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

                        Table 16: XP Storm Developed Unmitigated Peak Flow Results – Lot 7 (South) (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               0.143      0.161      0.218       0.255        0.290          0.308       0.339
                           25               0.138      0.156      0.212       0.254        0.292          0.306       0.339
                           30               0.126      0.143      0.195       0.234        0.270          0.287       0.319
                           45               0.115      0.130      0.179       0.211        0.242          0.266       0.299
                           60               0.121      0.138      0.196       0.237        0.277          0.304       0.339
                           90               0.105      0.121      0.176       0.210        0.244          0.253       0.283
                           120              0.102      0.117      0.171       0.207        0.242          0.249       0.280
                           180              0.065      0.075      0.111       0.134        0.157          0.167       0.189
                        Critical            0.143      0.161      0.218       0.255        0.292          0.308       0.339
                  Critical Even (Min)         20         20         20           20          25            20           20


        Discharge hydrographs for the existing model have been included in Appendix F.

4.2.6   Detention Basin Design


        For the developed mitigated scenario, storage nodes representing the proposed detention basins were included in the
        model. Flows from all three development catchments were routed to the assigned detention tanks for each catchment.


        The storage node inputs were sourced based on in-ground tanks for all three catchments, as well as the proposed bio-
        basins discussed in Section 5. The six detention tanks modelled for each of the three catchments are outlined in Table 17.

                                 Table 17: XP Storm Developed Model Hydraulic Routing
          Development Sub-Catchment    Invert Elevation Internal Height  Surface Area                           Approximate Volume
                                                       (RL)                (m)                (m2)                     (m3)
                  Lot 3 Detention Tank                 5.50                2.5                 800                    2,000
                Lot 3 Bio-Retention Basin              3.80                1.5                 560                     840
            Lot 7 (North) Detention Tank               6.50                1.8                 110                     200
         Lot 7 (North) Bio-Retention Basin             6.30                1.8                    27                    49
           Lot 7 (South) Detention Tank                6.50                1.8                 160                     228
         Lot 7 (South) Bio-Retention Basin             6.30                1.8                    33                    60


        The outlets to each of the three detention tanks were modelled as per the below:


            •      Lot 3 Catchment:
                       o    Detention Tank:
                                   ▪   Low-flow outlet: 150mm diameter orifice with invert at RL 5.50m;
                                   ▪   Mid-flow outlet: 300mm diameter orifice with invert at RL 6.90m;
                                   ▪   High-flow outlet: 525mm diameter orifice with invert at R: 6.90m; and
                                   ▪   High-flow weir: 10m long weir with crest height at RL 7.20m.
                       o    Bio-Retention Basin:
                                   ▪   Low-flow outlet: 300mm diameter orifice with invert at RL 5.30m;
                                   ▪   Mid-flow outlet: 300mm diameter orifice with invert at RL 6.60m;
                                   ▪   High-flow outlet: 100mm diameter orifice with invert at R: 6.80m; and
                                   ▪   High-flow weir: 10m long weir with crest height at RL 7.65m.




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