Changes

Take a look at the downloadable Stormwater Tree Trenches Fact Sheet below for a .pdf overview of this LID Best Management Practice:

Take a look at the downloadable Stormwater Tree Trench Fact Sheet below for a .pdf overview of this LID Best Management Practice:

{{Clickable button|[[File:Treetrench.png|200 px|link=https://wiki.sustainabletechnologies.ca/images/4/4e/Tree_trenches_final_Update.pdf]]}}

{{Clickable button|[[File:Treetrench.png|200 px|link=https://wiki.sustainabletechnologies.ca/images/7/77/Tree_trenches_2022.pdf]]}}

==Planning considerations==

==Planning considerations==

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 <ref>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</ref>. For more detailed information on planning (site) considerations see [[Bioretention]].

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 <ref>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</ref>.  

 

For information about constraints to infiltration practices, and approaches and tools for identifying and designing within them see [[Infiltration]].

===Site Topography===

===Site Topography===

Maintaining a separation of 1 m between the elevations of the bottom of the trench and the seasonally high water table, or top of bedrock, is recommended. Lesser or greater values may be considered based on groundwater mounding analysis. See [[Groundwater]] for further guidance and spreadsheet tool.

Maintaining a separation of 1 m between the elevations of the bottom of the trench and the seasonally high water table, or top of bedrock, is recommended. Lesser or greater values may be considered based on groundwater mounding analysis. See [[Groundwater]] for further guidance and spreadsheet tool.

===Soil===

===Native Soil===

Tree trenches can be constructed over any soil type, but hydrologic soil group A and B are best for achieving water balance objectives. Facilities designed to infiltrate water should be located on portions of the site with the highest infiltration rates. Native soil infiltration rate at the proposed location and depth should be confirmed through in-situ measurements of hydraulic conductivity under field saturated conditions.

Tree trenches can be constructed over any soil type, but hydrologic soil group A and B are best for achieving water balance objectives. Facilities designed to infiltrate water should be located on portions of the site with the highest infiltration rates. Native soil infiltration rate at the proposed location and depth should be confirmed through in-situ measurements of hydraulic conductivity under field saturated conditions. For guidance on infiltration testing and selecting a design infiltration rate see [[Design infiltration rate]].

===Drainage Area===

===Drainage Area===

===[[Karst]]===

===[[Karst]]===

Tree trenches designed to drain primarily by infiltration are unsuitable in areas of known or implied karst topography.

Tree trenches designed to drain primarily by infiltration are unsuitable in areas of known or implied karst topography.

==Design==

==Design==

[[File:DepressedDrain_SoilCell.png|thumb|500px|A surface [[inlets|inlet]] configuration featuring a depressed drain routing water collected from the street to an enclosed area infiltrating water to soil cells underneath.]]

[[File:DepressedDrain_SoilCell.png|thumb|500px|A surface [[inlets|inlet]] configuration featuring a depressed drain routing water collected from the street to an enclosed area infiltrating water to soil cells underneath. Source: Emmons & Olivier Resources]]

Things to consider in design:

Things to consider in design:

*If the trench is unlined it is hydraulically similar to a full- or partial-infiltration design [[bioretention]] cell and should provide similar water quality benefits.   

*If the trench is unlined it is hydraulically similar to a full- or partial-infiltration design [[bioretention]] cell and should provide similar water quality benefits.   

*If the trench features an impermeable liner and underdrain it is hydraulically similar to a large [[stormwater planter]] or no-infiltration design [[bioretention]] cell and should provide similar water quality benefits.  

*If the trench features an impermeable liner and underdrain it is hydraulically similar to a large [[stormwater planter]] or no-infiltration design bioretention cell and should provide similar water quality benefits.  

*Depending on design details tree trenches may retain a significant volume of stormwater within the planting soil and internal water storage layer and provide runoff volume reduction benefit.   

