Attachment 6 - Stormwater Management Plan and Engineering Response. · MCU23/0078

                        Table 19: XP Storm Developed Mitigated Peak Flow Results – Lot 7 (North) (m3/sec)
                        Storm Duration                                   ARI (Years)
                              (min)            1        2        5        10           20       50         100
                        20                   0.011     0.012   0.014     0.016      0.017     0.019       0.020
                        25                   0.011     0.013   0.015     0.017      0.018     0.020       0.023
                        30                   0.012     0.013   0.016     0.018      0.019     0.022       0.031
                        45                   0.013     0.014   0.017     0.019      0.021     0.036       0.055
                        60                   0.013     0.014   0.018     0.020      0.028     0.043       0.066
                        90                   0.013     0.015   0.019     0.021      0.033     0.053       0.073
                        120                  0.013     0.015   0.019     0.024      0.035     0.052       0.069
                        180                  0.013     0.015   0.019     0.025      0.035     0.048       0.082
                        Critical             0.013     0.015   0.019     0.025      0.035     0.053       0.082
                        Critical Event        45        90      90        180       120         90         180


                        Table 20: XP Storm Developed Mitigated Peak Flow Results – Lot 7 (North) (m3/sec)
                        Storm Duration                                   ARI (Years)
                              (min)            1        2        5        10           20       50         100
                        20                   0.013     0.014   0.017     0.019      0.021     0.023       0.026
                        25                   0.014     0.015   0.018     0.020      0.022     0.026       0.036
                        30                   0.014     0.016   0.019     0.021      0.023     0.034       0.043
                        45                   0.016     0.017   0.021     0.023      0.034     0.047       0.064
                        60                   0.016     0.018   0.022     0.027      0.040     0.052       0.080
                        90                   0.016     0.018   0.023     0.033      0.044     0.064       0.091
                        120                  0.017     0.018   0.023     0.036      0.046     0.065       0.089
                        180                  0.016     0.018   0.023     0.036      0.047     0.062       0.098
                        Critical             0.017     0.018   0.023     0.036      0.047     0.065       0.098
                        Critical Event        120       60      90        120       180        120         180


4.2.8   Hydraulic Impacts on Downstream Waterway Corridor


        A comparison of critical peak flows for the existing and developed mitigated scenarios has been included in Table 21, 22
        and 23. 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 3,377m3.
        Note that 949m3 of this volume is provided within the three bio-retention basins across each of the three basins, with the
        remainder of this volume provided in below-ground detention tanks.


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




                                                     www.bornhorstward.com.au                                             Page 14