Stormwater Tree Trenches
Trees can be incorporated into bioretention cells with other plant types, or otherwise into their own planting pits.
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).
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 .
http://www.mdpi.com/2072-4292/9/11/1202/pdf http://lfs-mlws.sites.olt.ubc.ca/files/2014/10/an_analytical_model_of_rainfall_interception_by_urban_trees.pdf https://www.nrcan.gc.ca/earth-sciences/land-surface-vegetation/biophysical-parameters/9162 https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/1999WR900003
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,
- catch basins and distribution pipes, and
- direct infiltration from permeable paving.
|Scientific Name||Common Name||Soil Moisture
|Partial shade tolerance||Drought Tolerance
|Pollution tolerance||Compaction tolerance||STEP Star||Illustration|
|Acer rubrum||Red Maple|
|Acer saccharinum||Silver Maple|
|Acer saccharum ssp. saccharum||Sugar Maple|
|Acer x freemanii||Hybrid Maple / Freeman Maple|
|Alnus incana||Speckled Alder / White Alder|
|Betula papyrifera||Paper Birch|
|Carpinus caroliniana||American hornbeam / Blue Beech|
|Carya cordiformis||Bitter-nut Hickory|
|Carya ovata||Shag-bark Hickory|
|Celtis occidentalis||Common Hackberry|
|Fraxinus americana||White Ash|
|Fraxinus nigra||Black Ash|
|Fraxinus pennsylvanica||Green Ash|
|Gleditsia tricanthos var. inermis||Thornless Honey Locust|
|Gymnocladus dioicus||Kentucky Coffeetree|
|Juglans nigra||Black Walnut|
|Juniperus virginiana||Eastern Red Cedar|
|Larix laricina||Tamarack / American Larch|
|Liriodendron tulipifera||Tulip Tree|
|Picea glauca||White Spruce|
|Picea pungens||Colorado Spruce|
|Pinus mugo||Mugo Pine|
|Pinus strobus||Eastern White Pine|
|Populus balsamifera ssp. balsamifera||Balsam Poplar|
|Populus deltoides||Eastern Cottonwood|
|Populus grandidentata||Large-tooth Aspen|
|Populus tremuloides||Trembling Aspen|
|Prunus serotina||Wild Black Cherry|
|Quercus alba||White Oak|
|Quercus bicolor||Swamp White Oak|
|Quercus macrocarpa||Bur Oak|
|Quercus muehlenbergii||Chinquapin oak / Yellow oak|
|Quercus palustris||Pin Oak|
|Quercus rubra||Red Oak|
|Salix amygdaloides||Peachleaf Willow|
|Salix lucida||Shining Willow|
|Salix nigra||Black Willow|
|Thuja occidentalis||Eastern White Cedar|
|Tilia americana||American Basswood|
|Ulmus americana||American Elm|
Performance and research
Birch trees in parking lot bioretention 'IMAX site' Mississauga, ON
Trees in parking lot bioretention 'IMAX site' Mississauga, ON
Open tree pits
Extended tree pit planting in USA
Photo credit: USEPA
Soil cells under construction.
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.
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.
- 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