Difference between revisions of "Infiltration trenches"

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This article is about underground systems which distribute concentrated flow along a level, linear facility to promote infiltration to native soils. <br>
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For a similar structure, which differs in being designed to receive excess flow and convey it, whilst promoting infiltration to native soils, see [[exfiltration trenches]].
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[[File:Kortright trench.PNG|thumb|The infiltration trench at Kortright is topped with [[filter fabric]] and decorative [[stone]], both of which provide some [[pretreatment]] and can easily be removed and replaced as an occasional maintenance task. For more details click [https://sustainabletechnologies.ca/app/uploads/2016/08/BioVSTrench_TechBrief__July2015.pdf here] ]] 
 
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===Overview===
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==Overview==
<p>As their name suggests infiltration trenches work primarily to infiltrate and convey stormwater. They are an underground facility and are excellently suited to connecting areas of the treatment train.</p>
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{{float right|{{#widget:YouTube|id=DLXsb1FwKD4}}}}
{{TextBox|1=Infiltration trenches are an ideal technology for:  
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As their name suggests infiltration trenches work primarily to infiltrate and convey stormwater. They are an underground facility and are excellently suited to connecting other components in the treatment train.
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{{textbox|1=Infiltration trenches are an ideal technology for:  
 
*Installing below any type of surface or landscape
 
*Installing below any type of surface or landscape
 
*Balancing the requirements to infiltrate excess stormwater whilst conveying excess}}
 
*Balancing the requirements to infiltrate excess stormwater whilst conveying excess}}
    <p><strong>The fundamental components of an infiltration trench are:</strong>
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'''The fundamental components of an infiltration trench are:'''
*Layers of [[Reservoir_gravel|coarse aggregate]] to bed the chambers and redistribute water.  
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*Layers of [[Reservoir_gravel|coarse aggregate]] to bed the pipe, store and redistribute water.  
 
*[[Pipes|Perforated pipe]]  
 
*[[Pipes|Perforated pipe]]  
*[[Geotextiles|Filter fabric a.k.a geotextile]]
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*[[Geotextile]]
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==Planning considerations==
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As shown in the illustration above a surface inlet to an infiltration trench may simply be a channel of decorative [[stone]] supported by a [[geotextile]]. So that at grade it may be indistinguishable from a [[gravel diaphragm]]. In function though, the decorative surface course of the infiltration trench needs to remain free-draining down into the trench, whereas the gravel diaphragm is designed to spill over onto adjacent land, leaving sediment behind in the [[gravel]] or [[stone]] channel.
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<gallery mode="packed" widths=300px heights=300px>
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==Design==
Infiltration trench.png| Schematic diagram of an underground infiltration trench
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===Sizing===
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'''[[Infiltration: Sizing and modeling]]'''
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*Virginia up to 10' (3 m) deep. <ref>Viriginia Department of Transport. (2010). VDOT BMP Design Manual of Practice. Retrieved March 15, 2018, from http://www.virginiadot.org/business/resources/LocDes/BMP_Design-Manual/Chapter_8_Infiltration_Trench.pdf</ref>
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*Minnesota up to 12' (3.6 m) deep. <ref>Design criteria for Infiltration trench. (2016, September 21). Minnesota Stormwater Manual, . Retrieved 13:25, April 4, 2018 from https://stormwater.pca.state.mn.us/index.php?title=Design_criteria_for_Infiltration_trench&oldid=28702.</ref>
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*"...not normally be deeper than 3 to 4 m in order to maximise the length of the flow path to the water table through the unsaturated zone." <ref>Design of soakaways (2015) www.tiipublications.ie/library/DN-DNG-03072-01.pdf</ref>
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*There is a cost implication with digging deeper practices, trench boxes may be required to retain the side walls during construction.
===Design===
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<h4>Sizing</h4>
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==Materials==
{{:Infiltration: Sizing and modeling}}
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===Aggregate===
----
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{{:Reservoir aggregate}}
===Materials===
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{{:Gravel}}
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===Perforated Pipe===
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{{:Pipes}}
 
*[[Geotextiles]]
 
*[[Geotextiles]]
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==Construction==
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*[[Construction]]
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==Gallery==
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{{:Infiltration trenches: Gallery}}
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===Construction===
 
