20220206 48 Elm St SWMP

                                            Figure 3.2 – DRAINS Pre-development catchment




                                           Figure 3.3 – DRAINS Post-development catchments


It should be noted that the total site area in the proposed condition is greater than the existing site area due to
proposed awnings over the footpath. 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

                                                             Qexisting   Qproposed    Qchange      Qchange
                                        AEP (2100)
                                                             (m³/s)      (m³/s)       (m³/s)        (%)
                                           0.5 EY             0.026       0.032       0.006         23%
                                             10%              0.044       0.047       0.003          7%
                                             5%               0.050       0.055       0.005         10%
                                             2%               0.057       0.065       0.008         14%
                                             1%               0.063       0.072       0.009         14%



The development of the site will therefore increase the total peak flows from the site under all storm events.
Attenuation is required to mitigate the outflows to ensure that the development does not exceed the
predevelopment levels to minimise impacts to the downstream environment.


Project number 20220206                                                                                      Page 8 of 19
File 20220206 48 Elm St SWMP, 2023-02-03 Revision 1

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