Attachment 1 - Stormwater Management Plan

                            Table 3.1 Existing and proposed unmitigated site peak discharge rates

                                     53 Doonella Street                                 55 Doonella Street                        Total
              A.E.P          Qexisting         Qproposed          Qchange        Qexisting      Qproposed            Qchange     Qchange
                             (m³/s)            (m³/s)             (m³/s)         (m³/s)         (m³/s)               (m³/s)      (m³/s)

              1EY           0.017              0.019          0.002             0.018           0.02             0.002          0.004
              50%           0.019              0.024          0.005             0.021           0.022            0.001          0.006
              0.5EY         0.022              0.026          0.004             0.024           0.026            0.002          0.006
              20%           0.029              0.033          0.004             0.032           0.032            0              0.004
              10%           0.039              0.04           0.001             0.039           0.04             0.001          0.002
              5%            0.044              0.046          0.002             0.044           0.045            0.001          0.003
              2%            0.05               0.053          0.003             0.051           0.053            0.002          0.005
              1%            0.056              0.06           0.004             0.056           0.058            0.002          0.006


            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 the proposed rainwater tanks to be provided for the development. The reuse
            portion of the tank was assumed to be full at the time of the storm so only the attenuation
            portion contributes to flow mitigation. The attenuation portion of the rainwater tanks was
            modelled as storage nodes with 2 1.5kL storage volumes provided per development. An
            iterative sizing process was used to determine a low flow outlet of 35mm and high flow
            outlet of 100mm would provide the required flow rates.

            Using this mitigated development model, the proposed developed flows were again
            compared to the existing state as shown below in Table 3.2 Existing and proposed
            mitigated site peak discharge rates.

                             Table 3.2 Existing and proposed mitigated site peak discharge rates

                                          53 Doonella Street                                 55 Doonella Street                   Total
                    A.E.P          Qexisting          Qproposed       Qchange       Qexisting     Qproposed           Qchange    Qchange
                                   (m³/s)             (m³/s)          (m³/s)        (m³/s)        (m³/s)              (m³/s)     (m³/s)

              1EY              0.017              0.014             -0.003          0.018        0.015               -0.003     -0.006
              50%              0.019              0.018             -1E-03          0.021        0.016               -0.005     -0.006
              0.5EY            0.022              0.021             -0.001          0.024        0.021               -0.003     -0.004
              20%              0.029              0.028             -0.001          0.032        0.027               -0.005     -0.006
              10%              0.039              0.035             -0.004          0.039        0.035               -0.004     -0.008
              5%               0.044              0.042             -0.002          0.044        0.041               -0.003     -0.005
              2%               0.05               0.048             -0.002          0.051        0.048               -0.003     -0.005
              1%               0.056              0.052             -0.004          0.056        0.051               -0.005     -0.009


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