Approved Plans - MCU18-0097 · MCU18/0097

                 GOOD SHEPHERD LUTHERAN COLLEGE                                                                 ODYSSEY CONSULTING GROUP
                 Lot 30 on SP170751                                                                  Conceptual Stormwater Management Plan
                 115 Eumundi Noosa Road, Noosaville                                                                        Project No: K4277

                          The 2, 10 and 100 year ARI storm events were analysed for all standard durations ranging from 10
                          minutes to 180 minutes. It was determined that the 25 minute storm is the critical duration for the
                          peak site discharge for both the pre development and post development scenarios. The combined
                          peak discharge rates for the site calculated by the DRAINS model is shown below for both scenarios.

                          Table 13:      Peak Discharge Rate for Site (m3/s)
                                                                       Q2                      Q10                         Q100


                                  Pre Development                    0.104                 0.169                          0.277


                           Post Development (unmitigated)            0.163                 0.264                          0.427


                          As the development will increase peak discharge rates from the site, onsite detention will be required
                          to attenuate runoff to pre development levels.

                 4.3      Detention Volume
                          The following detention storage parameters were found to achieve the target mitigated pre
                          development flow rates:

                          Table 14:      Detention Tank A Parameters
                            Detention Tank Base Surface Area                                                60 m2
                            Detention Tank Top Surface Area                                                 60 m2
                            Detention Tank Invert Level                                                    7.70 m
                            Detention Tank Height (including 300mm freeboard)                                2m
                            Low Flow Outlet Orifice (at invert of detention tank)                         240 mm
                            Mid Flow Orifice Diameter (at 0.63 m above invert of
                                                                                                          120 mm
                            detention area)
                            High Flow Weir (at 1.58 m above invert of detention
                                                                                                            1.8 m
                            tank)
                            Detention Volume (not including freeboard)                                     100 m3

                          The 25 minute design storm was the critical storm event for determining the required volume within
                          the tank. A comparison of the pre development, post development and mitigated flow rates based on
                          the above arrangement is shown in Table 15 followed by the hydrograph in Figure 3 for the critical
                          duration of the Q100 storm event.

                          Table 15:      Comparison of Pre Development, Post Development and Mitigated Flow Rates for Catchment B
                            Average Recurrence Interval                                    2                    10                100
                            DRAINS Pre Development Flow Rate            m3/s             0.104                0.169               0.277
                            DRAINS Post Development Flow Rate
                                                                        m3/s             0.163                0.264               0.427
                            Catchment A Q100
                            DRAINS Mitigated Development Flow Rate      m3/s             0.104                0.168               0.274




                 K4277-0002-E                                            18 June 2019                                             Page 8 of 14
Document Set ID: 20894174
Version: 1, Version Date: 03/07/2019