Stormwater Technical Memo · MCU23/0096

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    Arts Centre




Figure 1. Masterplan for Good Shepherd. Arts Centre is Building no. 1.




3       ASSESSMENT METHOD

To quantify the extent of changes between the existing and proposed development, the
Masterplan layout was transposed over a Nearmap image. Figure 2 highlights the approximate
extent of the Arts Centre upgrade. A surface-split comparison has been estimated based on this
overlay and a shown in Table 1.




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Figure 2. Extent of Proposed Arts Centre (right) transposed on existing (left).



Table 1. Estimated Surface-Split Breakdown. Note: the garden and green corridor attached to the proposed
building are included in the area calculations.

 Surface-Split                                          Existing                    Proposed
 Roof Area (m2)                                            0                          1,200
 Road/Pathway (m2)                                       1,200                          0
 Garden/Open Space (m2)                                    0                           165
 Total (m2)                                              1,200                        1,365



4      HYDROLOGIC ANALYSIS
In accordance with the Queensland Urban Drainage Manual, peak stormwater flows are
calculated based on impervious fractions. As shown in Table 2, the impervious fraction between
the existing and proposed areas do not significantly change. This indicates that there will not be
any significant changes to peak flows, and as such, detention is not required.
Table 2. Impervious Fraction Estimate.

 Hydrological Assessment                                Existing                    Proposed
 Impervious Area (m2)                                    1,200                        1,200
 Impervious Fraction (%)                                   88                          88




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5             WATER QUALITY ANALYSIS
Stormwater quality modelling is based on split surface areas and their associated export pollutant
load. As per Table 1, above, the roof area increases by approximately 1,200 m2, while the road
area decreases by approximately 1,200m2. In accordance with MUSIC Modelling Guidelines, roof
pollutant export values are significantly less than road pollutant export parameters (see Table 3). As
such, it could be expected that stormwater pollutant loads would decrease with the proposed
developed. Therefore, no additional stormwater quality improvement devices are required.


Table 3. Pollutant Export Parameters.

 Pollutant Export Parameters for Split Catchment Land-use (Log10 values)
      Land         Split   Flow Type                TSS                  TP                      TN
       Use                                Mean        Std. Dev    Mean        Std. Dev    Mean        Std. Dev
                   Roof    Baseflow     N/A           N/A        N/A          N/A        N/A      N/A
                           Stormflow    1.3           0.38       -0.89        0.34       0.37     0.34
 Commercial




                  Roads    Baseflow     0.78          0.39       -0.6         0.5        0.32     0.3
                           Stormflow    2.43          0.38       -0.3         0.34       0.37     0.34
                 Ground    Baseflow     0.78          0.39       -0.6         0.5        0.32     0.3
                           Stormflow    2.16          0.38       -0.39        0.34       0.37     0.34
 Source: Table 3.9 (MUSIC Modelling Guidelines).



6             CONCLUSION

As there have been no significant changes to the overall impervious area associated with the
proposed Arts Centre, it has been determined that no additional detention or stormwater quality
improvement devices are required. This advice is based on the current Masterplan layout (Burling
Brown’s drawing: GSL05-SK-02, Dated 24/2/23) and aligns with QUDM (2017) and MUSIC Modelling
Guidelines (2018) requirements, and Noosa Shire Council requirements.


If Council require further explanation of the above or additional information, please contact the
undersigned at [email protected]             DISCLAIMER

This report is prepared by Colliers for exclusive use by its client only. No responsibility is accepted for
the use of or reliance upon this report in whole or in part by any third party.
The sole purpose of this report and the associated services performed by Colliers is to display
information in accordance with the scope of services set out in the contract/quotation between
Colliers and its client. The scope of works and services were defined by the requests of the client,
by the time and budgetary constraints imposed by the client, and by the availability of access to
site/s and information.
This report is prepared with information supplied by the client and possibly others which is presumed
to be accurate and complete. No responsibility is accepted for information that is withheld,
incorrect or that is inaccurate, nor for changes to the conditions over the passage of time or from
latent circumstance or conditions. No warranty or guarantee is made in relation to the data,
findings and conclusions expressed in this report.




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This report has been compiled at the level of detail specified in the report and no responsibility is
accepted for interpretations made at more detailed levels than so indicated.
Yours faithfully
Colliers Engineering and Design




Kelly McKendry
Director – Water & Environment
RPEQ 09298




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