Swmp

                              Table 3.1 Existing and proposed unmitigated site peak discharge rates

                                                                   206 David Low Way
                                                                                                     Qchange
                                           A.E.P              Qexisting   Qproposed     Qchange       (%)
                                                              (m³/s)      (m³/s)        (m³/s)
                                            1EY                0.014       0.015         0.001         7%
                                            50%                0.016       0.018        0.002         13%
                                          0.2 EY               0.024       0.026        0.002          8%
                                            10%                0.031       0.031        0.000          0%
                                            5%                 0.035       0.036        0.001          3%
                                            2%                 0.041       0.041        0.000          0%
                                    1%             0.046      0.045     -0.001      -2%
The site has resulted in some small increases to peak run-off for a number of the modelled storm events. Attenuation
will therefore be provided to each unit to ensure that peak flow rates from the site are not increased as a result of
the development.

The site was remodelled splitting the developed site into it’s roof catchment, and the remaining catchment. An
attenuation node was connected to the roof catchment, with an iterative sizing used to determine the required
attenuation volume and low flow orifice outlet the achieve no net increase. Based on this process, providing 2kL of
attenuation storage per dwelling, with a low flow orifice outlet with 35mm diameter at the base of the attenuation
volume, resulting peak flows have been calculated and presented below in Table 3.2.

                               Table 3.2 Existing and proposed attenuated site peak discharge rates

                                                                   206 David Low Way
                                                                                                     Qchange
                                           A.E.P              Qexisting     QOSD        Qchange       (%)
                                                              (m³/s)       (m³/s)       (m³/s)
                                            1EY                0.014        0.013       -0.001         -7%
                                            50%                0.016       0.014        -0.002        -13%
                                          0.2 EY               0.024       0.021        -0.003        -13%
                                            10%                0.031       0.027        -0.004        -13%
                                            5%                 0.035       0.033        -0.002         -6%
                                            2%                 0.041       0.040        -0.001         -2%
                                            1%                 0.046       0.044        -0.002         -4%



As peak flow has been reduced for all modelled storm events, the development does not worsen drainage
conditions as a result of the increased impervious area and it’s discharge to the north is able to constitute a Lawful
Point of Discharge for the development.

The required attenuation is able to be provided within the capacity of the proposed 18kL in ground concrete tanks
that are to be provided within the driveways for each unit.


     3.1. Sustainable Building Code
Rainwater reuse for the development will be provided with 2 x 18kL in ground concrete rainwater tanks capturing
roof run-off from each unit. The tanks will be plumbed for reuse to greywater demands including external
irrigation, and internal toilets and laundry areas in compliance with the Noosa Council Sustainable Building Code.




Project number 20230023                                                                                          Page 8 of 14
File 20230023 206 David Low Way SWMP.docx, 2023-10-17 Revision 1

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