Infiltration trenches

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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 areas of 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:

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Design

Sizing

Drainage timeDetailsUnderdrainInfiltrationInfiltration: TestingSelect BMP typeBioretention: Sizing
This is an image map; clicking on components will load the appropriate article.
  • To calculate the required depth of an infiltration facility in a specified footprint area...
  • To calculate the required footprint area of an infiltration facility with a known depth constraint....
  • To calculate the drainage timeThe period between the maximum water level and the minimum level (dry weather or antecedent level). of ponded water on the surface of a facility footprint...
  • To calculate the drainage timeThe period between the maximum water level and the minimum level (dry weather or antecedent level). of an underground infiltration facility...

The sizing calculations require that most of the following parameters be known or estimated. The exceptions are the depth (d) and the permeable footprint area of the practice (Ap), as only one of these is required to find the other. Note that some of these parameters can be limited by site conditions and factors influencing constructability:

  1. The maximum total depth will be limited by construction practices i.e. usually ≤ 2 m to avoid the need for benching and shoring open cut excavations.
  2. The maximum total depth may be limited by the conditions underground (e.g. 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. or underlying geology/infrastructure).
  3. The maximum total depth may be limited by the desire to install the practice below the maximum frost penetration depth in the proposed location.
  4. The maximum total depth may be limited by the desire to support vegetation cover over it (e.g. at least 30 cm of planting soil backfill over the BMPBest management practice. State of the art methods or techniques used to manage the quantity and improve the quality of wet weather flow. BMPs include: source, conveyance and end-of-pipe controls. to support grasses)
  5. Infiltration trenches, chambers and bioretention have a maximum recommended I/P ratioThe ratio of the impervious catchment (drainage) area to the pervious (footprint) area of the receiving BMP. of 20.
Inputs
Symbol Units Parameter
D h Duration of design storm
i mm/h Intensity of design storm
f' mm/h Design infiltration rate of the underlying native soilThe natural ground material characteristic of or existing by virtue of geographic origin., calculated from measured infiltration rate and applied safety factor
n - Porosity of 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. or other void-forming fill material(s) in the storage reservoirAn underlying bed filled with aggregate or other void-forming fill material that temporarily stores stormwater before infiltrating into the native soil or being conveyed by an underdrain pipe. of the practice.
*Note: For systems that have significant storage in open chambers surrounded by clear stone 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., an effective porosity value (n') may be estimated for the whole installation and used in the calculations below. Effective porosity will vary according to the geometry of the storage chambers, so advice should be sought from product manufacturers. Permit applications should include the basis for n' estimates.
Ai m2 CatchmentThe land draining to a single reference point (usually a structural BMP); similar to a subwatershed, but on a smaller scale. imperviousA hard surface area (e.g., road, parking area or rooftop) that prevents or retards the infiltration of water into the soil. area
dr m Water storage reservoirAn underlying bed filled with aggregate or other void-forming fill material that temporarily stores stormwater before infiltrating into the native soil or being conveyed by an underdrain pipe. depth. For practices without an underdrainA perforated pipe used to assist the draining of soils. (i.e. full infiltration design), dr is the total depth of the practice (i.e. includes surface ponding and filter mediaThe engineered soil component of bioretention cell or dry swale designs, typically with a high rate of infiltration and designed to retain contaminants through filtration and adsorption to particles. depths). For practices with an underdrainA perforated pipe used to assist the draining of soils. (i.e. partial infiltration design), dr is the depth below the invert of the underdrainA perforated pipe used to assist the draining of soils. perforated pipe outlet.
Ap m2 Permeable footprint area of the practice. For practices where runoffThat potion of the water precipitated onto a catchment area, which flows as surface discharge from the catchment area past a specified point.Water from rain, snow melt, or irrigation that flows over the land surface. is directed to a surface ponding area, Ap is the surface ponding area. For practices where runoffThat potion of the water precipitated onto a catchment area, which flows as surface discharge from the catchment area past a specified point.Water from rain, snow melt, or irrigation that flows over the land surface. is directed to a subsurface water storage reservoirAn underlying bed filled with aggregate or other void-forming fill material that temporarily stores stormwater before infiltrating into the native soil or being conveyed by an underdrain pipe., Ap is the footprint area of the storage reservoirAn underlying bed filled with aggregate or other void-forming fill material that temporarily stores stormwater before infiltrating into the native soil or being conveyed by an underdrain pipe., Ar
x m Perimeter of the practice
Kf mm/h Minimum acceptable saturated hydraulic conductivityA parameter that describes the capability of a medium to transmit water. of the filter media or planting soil used in the practice, when compacted to 85% maximum dry density

