Refernce Documents - RAL25 0001

                     Table 5.2.2-5 shows a comparison of the peak flow depths and Water Surface Level within
                     the model Link 31 downstream of the Hoy Road crossing for the pre and post
                     development scenarios. Whilst a minor increase in flow was observed for the critical 63%
                     and 39% AEP peak flow in Table 5.2.2-4, there is no discernible change to the associated
                     flow depth and water surface levels and will not result in an adverse impact on the
                     downstream properties.
                                          Table 5.2.2-5 XP Storm Model Results – Peak Depth and WSL
                                         AEP      Pre Dev      Post Dev    Difference    Pre WSL       Post WSL
                                                 Depth (m)     Depth (m)       (m)         (m)           (m)
                                                  Link 31       Link 31                  Node 31       Node 31
                                         63%        0.15          0.18          0.03      97.47         97.50
                                         39%        0.21          0.21          0.00      97.53         97.53
                                         18%        0.26          0.25         -0.01      97.58         97.57
                                         10%        0.29          0.27         -0.02      97.61         97.59
                                         5%         0.32          0.29         -0.03      97.64         97.61
                                         2%         0.35          0.32         -0.03      97.67         97.64
                                         1%         0.38          0.36         -0.02      97.70         97.68


                     Peak flow characteristics at the Hoy Road crossing are shown in Table 5.2.2-6.
                                                Table 5.2.2-6 Hoy Rd Crossing Flow Characteristics
                            AEP         Flow    Max Velocity   Depth of Flow      Max    Velocity DS    US WSL    DS WSL
                                       (m3/s)     Through      Over Causeway     Depth      (m/s)        (m)        (m)
                                                 Pipe (m/s)         (m)           (m)
                            63%         2.1         1.14             0.0          0.58      1.34         98.02    97.88
                            39%         2.9         1.37             0.0          0.74      1.53         98.17    97.94
                            18%         3.9         1.75             0.0          0.94      1.70         98.36    98.01
                            10%         4.6         2.08             0.0          1.07      1.80         98.48    98.05
                             5%         5.4         2.34             0.0          1.23      1.89         98.70    98.10
                             2%         6.6         2.59            0.06          1.39      2.00         98.88    98.15
                             1%         8.0         2.70            0.12          1.48      2.12         98.94    98.22


                     The results indicate that some smaller duration and AEP storm events (10min, 15min,
                     20min and 30min durations) have not achieved non-worsening of discharge for their
                     equivalent event. This is a result of the ARR pervious initial losses reducing the volume
                     of runoff significantly due to the volume of the storm being less than the initial losses,
                     for example. A 63% AEP 30minute storm volume including pre-burst is 29.92mm while
                     the ARR initial loss is 35 mm.


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Document Set ID: 23448644
Version: 1, Version Date: 13/01/2025