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]]}}

'''Stormwater tree trench installations include:'''

'''Stormwater tree trench installations include:'''

* Overlying impermeable or [[permeable pavements]]

* Overlying impermeable or [[permeable pavements]]

* Trees (tolerant to northern. urban conditions)

* Trees (tolerant to northern urban conditions)

* Planting soil

* Planting soil

* Modular soil support or "soil cell" structures (optional)

* Modular soil support or "soil cell" structures (optional)

==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===

Typical contributing drainage areas are between 150-300 m2 per tree, with a maximum of 450 m2 per tree.

Typical contributing drainage areas are between 150 to 300 m² per tree, with a recommended maximum of 450 m² per tree.  For optimal performance recommended ratios of impervious drainage area to pervious facility footprint area (I:P area ratio) range from 5:1 on low permeability soils (HSG C and D) to 15:1 on high permeability soils (HSG A and B).

===Setback from Buildings===

===Setback from Buildings===

===[[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.   

===Soil Volume===

===Soil Volume===

Each tree planted should have access to a minimum 30 m³ of soil volume, including the growing medium within the tree pit and growing or structural soil medium below adjacent supported pavement. If more than one tree shares the same trench a minimum 20 m³ of soil per tree may be acceptable.

Each tree planted should have access to a minimum 30 m³ of soil volume, including the growing medium within the tree pit and growing or structural soil medium below adjacent supported pavement. If more than one tree shares the same trench a minimum 20 m3 of soil per tree may be acceptable. It should be noted that structural soils are mostly filled with rock and will therefore have much lower soil volumes.  However, trees have been found to grow reasonably well in these soils because roots only occupy a portion of the total soil medium. 

 

 

 

 

===Modular Soil Support Systems===

===Modular Soil Support Systems===

===Structural Soil Medium===

===Structural Soil Medium===

Structural soil is an engineered soil medium that can be compacted to support sidewalk or roadway pavement installation requirements while also permitting tree root growth. Structural soil medium filled trenches are installed adjacent to tree pits to provide room for tree roots to spread out under the supported pavement portion of the tree trench.

Structural soil is an engineered soil medium that can be compacted to support sidewalk or roadway pavement installation requirements while also permitting tree root growth. Structural soil medium filled trenches are installed adjacent to tree pits to provide room for tree roots to spread out under the supported pavement portion of the tree trench.  The available soil for root growth ranges from 25 to 33% depending on the stone size.  Larger stone sizes will typically allow for greater soil volume.

===Structural Concrete Panels===

===Structural Concrete Panels===

<imagemap>

<imagemap>

File:SWTT Low Perm Soil Cells Final.png|thumb|left|450px|'''Tree trench with soil cells on low permeability subsoil''' - This tree trench configuration features an overflow outlet storm sewer pipe connection in the catch basin and underdrain to allow excess water to leave the practice. The underdrain perforated pipe is embedded in the aggregate base due to the slow drainage rate of the subsoil. Solid standpipes connected to the underdrain and distribution perforated pipes provide access for inspection and maintenance tasks over the lifespan of the facility. <span style="color:red">'''''Note''': The following is an "image map", feel free to explore the image with your cursor and click on highlighted labels that appear to take you to corresponding pages on the Wiki.''</span>

File:SWTT Low Perm Soil Cells Final.png|thumb|left|400px|'''Tree trench with soil cells on low permeability subsoil''' - This tree trench configuration features an overflow outlet storm sewer pipe connection in the catch basin and underdrain to allow excess water to leave the practice. The underdrain perforated pipe is embedded in the aggregate base due to the slow drainage rate of the subsoil. Solid standpipes connected to the underdrain and distribution perforated pipes provide access for inspection and maintenance tasks over the lifespan of the facility. <span style="color:red">'''''Note''': The following is an "image map", feel free to explore the image with your cursor and click on highlighted labels that appear to take you to corresponding pages on the Wiki.''</span>

rect 1494 1440 1584 1530 [[Overflow|Overflow to Underdrain]]  

rect 1494 1440 1584 1530 [[Overflow|Overflow to Underdrain]]  