*Depending on design details tree trenches may retain a significant volume of stormwater within the planting soil and internal water storage layer and provide runoff volume reduction benefit.   

==Benefits of trees==

==Benefits of trees==

Stormwater Tree Trenches help support healthy street trees in urban settings where conventional plantings have limited space for root establishment. Trees play a critical role in stormwater management from reducing runoff through canopy interception, evapotranspiration, filtering out pollutants, and increasing infiltration capacity of soils, to retaining runoff. Trees also provide a myriad other environmental benefits, from shading impervious surfaces and thereby reducing urban heat island effects, to providing wildlife habitat and improving the aesthetics of streets and neighbourhoods. Research has shown that healthy trees increase property values, retail spending and contribute to a sense of community pride and safety.

Stormwater tree trenches help support healthy street trees in urban settings where conventional plantings have limited space for root establishment. Trees play a critical role in stormwater management from reducing runoff through canopy interception, evapotranspiration, filtering out pollutants, and increasing infiltration capacity of soils, to retaining runoff.<ref>Berland, A., Shiflett, S.A., Shuster, W.D., Garmestani, A.S., Goddard, H.C., Herrmann, D.L. and Hopton, M.E. 2017. The role of trees in urban stormwater management. Landscape and urban planning, 162, pp.167-177. https://pdf.sciencedirectassets.com/271853/1-s2.0-S0169204617X00030/1-s2.0-S0169204617300464/Adam_Berland_green_infrastructure_2017.pdf</ref>, <ref>Kuehler, E., Hathaway, J. and Tirpak, A. 2017. Quantifying the benefits of urban forest systems as a component of the green infrastructure stormwater treatment network. Ecohydrology, 10(3), p.e1813. https://www.srs.fs.usda.gov/pubs/ja/2017/ja_2017_kuehler_001.pdf</ref> Trees also provide a myriad other environmental benefits, from shading impervious surfaces and thereby reducing urban heat island effects, to providing wildlife habitat and improving the aesthetics of streets and neighbourhoods. Research has shown that healthy trees increase property values, retail spending and contribute to a sense of community pride and safety.

Below is a list of trees that are known to tolerate conditions in northern (Zone 3) urban stormwater tree trenches.

Below is a list of trees that are known to tolerate conditions in northern (Zone 3) urban stormwater tree trenches.

| Quercus bicolor || White Oak

| Quercus bicolor || White Oak

|-

|-

| Quercus macrocarpa || Burr Oak

| Quercus macrocarpa || Bur Oak

|-

|-

| Quercus rubra || Red Oak

| Quercus rubra || Red Oak

===Tree planting best practices===

===Tree planting best practices===

An extensive compendium of recommended standard tree planting details and specifications are available from [http://www.jamesurban.net/specifications James Urban].

An extensive compendium of recommended standard tree planting details and specifications are available from [http://www.jamesurban.net/specifications James Urban].  

 

 

 

==Inspection and maintenance==

==Inspection and maintenance==

==Performance==

==Performance==

To read about the use of stormwater tree trenches featuring soil cells in the Greater Toronto Area see the STEP case study on [https://sustainabletechnologies.ca/app/uploads/2018/10/Queensway-Case-Study_FINAL.pdf The Queensway Sustainable Sidewalk Pilot Project] in the City of Toronto. Evaluations of the project found that stormwater tree trenches are able to increase the urban street tree canopy coverage while requiring minimal surface area below, and provide stormwater benefits associated with TSS and heavy metal contaminant removal and runoff volume reduction, with lower routine maintenance costs than other surface practices like bioretention.<ref>STEP. 2018. The Queensway Sustainable Sidewalk Pilot Project - Case Study: Low impact Development Series. https://sustainabletechnologies.ca/app/uploads/2018/10/Queensway-Case-Study_FINAL.pdf.</ref>

