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Building a Healthier Tomorrow with
Passively Irrigated Street Trees &
Open Space
Sally Boer, Dr Peter Breen, Dr Dale Browne, Dylan
Cain, Steve Buck – E2Designlab
Glenn Browning – Healthy Land and Water- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
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Passive Watering – Self watering –
Passive Irrigation – Water Wise
Passive Watering - What & Why
Tree Pits – modelling & results
Wicking Beds – modelling & results
What’s Next - Healthy Land & Water
Initiatives
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Self Watering = get water where it is
needed and let nature do the rest
PASSIVELY WATERED
TREE PITS
What’s wrong with this picture?
Constrained tree pit and sealed surface = unhealthy tree and limited canopy
Conventional drainage = missed opportunity for passive irrigation and stormwater treatment
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Soil
volu
me
(m3)
Tree canopy diameter (m)
Comparison of soil volume, canopy and diameter for a containerised tree pit - Brisbane
soil volume for frequent irrigation (weekly) soil volume for no irrigation
Base case
Test case: Enhanced tree pit with passive irrigation
Step-change in expected tree
canopy cover
Hitchmough, J. 1994
Research – Tree Growth
• “Trees in pits with an underdrain showed double the growth of conventionally planted street trees receiving no stormwater.”
• “Tree growth can be substantially increased by directing stormwater into tree pits, however, waterlogging conditions should be avoided”
Economic Benefit
Lyndal Plant – University of Queensland, Urban Forester
Andrew Coutts and Nigel Tapper, CRC Water Sensitive Cities
Urban Heat Island
TREE PIT MODELLING
Tree Pit Modelling
∕ Rainfall Analysis - to confirm the most appropriate rainfall data set for each climatic region
∕ Soil Moisture Modelling -evapotranspiration modelling and soil moisture data analysis to determine to occurrence of overly saturated conditions (too wet) and identification of dry spells below wilting point (too dry)
∕ MUSIC Modelling - water quality modelling to demonstrate stormwater pollutant removal performance
Modelling Variables
∕ Treatment to catchment area ratio (TCAR): 1% to 10%
∕ MUSIC Potential evapotranspiration factor (PET): 1.50 (low to medium water use trees) and 1.85 (high water use trees)
∕ Planting media: Filter media (100 mm/hr hydraulic conductivity) and landscape topsoils (50 mm/hr hydraulic conductivity)
∕ Submerged zone (0.3m deep): with and without
Soil Moisture Modelling & Analysis
∕ Accelerated Analysis Tool - involves
several steps:
– Numerous model simulations and the
generation of long time series of soil
moisture data from each model run
– Preparation of graphs for cumulative
frequency of exceedance
– Preparation of graphs for spells
below/above specified thresholds
– Collation of results for comparison
Suitable TCARs
Min Max Min Max Min Max Min Max Min Max Min Max
A Yes Sandy Loam Low N/A N/A 4% 10% N/A N/A 3% 10% 4% 10% 3% 10%
B Yes Sandy Loam High N/A N/A 4% 7% N/A N/A 3% 10% 4% 10% 3% 10%
C Yes Loamy Sand Low 7% 10% 3% 8% 3% 10% 3% 10% 3% 10% 2% 10%
D Yes Loamy Sand High 7% 10% 3% 7% 3% 10% 3% 10% 3% 10% 2% 10%
E No Sandy Loam Low N/A N/A 4% 6% N/A N/A 3% 10% 4% 10% 3% 10%
F No Sandy Loam High N/A N/A 4% 4% N/A N/A 3% 10% 4% 10% 3% 10%
G No Loamy Sand Low 7% 10% 3% 5% 2% 10% 3% 10% 3% 10% 2% 10%
H No Loamy Sand High 7% 10% 3% 4% 2% 10% 2% 10% 3% 10% 2% 10%
Design Wicking
Zone
Present
Soil Type Tree
Water Use
(PET)
Design Variables Tree Pit Surface Area to Catchment Area Ratios
Sunshine Coast Ipswich Rockhampton Mackay Townsville Cairns
Townsville Tree Height
(m)
Soil Volume
(m3)
Tree Water Use
(1)
Soil Type
(2)
Wicking Zone
Present
MAX MIN MAX (m2) MIN(m2)
Large Tree 15 40 High Sandy Loam Yes 4% 7% 1000 571
No 4% 4% 1000 1000
Loamy Sand Yes 3% 7% 1333 571
No 3% 4% 1333 1000
Low Sandy Loam Yes 4% 10% 1000 400
No 4% 6% 1000 667
Loamy Sand Yes 3% 8% 1333 500
No 3% 5% 1333 800
Medium Tree 12 20 High Sandy Loam Yes 4% 7% 500 286
No 4% 4% 500 500
Loamy Sand Yes 3% 7% 667 286
No 3% 4% 667 500
Low Sandy Loam Yes 4% 10% 500 200
No 4% 6% 500 333
Loamy Sand Yes 3% 8% 667 250
No 3% 5% 667 400
Small Tree 7 12 High Sandy Loam Yes 4% 7% 300 171
No 4% 4% 300 300
Loamy Sand Yes 3% 7% 400 171
No 3% 4% 400 300
Low Sandy Loam Yes 4% 10% 300 120
No 4% 6% 300 200
Loamy Sand Yes 3% 8% 400 150
No 3% 5% 400 240
Target Catchment
Area Ratio
Optimal Catchment
Area (3)
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Applying the outcomes
∕ Greenfield development greatest opportunity
∕ Retrofit situations, site constraints may limit tree pit size, catchment area and under underdrainage connections
∕ Modelling allows the design team to make informed decisions
– “Too Wet” = trees adapted to wet feet and/or restricted inlet
– “Too Dry” = drought tolerant trees and/or supplementary irrigation
∕ Understanding of likely soil conditions to make informed design choices.