<imagemap>

<imagemap>

File:SWTT High Perm Soil Cells Final.png|thumb|right|450px|'''Tree trench with soil cells on high permeability subsoil''' - This tree trench configuration features an overflow outlet storm sewer pipe connection in the catch basin and underdrain to allow excess water to leave the practice. The underdrain perforated pipe is embedded in the growing medium which factors in the fast drainage rate of the subsoil. A monitoring well screened within the aggregate base of the trench is included so drainage performance can be evaluated over its operating lifespan. <span style="color:red">'''''Note''': The following is an "image map", feel free to explore the image with your cursor and click on highlighted labels that appear to take you to corresponding pages on the Wiki.''</span>

File:SWTT High Perm Soil Cells Final.png|thumb|right|400px|'''Tree trench with soil cells on high permeability subsoil''' - This tree trench configuration features an overflow outlet storm sewer pipe connection in the catch basin and underdrain to allow excess water to leave the practice. The underdrain perforated pipe is embedded in the growing medium which factors in the fast drainage rate of the subsoil. A monitoring well screened within the aggregate base of the trench is included so drainage performance can be evaluated over its operating lifespan. <span style="color:red">'''''Note''': The following is an "image map", feel free to explore the image with your cursor and click on highlighted labels that appear to take you to corresponding pages on the Wiki.''</span>

rect 1494 1440 1584 1530 [[Overflow|Overflow to Underdrain]]  

rect 1494 1440 1584 1530 [[Overflow|Overflow to Underdrain]]  

<imagemap>

<imagemap>

File:SWTT Struct Soil Med High Perm Final.png|thumb|center|450px|'''Tree Trench with structural soil medium on high permeability subsoil''' - This tree trench configuration features structural soil medium as pavement support, as an alternative to soil cells that improves adaptability around utilities.  An overflow outlet storm sewer pipe connection in the catch basin and underdrain are included to allow excess water to leave the practice. The underdrain perforated pipe is embedded in the growing medium which factors in the fast drainage rate of the subsoil. A monitoring well screened within the aggregate base of the trench is included so drainage performance can be evaluated over its operating lifespan.  <span style="color:red">'''''Note''': The following is an "image map", feel free to explore the image with your cursor and click on highlighted labels that appear to take you to corresponding pages on the Wiki.''</span>

File:SWTT Struct Soil Med High Perm Final.png|thumb|center|400px|'''Tree Trench with structural soil medium on high permeability subsoil''' - This tree trench configuration features structural soil medium as pavement support, as an alternative to soil cells that improves adaptability around utilities.  An overflow outlet storm sewer pipe connection in the catch basin and underdrain are included to allow excess water to leave the practice. The underdrain perforated pipe is embedded in the growing medium which factors in the fast drainage rate of the subsoil. A monitoring well screened within the aggregate base of the trench is included so drainage performance can be evaluated over its operating lifespan.  <span style="color:red">'''''Note''': The following is an "image map", feel free to explore the image with your cursor and click on highlighted labels that appear to take you to corresponding pages on the Wiki.''</span>

rect 1605 3079 1983 3500 [[Stormwater Tree Trenches: Specifications|Structural Soil Medium]]

rect 1605 3079 1983 3500 [[Stormwater Tree Trenches: Specifications|Structural Soil Medium]]

==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.

===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==

Tree trenches have fewer maintenance requirements than bioretention cells or bioswales, but maintenance is still critical to their success. The most critical maintenance task is the removal of trash, sediment and debris accumulated in inlet structure sumps, gravel diaphragms and tree openings at curb cuts. This should be done at least once per year, however the frequency will depend on pavement uses, traffic volumes and tree canopy size. Inspect new trenches closely during the first two years of operation to measure the rate of accumulation and set an optimal maintenance frequency.  

Tree trenches have fewer maintenance requirements than bioretention cells or bioswales, but maintenance is still critical to their success. The most critical maintenance task is the removal of trash, sediment and debris accumulated in inlet structure sumps, gravel diaphragms and tree openings at curb cuts. This should be done at least once per year, however the frequency will depend on pavement uses, traffic volumes and tree canopy size. Inspect new trenches closely during the first two years of operation to measure the rate of accumulation and set an optimal maintenance frequency.  