This spreadsheet tool has been set up to perform all of the infiltration practice sizing calculations shown below
Download the infiltration practice sizing tool

To calculate the required storage reservoirAn underlying bed filled with aggregate or other void-forming fill material that temporarily stores stormwater before infiltrating into the native soil or being conveyed by an underdrain pipe. footprint area where the depth is fixed or constrained (1D drainageNatural or artificial means of intercepting and removing surface or subsurface water (usually by gravity).)

To ensure that the water storage capacity of the facility is available at the onset of a storm event, it is recommended to size the storage reservoirAn underlying bed filled with aggregate or other void-forming fill material that temporarily stores stormwater before infiltrating into the native soil or being conveyed by an underdrain pipe. despth, dr, based on the depth of water that will drain via infiltration between storm events. So dr can be calculated as
: <math>d_{r} = (\frac{f'}{1000}) \times t </math> Where
f' = design infiltration rate of the native soilThe natural ground material characteristic of or existing by virtue of geographic origin. (mm/h)
t = drainage time, based on local criteria or long-term average inter-event period for the location.

In many locations there may be a limited depth of soil available above the seasonally high 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. or top of bedrock elevation into which stormwater may be infiltrated. In such cases the required storage needs to be distributed more widely across the landscape.
Where the storage reservoirAn underlying bed filled with aggregate or other void-forming fill material that temporarily stores stormwater before infiltrating into the native soil or being conveyed by an underdrain pipe. depth is fixed or constrained the footprint area of the water storage reservoirAn underlying bed filled with aggregate or other void-forming fill material that temporarily stores stormwater before infiltrating into the native soil or being conveyed by an underdrain pipe., Ar can be calculated: <math>A_{r}=\frac{i \times D \times Ai}{(n\times d_{r})+f'D}</math>

To calculate the required storage reservoirAn underlying bed filled with aggregate or other void-forming fill material that temporarily stores stormwater before infiltrating into the native soil or being conveyed by an underdrain pipe. depth where the area is fixed or constrained (1D drainageNatural or artificial means of intercepting and removing surface or subsurface water (usually by gravity).)

On densely developed sites, the surface area available for the practice may be constrained. In such cases the required storage reservoirAn underlying bed filled with aggregate or other void-forming fill material that temporarily stores stormwater before infiltrating into the native soil or being conveyed by an underdrain pipe. depth, dr of the bioretentionA shallow excavated surface depression containing prepared filter media, mulch, and planted with selected vegetation. cell or infiltration trench can be calculated based on available surface area, Ap:

<math>d_{r}=\frac{D\left[\left( \frac{Ai}{Ap} \right )i-f' \right]}{n}</math>

Note that in most cases the results of this calculation will be very similar to those from the equation below assuming three-dimensional drainageNatural or artificial means of intercepting and removing surface or subsurface water (usually by gravity)..

To calculate the required storage reservoirAn underlying bed filled with aggregate or other void-forming fill material that temporarily stores stormwater before infiltrating into the native soil or being conveyed by an underdrain pipe. depth, where the area is fixed or constrained (3D drainageNatural or artificial means of intercepting and removing surface or subsurface water (usually by gravity).)

On densely developed sites, the surface area available for the facility may be constrained. In such cases the required water storage reservoirAn underlying bed filled with aggregate or other void-forming fill material that temporarily stores stormwater before infiltrating into the native soil or being conveyed by an underdrain pipe. depth of the bioretentionA shallow excavated surface depression containing prepared filter media, mulch, and planted with selected vegetation. cell or infiltration trench, d, can be calculated assuming three-dimensional drainage as follows

<math>d_{r}=a[e^{\left ( -bD \right )} -1]</math>

Where

<math>a=\frac{A_{r}}{x}-\frac{i\times A_{i}}{x\times f'}</math>

and

<math>b=\frac{x\times f'}{n\times A_{r}}</math>
(The rearrangement to calculate the required footprint area of the facility for a given depth assuming three-dimensional drainage is not available at this time. Elegant submissions are invited.)

