RFI - 20220072 Ross Cr SWMP

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

                                                                        Ross Crescent
                                                                                                      Qchange
                                           A.E.P               Qexisting    Qproposed    Qchange       (%)
                                                               (m³/s)       (m³/s)       (m³/s)
                                             1EY                0.017        0.017        0.000         0%
                                            50%                 0.019        0.021       0.002         11%
                                           0.2 EY               0.028        0.030       0.002          7%
                                            10%                 0.037        0.037          0           0%
                                             5%                 0.042        0.042          0           0%
                                             2%                 0.048        0.049       0.001          2%
                                             1%                 0.054        0.054       0.000          0%



As expected, the site has increased the total peak flows from the site for a number of storm events. The magnitude
of the change is considered acceptable as the increase in flow rate for frequent events is only 2L/s from the existing
site, and an increase of 1L/s for a 1 in 50 year event – a rare frequency rate. This change is considered relatively
insignificant.

In addition, the surrounding land parcels are not subject to flooding risks due to:

     •    Elevation of the land; and
     •    Rapid infiltration of groundwater into the soil.

As the drainage characteristics of the site have not been significantly altered and are unlikely to result in impacts to
downstream properties, no attenuation of peak flows is proposed for the development.




Project number 20220072
File RECOR Preliminary Stormwater Management Report - 20220072.docx, 2022-09-02                                   Page 8 of 14
Revision 1


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