See further details here: [[Stormwater Tree Trenches: Maintenance]]

See further details here: [[Stormwater Tree Trenches: 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.<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

Performance and Risk Assessment - Technical Report. https://cvc.ca/wp-content/uploads//2021/07/TechReport_CPW_Final.pdf</ref>

Performance and Risk Assessment - Technical Report. https://cvc.ca/wp-content/uploads//2021/07/TechReport_CPW_Final.pdf</ref>

</br>

</br>

{|class="wikitable"

{|class="wikitable"

|+Volumetric runoff reduction from bioretention

|+Volumetric runoff reduction from Stormwater Tree Trench/Bioretention

|-

|-

!'''LID Practice'''

!'''LID Practice'''

|-

|-

|rowspan="4" style="text-align: center;" | Bioretention without underdrain

|rowspan="4" style="text-align: center;" | Bioretention without underdrain

|style="text-align: center;" |Connecticut

|style="text-align: center;" |Connecticut

|style="text-align: center;" |99%

|style="text-align: center;" |99%

|style="text-align: center;" |70%

|style="text-align: center;" |70%

|style="text-align: center;" |Emerson and Traver (2004)<ref>Emerson, C., Traver, R. 2004. The Villanova Bio-infiltration Traffic Island: Project Overview. Proceedings of 2004 World Water and Environmental Resources Congress (EWRI/ASCE). Salt Lake City, Utah, June 22 – July 1, 2004. https://ascelibrary.org/doi/book/10.1061/9780784407370</ref>

|style="text-align: center;" |Emerson and Traver (2004)<ref>Emerson, C., Traver, R. 2004. The Villanova Bio-infiltration Traffic Island: Project Overview. Proceedings of 2004 World Water and Environmental Resources Congress (EWRI/ASCE). Salt Lake City, Utah, June 22 – July 1, 2004. https://ascelibrary.org/doi/book/10.1061/9780784407370</ref>

|-

|-

|rowspan="8" style="text-align: center;" | Bioretention with underdrain

|rowspan="8" style="text-align: center;" | Bioretention with underdrain

|style="text-align: center;" |'''<u><span title="Note: Runoff reduction estimates are based on differences in runoff volume between the practice and a conventional impervious surface over the period of monitoring.">82%*</span></u>'''

|style="text-align: center;" |'''<u><span title="Note: Runoff reduction estimates are based on differences in runoff volume between the practice and a conventional impervious surface over the period of monitoring.">82%*</span></u>'''

|style="text-align: center;" |Mahmoud, ''et al.'' (2019)<ref>Mahmoud, A., Alam, T., Rahman, M.Y.A., Sanchez, A., Guerrero, J. and Jones, K.D. 2019. Evaluation of field-scale stormwater bioretention structure flow and pollutant load reductions in a semi-arid coastal climate. Ecological Engineering, 142, p.100007. https://www.sciencedirect.com/science/article/pii/S2590290319300070</ref>

|style="text-align: center;" |Mahmoud, ''et al.'' (2019)<ref>Mahmoud, A., Alam, T., Rahman, M.Y.A., Sanchez, A., Guerrero, J. and Jones, K.D. 2019. Evaluation of field-scale stormwater bioretention structure flow and pollutant load reductions in a semi-arid coastal climate. Ecological Engineering, 142, p.100007. https://www.sciencedirect.com/science/article/pii/S2590290319300070</ref>

|-

|-

|style="text-align: center;" |Virginia

|style="text-align: center;" |Virginia

|style="text-align: center;" |DeBusk and Wynn (2011)<ref>DeBusk, K.M. and Wynn, T.M., 2011. Storm-water bioretention for runoff quality and quantity mitigation. Journal of Environmental Engineering, 137(9), pp.800-808. https://www.webpages.uidaho.edu/ce431/Articles/DeBusk-ASCE-2011.pdf</ref>