Time required to drain surface ponded water (1D drainageNatural or artificial means of intercepting and removing surface or subsurface water (usually by gravity).)

The following equation assumes one dimensional drainage over the surface ponding area. It is best applied to calculate the maximum duration of ponding on the surface of bioretention cells, and upstream of the check dams of bioswales and enhanced grass swales to ensure all surface ponding drains within 48 hours. To calculate the time (t) to fully drain surface ponded water through the filter mediaThe engineered soil component of bioretention cell or dry swale designs, typically with a high rate of infiltration and designed to retain contaminants through filtration and adsorption to particles. or planting soil: <math>t=\frac{d_{p}'}{K_{f}}</math> Where
dp' is the effective or mean surface ponding depth (mm).
Kf is the minimum acceptable saturated hydraulic conductivityA parameter that describes the capability of a medium to transmit water. of the filter mediaThe engineered soil component of bioretention cell or dry swale designs, typically with a high rate of infiltration and designed to retain contaminants through filtration and adsorption to particles. or planting soil when compacted to 85% maximum dry density (mm/h).

Time to drain the storage reservoirAn underlying bed filled with aggregate or other void-forming fill material that temporarily stores stormwater before infiltrating into the native soil or being conveyed by an underdrain pipe.

The target drainage time for the active storage reservoirAn underlying bed filled with aggregate or other void-forming fill material that temporarily stores stormwater before infiltrating into the native soil or being conveyed by an underdrain pipe. depth of an infiltration facility is typically between 48 and 72 hours or based on the average inter-event period for the location. Contact the local municipality or conservation authority for criteria. See Drainage time for more information about how inter-event periods vary across Ontario and to help select what is suitable for the site.

Try the Darcy drainage timeThe period between the maximum water level and the minimum level (dry weather or antecedent level). calculator tool for estimating the time required to fully drain the water storage reservoirAn underlying bed filled with aggregate or other void-forming fill material that temporarily stores stormwater before infiltrating into the native soil or being conveyed by an underdrain pipe. of the facility assuming either one or three-dimensional drainageNatural or artificial means of intercepting and removing surface or subsurface water (usually by gravity).:
Download the Darcy drainage time calculator

Three footprint areas of 9 m2.
From left to right x = 12 m, x = 20 m

For some geometries, particularly deep or linear facilities, it desirable to account for lateral drainageNatural or artificial means of intercepting and removing surface or subsurface water (usually by gravity)., out the sides of the storage reservoirAn underlying bed filled with aggregate or other void-forming fill material that temporarily stores stormwater before infiltrating into the native soil or being conveyed by an underdrain pipe.. The following equation makes use of the hydraulic radius (Ar/x), where x is the perimeter (m) of the facility.
Maximizing the perimeter of the water storage reservoirAn underlying bed filled with aggregate or other void-forming fill material that temporarily stores stormwater before infiltrating into the native soil or being conveyed by an underdrain pipe. of the facility will enhance drainage performance and directs designers towards longer, linear shapes such as infiltration trenches and bioswales. See illustration for an example.

To calculate the time (t) to fully drain the facility assuming three-dimensional drainageNatural or artificial means of intercepting and removing surface or subsurface water (usually by gravity).: <math>t=\frac{n\times A_{r}}{f'\times x}ln\left [ \frac{\left (d_{r} \frac{A_{r}}{x} \right )}{\left(\frac{A_{r}}{x}\right)}\right]</math> Where "ln" means natural logarithm of the term in square brackets
Adapted from CIRIA, The SUDS Manual C753 (2015).


Materials

This is a collection of three articles with the common theme of being 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. products for various applications in LIDLow Impact Development. A stormwater management strategy that seeks to mitigate the impacts of increased urban runoff and stormwater pollution by managing it as close to its source as possible. It comprises a set of site design approaches and small scale stormwater management practices that promote the use of natural systems for infiltration and evapotranspiration, and rainwater harvesting..

Underground construction 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.

For reservoirs

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 porosity of 0.4[1].

