Landscape architects, urban designers and open space planners specify the thing that has to keep a tree alive for fifty years. This page sets out the detail needed to draw the Tree Nurturing System (TNS™), which provides kerb-line retention and storage beneath street trees.
Under SA HB 214:2023 Urban Green Infrastructure – Planning and decision framework, a Standards Australia handbook, the node is an urban green infrastructure element. It integrates with the blue infrastructure network in the way the handbook describes at Clause 3.3.6. Under the Green Infrastructure Management Manual published by the Institute of Public Works Engineering Australasia (IPWEA), it is a hybrid green infrastructure asset, with engineered components supporting it.
Both documents are references for planning and managing green infrastructure, with no certification role. The TNS™ has no endorsement from Standards Australia or from IPWEA. BGI makes no compliance claim against SA HB 214:2023 or the manual. They matter here for a narrower reason: they give the thing you are drawing a name, an asset class, and a place on a register that gets funded. Where it sits in the frameworks →
Because canopy at maturity is a function of root space, the estimating methods in the Green Infrastructure Management Manual are the right place to start a streetscape detail.
Project the canopy area of the mature tree and multiply by a depth of 0.6 m. Soil volume requirements can extend two to three times the radius of the canopy. Methods based on mature trunk girth are possibly more accurate, because they allow for different foliage shapes.
With a structural cell arrangement the volume can be configured to suit the site. The same volume can run long and shallow beneath a footpath or deep and compact beneath a parking bay without changing the number the tree needs.
We size the cell and tank arrangement to the soil volume the species needs at maturity, not to a catalogue module count. Give us the species and the streetscape section and the volume comes back with the details.
Estimating methods above are paraphrased from the Green Infrastructure Management Manual, Appendix 1B-6.2 (p142), which also references the Soil Volume Simulator tool. The manual is the source and is worth reading in full.
The manual is blunt about it: a lack of water and nutrients are the biggest single killers of newly planted urban trees around the world. It also treats efficient irrigation as essential through the first three years.
Establishment is the risk window, and the manual calls for regular watering for up to three years to secure optimal root growth. Most canopy plans are costed as though that watering will happen.
Where conventional drainage pipes water past the tree, the node routes road runoff into the root zone on every rain event. No reticulated irrigation line, no water-truck roster to hold for three years.
Because a waterlogged pit goes anaerobic and kills the tree, sufficient drainage has to be designed in early. In this arrangement a relief line takes the excess once the storage is full.
The structural cell arrangement carries the pavement load, which keeps the growing medium from compacting toward the density of the road base. Air stays in the profile for the soil and roots.
The detail sheet carries eleven items, each naming the standard that governs it where there is one.
Projected canopy area of the mature tree multiplied by a depth of 0.6 m, or a method based on mature trunk girth. State the target species and the resulting volume on the drawing – it is the number every later decision is checked against.
Specified as a soil to AS 4419, Soils for landscaping and garden use, and not as a filter cartridge.
AS 2303, Tree stock for landscape use, governs what arrives on site, which is where most canopy targets are quietly lost.
Cell type, layout and depth, set to the soil volume rather than to a module count. Resolve it early enough to be built during the civil or groundwork stage – it cannot be retro-fitted into a finished pavement box.
In paved areas, roots deflected downwards by at least 300 mm to prevent paving heave.
A relief line, a set overflow level, and an observation well so the profile can be checked without excavation. A waterlogged pit goes anaerobic and kills the tree – drainage is as much of the specification as water is.
Specify a means of getting air below ground, with the cell arrangement holding structure under traffic load so the profile does not compact toward the density of the road base.
Underground guying is preferred in urban areas – unobtrusive, supporting from below, and without the later structural problems that staking and tying can cause.
Grilles, vertical guards or equivalent where vandalism risk warrants them.
The EnviroKerb® unit and the EnviroKerb Tray Inlet (ETI) are Class D rated and fully trafficable where they sit in the traffickable zone, with a 1000 × 600 mm precast kerb body.
Establishment watering, weeding, sediment monitoring and flushing of the subsurface drainage. Provided with the approval documentation. The maintenance case →
Items 01 and 04–09 follow the design process set out in the Green Infrastructure Management Manual, Appendix 1B-6.2 (p142), paraphrased. Items 10 and 11 are BGI’s. Standard drawings and node details for the selected variant are issued with the specification package. The specification package →
Each node serves the smallest practicable contributing area, which holds the runoff at the kerb line nearest its source, so none of it is accumulated and conveyed. For a designer that has one practical consequence: the water budget for the tree and the drainage strategy for the street stop competing for the same section.
Where quality obligations sit. The arrangement is assessed on retention and storage of stormwater at the source. Where a development also carries stormwater quality obligations, those are met by separate, appropriately certified measures. The TNS™ is not offered as a substitute for a certified quality device where one is required.
We’ll size the soil volume and the cell arrangement, and issue the details to drop into your drawing set.
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