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

3.3.4 Soil Media Fill
Selecting the appropriate soil media is critical for
                                                                                    Determine Primary
ensuring a healthy tree, and with respect to integrated                             Project Objectives
stormwater applications that stormwater treatment
objectives can be met.
Typically a growing media with a suitable organic
content is specified for standard street tree installations,
and they are formulated to sustain trees both
nutritionally and physically (provide adequate nutrients
                                                                     Horticultural and
                                                                                                         Horticultural
and water holding capacity).                                          Water Quality
                                                                                                         Objectives
                                                                       Objectives
For WSUD tree systems the key objective is to ensure
that the soil medium can sustain a healthy tree as
well as provide a suitable well-draining medium for
stormwater filtration and pollutant retention.
                                                                     Select mix of fills
For a WSUD tree pit system incorporating bioretention                 (growing media
                                                                                                       Select growing
                                                                                                          media fill
filter media, the soil profile will usually consist of               and filter media)
three layers.
  1. Filter media (minimum 750mm deep or as specified
     in the engineering design)                                 Filter media to be specified
                                                                  around the root ball and
                                                                                                   Similar to typical street
  2. Transition Layer (100mm deep coarse sand)                 where necessary to intercept
                                                                                                      tree configuration.
                                                                 stormwater inflows. A low
                                                                                                     Suitable for passive
  3. Drainage Layer (150mm deep fine washed gravel)             fines growing media to be
                                                                                                  watering applications only.
                                                               specified around the extents
The soil media fill specified for a WSUD tree system will           of the Strataflow pit.

vary depending on the project objectives and the site
context. Designers should consider the application,
context, and project objectives prior to selecting a                  Refer to WSUD
                                                                                                    Refer to Citygreen’s
                                                                     Strataflow Tree Pit
suitable soil media specification. The figure below                                                  standard Growing
                                                                  standard drawings and
                                                                                                    Media Specifications
provides a basic decision tree to assist designers in            soil media specifications

selecting the appropriate soil media a fill.


3.3.5 Tree and Plant Selection
Ideal tree species to be planted within a WSUD or Bioretention Tree Pit are those which have the following traits;
  • Effective for removal for nutrients in stormwater
  • Can grow and develop in freely draining filter media
  • Can tolerate variable periods of inundation.
  • Ideally non-deciduous
  • Preferably native and occur naturally in the local area
  • Where trees are planted in a raingarden they need to have relatively sparse canopies to allow light penetration to
    support dense groundcover vegetations.
A basic list of recommended tree species for WSUD tree pit systems has been compiled as shown in Table 1. This is
by no means an exhaustive list of tree species suited to WSUD tree systems. The tree species listed display some or
all of the desirable traits for tree species planted within bioretention systems. The tree species listed occur in various
regions across Eastern Australia and should be specified if they are suited to the local environment and site conditions.
Ideally a qualified professional should tailor a site specific planting plan incorporating appropriate tree species.




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