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 porosity). Porosity and permeability are directly influenced by the size, gradation and angularity of the particles [2]. 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


For choking/choker layers

medium sized 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., free from finesSoil particles with a diameter less than 0.050 mm.

In bioretention systems a choker layer of ≥ 100 mm depth is the recommended method to prevent migration of finer filter media into the underlying storage reservoir aggregate. These same mid-sized 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 are recommended for use in Stormwater planter underdrains and may be useful in the fine grading of foundations courses for permeable paving.

Suitable materials include:

High performance bedding (HPB)
Clean, angular 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. screened to between 6 and 10 mm. Widely available and designed specifically for drainage applications. Free from finesSoil particles with a diameter less than 0.050 mm. by definition.
HL 6
Is a clean, angular 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. screened between 10 and 20 mm. Free from finesSoil particles with a diameter less than 0.050 mm. by definition.
Pea Gravel
Rounded natural 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., screened between 5 and 15 mm, and washed free from finesSoil particles with a diameter less than 0.050 mm..

In most scenarios, a geotextile layer is unnecessary and has been associated with rapid decline and clogging in some circumstances.


OPS 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.

Of the standard 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 in the standard OPSS.MUNI 1010 only 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. O is recommended as a substitute for clear stone in LIDLow Impact Development. A stormwater management strategy that seeks to mitigate the impacts of increased urban runoff and stormwater pollution by managing it as close to its source as possible. It comprises a set of site design approaches and small scale stormwater management practices that promote the use of natural systems for infiltration and evapotranspiration, and rainwater harvesting. construction.

Where 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. O is substituted for clear stone in underground reservoir structures, the porosity used in design calculations shall be 0.3 unless laboratory testing proves otherwise.

Examples of BMPs with underground reservoirs include Underdrains, infiltration trenches, permeable paving, infiltration chambers, exfiltration trenches.

All other mixes must be avoided for free drainage or storage as they are permitted to contain a higher enough proportion of finesSoil particles with a diameter less than 0.050 mm. to reduce permeability below 50 mm/hr.

For more information see OPS aggregates

Landscaping 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.

This rain gardenA lot level bioretention cell designed to receive and detain, infiltrate and filter runoff, typically used for discharge from downspouts. in a school yard uses stone as both decorative edging and for erosion controlIncludes the protection of soil from dislocation by water, wind or other agents..
This bioswaleLinear bioretention cell designed to convey, treat and attenuate stormwater runoff. The engineered filter media soil mixture and vegetation slows the runoff water to allow sedimentation, filtration through the root zone, evapotranspiration, and infiltration into the underlying native soil. in a parking lot uses stone at the inlets and along the bottom of the swaleA shallow constructed channel, often grass-lined, which is used as an alternative to curb and channel, or as a pretreatment to other measures. Swales are generally characterized by a broad top width to depth ratio and gentle grades. to prevent erosion(1) The wearing away of the land surface by moving water, wind, ice or other geological agents, including such processes as gravitation creep; (2) Detachment and movement of soil or rock fragments by water, wind, ice or gravity (i.e. Accelerated, geological, gully, natural, rill, sheet, splash, or impact, etc)., as the sides are sloped.

For advice on 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. used in underdrains, see Reservoir aggregate.

Stone or gravel can serve as a low maintenance decorative feature, but it may also serve many practical functions on the surface of an LIDLow Impact Development. A stormwater management strategy that seeks to mitigate the impacts of increased urban runoff and stormwater pollution by managing it as close to its source as possible. It comprises a set of site design approaches and small scale stormwater management practices that promote the use of natural systems for infiltration and evapotranspiration, and rainwater harvesting. practice.

Stone for erosion controlIncludes the protection of soil from dislocation by water, wind or other agents.

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. used to line swales or otherwise dissipate energy (e.g. in forebays) should have high angularity to increase the permissible shear stress applied by the flow of water. [3] However, in some surface landscaped applications there may be a desire to use a rounded 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. such as 'river rock' for aesthetic reasons. Rounded stones should be of sufficient size to resist being moved by the flow of water. Typical stone for this purpose ranges between 50 mm and 250 mm. The larger the stone, the more energy dissipation.