|style="text-align: center;" |DeBusk and Wynn (2011)<ref>DeBusk, K.M. and Wynn, T.M., 2011. Storm-water bioretention for runoff quality and quantity mitigation. Journal of Environmental Engineering, 137(9), pp.800-808. https://www.webpages.uidaho.edu/ce431/Articles/DeBusk-ASCE-2011.pdf</ref>

|-

|-

|style="text-align: center;" |China

|style="text-align: center;" |Maryland and North Carolina

|style="text-align: center;" |'''<u><span title="Note: Runoff reduction estimates are based on SWMM and RECARGA models applied to generate the runoff reduction percentages of a bioretention installation near one of China's and  expressway service area.">35 to 75%*</span></u>'''

|style="text-align: center;" |20 to 50%

|style="text-align: center;" |Gao, ''et al.'' (2018)<ref>Gao, J., Pan, J., Hu, N. and Xie, C., 2018. Hydrologic performance of bioretention in an expressway service area. Water Science and Technology, 77(7), pp.1829-1837.</ref>

|style="text-align: center;" |Li ''et al.'' (2009). <ref>Li, H., Sharkey, L.J., Hunt, W.F., and Davis, A.P. 2009. Mitigation of Impervious Surface Hydrology Using Bioretention in North Carolina and Maryland. Journal of Hydrologic Engineering. Vol. 14. No. 4. pp. 407-415.</ref>

|-

|-

|style="text-align: center;" |North Carolina

|style="text-align: center;" |North Carolina

|style="text-align: center;" |33 to 50%

|style="text-align: center;" |33 to 50%

|style="text-align: center;" |Hunt and Lord (2006). <ref>Hunt, W.F. and Lord, W.G. 2006. Bioretention Performance, Design, Construction, and Maintenance. North Carolina Cooperative Extension Service Bulletin. Urban Waterways Series. AG-588-5. North Carolina State University. Raleigh, NC.</ref>

|style="text-align: center;" |Hunt and Lord (2006). <ref>Hunt, W.F. and Lord, W.G. 2006. Bioretention Performance, Design, Construction, and Maintenance. North Carolina Cooperative Extension Service Bulletin. Urban Waterways Series. AG-588-5. North Carolina State University. Raleigh, NC.</ref>

|-

|-

|rowspan="5" style="text-align: center;" | Bioretention with underdrain & liner

|rowspan="5" style="text-align: center;" | Bioretention with underdrain & liner

|style="text-align: center;" |15 to 34%

|style="text-align: center;" |15 to 34%

|style="text-align: center;" |<span class="plainlinks">[https://sustainabletechnologies.ca/app/uploads/2019/10/STEP_Bioretention-Synthesis_Tech-Brief-New-Template-2019-Oct-10.-2019.pdf STEP (2019)]</span> <ref>STEP. 2019. Comparative Performance Assessment of Bioretention in Ontari0. Technical Brief. https://sustainabletechnologies.ca/app/uploads/2019/10/STEP_Bioretention-Synthesis_Tech-Brief-New-Template-2019-Oct-10.-2019.pdf.</ref>

|style="text-align: center;" |<span class="plainlinks">[https://sustainabletechnologies.ca/app/uploads/2019/10/STEP_Bioretention-Synthesis_Tech-Brief-New-Template-2019-Oct-10.-2019.pdf STEP (2019)]</span> <ref>STEP. 2019. Comparative Performance Assessment of Bioretention in Ontari0. Technical Brief. https://sustainabletechnologies.ca/app/uploads/2019/10/STEP_Bioretention-Synthesis_Tech-Brief-New-Template-2019-Oct-10.-2019.pdf.</ref>

|-

|-

|style="text-align: center;" |Queensland, Australia  

|style="text-align: center;" |Queensland, Australia  

|style="text-align: center;" |15 to 83%

|style="text-align: center;" |15 to 83%

|style="text-align: center;" |Hatt ''et al.'' (2009). <ref>Hatt, B. E., Fletcher, T. D., & Deletic, A. 2009. Hydrologic and pollutant removal performance of stormwater biofiltration systems at the field scale. Journal of Hydrology, 365(3), 310-321. doi:http://dx.doi.org/10.1016/j.jhydrol.2008.12.001</ref>

