RECOR Preliminary Stormwater Management Report - 20220198

                              Table 3.1 Existing and proposed unmitigated site peak discharge rates

                                                                       Delorme Street
                                                                                                       Qchange
                                           A.E.P               Qexisting     Qproposed    Qchange       (%)
                                                               (m³/s)        (m³/s)       (m³/s)
                                            1EY                0.021          0.024       0.003         14%
                                            50%                 0.025         0.028       0.003         12%
                                           0.2 EY               0.039         0.041       0.002          5%
                                            10%                 0.045         0.050       0.005         11%
                                             5%                 0.057         0.057       0.000          0%
                                             2%                 0.065         0.065       0.000          0%
                                             1%                 0.071         0.072       0.001          1%



As expected, the site has increased the total peak flows from the site for the majority of storm events. Attenuation
will be required to mitigate the outflows to ensure that the development does not exceed the predevelopment levels
to minimise impacts to the downstream environment.

The mitigated post-development model splits the catchment into a roof area, which drains to an on-site detention
(OSD) tank, and the remainder of the site which is not attenuated. An iterative process was used to determine a
suitable configuration of storage volume, low-flow, and high flow pipe outlets for the OSD to deliver the required
reduction of the flow rates from the site.

The result of the iterative sizing process determined that the OSD storage will need to provide an attenuation
capacity of 3,000L for each unit with the maximum possible roof area to be plumbed to the tank. A low flow outlet
consisting of a 57mm orifice plate is to be provided the base of the tank, and a 100mm high flow outlet at the head
of the tank will provide discharge for larger storm events.

Using this mitigated development model, the proposed developed flows were again compared to the existing state
as shown below in Table 3.2 Existing and proposed mitigated site peak discharge rates.

                                Table 3.2 Existing and proposed mitigated site peak discharge rates

                                                                      Wyandra Street
                                                                                                       Qchange
                                           A.E.P               Qexisting     Qmitigated   Qchange       (%)
                                                               (m³/s)        (m³/s)       (m³/s)
                                            1EY                0.021          0.021       0.000          0%
                                            50%                 0.025         0.024       -0.001         -4%
                                           0.2 EY               0.039         0.033       -0.006        -15%
                                            10%                 0.045         0.041       -0.004         -9%
                                             5%                 0.057         0.049       -0.008        -14%
                                             2%                 0.065         0.063       -0.002         -3%
                                             1%                 0.071         0.071       0.000          0%



As the total peak flows are equal to or below the existing site conditions for all storm events, the proposed OSD area
will provide the mitigation required for the peak flow storm events from the development.




Project number 20220198
File RECOR Preliminary Stormwater Management Report - 20220198, 2022-08-19                                         Page 9 of 15
Revision 1


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