In a proof-of-concept study of two stormwater tree trenches in Wilmington, North Carolina, Page et al. (2015) found that the soil-root matrix beneath the supported pavements can be used for stormwater control to achieve runoff volume reduction (80% over a yearlong evaluation period), pollutant retention, pavement stability and urban forestry goals.<ref> Page, J.L., Winston, R.J., Hunt, W.F. 2015. Soils beneath suspended pavements: An opportunity for stormwater control and treatment. Ecological Engineering. v.82. pp.40-48. https://www.sciencedirect.com/science/article/abs/pii/S0925857415001706 </ref>  To read about the use of stormwater tree trenches featuring soil cells in the Greater Toronto Area see the STEP [https://sustainabletechnologies.ca/app/uploads/2020/09/Soil-cells-tech-brief-FINAL.pdf technical brief] and [https://sustainabletechnologies.ca/app/uploads/2018/10/Queensway-Case-Study_FINAL.pdf case study] on the Queensway Sustainable Sidewalk Pilot Project in the City of Toronto. Evaluations of the project found that stormwater tree trenches are able to increase the urban street tree canopy coverage while requiring minimal surface area below, and provide stormwater benefits associated with TSS and heavy metal contaminant removal and runoff volume reduction, with lower routine maintenance costs than other surface practices like bioretention. <ref> STEP. 2018. The Queensway Sustainable Sidewalk Project https://sustainabletechnologies.ca/app/uploads/2018/10/Queensway-Case-Study_FINAL.pdf </ref> <ref> STEP. 2020. Assessing the Health of Toronto Street Trees Irrigated by Stormwater. https://sustainabletechnologies.ca/app/uploads/2020/09/Soil-cells-tech-brief-FINAL.pdf </ref> In a hydrologic study of the Queensway Sustainable Sidewalk project, Li et al. (2020) highlight the importance of inlet hydraulics and spatial distribution of inflow along the stormwater tree trench and propose an integrated modelling approach to simulate overall runoff control performance. <ref> Li, J., Alinaghaian, S., Joksimovic, D., Chen, L. An Integrated Hydraulic and Hydrologic Modeling Approach for Roadside Bio-Retention Facilities. Water. 2020, 12, 1248 https://www.mdpi.com/2073-4441/12/5/1248 </ref> Also see Credit Valley Conservation [https://cvc.ca/wp-content/uploads/2016/06/CaseStudy_CPW_Final.pdf Central Parkway LID case study] and [https://cvc.ca/wp-content/uploads//2021/07/TechReport_CPW_Final.pdf technical report] that summarize findings from evaluation of a stormwater tree trench featuring soil cells located in the median of a high-traffic road in Mississauga, Ontario. Monitoring showed the stormwater tree trench performed well over the eight storm events monitored with an average runoff volume reduction of 97%, and peak flow reduction of 96%. <ref>Credit Valley Conservation. 2016. Central Parkway: Road Right-of-Way Retrofits - Case Study. https://cvc.ca/wp-content/uploads/2016/06/CaseStudy_CPW_Final.pdf</ref> <ref>Credit Valley Conservation. 2016. Central Parkway: Low Impact Development Infrastructure

Also see Credit Valley Conservation [https://cvc.ca/wp-content/uploads/2016/06/CaseStudy_CPW_Final.pdf Central Parkway LID case study] and [https://cvc.ca/wp-content/uploads//2021/07/TechReport_CPW_Final.pdf and technical report] that summarize findings from a multi-year evaluation of a stormwater tree trench featuring soil cells located in the median of a high-traffic road in Mississauga, Ontario.

{|class="wikitable"

{|class="wikitable"

===Performance research===

===Performance research===

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).  

