Sealed Judgement

4                Stormwater Quality Modelling


The Model for Urban Stormwater Improvement Conceptualisation (MUSICX) (version 1.30.0)
software package was utilised to assess the behaviour of stormwater quality from the Site under the
pre-development and post-development conditions.
The modelling was undertaken using the Water by Design MUSIC Modelling Guidelines (Version 1.0,
2010).
Details of the MUSICX model setup are discussed in the following sections.


4.1              Rainfall Data
As per the MUSIC Modelling Guidelines, the following meteorological data was used:
x     The 6-minute time step rainfall series at Cooroy (Rainfall Station ID 040059), with a mean annual
      rainfall of 1,600 mm, and data from 1/1/1973 to 31/12/1983.
x     Evaporation data for Cooroy applied as monthly mean data, with a mean annual evaporation of
      1,628 mm.


4.1.1            Rainfall runoff parameters

Table 4-1 contains the rainfall and runoff parameters adopted in the following manner:

x     Pre-development scenario: the Forest land use was used to model the vegetated portion of
      the Site, while the Urban Residential land use was used to model a small portion of the external
      sealed road.

x     Post-development scenario: the Forest land use was adopted for the ground portion of the
      Site that will be retained undeveloped and the suspended walkways, while the Urban Residential
      land use was used for the roof and carpark areas.

Table 4-1       Rainfall Runoff Parameters

    Parameter                                              Land Use

                                                Forest          Urban Residential

    Rainfall threshold (mm)                        1                      1

    Soil storage capacity (mm)                    120                    500

    Initial storage (% capacity)                  10                     10

    Field capacity (mm)                           80                     200

    Infiltration capacity coefficient a           200                    211

    Infiltration capacity exponent b              1.0                    5.0

    Initial depth (mm)                            50                     50

    Daily recharge rate (%)                       25                     28

    Daily baseflow rate (%)                        3                     27

    Daily deep seepage rate (%)                    0                      0




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