Appendix D- Stormwater Management Plan · MCU23/0078

4.1.7   Hydraulic Impacts on Downstream Waterway Corridor


        A comparison of critical peak flows for the existing and developed mitigated scenarios has been included in Table 10, 11
        and 12. The hydraulic modelling undertaken has demonstrated that the proposed development will not cause a worsening
        impact downstream of the site in all storm events and that the detention has been adequately sized. Therefore, the
        required detention volume for all three catchments across the development in the 1% AEP storm event is 2,670m3.


        Discharge hydrographs, stage/water elevations for the detention basin and associated XP Storm outputs have been
        included in Appendix E of this report to demonstrate the performance of the proposed detention system.

                Table 13: XP Storm Existing and Developed Mitigated Peak Discharge Comparison – Site A (m3/sec)
                   ARI (Years)    Existing Critical Discharge   Developed Critical Discharge     Discharge Difference

               1                             0.134                          0.128                        -0.006
               2                             0.197                          0.179                        -0.018
               5                             0.431                          0.369                        -0.062
               10                            0.613                          0.536                        -0.077
               20                            0.813                          0.699                        -0.114
               50                            0.998                          0.896                        -0.102
               100                           1.182                          1.158                        -0.024

           Table 14: XP Storm Existing and Developed Mitigated Peak Discharge Comparison – Site B (North) (m3/sec)
                   ARI (Years)    Existing Critical Discharge   Developed Critical Discharge     Discharge Difference

               1                             0.013                          0.013                         0.000
               2                             0.018                          0.017                        -0.001
               5                             0.039                          0.037                        -0.002
               10                            0.054                          0.050                        -0.004
               20                            0.070                          0.061                        -0.009
               50                            0.083                          0.070                        -0.013
               100                           0.098                          0.097                        -0.001


           Table 15: XP Storm Existing and Developed Mitigated Peak Discharge Comparison – Site B (South) (m3/sec)
                   ARI (Years)    Existing Critical Discharge   Developed Critical Discharge     Discharge Difference

               1                             0.022                          0.016                        -0.006
               2                             0.031                          0.022                        -0.009
               5                             0.064                          0.046                        -0.018
               10                            0.087                          0.061                        -0.026
               20                            0.114                          0.104                        -0.010
               50                            0.136                          0.134                        -0.002
               100                           0.161                          0.161                         0.000




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