20210041 27 Bottlebrush Ave Stormwater

                                   Figure 3.2 – DRAINS Pre-development catchments




                                  Figure 3.3 – DRAINS 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

                                                    27 Bottlebrush Avenue                    Total
                                 A.E.P         Qexisting    Qproposed       Qchange          Qchange
                                               (m³/s)       (m³/s)          (m³/s)            (%)

                                1EY          0.011          0.015         0.004           36%
                                50%          0.013          0.017         0.004           31%
                                20%          0.019          0.024         0.005           26%
                                10%          0.023          0.028         0.005           22%
                                5%           0.029          0.033         0.004           14%
                                2%           0.033          0.039         0.006           18%
                                1%           0.036          0.043         0.007           19%


            As the site has increased the total peak flows from the site, attenuation storage will be
            required to mitigate the outflows to ensure that the development does not exceed the
            predevelopment levels.

            To determine the attenuation required, the model for the developed site was updated to
            include a proposed detention tank to be provided for the development. An iterative sizing
            process was used to determine both the sizing of the detention storage and the low flow
            outlet orifice that would attain the required peak flow rates from the site. Based on this


                                                                                                         Page 4 of 9
P +61 7 5211 1003       A 37 Mary St, Noosaville Qld 4566               E [email protected]     recorconsulting.com