20517 App J.pdf [As Published] · 132007.1259

Concept Stormwater Management Plan
Essence of Peregian

4.4 MUSIC Modelling Results

Computer modelling using MUSIC was undertaken for the existing and developed scenarios as described in
Section 4.3. The results of the various scenarios are compared in this section to show the effects of the proposed
water quality treatment train on pollutant loads and concentrations.

The first model run was that of the existing site (Model No. 1). Results from this model were desired in order to
gauge an idea of what stormwater runoff concentrations are leaving the existing site. The results are shown below
in Table 4.8.

Table 4.8; Existing Site Concentrations (Model No. 1)*

 

 

Pollutant Total Suspended Solids | Total Phosphorous | Total Nitrogen
(mg/L) (mg/L) (mg/L)
Concentration 155 0,393 2.24

 

 

 

 

 

 

*Concentrations given are median values.
Results show that runoff from the existing site has pollutant concentrations much higher than the water quality
guideline concentrations as listed in the Queensland Water Quality Guidelines for lowland streams. Therefore, it is
considered that since the existing site is not currently in a ‘natural’ state and because the existing site concentrations
are significantly higher than ideal, that load reduction targets are more appropriate to demonstrate the benefits of a
developed scenario water quality treatment train.

Concentration results from the Mitigated Site (Model No. 4) and Mitigated Site plus External Catchments
(Model No. 5) are presented for completeness in Table 4.9.

Table 4.9: Mitigated Site Concentrations (Model No’s. 4 and 5)*

 

 

 

 

 

Scenario Total Suspended Solids | Total Phosphorous | Total Nitrogen
(mg/L) (mg/L) (mgiL)

Mitigated Site

(Model No. 4) 28.7 0.147 175

Mitigated Site and External Catchment

(Model No. 5) 13.8. 0.098 1.66

 

 

 

 

*Concentrations given are median values.

It can be seen that median concentrations of the target pollutants have been dramatically reduced compared to
existing site concentrations. It should also be noted that the mitigated proposal includes rainwater tank reuse
measures that reduce the total outflow of runoff. This makes pollutant concentrations higher than if reuse was not
applied. Rainwater tank reuse reduces pollutant load, but can have a negative impact on concentration values.

Results from modelling of the various scenarios are presented in Table 4.10 below. Load retention targets were
derived from the percentage reduction required from the developed site only (Model No. 2). These have then been
compared with the load retention achieved from the total catchment {i.e. including some external catchment areas).

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