20220171 - 14 Wyandra St SWMP

                                           Figure 3.3 – DRAINS Post-development catchments




                                        Figure 3.4 – DRAINS Split 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)
                                             1EY                0.022        0.025        0.003        14%
                                            50%                 0.025        0.027       0.002          8%
                                           0.2 EY               0.037        0.040       0.003          8%
                                            10%                 0.047        0.049       0.002          4%
                                             5%                 0.056        0.056       0.000          0%
                                             2%                 0.064        0.064       0.000          0%
                                             1%                 0.070        0.071       0.001          1%



As expected, the site has increased the total peak flows from the site for a number 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.
Project number 20220171
File RECOR Preliminary Stormwater Management Report - 20220171.docx, 2022-08-24                                   Page 8 of 15
Revision 1


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