Tree canopies influence various components of the urban hydrologic cycle. Water losses occur via canopy interception and evaporation, transpiration, improved soil infiltration and percolation along root channels, and water table management, thereby attenuating stormwater runoff and reducing demands on drainage infrastructure. Canopy interception loss is relevant during and immediately after a storm event, while transpiration plays a role in managing soil moisture over the days and weeks between events. Canopy interception contributes to runoff volume reduction, delays the onset of peak flows and helps protect water quality.  Urban tree canopy interception and evaporation rates vary according to canopy type (e.g., closed vs. open), tree species attributes, season, and storm characteristics (e.g., rainfall intensity, duration and time between events). Berland ''et al''. (2017), call for greater consideration of arboriculture as a stormwater control measure in their literature review, noting that trees are compatible with various types of LID facilities and may improve the function of these installations through evapotranspiration and maintaining or improving drainage performance.<ref> Berland, A., Shiflett, S.A., Shuster, W.D., Garmestani, A.S., Goddard, H.C., Herrmann, D.L., Hopton, M.E. The role of trees in urban stormwater management. Landscape and Urban Planning. v.162. pp.167-177. https://www.sciencedirect.com/science/article/abs/pii/S0169204617300464?via%3Dihub </ref>  In a study of twenty tree species in Davis, California, Xiao and McPherson (2016) found that conifers generally stored more water than broadleaf deciduous species and that leaf surfaces have larger capacities to store rainfall than stem surfaces. <ref> Xiao, Q., McPherson, E.G.. 2016. Surface water storage capacity of twenty tree species in Davis, California. Journal of Environmental Quality. v.45. pp. 188-198. https://acsess.onlinelibrary.wiley.com/doi/abs/10.2134/jeq2015.02.0092 </ref>  Tree species with large mature sizes and high stomatal conductance (e.g., ''Quercus macrocarpa'', bur oak) were shown to markedly improve the function of parking lot bioretention swales in the City of Chicago, Illinois. <ref> Scharenbroch, B.C., Morgenroth, J., Maule, B. 2016. Tree species suitability to bioswales and impact on the urban water budget. Journal of Environmental Quality. v.45. pp. 199-206. https://acsess.onlinelibrary.wiley.com/doi/abs/10.2134/jeq2015.01.0060 </ref>

 

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).

[[File:TreeTranspiration.png|thumb|Trees suck! (Abstracted from Phyto, by K. Kennen)]]

[[File:TreeTranspiration.png|thumb|Trees suck! Comparison of transpiration rates of various tree species and ages (Abstracted from Phyto, by K. Kennen)]]

For more recent research on the water management benefits of urban trees, and modelling approaches see the following articles and projects.

For other recent research on the water management benefits of urban trees, and modelling approaches see the following articles and projects.

* [https://www.mdpi.com/2072-4292/9/11/1202 Estimating tree leaf area density with LIDAR (Li et al. 2017)]

* '''[https://open.library.ubc.ca/soa/cIRcle/collections/ubctheses/24/items/1.0378388 Stormwater tree trench and bioswale performance in Vancouver, BC (Vega 2019)]''' <ref> Vega, O.M. Green infrastructure in the City of Vancouver: performance monitoring of stormwater tree trenches and bioswales. UBC Theses and Dissertations. https://open.library.ubc.ca/soa/cIRcle/collections/ubctheses/24/items/1.0378388 </ref>

* [https://www.tandfonline.com/doi/full/10.1080/07011784.2017.1375865 Modelling rainfall interception by urban trees (Huang et al. 2017)]

** A study of a stormwater tree trench featuring structural soil medium and two bioswales in Vancouver, British Columbia found that these practices are effective in treating heavy metals, suspended solids and other typical stormwater pollutants, and are effective tools for reducing runoff volume by promoting infiltration to native soils.  

