RFI - 075-028 SWMP Report

        The calculated flows using the Rational Method were compared against the XPSWMM estimates for
        the catchment for 1%AEP pre and post development conditions. These are provided in Table E and
        show a reasonable calibration.



Table E - Rational Method vs XPSWMM Peak discharge (1%AEP)

                             Rational
                                         XPSWMM Difference
        Catchment            Method
                                          (m3/s)         (%)
                              (m3/s)
  C01 Pre Development         0.049       0.043         -12.3
  C01 Post Development        0.051       0.050         -2.1



                              Peak Flow Management

In order to ensure that the peak flow mitigation meets the requirements of Council’s Planning scheme policy
for development works. It is proposed to alleviate the increase of fraction impervious by installing a detention
tank connected to the roof and hardstand areas of the proposed development. XPSWMM Modelling was used
to design the detention and minor and major flow pipes from the detention system. The comparison of each
of the storm events is provided in and demonstrates that the installation of a detention tank will allow
mitigation of all events.



                              Storage calculation

The proposed design has resulted in a reduction in post development flows to the Ventura Street frontage
(LPD1). XPSWMM was used to model the storage requirements to ensure the post development flows were
not higher than the predevelopment flows at this location.
The peak flow management objectives have been addressed using detention storage. It is proposed to alleviate
the increase of fraction impervious by installing a detention tank connected to the roof and hardstand areas
of the proposed development. These detention tank will be sized to control the peak discharge and has been
calculated to total 4.6m3 based on the peak discharge temporal pattern. A slimline aboveground tank with 7m3
of capacity is suggested. This would allow 2.4m3 which could be used for site reuse.
The proposed design of the detention tank will consist of a single slimline tank with dimensions shown in Figure
5 (or similar approved). The tank has been designed with low flow discharges via a 20mm diameter orifice at
the base of the re-use and a second orifice (25mm diameter) 606mm above the base. The tank would also



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