H - Revised Integrated Water Management Plan by Cardno (inc MUSIC file) (13.09.19)

3.3.10 Trafficable Pavements
In applications where Strataflow Tree pit systems are installed beneath trafficable pavements, a geotechnical analysis
of the site subgrade should be undertaken to determine the appropriate specification and composition of the tree pit
drainage layer and substructure.
The tree pit’s foundation is the angular crushed rock material placed between the subgrade soils and the Strataflow base.
The site sub-grade bearing capacity and cover depth above the Strataflow system will determine the depth of crushed
angular rock required for the Strataflow Tree Pit foundation.
A geotechnical engineer may be required to review the installation of a Strataflow Tree Pit system where weak
subgrade material is present.


3.3.11 Management of Sediment and Gross Pollutants
Urban stormwater runoff typically carries with it pollutants
ranging from large debris and rubbish through to fine
particulate matter and dissolved chemicals. Stormwater
runoff should be ‘pre-treated’ as required prior to
discharge into the tree pit system and distribution into
the Strataflow matrix.
Stormwater pollutants that settle out and accumulate
within a Strataflow Matrix can clog the system over time
and may be difficult to remove in some cases without
significant intervention.
Fine particulate matter should be isolated up front and
filtered out prior to distribution throughout the system. By
capturing some of the pollution prior to the entry into the     Figure 6 – Example Pre-treatment for Street Tree
system, the service life of the system can be extended
and the ongoing maintenance burden can be reduced.
Pre-treatment systems vary greatly in terms of cost, complexity, and size and should be designed with consideration to
the project site and context. An appropriate pre-treatment device is one that excludes fine particulate matter from the
Strataflow system.
A few pre-treatment systems which are considered appropriate for the typical urban context include the following;
  • Sediment forebay and bioretention filter media;
  • Permeable pavement;
  • An inlet pit incorporating a filter screen/pit insert filter and a sump (example shown in Figure 6);
  • A Gross Pollutant Trap (GPT)


3.3.12 Irrigation
In most situations the supply of stormwater runoff for passive watering may need to be supplemented by active watering
(irrigation). Citygreen’s RootRain Arborvent is a dual inlet for deep watering and aeration and can be used to provide an
active watering conduit to the confined root zone within a tree pit system.
The active watering manifold should be installed higher in the profile than the drainage layer to prevent short circuiting of
irrigation water via slotted pipe underdrainage to the stormwater system. A non-woven geotextile sock can be fitted to
the active watering manifold to prevent the ingress of fines from the surrounding soil media.




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