Project overview
The WSUD trial aimed to improve shade and amenity for users of the Jamison shopping centre by providing more space and improved growing conditions for trees.
The trees within the Jamison Group Centre carpark were growing in small, raised islands of heavily compacted soil and were generally undersized and unhealthy. The carpark was lacking shade and had poor landscape amenity.
The WSUD tree pit trial studied the issue through the installation of a system that supports tree health and growth, provides localised stormwater treatment and reduces the need for supplementary watering of trees.
What is Water Sensitive Urban Design*?
Water Sensitive Urban Design (WSUD) is a way of planning our cities to minimise water runoff and ensure any runoff causes the least amount of damage. It is also about wise use of that water to improve our urban environment.
The key principles of WSUD are:
- to reduce the demand for potable (fit for drinking) water by using alternative sources of water such as rainwater and treated wastewater and encouraging water efficient appliances
- to minimise the generation of wastewater and to treat wastewater to a suitable standard for re-use and/or release into bodies of water.
- to treat urban stormwater to a quality where it can be reused and/or discharged to surface waters
- to use stormwater in the urban landscape to improve the visual and recreational amenity of developments.
*Reference: Environment, Planning and Sustainable Development Directorate
How it works
A structural tree pit is installed underground to increase the volume of soil available to the trees while supporting other uses, such as carparking and pedestrian footpaths, on the surface above.
The tree pit is filled with high quality soil and has enough root space for the healthy development of the selected tree species. The uncompacted soil, increased space and increased access to water helps extend the life of the tree, improves canopy cover, increases shade and cooling, improves landscape amenity, reduces ongoing irrigation and tree care and prevents uplift of pavement by tree roots.
The system is designed to allow stormwater from the surface of the carpark to flow into the structural soil cells to further enhance tree health and deliver a number of stormwater management benefits.
Site details
The Jamison tree pit runs a continuous linear trench beneath two rows of parking bays.
Tree growth, shade coverage and ambient temperature, soil moisture and water quality is measured by equipment installed in the tree pit and compared to results measured in traditional tree planting treatments within the carpark.
An additional 15 new trees were planted in existing spaces according to the traditional method at the same time as the trees are planted in the WSUD tree pit. Tree growth, temperature and soil moisture will be measured across both sites to allow a direct comparison of results between the two planting methodologies.
The tree species planted is Acer x freemanii ‘Jeffersred’ Autumn Blaze, an exotic deciduous tree (maple) that will grow approximately 13m high with a 10m spread. Planted trees should reach their mature size within 20 to 25 years.