  • Stone beds should be twice as thick as the largest stone's diameter.
  • If the stone bed is underlain by a drainage geotextile, regular inspection and possible replacement should be scheduled as there is a potential for clogging of this layer to occur.

Stone mulcha top dressing over vegetation beds that provides suppresses weeds and helps retain soil moisture in bioretention cells, stormwater planters and dry swales.

Finer inorganic mulcha top dressing over vegetation beds that provides suppresses weeds and helps retain soil moisture in bioretention cells, stormwater planters and dry swales. materials can be of value applied in areas with extended ponding times i.e. in the the centre of recessed, bowl shaped bioretention, stormwater planters, trenches or swale practices. Inorganic mulches resist movement from flowing water and do not float. Applying a thin layer of inorganic mulcha top dressing over vegetation beds that provides suppresses weeds and helps retain soil moisture in bioretention cells, stormwater planters and dry swales. over the top of wood based mulcha top dressing over vegetation beds that provides suppresses weeds and helps retain soil moisture in bioretention cells, stormwater planters and dry swales. has been shown to reduce migration of the underlying layer by around 25% [4]. Inorganic mulches which may be available locally, include:

  • Pea gravel
  • River rock/beach stone
  • Recycled glass
  • Crushed mussel shells

On-site verification

Steps in conducting a jar test to detect finesSoil particles with a diameter less than 0.050 mm. in construction materials

Specifying that aggregates for the construction of LIDLow Impact Development. A stormwater management strategy that seeks to mitigate the impacts of increased urban runoff and stormwater pollution by managing it as close to its source as possible. It comprises a set of site design approaches and small scale stormwater management practices that promote the use of natural systems for infiltration and evapotranspiration, and rainwater harvesting. practices must be free from finesSoil particles with a diameter less than 0.050 mm. is important. But checking that the delivered materials meet specification is essential to reduce problems with construction and longer term performance.

When possible, Construction Managers should observe the offloading of materials to watch for dust clouds. 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. or sand for LIDLow Impact Development. A stormwater management strategy that seeks to mitigate the impacts of increased urban runoff and stormwater pollution by managing it as close to its source as possible. It comprises a set of site design approaches and small scale stormwater management practices that promote the use of natural systems for infiltration and evapotranspiration, and rainwater harvesting. construction should not give rise to clouds of dust when dumped.

A simple jar test can be used to gauge the proportion of finesSoil particles with a diameter less than 0.050 mm. in an 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. product before acceptance.

Apparatus:

  • A large wide-mouthed jar - glass or clear plastic are both fine,
  • Tap water, and
  • 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. to be tested.

Method:

  1. Collect approximately 5 cm of material in the jar (or at least two complete layers of 50 mm clear stone),
  2. Add water to around 3/4 full,
  3. Secure cap and shake,
  4. Leave for at least 30 minutes and until the water is clear - plan to run the test overnight when possible,
  5. Examine the layer of 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. - if > 3 mm has been washed from 5 cm of product, the material should be rejected,

Note that the 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. may collect on top of, or at the bottom of the construction material.

External references


Construction

The following presents a summary of considerations when planning the construction of a low impact developmentA stormwater management strategy that seeks to mitigate the impacts of increased urban runoff and stormwater pollution by managing it as close to its source as possible. It comprises a set of site design approaches and small scale stormwater management practices that promote the use of natural systems for infiltration and evapotranspiration, and rainwater harvesting. project. More details can be found in the following reference:[5]

  • The site of the infiltration facility must remain outside the limit of disturbance and blocked from site traffic until construction of the facility begins, to prevent soil compaction by heavy equipment.
  • This area must not be used as the site of 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. basinsGround depression acting as a flow control and water treatment structure, that is normally dry. during construction, as the concentration of finesSoil particles with a diameter less than 0.050 mm. will reduce post-construction infiltrationThe slow movement of water into or through a soil or drainage system.Penetration of water through the ground surface..
  • This area must not be use as a staging area, for storing materials.
  • To prevent 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. from clogging the surface, stormwater must be diverted away from the facility until the drainage areaThe total surface area upstream of a point on a stream that drains toward that point. Not to be confused with watershed. The drainage area may include one or more watersheds. is fully stabilized.
  • As many infiltration facilities are installed in the road right-of-way or tight urban spaces, considerations of traffic control and utility conflicts must be part of the plans and inspections.