* [https://www.nrcan.gc.ca/earth-sciences/land-surface-vegetation/biophysical-parameters/9162 Optical Leaf Area Index In-situ Measurement (Leblanc 2011)]

* '''[https://www.sciencedirect.com/science/article/abs/pii/S0925857417306365 Stormwater infiltration capacity of street tree pits in New York City (Elliott et al. 2018)]''' <ref> Elliott, R.M., Adkins, E.R., Culligan, P.J, Palmer, M.I., Stormwater infiltration capacity of street tree pits: Quantifying the influence of different design and management strategies in New York City. Ecological Engineering. v.111. pp. 157-166. https://www.sciencedirect.com/science/article/abs/pii/S0925857417306365</ref>

* [https://www.wastormwatercenter.org/project/tree-project/ Washington Stormwater Center Tree Project]

** In a study of forty tree pits representing typical varieties of physical conditions in New York City, Elliott et al. found the most significant factor influencing infiltration rate was the presence of fencing or guard rails, with guarded tree pits having higher infiltration rates. Additionally, higher infiltration rates were associated with larger tree pit areas, built-up surface elevations and the combined presence of ground cover plantings and mulch.

* [http://dx.doi.org/10.1016/j.landurbplan.2017.02.017 Role of trees in urban stormwater management (Berland et al. 2017)]

* '''[https://www.sciencedirect.com/science/article/abs/pii/S0022169418306346?via%3Dihub Tree pit hydrology in Melbourne, Australia (Grey et al. 2018)]''' <ref>Grey, V., Livesley, S.J., Fletcher, T.D. and Szota, C. 2018. Tree pits to help mitigate runoff in dense urban areas. Journal of Hydrology, 565, pp.400-410. https://www.sciencedirect.com/science/article/abs/pii/S0022169418306346?via%3Dihub</ref>

* [https://www.sciencedirect.com/science/article/abs/pii/S0925857418302453?via%3Dihub Role of plants in bioretention performance (Dagenais et al. 2018)]

** Grey ''et al''. (2018), conducted a streetscape experiment to determine the runoff retention rate of tree pits in heavy [[Soil groups|clay soil]] with low exfiltration rates. Their research found that runoff retention is possible in even very dense urban streetscapes, and that sizing needs to be between 2.5% to 8% of the impervious catchment area (dependent upon tree pit exfiltration rates) to achieve 90% reduction in annual runoff.

* [https://www.sciencedirect.com/science/article/abs/pii/S0022169418306346?via%3Dihub Tree pit hydrology in Melbourne, Australia (Grey et al. 2018)]

* '''[https://ascelibrary.org/doi/10.1061/JSWBAY.0000865 Health of trees in bioretention (Tirpak et al. 2018)]'''<ref>Tirpak, R.A., Hathaway, J.M., Franklin, J.A. and Khojandi, A. 2018. The health of trees in bioretention: A survey and analysis of influential variables. Journal of Sustainable Water in the Built Environment, 4(4), p.04018011. https://ascelibrary.org/doi/10.1061/JSWBAY.0000865</ref>

* [https://onlinelibrary.wiley.com/doi/10.1002/eco.1813 Review of stormwater benefits of urban trees (Kuehler et al. 2017)]

**Tirpak ''et al.'' (2018), conducted a study on tree health in bioretention systems in southeastern U.S. Of the 6 species studied, only 1 showed greater health when grown in bioretention media compared to urban trees not planted in bioretention systems. Results show that species selection should be based on bioretention filter media analysis and compatability with the growing conditions found in bioretention systems.

* [https://ascelibrary.org/doi/10.1061/JSWBAY.0000865 Health of trees in bioretention (Tirpak et al. 2018)]

* '''[https://onlinelibrary.wiley.com/doi/10.1002/eco.1813 Review of stormwater benefits of urban trees (Kuehler et al. 2017)]'''<ref>Kuehler, E., Hathaway, J. and Tirpak, A. 2017. Quantifying the benefits of urban forest systems as a component of the green infrastructure stormwater treatment network. Ecohydrology, 10(3), p.e1813. https://www.srs.fs.usda.gov/pubs/ja/2017/ja_2017_kuehler_001.pdf</ref>

** Li, ''et al''. (2017), determine an effective means for leaf area density (LAD) estimation of a canopy of magnolia trees using high-resolution LiDAR data and ground measured leaf area index (LAI).

