RFI - Attachment E - SWMP Callaghan and Toth

                                                                                 Callaghan & Toth

         grassed area in the north of Lot 5. Swale 4 is 40m long, 4.2m top width with 1 in 4
         batters.

    2. New Grass Swale (Swale 2) – one new grass swale will collect stormwater flows from
       the Catchment 7 and Catchment 9 and divert the flows to the existing biobasin. The
       new swale is 40m long, 2.6m wide, with 1 in 3 batters.

    3. Existing Biobasin – the existing biobasin in Lot 7 is 12m x 12m giving a total filter area of
       144m2. It is proposed to treat the runoff from the new hardstand areas i.e. new access
       road, new pathways and the extra concrete/asphalt required to formalise the carpark
       areas adjacent the existing buildings.

         As this biobasin was constructed in 2006, it is proposed to refurbish the biobasin by
         replacing the filter media, installing new drainage pipes and outlet pit and lining the
         basin. The treated runoff will then be directed to the existing stormwater outlet which
         discharges to Cooroy Creek. The bio-retention component will remove the nutrients and
         retard flow.


4.3      MUSIC Model
4.3.1 Source Nodes

The existing source nodes within the existing development have been maintained as per the
original MUSIC model as industrial nodes for Lots 6 SP161035, Lot 15 SP301607 and Lot 3 & 4
SP173771 (Lot area = 1.5144 ha) with the road reserve of Lower Mill Road (area = 0.346 ha).
The source nodes have been updated to reflect any changes in the MUSIC modelling guideline.

The current proposed changes to Lot 5 and Lot 7 are defined using split catchment technique
and source nodes as per the 2010 guidelines.

This approach is considered acceptable as the existing industrial lots have already been
approved with the treatment system in place. The proposed changes to the car parking at the
Lower Mill sites do not change the existing industrial uses adjacent.

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
levels of imperviousness. The site has been related to an “Industrial” land use and pollutant
export parameters detailed in the Guidelines for this land use have been used for each node.




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2001 Lower Mill Carpark Extension SWMP                                            July 2020