Using urban trees as green infrastructure for our cities is arguably the most sustainable stormwater management solution available. The possibilities that exist to turn stormwater runoff from a hindrance to an opportunity are limitless. This presentation uses GreenBlue Urban’s 25 years of field experience, in conjunction with world-renowned researchers such as the University of Abertay Dundee and E2 Design Labs, to examine the opportunities available for integrating street tree planting with stormwater management systems for truly sustainable urban landscapes.
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Note: The following catalog of content covered in this webinar is time stamped to allow you to follow along or skip to sections of the video that are relevant to your questions. You can also search for content on this page using the FIND command in your browser (CTRL + F in Windows, Command + F in Mac OS.)
- Case Studies
In a forest environment, a tree is the only item above ground that intercepts water before it becomes storm water, and does something with it. It’s important to understand and replicate these benefits when designing an urban environment.
The average lifespan of a tree in an urban environment is 3 to 8 years.
50% of trees planted in urban areas do not reach their 10th birthday. Unfortunately, the biggest benefits from trees typically begin at 10 years, including:
Canopy collection of storm water
Evapotranspiration from root system into canopy
Health and wellbeing
Interdisciplinary collaboration in sustainable infrastructure (6:45):
- Landscape architect
- Civil engineer
- Urban designer
Challenges of green infrastructure in the urban environment include (7:20):
- Soil Compaction
Root growth (8:20)
Healthy root systems make for healthy trees and stormwater management.
Fibrous roots (thumb width or smaller) are critical to the health of the tree, as well as the benefits of stormwater management. The higher ratio of fibrous rooting means the higher stormwater take-up and pollutant reduction.
Root growth in forest-like conditions (9:20)
In a forest, most of the root zone will be in the top 12 to 24 inches of soil. (At 48 inches, conditions such as high compaction, anaerobic soils, and poor nutrient zones start taking effect.)
A tree’s root extension can easily be up to 2 or 3 times the diameter of the tree’s canopy.
Anything over 80% soil compaction restricts root growth.
To calculate a typical tree’s soil volume, multiply the tree’s canopy diameter at its mature state by 2 feet in depth.
Why we need tree protection (11:30)
Tree guards (12:00)
Make sure tree guards are:
- Large enough for the enhancement of a large tree (20 to 24 inches in diameter at the base and top)
- Not so high that they encroach into the tree’s limb system
Tree grates (12:55)
Foot traffic is the #1 killer of trees in the urban environment. That’s why ground protection of trees, as with tree grates, is critical.
Tree grates should:
- Have a 20- to 24-inch opening
- Allow for irrigation, aeration, and uncompacted soil – especially within the first 3 to 5 years.
Resin bonded stone products (14:55)
Why we need root management (15:30)
Root management means protection of the urban infrastructure that roots can potentially damage.
Ribbed root barriers (16:05)
Ribbed root barriers ensure that roots keep growing downward into soil, rather than upward into sidewalks and hardscapes.
Modular root barriers (16:52)
Applied around rootballs, modular root barriers prevent roots from girdling or swirling.
Why we need tree irrigation & aeration (17:57)
Hardscapes above urban trees cause the buildup of organic gases, which in turn cause root dieback.
Deep irrigation and aeration (19:00)
Aeration below ground maximizes irrigation into the rootball zone and disperses the buildup of gases.
Hardscape inlets (19:35)
Softscape inlets (19:45)
When putting softscape below hardscape, it’s critical to make sure it’s aerated and irrigated.
Smooth root barriers (21:05)
Smooth root barriers are meant to protect utilities from damage.
Why we need underground guying (21:40)
Staking can damage trees and pose a danger to pedestrians.
Rootball guying systems (22:30)
When specifying these types of systems, make sure there’s a strap or other material extending over the rootball to prevent the wires from cutting through.
Question: What’s the difference between ribbed and smooth root barriers? (23:30)
Answer: A ribbed barrier manages ribs downward and keeps them in the same growing zone. A smooth barrier simply protects other areas from root intrusion.
Question: How do deep-root watering systems compare with ring watering systems? (24:36)
Answer: These systems are all compatible and below round. The first ring, or loop, is typically installed 4 to 8 inches out from the rootball shoulder, and about 4 to 8 inches down, and is the watering system that helps establish the rootball after immediate transplanting. The secondary system is installed beneath the hardscape in order to draw the roots outward and remove organic gases. Shape and size of these systems isn’t necessarily important.
Why we need soil cells (25:50)
Soil cells provide uncompacted soil volume below ground to allow for healthy root growth.
Filling soil cells (28:30)
Soil cells infiltration (29:20)
Tree roots in soil cells after 4 years (30:50)
Engineered requirements of soil cells (31:15)
Note that soil cells also need to account for the wheel weight of vehicles.
Stormwater management (32:15)
Stormwater harvesting with low-impact development (LID) tree pits (32:29)
Note: These pits are not recommended in northern climates, where high quantities of salt are used for de-icing roads.
How LID tree pits work (34:00)
ArborFlow LID tree pits results (35:08)
Linear drains (37:45)
Curb inlets (37:50)
Stormwater storage (38:05)
The “3 P’s of sustainable infrastructure”: plan, provide, protect (39:07)
Linked tree pits may be used in (39:15):
- Parking lots
- Plazas & shared spaces
- Road medians
- Rooftops & on-structure
Pace University (40:45)
Chicago River Walk (41:10)
Hatcher Road (Phoenix, AZ) (41:30)
Emmen Center Square (Emmen, Netherlands) (42:31)
Delta Hotel (Ottawa, Ontario, Canada) (43:06)
Navy Pier (Chicago, IL) (43:43)
Leslie Street (Toronto, Ontario, Canada) (44:42)
What happens without correct design? (46:21)
Problems such as “containerized tree beds” and non-aerated soil
The first tree planted in soil cells (47:40)
Sustainable infrastructure is development that meets the needs of present society without compromising the ability of future generations to meet their own. (48:42)
Site review & installation (48:53)
Design services (49:00)
Resource Center: greenblue.com/resource-centre
CAD Drawings: greenblue.com/cad-drawings
Soil Volume Calculator: greenblue.com/soil-calculator
Conferences & Exhibitions/Presentations: greenblue.com/na/conferences/
Approaches for convincing clients to opt for sustainable infrastructure (50:25)
Jeremy recommends falling back on manufacturers of these types of systems for resources and case studies.
For a list of countries, cities, and states that accept these types of development practices, contact GreenBlue (52:50)