Amended Stormwater Plan · MCU18/0019

SC7440 – Goodchap St, Noosa                                                                              17




  Node                    Pre-Development                                  Post-Development
                   HGL (m)             Downstream U/G           Hydraulic Grade        Downstream Flow
                                                     3
                                       Flow Rate (m /s)          Line (HGL) (m)            Rate (m3/s)
   A.2               2.848                   0.186                    2.841                   0.177
  A.3.1              3.199                   0.050                    3.043                   0.034
   A.5               3.366                   0.068                    3.189                   0.064
   A.1               2.644                   0.186                    2.628                   0.177
             Table 4.5 – Pre vs. Post-Development External Network Results (2yr Event)


  Node                    Pre-Development                                  Post-Development
                   HGL (m)             Downstream U/G           Hydraulic Grade        Downstream Flow
                                                     3
                                       Flow Rate (m /s)          Line (HGL) (m)            Rate (m3/s)
   A.2               3.097                   0.248                    3.035                   0.224
  A.3.1            3.512 (S)                 0.062                    3.325                   0.045
   A.5             3.766 (S)                 0.084                    3.470                   0.069
   A.1               2.783                   0.248                    2.726                   0.224
             Table 4.5 – Pre vs. Post-Development External Network Results (10yr Event)
                                 *Note: (S) denotes a surcharging node


  Node                    Pre-Development                                  Post-Development
                   HGL (m)             Downstream U/G           Hydraulic Grade        Downstream Flow
                                                     3
                                       Flow Rate (m /s)          Line (HGL) (m)            Rate (m3/s)
   A.2               3.153                   0.257                    3.172                   0.254
  A.3.1            3.549 (S)                 0.062                  3.527 (S)                 0.050
   A.5             3.795 (S)                 0.084                  3.794 (S)                 0.082
   A.1               2.816                   0.257                    2.804                   0.255
            Table 4.5 – Pre vs. Post-Development External Network Results (100yr Event)
                                 *Note: (S) denotes a surcharging node

The results demonstrate that the proposed on-site detention volume generally provided at least equal or
reduced HGL levels and flow rates compared to the pre-development scenario. Furthermore, it was found
that the surcharging gully inlets in the pre-development 10 year event do not surcharge in the post-
development design due to the reduction in flow. The proposed stormwater management plan therefore
satisfies both Council and QUDM requirements for non-worsening discharge.