Application
TURF WICKING BEDS
Benefits
∕ Turf can access water while the space is
occupied during the day, irrigation does not need
to be scheduled.
∕ There is physical separation between people
using the space and the stormwater such that it
is a very safe form of stormwater harvesting
∕ Very efficient, no loss due to evaporation of aerial
spray and the turf will not be over irrigated as it
will use only the volume of water required.
∕ Encourages deep high-growth root zones for
stronger more resilient turf. This facilitates
quicker wear recovery.
∕ Even turf colour and increased visual amenity
Benefits
∕ Nutrients within the stormwater support turf
growth, reducing
the need for fertiliser applications
∕ Uptake of stormwater and associated nutrients
reduce pollutant loads to the receiving
environment
∕ Overflow relief and drainage increases the
usability of the space after heavy rainfall and
provides improved access for mowing and
maintenance
∕ Healthy and well-watered turf has also been
found to increase CO2 capture and also have a
significantly lower temperature
Gladstone East Shores Parkland
Ashley Broadbent 2017 CRC Water Sensitive Cities
Best practice guidelines for holistic open space turf management in Sydney, Sydney Water 2011
WICKING BED MODELLING
Wicking Bed Modelling
∕ Storage – depth and porosity of the
wicking zone
∕ Source - catchment & pre-treatment
∕ Demand – surface area, climatic
conditions and water use by the turf
(crop factor)
Wicking Bed Modelling
∕ MUSIC Modelling:
– Wicking beds modelled using bioretention nodes to enable soil moisture to be assessed; and
– Wicking beds modelled using tank nodes with reuse equal to PET, to assess reliability and wicking bed volume.
• A media filtration node (porous pavement) was included upstream of the tank to represent pre-treatment for gross pollutants and coarse to medium sized sediment.
– Stormwater treatment performance = volume used by the lawn (conservative)
Modelling Variables – Soil Moisture
∕ Bioretention Node:
– Treatment to catchment area ratio
(TCAR): 1% to 15%
– MUSIC Potential evapotranspiration
factor (PET): 1.00
– Planting media: Filter media (100 mm/hr
hydraulic conductivity)
– Submerged zone (0.3m deep)
Modelling Variables - Reliability
∕ Tank Node:
– 3x wicking storage volumes (100mm,
250mm and 400mm)
– Porosity within the range of sand (low
0.35) and proprietary storage cells (high
0.95)
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Applying the outcomes
∕ Driver is a reliable source of non-potable water for irrigation, resulting in healthy resilient turf and using stormwater as a resource.
∕ Suitable for sites where quality open space is desired for aesthetics and/or functionality (e.g. sportsfields)
∕ area of wicking lawn is typically large compared to the contributing catchment area
∕ catchment area to ensure a reliable source ofirrigation for these systems (i.e. >70% reliability) canbe as little as 2 times the surface area of the lawn
∕ scalable and can be applied to large sportsfields through to small podium landscape garden beds
∕ Further research, modelling refinement and validation required to firm up the stormwater treatment performance
Application
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Outcomes
∕ Defined design parameters for the six climatic zones in QLD to deliver multiply benefits
∕ Gives confidence that these systems can be successful in a variety of climatic regions
∕ Easy to apply sizing guides
∕ Designs can be led by landscape architects in collaboration with other disciplines
∕ Can you easily replicated for other regions
∕ Pilot projects and monitoring of built systems required to validate the modelling
WHAT’S NEXT
Coming Soon
hlw.org.au/livingwaterwaysMUSIC Guideline
Ph
oto
: Cel
este
Mo
rga
n E
2D
esig
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Passive Irrigation - Street trees and Wicking Beds
Factsheet available at https://hlw.org.au/water-wise-street-trees/
https://hlw.org.au/water-wise-street-trees/
Acknowledgements∕ Chris Manning - Townsville City Council
∕ Ben Walker – Ipswich City Council
∕ Luke Galea – Mackay Regional Council
∕ Dr David Doley- University of Qld
∕ Adrian Crocetti - Healthy Land and Water
∕ All of our project partners:
