Att 1 - Engineering - RFI Reponse · MCU21/0117.01

                                                                                      23098/WB
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Item 4:     Provide an updated SWMP which contains additional detail plus revised modelling (as
            necessary) to address the following:

            i.     Revise the pervious initial losses used in the XPSTORM model to be consistent
                   with ARR DataHUB burst losses.

            ii.    Provide a figure showing the XPSTORM model layout and describe how surface
                   areas have been modelled as bypassing the detention tanks in all events and
                   how flows in excess of Q20 from roof areas bypass the tanks

            iii.   Undertake an assessment for the 1%AEP event at year 2100 by increasing the
                   1%AEP rainfall intensities by 20%

Response: The amended stormwater detention design has been remodelled in the Watercom
          DRAINS detention modelling program using the Initial Loss Continuing Loss (IL-CL)
          hydrological model. Based on ARR DataHUB’s burst losses, the pervious area initial
          loss (mm) and the pervious area continuing loss (mm/hr) values used in the model are
          32 and 2.6, respectively.

            Refer to the updated Site Based Stormwater Management Plan (23098 – SBSMP – Rev
            4) showing the post-development mitigated model. With the addition of the 20%
            increase in rainfall intensities to address climate change considerations, the updated
            modelling has been completed to ensure all flows will be mitigated in the tanks up
            to a Q100 storm event.

Please contact me if you have any further queries on (07) 3369 8411.


Yours faithfully,
MORGAN CONSULTING ENGINEERS PTY LTD




Henry Morgan       MIEAust CPEng RPEQ 11950

Enclosed:           23098 – SBSMP – Rev 4