Line 24: | Line 24: | ||
In addition to runoff reduction and stormwater treatment, street trees and tree boxes provide a range of community benefits. Trees contribute to air pollution reduction, <span title="The process of capturing and storing atmospheric carbon dioxide.> '''carbon sequestration'''</span>, reduction in <span title="an urban area having higher average temperature than its rural surroundings owing to the greater absorption, retention, and generation of heat by its buildings, pavements, and human activities."> '''heat island'''</span> effect, habitat creation for wildlife, and can be used as tools for <span title="Adjustments in ecological, social, or economic systems in response to actual or expected climatic stimuli and their effects or impacts."> '''climate adaptation'''</span>. <span title="Green stormwater infrastructure (GSI) describes practices that use natural systems (or engineered systems that mimic or use natural processes) to capture, clean, and infiltrate stormwater; shade and cool surfaces and buildings; reduce flooding, create wildlife habitat; and provide other services that improve environmental quality and communities’ quality of life. (City of Tucson)"> '''Green stormwater infrastructure'''</span> (GSI) trees are often planted in highly visible areas and are subject to public interaction, vandalism, and winter <span title="Deicing typically refers to removal of salt from impervious surfaces, such as roads, driveways, parking lots, and sidewalks. Chemicals, most commonly sodium chloride, are often used for deicing."> '''deicing'''</span>, but trees typically remain resilient with proper maintenance. | In addition to runoff reduction and stormwater treatment, street trees and tree boxes provide a range of community benefits. Trees contribute to air pollution reduction, <span title="The process of capturing and storing atmospheric carbon dioxide.> '''carbon sequestration'''</span>, reduction in <span title="an urban area having higher average temperature than its rural surroundings owing to the greater absorption, retention, and generation of heat by its buildings, pavements, and human activities."> '''heat island'''</span> effect, habitat creation for wildlife, and can be used as tools for <span title="Adjustments in ecological, social, or economic systems in response to actual or expected climatic stimuli and their effects or impacts."> '''climate adaptation'''</span>. <span title="Green stormwater infrastructure (GSI) describes practices that use natural systems (or engineered systems that mimic or use natural processes) to capture, clean, and infiltrate stormwater; shade and cool surfaces and buildings; reduce flooding, create wildlife habitat; and provide other services that improve environmental quality and communities’ quality of life. (City of Tucson)"> '''Green stormwater infrastructure'''</span> (GSI) trees are often planted in highly visible areas and are subject to public interaction, vandalism, and winter <span title="Deicing typically refers to removal of salt from impervious surfaces, such as roads, driveways, parking lots, and sidewalks. Chemicals, most commonly sodium chloride, are often used for deicing."> '''deicing'''</span>, but trees typically remain resilient with proper maintenance. | ||
− | O&M of tree trenches and boxes generally requires a low level of effort and expertise, and street trees can have life spans of up to 60 years ( | + | O&M of tree trenches and boxes generally requires a low level of effort and expertise, and street trees can have life spans of up to 60 years ([https://www.chesapeakebay.net/documents/Urban_Tree_Canopy_EP_Report_WQGIT_approved_final.pdf Cappiella et al.], 2016). <span title="Green stormwater infrastructure is designed to mimic nature and capture rainwater where it falls. Green infrastructure reduces and treats stormwater at its source while while also providing multiple community benefits such as improvements in water quality, reduced flooding, habitat, carbon capture, etc."> '''Green infrastructure'''</span> managers do share common issues and concerns related to trees. The most common O&M concerns for tree trenches and tree boxes include |
*general poor health, | *general poor health, | ||
*insufficient water for growth, | *insufficient water for growth, |
This page provides guidance for operation and maintenance (O&M) of tree trenches and tree boxes. A tree trench is a bioretention practice that contains one or more trees. Tree trenches and boxes may be designed as infiltration or filtration (underdrained) systems.
Supplemental information can be found on the page called Operation and maintenance of tree trenches and tree boxes - supplemental information. Supplemental information includes the following.
In addition to runoff reduction and stormwater treatment, street trees and tree boxes provide a range of community benefits. Trees contribute to air pollution reduction, carbon sequestration, reduction in heat island effect, habitat creation for wildlife, and can be used as tools for climate adaptation. Green stormwater infrastructure (GSI) trees are often planted in highly visible areas and are subject to public interaction, vandalism, and winter deicing, but trees typically remain resilient with proper maintenance.
O&M of tree trenches and boxes generally requires a low level of effort and expertise, and street trees can have life spans of up to 60 years (Cappiella et al., 2016). Green infrastructure managers do share common issues and concerns related to trees. The most common O&M concerns for tree trenches and tree boxes include
The sections below describe best practices to prevent or minimize these common problems.
Tree trenches and tree boxes have a very small footprint and should be designed to treat a relatively small drainage area. Surface area and surface area to drainage area ratio are key design characteristics. Design specifications will vary based on the selected filter media and filter box manufacturer. Properly sizing and designing the tree box will help prevent O&M issues. Designers should consider:
Designers should also consider the maintenance schedules and tasks when locating tree trenches or tree boxes on their site. The small surface area of tree boxes makes them versatile, however, they should be placed within areas that are easily accessible to ensure proper maintenance. Maintenance of tree trenches and tree boxes does not require large or heavy equipment, but routine maintenance should be expected once or twice a year. Designers can incorporate solutions to facilitate these maintenance activities:
Designers should consult and include any local requirements regarding green infrastructure. O&M considerations often depend on whether the practice is located on public land, private land, or in the public right of way. For example, plantings in the public right of way that conflict with any traffic safety considerations could require increased O&M, such as pruning or complete removal.
