2160 IWMP Report_Jan2022

                                                                                  Callaghan & Toth

4.        WATER QUALITY MANAGEMENT PLAN
4.1       Proposed On-Site Stormwater Treatment Process

The developed site was divided into MUSIC model sub-catchments as shown on Plan No.
2160-01. The proposed treatment train for the development site is illustrated on Plan No. 2160-
02 and 2160-03 listed below:

1. Three Rainwater tanks - Two existing Rainwater Tanks both 24,000 litre, collect water from
   the Kauri and Cedar building rooves. The tanks are underground and have potable top-up
   when 90% empty with an overflow pipe discharging to the bioretention basin.

     An additional rainwater tank (24,000 litre) is proposed with the increase in roof area, to be
     located with the existing tank located on the south-west corner of the Kauri building. The
     tank capacity is to be adequate for the supply of washing machine cold water, toilets, and
     landscaping.

2. One existing Bioswale collects water from the rainwater tanks and carparks areas. The
   bioswale is 28m long with a filter media width of 1m, giving a filter media area of 28m2. This
   bioswale flows to the biobasin which further treats the stormwater.

3. The existing Bioretention Basin treats the stormwater runoff from the access roads, car
   parks, verge and rainwater tank overflow. The treated runoff is then directed to a vegetated
   area within the property prior to flowing to the unnamed tributary of Six Mile Creek. The bio-
   retention component will remove the nutrients, heavy metals, and retard flow.

The Bioretention Basin will be unlined and in combination with the rainwater tanks, act as a
Detention basin to attenuate stormwater flows from the site.


4.2       MUSIC Model
4.2.1 Source Nodes

Catchment areas of source nodes within the proposed development have been identified as
sub-catchments such as roofs, carparks, road and verge areas. MUSIC allows for the
characteristics of these source nodes to be amended to ensure that accurate pollution
generation and hydraulic characteristics are used to generate stormwater runoff within the
model.

Table 4.1 below details the sub-catchments used in the MUSIC model, land use, percent
imperviousness and area of each sub-catchment.

The MUSIC Modelling Guidelines for South-East Queensland – Version 1 December 2010 have
been used to set level of imperviousness. The site has been related to a “Commercial” land
use and pollutant export parameters detailed in the Guidelines for this land use have been used
for each node.




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2160, Kabara Upgrade, Cooroy             IWMP.doc                               January 2022