* '''[https://www.tandfonline.com/doi/full/10.1080/07011784.2017.1375865 Modelling rainfall interception by urban trees (Huang et al. 2017)]'''<ref>Huang, J.Y., Black, T.A., Jassal, R.S. and Lavkulich, L.L. 2017. Modelling rainfall interception by urban trees. Canadian Water Resources Journal/Revue canadienne des ressources hydriques, 42(4), pp.336-348. https://www.researchgate.net/profile/LesLavkulich/publication/320085997_Modelling_rainfall_interception_by_urban_trees/links/59fc87bf0f7e9b9968bdc715/Modelling-rainfall-interception-by-urban-trees.pdf</ref>

** Huang, ''et al''. (2017), developed an analytical model to compare rainfall interception rates between four deciduous tree species (white oak, Norway maple, green ash and cherry). The ratio of evaporation rate to rainfall rate was the most dynamic differing parameter amongst the trees selected. The study was able to provide some information on improved tree selection in urban environments.

* '''[https://www.nrcan.gc.ca/earth-sciences/land-surface-vegetation/biophysical-parameters/9162 Optical Leaf Area Index In-situ Measurement (Leblanc 2011)]<ref>Abuelgasim, A. A., & Leblanc, S. G. (2011). Leaf area index mapping in northern Canada. International journal of remote sensing, 32(18), 5059-5076. https://www.academia.edu/download/55035075/Leaf_area_index_mapping_in_northern_Canada.pdf'''</ref>

** Abuelgasim, A. and Leblanc, S. G. (2011), discuss how  NRCan have developed methods to measure the leaf density in vegetation canopies with minimum destructive sampling. The measured quantity, Leaf Area Index (LAI), is used in estimates of carbon absorption by plants.

* '''[https://www.wastormwatercenter.org/project/tree-project/ Washington Stormwater Center Tree Project]<ref>Washington Stormwater Center. 2022. Tree Project. https://www.wastormwatercenter.org/project/tree-project/'''</ref>

===Modelling tools===

===Modelling tools===

i-Tree is a free software suite developed by the USDA Forest Service and partners that assesses tree and forest structure, ecosystem services, and value of a community’s tree resources. See external links below for further details and tool downloads.

[https://www.itreetools.org/ i-Tree] is a free software suite developed by the USDA Forest Service and partners that assesses tree and forest structure, ecosystem services, and value of a community’s tree resources. See external links below for further details and tool downloads.

* [https://www.itreetools.org/tools iTree Tools overview]  

* [https://www.itreetools.org/tools iTree Tools Overview]  

* [https://www.itreetools.org/documents/552/International_iTree_Tools_Summary_17Jan2019.pdf iTree Tools international users summary]

* [https://www.itreetools.org/documents/552/International_iTree_Tools_Summary_17Jan2019.pdf iTree Tools international users summary]

* [http://www.itreetools.org/eco/international.php iTree Eco International]

* [http://www.itreetools.org/eco/international.php iTree Eco International]

*[https://citygreen.com/stratavault/ CityGreen - Stratavault]

*[https://citygreen.com/stratavault/ CityGreen - Stratavault]

*[http://cupolex.ca/ Cupolex]

*[http://cupolex.ca/ Cupolex]

*[http://www.deeproot.com/index.php Deeproot - Silva Cell]

*[http://www.deeproot.com/index.php Deeproot - Silva Cell]

*[https://greenblue.com/na/products/rootspace/ GreenBlue Urban - RootSpace]

*[https://greenblue.com/na/products/rootspace/ GreenBlue Urban - RootSpace]

*[https://www.storm-tree.com Storm-Tree]

*[https://www.storm-tree.com Storm-Tree]

Also see references as direct web page links above.

Also see references as direct web page links above.

[[Category:Green infrastructure]]

[[Category: Green infrastructure]]