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no edit summary
{|class="wikitable"
{|class="wikitable"
|+Specifications for Enhanced Swales / Bioswales / Grass Wales / Dry Swales
|+Specifications for Stormwater Tree Trenches
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!Material
!Material
|'''Site Layout'''
|'''Site Layout'''
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* Should be Canadian Soil Classification System sandy loam with combined silt- and clay-sized content between 18-35%; and sand- to fine gravel-sized content (0.074 to 5 mm dia.) between 65-82%.
* Enhanced swales typically treat drainage areas of two hectares or less
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* Growing medium compacted to 80-90% below the tree root ball to prevent settling.
* Swale total width should be 2 metres or greater and bottom width between 0.75 and 3.0 metres. Swale length between check dams should be ≥ 5 m.
* Bioretention filter media (see [https://wiki.sustainabletechnologies.ca/wiki/LID_BMP_Fact_Sheets#Bioretention| Bioretention Fact Sheet]) may be suitable for use as growing medium, depending on climate and tree species.
* Side slopes should be no steeper than 1:3 (33%) for mowing maintenance. Gentler slopes (e.g. 1:4 or 25%) are encouraged where runoff enters the swale as sheet flow.
* A maximum flow depth of 0.1 m is recommended during the design storm event
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|'''Inlets'''
|'''Inlets'''
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* Structural soils consist of 3 components, mixed in the following proportions by weight: crushed stone (79.07%), clay loam soil (20%), and hydrogel tackifier (0.03%).
* For concentrated overland flow:
* Total moisture at mixing should be 10% as per AASHTO T-99 optimum moisture.
** Catch basins or other inlet structures should be located at all sag points in the gutter grade and immediately upgrade of median breaks, crosswalks and street intersections.
* The clay loam soil should conform to the Canadian soil classification system (gravel <5%, sand 25-30%, silt 20-40%, clay 25-40%). Organic matter should range between 2 to 5% by dry weight.
** Inlet types include curb openings (modified curbs, spillways), side inlet catch basins, trench drains or other pre-fabricated inlet structures.
* Hydrogel (potassium propenoate-propenamide copolymer), is added as a tackifier to prevent separation of the stone and soil during mixing and installation.
** Spillways aid in turning flow 30, 45 or 90 degrees into the practice.
** Incorporate concrete aprons at curb opening or spillway locations to increase inflow effectiveness.
** If the inlet structure itself does not provide sedimentation or filtration pre-treatment, incorporate a pre-treatment feature at curb opening or spillway location to isolate sediment, trash and debris for ease of removal.
** Provide a 75 to 150 mm drop in elevation between the inlet invert and grass or mulch surface, pre-treatment feature or concrete apron.
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* Crushed stone (granite or limestone) narrowly graded from 20 to 40 mm diameter, highly angular with no fines.
* [[Curb cuts|Spillways]] turn flow into enhanced swale at 30, 45 or 90 degrees
* The entire pile is turned and mixed until a uniform blend is produced. The structural soil is then installed and compacted in 150 mm lifts.
* A 75 to 150 mm drop in elevation between the inlet invert and grass or mulch surface, pre-treatment feature or concrete apron.
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|'''Pre-Treatment'''
|'''Pre-treatment'''
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* Decompact native subgrade soil under tree openings and between granular bases of modular soil support structure rows during installation for better infiltration drainage performance.
* [[Level spreader]]: A shallow trench structure (with concrete, metal or wood lip), graded to be level and installed parallel to the pavement edge or flush curb.
* [[Geotextile]] and stone filter [[inlets]]: Square or rectangular curb openings located directly over the practice, filled with clean aggregate, covered with a layer of geotextile filter fabric and stone, graded level or gently sloped and installed at concentrated overland flow inlets (e.g. curb cuts).
* Catch basin, manhole, or other inlet structure sumps in combination with a shield, baffle, trap, or filter insert device, or goss trap are used to pre-treat concentrated overland flow. They can be designed to retain both coarse and fine particulate sediments in the sump, and floatables (hydrocarbons, trash and debris). A variety of proprietary pre-treatment devices are available.
* [[Forebay]]: Constructed to an appropriated length to width ratio and sized to accommodate appropraite ponding volume of the surface ponding storage requirement. To be used with concentrated overland flow inlets.
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* Structural concrete panel is 250 mm thick, contains rebar reinforcements and sits on equal-sized concrete footing supports on rows of modular soil support structures
* Recommended sizing for [[Level spreader]]:
* Modular soil supports are supported by a minimum 150 mm base of compacted granular material.
** 1.4 m of length for every 0.01 m³/s of inflow during the design storm event,
** width of 300 mm or 3 times inflow pipe diameter,
** depth of 200 mm or half the inflow pipe diameter. Used with overland sheet flow inlets.
* Elevation change of 75 to 100 mm from pavement to top of the stone cover. Stone cover may be 50 to 150 mm diameter crushed angular stone, river rock/beach stone or rip rap.
