Appendix D- Stormwater Management Plan · MCU23/0078

        acceptable detention sizing and non-worsening on downstream properties through comparison of the results obtained for
        existing and developed mitigated scenarios.


4.1.1   Existing Scenario Model


        Initially the existing XP Storm model was built using catchments’ parameters outlined in Table 1. The initial and continuing
        loss properties were assumed from site investigations and recent experience with stormwater modelling in the subject
        area.
                                                Table 1: XP Storm Existing Model Parameters
                         Parameter                     Site A                      Site B - North                 Site B - South
                                             Pervious     Impervious        Pervious       Impervious      Pervious       Impervious
                                              Data              Data            Data            Data           Data           Data
                         Area (ha)             3.46               -             0.249            -             0.45             -
                         Slope (%)                      2.7                               1                             1.5
                         Mannings ‘n’          0.05               -             0.015            -             0.015            -
                         Initial Loss
                                               27                 0              27              0              27              0
                         (mm)
                         Continuing
                                               2.6                0              2.6             0              2.6             0
                         Loss (mm/hr)
                         Laurenson ‘n’        -0.285            -0.285       -0.285           -0.285        -0.285            -0.285


4.1.2   Results for Existing Scenario


        Table 2, Table 3, and Table 4 indicates the existing total peak discharge rate for the site as outputted by XP storm for Site
        A, Site B North Site B South. The critical storm duration for the existing catchment was determined by simulating all storm
        events from the 1 to 100-year ARI storm events for 20, 25, 30, 45, 60, 90, 120 and 180-minute durations. The critical storm
        events can be seen within tables below.


                                        Table 2: XP Storm Existing Peak Flow Results – Site A (m3/sec)
                                                                            ARI & AEP
                  Storm Duration
                                           1 Years      2 Years          5 Years        10 Years       20 Years        50 Years        100 Years
                       (min)
                                            63%          39%              18%            10%             5%              2%               1%
                         20                0.000         0.000           0.062           0.153          0.313           0.400            0.566
                         25                0.000         0.001           0.138           0.239          0.371           0.577            0.741
                         30                0.000         0.020           0.209           0.327          0.471           0.686            0.852
                         45                0.029         0.080           0.307           0.454          0.640           0.840            1.014
                         60                0.068         0.134           0.360           0.556          0.727           0.942            1.115
                         90                0.116         0.184           0.418           0.606          0.801           0.998            1.182
                        120                0.132         0.186           0.431           0.597          0.793           0.970            1.163
                        180                0.134         0.197           0.425           0.613          0.813           0.975            1.171
                      Critical             0.134         0.197           0.431           0.613          0.813           0.998            1.182
                Critical Even (Min)         180           180             120             180            180             90               90




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