20220237 73 Southern Cross Pde SWMP

                                           Figure 3.2 – DRAINS Post-development catchments


The results of the modelling against the range of design storms for the development under the existing and
proposed development conditions are shown in Table 3.1 Existing and proposed unmitigated site peak discharge
rates.
                              Table 3.1 Existing and proposed unmitigated site peak discharge rates

                                                                       Wyandra Street
                                                                                                     Qchange
                                           A.E.P               Qexisting   Qproposed    Qchange       (%)
                                                               (m³/s)      (m³/s)       (m³/s)
                                        63.2% AEP               0.022       0.024        0.002         9%
                                           0.5 EY               0.029       0.031       0.002          7%
                                           0.2 EY               0.038       0.041       0.003          8%
                                         10% AEP                0.049       0.049       0.000          0%
                                          5% AEP                0.055       0.056       0.001          2%
                                          2% AEP                0.064       0.064       0.000          0%
                                          1% AEP                0.072       0.072       0.000          0%



The results show that the site has increased the total peak flows from the site for a number of storm events however
these changes are typically restricted to the more frequent less severe storm events, where pervious areas have
greater impact through infiltration losses.

The overall magnitude of the increase resulting from the development is small, with a maximum increase of 3L/s
predicted by the modelling for any storm event. This level of change is not considered likely to result in any significant
impacts or damage to the downstream receiving environment and therefore no attenuation is considered necessary
for the proposed development.




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Project number 20220237
File 20220237 73 Southern Cross Pde SWMP.docx, 2022-10-31 Revision 1
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