Difference between revisions of "Stormwater Tree Trenches"

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==Soil cells==
 
==Soil cells==
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These are (usually plastic) supporting structures placed around the trees and beneath adjacent paved areas. They prevent compaction to the roots of the tree and prevent root damage to the paving. They are sometimes configured to receive stormwater and to enclose ponded water which can then infiltrate the soil surrounding the tree.  
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[[File:DepressedDrain_SoilCell.png|frame|Depressed drain inlet into soil cells]]
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These are (usually plastic) supporting structures placed around the trees and beneath adjacent paved areas. They prevent compaction to the roots of the tree and prevent root damage to the paving. They are sometimes configured to receive stormwater and to enclose ponded water which can then infiltrate the soil surrounding the tree, for instance in a depressed drain [[inlets|inlet]] design as presented in the image to the right.  
 
Things to consider in design:
 
Things to consider in design:
 
*If the system is unlined it is hydraulically equivalent to a [[bioretention]] cell and provides similar water quality benefits.   
 
*If the system is unlined it is hydraulically equivalent to a [[bioretention]] cell and provides similar water quality benefits.   

Revision as of 15:12, 11 August 2020

Soil cellsSoil cellsBioretention: Filter mediaChoking layerReservoir gravelReservoir gravelReservoir gravelForebaysForebaysForebaysForebaysSlotted drainDepressed drainTreesTreesPerennials: ListPerennials: ListPerennials: ListOverflowOverflowUnderdrain
This is an image map of an extended tree pit, clicking on components will load the appropriate article.

Overview[edit]

Trees can be incorporated into bioretention cells with other plant types, or otherwise into their own planting pits.


Planning considerations[edit]

A commonly held view is that a tree's root system will be similar to it's visible crown. For many trees, this is not the case, as roots will more often spread much more widely, but to a shallower depth [1]. For more detailed information on planning (site) considerations see Bioretention

Planting in slopes[edit]

Smooth slopes should be amended into localised terraces by the Landscape Architect when planting large trees into slopes > 5 %. [2]

Design[edit]

There are many design configuration options for including trees into stormwater management plans.

Soil cells[edit]

Depressed drain inlet into soil cells

These are (usually plastic) supporting structures placed around the trees and beneath adjacent paved areas. They prevent compaction to the roots of the tree and prevent root damage to the paving. They are sometimes configured to receive stormwater and to enclose ponded water which can then infiltrate the soil surrounding the tree, for instance in a depressed drain inlet design as presented in the image to the right. Things to consider in design:

  • If the system is unlined it is hydraulically equivalent to a bioretention cell and provides similar water quality benefits.
  • If the system is lined and underdrained it is hydraulically similar to a large stormwater planter. Depending on the design detail it may retain significant stormwater within the planting soil volume and will provide water quality benefits.

Species selection[edit]

Trees: List

Planting pit sizing[edit]

Bioretention: Sizing

Inlets[edit]

Multiple methods for distribution and conveyance of runoff into the system are recommended for redundancy and conservative designs. Combinations may be made of:

  • tree well flow,
  • catchbasins and distribution pipes, and
  • direct infiltration from permeable paving.

See also Inlets and pretreatment

Underdrain[edit]

Underdrain

Performance[edit]

Interception[edit]

Tree canopies intercept and store rainfall, thereby modifying stormwater runoff and reducing demands on urban stormwater infrastructure (Xiao et al., 1998; Xiao et al., 2000; Xiao and McPherson, 2002; Xiao et al., 2006). Canopy interception reduces both the actual runoff volumes, and delays the onset of peak flows (Davey Resource Group, 2008).

The extent of interception is influenced by a number of factors including tree architecture and it has been estimated that a typical medium-sized canopy tree can intercept as much as 9000 litres of rainfall year. (Crockford and Richardson, 2000).

A study of rainfall interception by street and park trees in Santa Monica, California found that interception rates varied by tree species and size, with broadleaf evergreen trees provided the most rainfall interception (Xiao and McPherson, 2002). Rainfall interception was found to range from 15.3% for a small jacaranda (Jacaranda mimosifolia) to 66.5% for a mature brush box (Tristania conferta now known as Lophostemon confertus). Over the city as a whole the trees intercepted 1.6% of annual precipitation and the researchers calculated that the annual value of avoided stormwater treatment and flood control costs associated with this reduced runoff was US$110,890 (US$3.60 per tree).

Transpiration[edit]

Trees suck! (Abstracted from Phyto, by K. Kennen)

Galleries[edit]

Open tree pits[edit]

  • Rainwater harvesting cistern, which discharges to tree pits during dry conditions. Image credit Mississippi WMO

  • Extended tree pit planting in USA
    Photo credit: USEPA

  • A right of way bioswale installed by the New York City Department of Environmental Protection on Dean Street, Brooklyn

Soil cells[edit]

  • Soil cells under construction.

  • Soil cell installation on Central Parkway in Mississauga.

  • Built in 2014, this stormwater planter on Central Parkway in Mississauga uses supported soil cells and is functioning well.

  • Soil Cell installation along the Moynes and Berl Avenues on north side of The Queensway in Toronto. The picture depicts stormwater distribution pipes through the system, used to help provide water to the trees that will be later planted in the BMP feature.
    Photo credit: City of Toronto

  • Silva Cell “top” deck prior to organic layer and screenings for pavers. Photo credit: City of Toronto

  • Soil Cells being installed along Edgewater Drive for Waterfront Toronto.
    Photo credit: DeepRoot

  • Stormwater Tree Trenches at East Bayfront Promenade, Toronto.
    Photo credit: DeepRoot

  • Seawall Soil Cells (Tree Trenches) located in Vancouver.
    Photo credit:City of Vancouver

  • Stormwater tree trenches designed with a structural concrete pad over top of the installation.
    Photo credit:DeepRoot

External links[edit]

In our effort to make this guide as functional as possible, we have decided to include proprietary systems and links to manufacturers websites.
Inclusion of such links does not constitute endorsement by the Sustainable Technologies Evaluation Program.
Lists are ordered alphabetically; link updates are welcomed using the form below.

  1. ↑ Crow, P. (2005). The Influence of Soils and Species on Tree Root Depth. Edinburgh. Retrieved from https://www.forestry.gov.uk/pdf/FCIN078.pdf/$FILE/FCIN078.pdf
  2. ↑ Wilkus A., 'Slope Style', Landscape Architecture Magazine, April 2018, accessed 21 December 2018, https://landscapearchitecturemagazine.org/2018/04/24/slope-style/

The portion of water precipitated onto a catchment area, which then 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.

An alternative practice to traditional impervious pavement, prevents the generation of runoff by allowing precipitation falling on the surface to infiltrate through the surface course into an underlying stone reservoir and, where suitable conditions exist, into the native soil.

A perforated pipe used to assist the draining of soils.

The interception, storage and eventual evaporation of rainfall from vegetation canopies.

The interception, storage and eventual evaporation of rainfall from vegetation canopies.

Any form of rain or snow.

Tank used to store rainwater (typically roof runoff) for later use.

Linear 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.

A vegetated practice that collects and treats stormwater through sedimentation and filtration. Contributions to water cycle/water balance are through evapotranspiration only; no infiltration.

Best 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.

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