* Forebay: 2:1 length to width ratio and sized to accommodate ponding volume of 25%
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|'''Planting Soil/ Filter Media'''
|'''Planting Soil/ Filter Media'''
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* Aggregates are used in modular soil support systems below the structures as the trench base layer, and sometimes, on top of the structures, as the pavement base layer.
* [[Topsoil|Planting soil]] - use for enhanced grass swales
* [[Bioretention: Filter media|Filter Media Blend A]]
* [[Bioretention: Filter media|Filter Media Blend B]]
* [[Sand]]
* [[Topsoil]]
* [[Organic matter|Organic Material]] -
* [[Additives]] - Should be material low in available phosphorus such as leaf and yard waste compost, untreated woodchips, shredded paper or coir.
* [[Grain size analysis|Particle-size distribution]]
* [[Phosphorus|Other Parameters - Phosphorus (Plant Available or Extractable)]]
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* Specifications for aggregate base materials determined by the designing Engineer based on varying levels of structural loading and hydraulic requirements.
* For Planting Soil - hydraulic conductivity, saturated (ASTM D2434) at 85% maximum dry density (ASTM D698) should be of 15 - 300 mm/h.
* Filter Media Blend A:
** Drainage rate priority:
*** Use when I:P ratio ≥15:1,
*** 3 parts sand to 1 part organic material or additives,
*** Porosity of 0.4,
*** hydraulic conductivity, saturated (ASTM D2434) at 85% maximum dry density (ASTM D698) should be of 75 - 300 mm/h.
* Filter Media Blend B:
** Water quality treatment priority:
*** Use when improved metals and phosphorus retention and/or more diverse planting options are desired,
*** 3 parts sand to 2 parts topsoil to 1 part organic material or additives
*** porosity of 0.35,
*** hydraulic conductivity, saturated (ASTM D2434) at 85% maximum dry density (ASTM D698) should be 25 to 300 mm/h.
* Sand
** Should be coarse and have a fineness modulus index between 2.8 and 3.1 according to ASTM C33/C33M
* Topsoil
** Must contain at least 9%, and not greater than 36% clay-sized particles and have a sodium absorption ratio less than 15.
* Organic material
** Organic matter (ASTM F1647) should make up 3 to 10% of the filter media by dry weight.
* Additives: Typically 5 to 10% by volume of the filter media blend (follow product manufacturer instructions where applicable).
* Particle-size distribution (ASTM D7928):
** <25% silt-and clay-sized particles combined (smaller than 0.05 mm); 3 to 12% claysized particles (0.002 mm or smaller).
* Other parameters: Phosphorus (Plant Available or Extractable):
** should be between 10 and 40 ppm, and cation exchange capacity (ASTM D7503) >10 meq/100 g.
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|'''Check Dams'''
|'''Check Dams'''
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* Geotextile material specifications should conform to Ontario Provincial Standard Specification (OPSS) 1860 for Class II geotextile fabrics.
* Low head dams to slow concentrated flow and promote settling and infiltration. Dam height depends on depth of ponded water that will infiltrate in the required drainage time. May be constructed of any resilient and waterproof material including concrete, metal and stone (typically <150mm rip rap) and may have spillways incorporated into their profile to direct water to the centre of the swale. Should include stone cover on the down-gradient side for erosion control.
* Geotextile installed on tree trench sides and around perforated distribution and underdrain pipes should be woven monofilament or non-woven needle punched fabrics. '''Note''': Woven slit film and non-woven heat bonded fabrics should not be used as they are prone to clogging.
* [[Check dam]] spacing should be based on the slope and desired ponding volume. They should be spaced far enough apart to allow access for maintenance equipment (e.g., mowers)
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* Where a root barrier is needed to prevent the migration of roots out of the tree trench, use impermeable ribbed barrier material with a thickness of 1-2 mm.
* May be constructed of any resilient and waterproof material including concrete, metal and stone (typically <150mm rip rap)
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|'''Plants'''
|'''Plants'''
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* A standpipe from the underdrain pipe to the growing medium or pavement surface can be used for inspection and maintenance. The top of the standpipe should be covered with a sealable cap and secured with a vandal-proof fastener.
* Enhanced grass swales may be planted with sod or seed.
**If using seed, stabilize swale with [[erosion control blankets]].
** Bioswale planting plans should feature a mixture of deeply rooting perennials adapted to both wet and dry conditions and
local climate.
** If using a native seed mix, include a cover crop of oats, winter wheat, or rye to stabilize the swale in the short term.
** Road salt tolerance should be considered if facility will receive pavement runoff.
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* Should be minimum 150 mm dia. perforated HDPE or equivalent material, smooth interior wall and continuously perforated with geotextile sock
* For [[Bioswale]] planting plans should feature a mixture of deeply rooting perennials adapted to both wet and dry conditions and
local climate.
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