegetated filter strips can also remove portions of other pollutants in runoff, including small particulates, <span title="A compound of hydrogen and carbon, such as any of those which are the chief components of petroleum and natural gas."> '''hydrocarbons'''</span>, heavy metals and nutrients such as phosphorus and nitrogen. Filter strips remove pollutant load through sedimentation, filtration, infiltration, biological uptake, and microbial activity.
  
The water quality benefit of a vegetated filter strip is dependent upon factors such as the length of the flow path and slope, stormwater flow rate through the vegetated filter strip, the type, density, and length of vegetation, the ability to maintain sheet flow through the vegetated filter strip and the soil properties that influence infiltration rate. The ability to maintain sheet flow is often cited as a crucial factor for the success of filter strips (lakesuperiorstreams.org; Virginia DEQ, 1999)
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The water quality benefit of a vegetated filter strip is dependent upon factors such as the length of the flow path and slope, stormwater flow rate through the vegetated filter strip, the type, density, and length of vegetation, the ability to maintain sheet flow through the vegetated filter strip and the soil properties that influence infiltration rate. The ability to maintain sheet flow is often cited as a crucial factor for the success of filter strips ([https://lakesuperiorstreams.org/ Lake Superior Streams]; Virginia DEQ, 1999)
  
In general, pretreatment vegetated filter strips are very effective at removing solids from stormwater if there is adequate flow path length and if sheet flow is maintained through the BMP with low rate of flow (Goel et al., 2004; Abu-Zreig et al., 2003; Gharabaghi et al., 2000).
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In general, pretreatment vegetated filter strips are very effective at removing solids from stormwater if there is adequate flow path length and if sheet flow is maintained through the BMP with low rate of flow (Goel et al., 2004; Abu-Zreig et al., 2003; Gharabaghi et al., 2000; see [[References for pretreatment]]).
  
 
===Performance of pretreatment vegetated filter strips===
 
===Performance of pretreatment vegetated filter strips===
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*[[Photo gallery for pretreatment]]
 
*[[Photo gallery for pretreatment]]
  
[[Category:Pretreatment]]
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[[Category:Level 3 - Best management practices/Guidance and information/BMP overview]]
 +
[[Category:Level 3 - Best management practices/Pretreatment practices‏‎/Filtration devices]]
 
</noinclude>
 
</noinclude>

Latest revision as of 18:39, 13 December 2022

image
image of filter strip
The vegetated filter strip in this photo is pretreatment for a bioswale. Photo courtesy of Alisha Goldstein, U.S. EPA.

It is important to tailor a pretreatment practice to the specific site and type of receiving structural stormwater best management practice (BMP). Many factors influence the choice of pretreatment practices, including but not limited to: (1) contributing area characteristics ( contributing drainage area, connected imperviousness, land uses, soils, slopes, dominant vegetation, source controls in place, and availability of public lands ); (2) existing infrastructure (above and below ground); and (3) type of structural stormwater BMP with infiltration/ filtration BMPs having that have the greatest need for removal of solids prior to treatment areas. The following section describes the specific strengths, weaknesses, and applicability of pretreatment vegetated filter strips.

Processes

Pretreatment vegetated filter strips are designed to provide sedimentation and screening (by vegetation) to treat stormwater runoff prior to entering a structural stormwater BMP. Pretreatment vegetated filter strips are especially effective at capturing excess sediment in stormwater runoff by settling solids. Pretreatment vegetated filter strips provide limited (due to size) volume reduction, peak flow reduction, infiltration, and biological treatment. Stormwater management processes not provided in pretreatment vegetated filter strips include filtration and sorption.

Applicability and suitability

Pretreatment practices are NOT stand-alone treatment practices and should only be installed in conjunction with a treatment practice immediately downstream. The applicability of pretreatment vegetated filter strips with regard to the cold climate, retrofits, highly urban and ultra-urban environments and other considerations is presented below.

Cold Climate Suitability

During winter months, pretreatment vegetated filter strips will become frozen and covered by ice and snow to some extent. This will diminish the effectiveness of the practice if flows become channelized, resulting in reduced trapping of sediments. Once the snow and ice melts, sheet flow is re-established, and vegetation actively removes sediment, pretreatment filter strips will provide some snowmelt treatment. Pretreatment vegetated filter strips are often less effective during cold climate conditions due to reduced biological activity (dormant vegetation) and reduced settling velocities. Storing snow on pretreatment vegetated filter strips is not recommended because it will extend the duration of ineffective treatment due to increased snowpack. In rare instances, some types of invasive annual vegetation reduce perennial cover which results in periods of unestablished vegetation during periods of runoff (e.g., winter thaws and spring snowmelt events) and less pretreatment.

Retrofit Suitability

Pretreatment vegetated filter strips tend to require more space than other pretreatment practices, which often limits retrofit suitability.

Ultra-Urban Suitability

Pretreatment vegetated filter strips tend to require more space than other pretreatment practices, and thus they are often not suitable in ultra-urban settings where space is limited.

Other Considerations

Channelized inflows to the pretreatment vegetated filter strips must be avoided because concentrated flows will reduce the effectiveness of the practice. For some sites, footprint area is a constraint because pretreatment vegetated filter strips often require more surface area than other pretreatment practices. Pretreatment vegetated filter strips are not designed to infiltrate water, but treatment filter strips are suitable as part of a structural stormwater BMP

Applicability to MPCA stormwater permits

If designed properly, this practice meets the intent of the Construction stormwater permit, as pretreatment for an infiltration or filtration system.