{{:Infiltration: Construction}}
 
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===Incentives and Credits===
 
<h4>In Ontario</h4>
 
<h4>LEED BD + C v. 4</h4>
 
{{:LEED: Rainwater management}}
 
<h4>SITES v.2 </h4>
 
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{{:Feedback}}
 
 
[[category:infiltration]]
 
[[category:infiltration]]

Latest revision as of 19:16, 18 June 2019

This article is about underground systems which distribute concentrated flow along a level, linear facility to promote infiltration to native soils.
For a similar structure, which differs in being designed to receive excess flow and convey it, whilst promoting infiltration to native soils, see exfiltration trenches.

The infiltration trench at Kortright is topped with filter fabric and decorative stone, both of which provide some pretreatment and can easily be removed and replaced as an occasional maintenance task. For more details click here

Overview

As their name suggests infiltration trenches work primarily to infiltrate and convey stormwaterSurface runoff from at-grade surfaces, resulting from rain or snowmelt events.. They are an underground facility and are excellently suited to connecting other components in the treatment trainStormwater management following the hierarchical approach: Source Control measures, Conveyance Control measure and End of Pipe treatment to achieve the water quality and water balance target for lot level development of the preferred strategy.A combination of lot level, conveyance, and end-of-pipe stormwater management practices..

Infiltration trenches are an ideal technology for:

  • Installing below any type of surface or landscape
  • Balancing the requirements to infiltrate excess stormwater whilst conveying excess

The fundamental components of an infiltration trench are:

Planning considerations

As shown in the illustration above a surface inlet to an infiltration trench may simply be a channel of decorative stone supported by a geotextile. So that at grade it may be indistinguishable from a gravel diaphragm. In function though, the decorative surface course of the infiltration trench needs to remain free-draining down into the trench, whereas the gravel diaphragmA level spreading device placed at a runoff discharge location, perpendicular to flow, to maintain sheet flow and distribute runoff as evenly as possible across a pervious area or stormwater infiltration practice. A gravel diaphragm acts as a pretreatment device, settling out suspended sediments before they reach the practice. is designed to spill over onto adjacent land, leaving sedimentSoil, sand and minerals washed from land into water, usually after rain. They pile up in reservoirs, rivers and harbors, destroying fish-nesting areas and holes of water animals and cloud the water so that needed sunlight might not reach aquatic plans. Careless farming, mining and building activities will expose sediment materials, allowing them to be washed off the land after rainfalls. behind in the gravel or stone channel.

Design

Sizing

Infiltration: Sizing and modeling

  • Virginia up to 10' (3 m) deep. [1]
  • Minnesota up to 12' (3.6 m) deep. [2]
  • "...not normally be deeper than 3 to 4 m in order to maximise the length of the flow path to the water tableThe upper surface of the zone of saturation, except where the surface is formed by an impermeable body.Subsurface water level which is defined by the level below which all the spaces in the soil are filled with water; The entire region below the water table is called the saturated zone. through the unsaturated zone." [3]
  • There is a cost implication with digging deeper practices, trench boxes may be required to retain the side walls during construction.

Materials

AggregateA broad category of particulate material used in construction, including sand, gravel, crushed stone, slag, recycled concrete and geosynthetic aggregates, and available in various particulate size gradations.

Note the uniform size and angularity of this clear stone sample. Note also that the fragments all appear to have a film of fine particles adhering; this material would be improved by being washed prior to use.

This article gives recommendations for aggregateA broad category of particulate material used in construction, including sand, gravel, crushed stone, slag, recycled concrete and geosynthetic aggregates, and available in various particulate size gradations. to be used to store water for infiltrationThe slow movement of water into or through a soil or drainage system.Penetration of water through the ground surface.. This is usually called 'Clear stone' at aggregateA broad category of particulate material used in construction, including sand, gravel, crushed stone, slag, recycled concrete and geosynthetic aggregates, and available in various particulate size gradations. yards.

To see an analysis of Ontario Standard Specifications for granularGravel, or crushed stone of various size gradations (i.e., diameter), used in construction; void forming material used as bedding and runoff storage reservoirs and underdrains in stormwater infiltration practices. materials, see OPSS aggregates.