Sequencing

The following is a typical construction sequence to properly install an infiltration practice:

  1. The area should be fully protected by siltSoil or media particles smaller than sand and larger than clay (3 to 60 m) fence or construction fencing to prevent compaction by construction traffic and equipment.
  2. Installation may only begin after entire contributing drainage areaThe total surface area upstream of a point on a stream that drains toward that point. Not to be confused with watershed. The drainage area may include one or more watersheds. has been either stabilized or flows have been safely routed around the area. The designer should check the boundaries of the contributing drainage areaThe total surface area upstream of a point on a stream that drains toward that point. Not to be confused with watershed. The drainage area may include one or more watersheds. to ensure it conforms to original design.
  3. The pretreatmentInitial capturing and removal of unwanted contaminants, such as debris, sediment, leaves and pollutants, from stormwater before reaching a best management practice; Examples include, settling forebays, vegetated filter strips and gravel diaphragms. part of the design should be excavated first and sealed until full construction is completed.
  4. Excavators or backhoes working adjacent to the proposed infiltration area should excavate to the appropriate design depth.
  5. The soil in the bottom of the excavation should be ripped to promote greater infiltrationThe slow movement of water into or through a soil or drainage system.Penetration of water through the ground surface..
  6. Any accidental 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. accumulation from construction should be removed at this time.


  1. Excavate subsurface water storage reservoirAn underlying bed filled with aggregate or other void-forming fill material that temporarily stores stormwater before infiltrating into the native soil or being conveyed by an underdrain pipe. to base elevation,
  2. Check base elevation and slope,
  3. Fracture/rip bottom and roughen side of the excavation to remove smeared surfaces,
  4. Install optional geotextiles (or liner for biofilter); overlapping according to design drawings,
  5. Install coarse reservoir gravel, and any void forming structures (e.g. underdrains, infiltration chambers, or wells),
  6. Check elevation and slope at top of reservoir,
  7. Install choking layer and optional 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. (typically only over the perforated pipe),
  8. Check elevation and slope at top of choking layer,
  9. Install filter media with additional 30 cm over finish grade of the filter bed,
  10. Thoroughly saturate and allow to settle for at least one week. After this time, tamp manually to check settling is complete. Alternatively, installations made in the fall can be left to settle over the whole winter season at this point,
  11. Install temporary erosion and 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. control practices,
    Conduct all other site construction activities (buildings/servicing etc.)
  12. Check condition of bioretentionA shallow excavated surface depression containing prepared filter media, mulch, and planted with selected vegetation. after settling period, remediate any deficiencies,
  13. Install curbs and pavements and concrete pretreatment devices,
  14. Check elevations of curb cuts and other inlets
  15. Install erosion controlIncludes the protection of soil from dislocation by water, wind or other agents. to all inlets!!
  16. Remove excess filter mediaThe engineered soil component of bioretention cell or dry swale designs, typically with a high rate of infiltration and designed to retain contaminants through filtration and adsorption to particles. along with any accumulated construction 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.,
  17. Install any surface applied additives,
  18. Conduct fine grading to surface of filter bed, checking elevations/slopes/compaction,
  19. Apply stone or mulch cover for decorative systems, or turf reinforcement for grassed systems,
  20. Install erosion control blankets or matting
  21. Plant or lay sod,
  22. Saturated system thoroughly to settle filer media particles around the roots of new plants,
  23. Irrigated the system as required to establish healthy vegetation cover,
  24. Inspect and remediate deficiencies after any significant rainfall within the next 3 months or remainder of the first growing season.



Facilities containing media

BioretentionA shallow excavated surface depression containing prepared filter media, mulch, and planted with selected vegetation.

Sequencing depends on the design:

  • Full infiltrationThe slow movement of water into or through a soil or drainage system.Penetration of water through the ground surface.:Pack 50 mm diameter clear stone to storage design depth, top with 100 mm of the choker course,
  • Partial infiltrationThe slow movement of water into or through a soil or drainage system.Penetration of water through the ground surface.:Place design depth of 50 mm diameter clear stone for the infiltration volume on bed and then lay the perforated underdrainA perforated pipe used to assist the draining of soils. pipe over it. Pack more clear stone to 75 mm above the top of the underdrainA perforated pipe used to assist the draining of soils., top with 100 mm of choker layer.