The designer should also provide a site-specific O&M plan that includes the following:
Additional information that should be included in O&M plans is described in the “Post-Construction Phase O&M Considerations” section. Example O&M plans are also provided further down.
Proper construction methods and sequencing play a significant role in reducing O&M problems. Some key items during the construction phase include:
Post-construction maintenance is performed on tree trenches and tree boxes to maintain proper infiltration, filtration, and to promote healthy vegetation. Immediately after construction, short-term maintenance goals include efforts to establish and keep the tree healthy. Not all trees are guaranteed to survive the establishment phase, so care should be taken to inspect the health following construction. Important post-construction considerations are provided below.
Overview and schedule of general maintenance activities for tree trenches and tree boxes
Link to this table
Activity | Frequency | Time period | Level of effort | O&M benefita |
---|---|---|---|---|
Check that there is no ponding within the box or trench. | At least twice after storm events > 0.5 inches | Within the first 6 months | 1-2 hours | 1,5 |
Check for evidence of clogging in the media. | At least twice after storm events > 0.5 inches | Within the first 6 months | 1-2 hours | 1 |
Supplemental watering, during drier periods, particularly if keeping stormwater offline trees are established. | 1/week initially | During first two months of the growing season | 1-2 hours | 2,3,4,5,6 |
As needed | First growing season | 1-2 hours | 2,3,4,5,6 | |
Remove any weeds present | As needed | First growing season | 1-2 hours | 2,3,4,5,6 |
Remove any trash or debris | As needed | First growing season | 1-2 hours | 1,2,3,4,5,6 |
Add mulch if layer is less than 3 inchesb | As needed | First growing season | 1-2 hours | 4,5 |
Clean root collar | Annually | During growing season | 1-2 hours | 1 |
Remove stakes | As needed | End of growing season | 1-2 hours | 5 |
Inspect tree health | Biannually and after large storms | First growing season | 1-2 hours | 1,2,5,6 |
Activity | Frequency | Time period | Level of effort | O&M benefita |
Check that there is no ponding within the box or trench. | Biannually | Any time when ground is not frozen | 1-2 hours | 1,5 |
Check for evidence of clogging | Biannually | In spring and fall | 1-2 | 1 |
Supplemental watering during drier periods | As needed or when soil is dry 3 inches below the surface | Dry periods until roots are established | 1-2 hours | 2,3,4,5,6 |
Remove any weeds present | As needed | During growing season | 1-2 hours | 2,3,4,5,6 |
Remove any trash or debris | As needed | Any time | 1-2 hours | 1,2,3,4,5,6 |
Add mulch if layer is less than 3 inches | Annually | During growing season | 1-2 hours | 4,5 |
Remove stakes (if still present) | Once | End of second growing season | 1-2 hours | 5 |
Prune excess growth |
|
End of winter or early spring | 1-2 hours | 2,5,6 |
Inspect tree health and safety | Biannually and after large storms | During growing season | 1-2 hours | 1,2,5,6 |
Activity | Frequency | Time period | Level of effort | O&M benefita |
After long term operation of the practice, some occasional and infrequent maintenance activities might be required, such as tree or media replacement. | As needed | As needed | Could be significant depending on the activity | 1,2,3,4,5,6 |
aKey to Maintenance Benefits:
|
Common problems and how to troubleshoot them for tree trenches and tree boxes
Link to this table
Symptom | Possible causes | Solution |
---|---|---|
Standing water within the infiltration area for more than 48 hours | This might be because a pretreatment is no longer working, or there are excessive sediment loads due to erosion or high sediment loads from the contributing area. |
|
Rainwater does not appear to flow to the infiltration/filtration area | Leaves, sediment, trash, or plant debris may be blocking the flow path to the inlet | Remove these materials on a regular basis |
Tree is not growing or shows signs of poor health during inspections |
|
Consult with an arborist. Check that plants are suited to the local conditions. |
Erosion or scouring around the inlet | Flow is obstructed by debris or improper grading | Correct for drainage and flow path issues to make sure flows are evenly distributed. Make sure the flow paths are unobstructed |
Maintenance costs will vary on a number of factors, including but not limited to:
Maintenance costs for trees and tree boxes should be relatively low compared to other green infrastructure practices, partially due to its size. Routine maintenance can take as little as 30 minutes per unit and does not require any special training, tools, or machinery. Because routine maintenance does not require any specialized training, the range of annual maintenance cost is around $100-$500 (CRWA). A study published in 2017 by ASCE describes the annual maintenance cost for a tree planter to be $260 per year, based on 2015 data from Fort Collins, CO (Clary, 2017).
Additional Detailed O&M Information
Example O&M Plans, Checklists, Reports, and Maintenance Agreements for tree trenches and tree boxes