|style="text-align: center;" |Hatt ''et al.'' (2009). <ref>Hatt, B. E., Fletcher, T. D., & Deletic, A. 2009. Hydrologic and pollutant removal performance of stormwater biofiltration systems at the field scale. Journal of Hydrology, 365(3), 310-321. doi:http://dx.doi.org/10.1016/j.jhydrol.2008.12.001</ref>

|-

|-

| colspan="2" style="text-align: center;" |'''<u><span title="Note: This estimate is provided only for the purpose of initial screening of LID practices suitable for achieving stormwater management objectives and targets.  Performance of individual facilities will vary depending on site specific contexts and facility design parameters and should be estimated as part of the design process and submitted with other documentation for review by the approval authority." >Runoff Reduction Estimate*</span></u>'''

| colspan="2" style="text-align: center;" |'''<u><span title="Note: This estimate is provided only for the purpose of initial screening of LID practices suitable for achieving stormwater management objectives and targets.  Performance of individual facilities will vary depending on site specific contexts and facility design parameters and should be estimated as part of the design process and submitted with other documentation for review by the approval authority." >Runoff Reduction Estimate*</span></u>'''

===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.sciencedirect.com/science/article/abs/pii/S0925857418302453?via%3Dihub Role of plants in bioretention performance (Dagenais et al. 2018)]<ref>Dagenais, D., Brisson, J. and Fletcher, T.D. 2018. The role of plants in bioretention systems; does the science underpin current guidance?. Ecological Engineering, 120, pp.532-545. http://www.phytotechno.com/wp-content/uploads/2018/10/Dagenais-2018-Bioretention.pdf</ref>

* '''[https://www.sciencedirect.com/science/article/abs/pii/S0048969721063749?via%3Dihub Stormwater runoff volume reduction benefits of urban street tree canopy (Selbig et al., 2022)]''' <ref> Selbig, W.R., Loheide II, S.P., Shuster, W., Scharenbroch, B.C., Coville, R.C., Kruegler, J., Avery, W., Haefner, R., Nowak, D. Quantifying stormwater runoff volume reduction benefit of urban street tree canopy. Science of the Total Environment. v.806 (2022) 151296. https://www.sciencedirect.com/science/article/abs/pii/S0048969721063749?via%3Dihub </ref>

* [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>

** In a paired-catchment study design involving medium density residential areas in Wisconsin, with removal of 29 mature green ash and Norway maple street trees as the treatment, tree removal resulted in a 4% increase in runoff volume over the evaluation period, while peak discharge was generally not affected.  Runoff volume reduction benefit of the street tree canopy was estimated at 6376 L per tree, which is similar to values reported in previous studies based largely on simulation.

* [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://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>