Stormwater planters

  • Place an impermeable liner on the bed with 150 mm overlap on sides. Lay the perforated underdrainA perforated pipe used to assist the draining of soils. pipe, Pack 50 mm diameter clear stone to 75 mm above top of underdrainA perforated pipe used to assist the draining of soils., top with 100 mm of choker layer;

Rain gardens

No storage or drainage is required, filter mediaThe engineered soil component of bioretention cell or dry swale designs, typically with a high rate of infiltration and designed to retain contaminants through filtration and adsorption to particles. or amended topsoil is laid onto native soils

Media installation

Media installed over the choker course in 0.3 m lifts until desired top elevation is achieved. Each lift must be thoroughly wetted and drained before adding the next. Wait three weeks to check for settling, and add additional media and regrade as needed.

  • Prepare planting holes for any trees and shrubs, install vegetation, and water accordingly.
  • Install any temporary irrigationHuman application of water to agricultural or recreational land for watering purposes. City of Toronto Wet Weather Flow Management November 2006 47.
  • Plant landscaping materials as shown in the landscaping plan, and water them weekly in the first two months.
  • Lay down surface cover in accordance with the design (mulcha top dressing over vegetation beds that provides suppresses weeds and helps retain soil moisture in bioretention cells, stormwater planters and dry swales., riverstone, or turf).
  • Conduct final construction inspection, checking inlet, pretreatmentInitial capturing and removal of unwanted contaminants, such as debris, sediment, leaves and pollutants, from stormwater before reaching a best management practice; Examples include, settling forebays, vegetated filter strips and gravel diaphragms., bioretentionA shallow excavated surface depression containing prepared filter media, mulch, and planted with selected vegetation. cell and outlet elevations.
  • Remove erosion and 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. controls, only when the entire drainage areaThe total surface area upstream of a point on a stream that drains toward that point. Not to be confused with watershed. The drainage area may include one or more watersheds. is stabilized.

Checklists




Incentives and Credits

In Ontario

LEED BD + C v. 4

Sustainable sites: Rainwater management (up to 3 points)

  • Two points (or 1 point for Healthcare) will be awarded if the project manages "the runoffThat potion of the water precipitated onto a catchment area, which flows as surface discharge from the catchment area past a specified point.Water from rain, snow melt, or irrigation that flows over the land surface. from the developed site for the 95th percentile of regional or local rainfall events."
  • Three points (or 2 points for Healthcare) will be awarded if the project manages "the runoffThat potion of the water precipitated onto a catchment area, which flows as surface discharge from the catchment area past a specified point.Water from rain, snow melt, or irrigation that flows over the land surface. from the developed site for the 98th percentile of regional or local rainfall events."
    OR
  • For zero-lot-line projects only, 3 points (or 2 points for Healthcare) will be awarded if the project manages "the runoffThat potion of the water precipitated onto a catchment area, which flows as surface discharge from the catchment area past a specified point.Water from rain, snow melt, or irrigation that flows over the land surface. from the developed site for the 85th percentile of regional or local rainfall events."

SITES v.2


  1. REDIRECT Special:ArticleFeedbackv5
  1. Porosity of Structural Backfill, Tech Sheet #1, Stormtech, Nov 2012, http://www.stormtech.com/download_files/pdf/techsheet1.pdf accessed 16 October 2017
  2. 2.0 2.1 2.2 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
  3. Roger T. Kilgore and George K. Cotton, (2005) Design of Roadside Channels with Flexible Linings Hydraulic Engineering Circular Number 15, Third Edition https://www.fhwa.dot.gov/engineering/hydraulics/pubs/05114/05114.pdf
  4. Simcock, R and Dando, J. 2013. Mulch specification for stormwater bioretention devices. Prepared by Landcare Research New Zealand Ltd for Auckland Council. Auckland Council technical report, TR2013/056
  5. [https://cvc.ca/wp-content/uploads/2013/03/CVC-LID-Construction-Guide-Book.pdf Construction Guide for Low Impact Development, CVC (2013)