Advantages and limitations

The advantages and limitations of pretreatment vegetated filter strips with regard to the pollutant removal capabilities, cost, ease of construction and maintenance, space and other design considerations and compatibility are discussed below.

Advantages

Pretreatment vegetated filter strips provide many advantages as a pretreatment practice. They effectively remove sediments from stormwater runoff. The construction of this practice is often relatively simple compared to other pretreatment practices, though it does require a level spreader along with establishment of vegetative cover including periodic vegetation maintenance. Pretreatment vegetated filter strips are often easily accessible which makes maintenance more manageable and often have less non-routine maintenance costs (e.g. do not require the use of heavy equipment). Pretreatment vegetated filter strips offer aesthetic aspects enhancing stormwater designs desired in Green infrastructure settings.

Limitations

Pretreatment vegetated filter strips require runoff to be conveyed in shallow, distributed sheet flow. To maintain their effectiveness, pretreatment vegetated filter strips require regular routine inspection and maintenance to remove accumulated sediment and debris. Sediment and debris that is not removed often results in bypass flow or channelization of erosive flows through the pretreatment vegetated filter strip. Sites requiring re-sloping/grading and imported specification soils often incur additional construction costs due to the use of heavy equipment and associated labor. High loadings of pollutants might damage the vegetation (e.g., vegetation adjacent to a roadway or parking lot with high application rates of deicers). Proper siting and design will improve long-term performance and reduce maintenance expenses. Although pretreatment vegetated filter strips are suitable for many receiving structural stormwater BMPs, space and site requirements (e.g., slope, flow distribution) are the most common limits for the applicability of this practice.

Water quantity treatment

Pretreatment vegetated filter strips are designed to ease maintenance and prolong the lifespan of the downstream structural stormwater BMP, and thus provide limited volume reduction (due to size). Pretreatment vegetated filter strips are not to be confused with the structural stormwater BMP treatment vegetated filter strips, which are designed and used as a stand-alone structural stormwater BMP to reduce stormwater runoff volumes.

Water quality treatment

image of vegetated filter strip
Vegetated filter strips filter solids and debris from stormwater runoff before the runoff enters the treatment practice. In this image, the filter strip is treating runoff prior to the runoff entering a detention pond. Source: StormwaterPartners

Properly designed pretreatment vegetated filter strips slow runoff velocities and allow sediment to settle. Pretreatment vegetated filter strips can also remove portions of other pollutants in runoff, including small particulates, hydrocarbons, heavy metals and nutrients such as phosphorus and nitrogen. Filter strips remove pollutant load through sedimentation, filtration, infiltration, biological uptake, and microbial activity.

The water quality benefit of a vegetated filter strip is dependent upon factors such as the length of the flow path and slope, stormwater flow rate through the vegetated filter strip, the type, density, and length of vegetation, the ability to maintain sheet flow through the vegetated filter strip and the soil properties that influence infiltration rate. The ability to maintain sheet flow is often cited as a crucial factor for the success of filter strips (Lake Superior Streams; Virginia DEQ, 1999)

In general, pretreatment vegetated filter strips are very effective at removing solids from stormwater if there is adequate flow path length and if sheet flow is maintained through the BMP with low rate of flow (Goel et al., 2004; Abu-Zreig et al., 2003; Gharabaghi et al., 2000; see References for pretreatment).

Performance of pretreatment vegetated filter strips

Caution: Available information on performance of settling devices is limited and should be viewed with caution. This information should not be used for design purposes.

The following discussion provides a summary of information found in the literature. The information provides a general summary and indication of the range of pollutant removal and should not be used for design purposes.

Solids removal can vary between 50 and 98 percent depending on filter strip characteristics (NJ DEP, 2014; Goel et al., 2004; Abu-Zreig et al., 2003; Gharabaghi et al., 2000). Gharabaghi et al., 2000 found that 50 percent of sediments settled in the first 2.5 meters of a vegetated filter strip and an additional 25 to 45 percent of sediments settled in the next 2.5 meters. They also concluded that increased solids removal was minimal in flow path lengths greater than 10 meters. Some stormwater manuals require a minimum filter strip length of 10 feet with a slope of less than 2 percent (Inver Grove Heights, 2006; Wisconsin Department of Natural Resources, 2014). Other manuals specify that the minimum length for filter strips is 25 feet with a slope of less than 2 percent (Virginia DEQ, 1999), and requires four feet be added to the length for each 1 percent of slope greater than 2 percent. Virginia DEQ (1999) suggests that an ideal filter strip length is between 80 and 100 feet.

Assuming no infiltration, phosphorus removal is due to settling of solids and ranges from 32 to 79 percent based on the length of the flow path (Abu-Zreig et al., 2003). Some removal of dissolved nutrients occurs if the filter strip is designed to infiltrate water.


Related pages

To see the above pages as a single page, link here

Pretreatment sizing for basins and filters strips

Guidance for managing sediment and wastes collected by pretreatment practices

Tables

Other information and links

This page was last edited on 13 December 2022, at 18:39.