* [http://dx.doi.org/10.1016/j.landurbplan.2017.02.017 Role of trees in urban stormwater management (Berland et al. 2017)]<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?X-Amz-Security-Token=IQoJb3JpZ2luX2VjEKX%2F%2F%2F%2F%2F%2F%2F%2F%2F%2FwEaCXVzLWVhc3QtMSJIMEYCIQCZXwSBcpYyzpM2wUzYeieJafT7aphyPRju0dqWpB2RAQIhAK6byagfy%2FvfGH2oYwWn5h9ZB5bTaWHjRCYyYTRf4iPNKvoDCB4QBBoMMDU5MDAzNTQ2ODY1IgyTqnqHLxo%2BGo9Hrmwq1wO9fUBqtr6opBWeX1hXNSOf8XwHPkg%2B9j42cslzhcjuld3toKrv6U9cOfI%2BPPOjMl09uxu8ogCeTtHcu3%2FP0l7ORgnyBtPUBxg9SenFp%2FTtPUgAZHXnJ%2BtTo%2BJJziRQFa5Pnq%2FsivKl%2Bl3M3czMgfswR9cfyS6ER1DpITUnCqbegcBxf8Lwds5yBJ8k2DGC3wMVML%2BolK7Xh%2BfKi9Lwm4UnaqCo2VBwOLcGqesCQvWGuef9qr%2Fb%2F8x1mQHa94rnJuYv3x%2FP1%2F1vZqdpNt48PLBSc1f%2BTK7dcoLBHVWrJKDVUNp%2B5EDTfOBDYk8njPsdr2mUbKUkMT9fl3hHyyoTk7bFXld9jO6mroO3ln1R9%2BKC%2BjhCVUH2WqdrAb3HDSZI6A9YWIunoovQAfgOiF%2BMQv2OKIO8vqb8pe2UGBfd9p%2FZph5ZOWS9Stl1VjozTUbuzJYH%2F0mFIePjy0C0ewzYqWlOGwtOnm04afyZvVtpDFZLIo%2BIj80kJnNecQMeyhTzeudP9HsDh1rwb8BkBeU%2FY938GUemN5tWuBsI9VeaupzS58wS%2BXvA0C6L9OPDfIi4q9zWUmktkpFU%2BznE1UcdY%2BpYa5wh0uQpPEbhL5nGSVr9yKRJlDKA2T4wnOWukQY6pAHSwT%2B7lEfmT1yqwrBgB%2B2OcFEYLDjKP1VG83QfO6dcaVt4bsKYvUeoEgApo3wBhRS%2FF9sCHLRDlApx0JJXqsgjK04%2F8jv1n3MXGVYIRitA4joeEPIvIBjozZ9PGZDMnJ4C5ZzGV%2F17BOu5YurV8LuLLXYGKKloun%2BloUqE%2F4z77DPqk4AMUQ%2BK4hkHHjyzetklwV2mpsAb2Rfo8elLfAPPENt5cg%3D%3D&X-Amz-Algorithm=AWS4-HMAC-SHA256&X-Amz-Date=20220311T215245Z&X-Amz-SignedHeaders=host&X-Amz-Expires=300&X-Amz-Credential=ASIAQ3PHCVTYXX7YBEHO%2F20220311%2Fus-east-1%2Fs3%2Faws4_request&X-Amz-Signature=1da7e68941bd0c9178426037f040f8654137a32a7b4e64d8169b55689a4da823&hash=5ba75d8d6cfb95b5405cfe9a59e72dff61308278b56f9a019f3b1ac1f4ba515f&host=68042c943591013ac2b2430a89b270f6af2c76d8dfd086a07176afe7c76c2c61&pii=S0169204617300464&tid=pdf-043e9887-4b0e-4934-9600-9450d2300884&sid=a7e291ac43cbb7419c8b3cb040531726e2a2gxrqa&type=client</ref>

** 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.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/Les-Lavkulich/publication/320085997_Modelling_rainfall_interception_by_urban_trees/links/59fc87bf0f7e9b9968bdc715/Modelling-rainfall-interception-by-urban-trees.pdf</ref>

* '''[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://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>

** 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.

* [https://www.mdpi.com/2072-4292/9/11/1202 Estimating tree leaf area density with LIDAR (Li et al. 2017)]<ref>Li, S., Dai, L., Wang, H., Wang, Y., He, Z., & Lin, S. (2017). Estimating leaf area density of individual trees using the point cloud segmentation of terrestrial LiDAR data and a voxel-based model. Remote sensing, 9(11), 1202. https://www.mdpi.com/2072-4292/9/11/1202/pdf</ref>

* '''[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.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>

** 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.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>

* '''[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>

**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://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>

** Kuehler, ''et al''. (2017) in their literature review found that urban trees can retain sizable amounts of annual rainfall in their crowns, delay the flow of stormwater runoff, substantially increase the infiltration capacity of urban soils, and provide transpiration of sequestered runoff. Tree canopy effectiveness is highest during short, low‐intensity storms and lower as rainfall volume and intensity increases.

* '''[https://www.mdpi.com/2072-4292/9/11/1202 Estimating tree leaf area density with LIDAR (Li et al. 2017)]<ref>Li, S., Dai, L., Wang, H., Wang, Y., He, Z., & Lin, S. (2017). Estimating leaf area density of individual trees using the point cloud segmentation of terrestrial LiDAR data and a voxel-based model. Remote sensing, 9(11), 1202. https://www.mdpi.com/2072-4292/9/11/1202/pdf'''</ref>

* '''[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===

*[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]]