For advice on decorative surface aggregatesA broad category of particulate material used in construction, including sand, gravel, crushed stone, slag, recycled concrete and geosynthetic aggregates, and available in various particulate size gradations. see Stone


Gravel used for underdrains in bioretention, infiltration trenches and chambers, and exfiltration trenches should be 20 or 50 mm, uniformly-graded, clean (maximum wash loss of 0.5%), crushed angular stone that has a void ratio of 0.4[4].

The clean wash to prevent rapid accumulation of finesSoil particles with a diameter less than 0.050 mm. from the aggregateA broad category of particulate material used in construction, including sand, gravel, crushed stone, slag, recycled concrete and geosynthetic aggregates, and available in various particulate size gradations. particles in the base of the reservoir. The uniform grading and the angularity are important to maintain pore throats and clear voids between particles. (i.e. achieve the void ratio). Porosity and permeability are directly influenced by the size, gradation and angularity of the particles [5]. See jar test for on-site verification testing protocols.

Gravel with structural requirements should also meet the following criteria:

  • Minimum durability index of 35
  • Maximum abrasion of 10% for 100 revolutions and maximum of 50% for 500 revolutions

Standard specifications for the gradation of aggregatesA broad category of particulate material used in construction, including sand, gravel, crushed stone, slag, recycled concrete and geosynthetic aggregates, and available in various particulate size gradations. are maintained by ASTM D2940


Perforated Pipe

Pipes are available with perforations on just one side, these should be situated on the lower half of the pipe. Pipes with 360° perforations should have a strip of geotextileFilter fabric that is installed to separate dissimilar soils and provide runoff filtration and contaminant removal benefits while maintaining a suitable rate of flow; may be used to prevent fine-textured soil from entering a coarse granular bed, or to prevent coarse granular from being compressed into underlying finer-textured soils. or membrane placed over the pipe to reduce the migration of finesSoil particles with a diameter less than 0.050 mm. from overlying media.

Perforated pipes are a common component of underdrains, infiltration trenches and exfiltration trenches.

Pipes should have been manufactured in conformity with the latest standards by the Canadian Standards Association (CSA) or ASTM International.

  • Perforated pipes should be continuously perforated, smooth interior HDPE (or equivalent material).
    • Wherever possible pipes should be ≥ 200 mm internal diameter to reduce clogging and to facilitate inspections and maintenance.
    • Smooth interior facilitates inspection and maintenance activities; internal corrugations can cause cameras or hydrojetting apparatus to become snagged.
    • A perforated pipe with many rectangular slots has better drainage characteristics than a pipe with similar open area provided by fewer circular holes [6].
  • Non-perforated pipes should be used for conveyance to and away from the facility, including overflow. It is good practice to extend the non-perforated pipe approximately 300 mm within the reservoir or practice to reduce the chance of migration from native soils clogging the pipe at the interface.

See also: flow through perforated pipe


Construction

Gallery


  1. Viriginia Department of Transport. (2010). VDOT BMP Design Manual of Practice. Retrieved March 15, 2018, from http://www.virginiadot.org/business/resources/LocDes/BMP_Design-Manual/Chapter_8_Infiltration_Trench.pdf
  2. Design criteria for Infiltration trench. (2016, September 21). Minnesota Stormwater Manual, . Retrieved 13:25, April 4, 2018 from https://stormwater.pca.state.mn.us/index.php?title=Design_criteria_for_Infiltration_trench&oldid=28702.
  3. Design of soakaways (2015) www.tiipublications.ie/library/DN-DNG-03072-01.pdf
  4. Porosity of Structural Backfill, Tech Sheet #1, Stormtech, Nov 2012, http://www.stormtech.com/download_files/pdf/techsheet1.pdf accessed 16 October 2017
  5. 5.0 5.1 5.2 Judge, Aaron, "Measurement of the Hydraulic Conductivity of Gravels Using a Laboratory Permeameter and Silty Sands Using Field Testing with Observation Wells" (2013). Dissertations. 746. http://scholarworks.umass.edu/open_access_dissertations/746
  6. Hazenberg, G., and U. S. Panu (1991), Theoretical analysis of flow rate into perforated drain tubes, Water Resour. Res., 27(7), 1411–1418, doi:10.1029/91WR00779.