----------------------------------------------- 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 -----------------------------------------------
51
Embed
Building a Healthier Tomorrow with Passively …...Building a Healthier Tomorrow with Passively Irrigated Street Trees & Open Space Sally Boer, Dr Peter Breen, Dr Dale Browne, Dylan
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Constrained tree pit and sealed surface = unhealthy tree and limited canopy
Conventional drainage = missed opportunity for passive irrigation and stormwater treatment
0
5
10
15
20
25
30
35
40
45
50
0 1 2 3 4 5 6 7 8 9 10
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)
∕ 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)
∕ 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