Stormwater Management Plan

GOOD SHEPHERD LUTHERAN COLLEGE                                                                     Odyssey Consulting Group
Lot 30 on SP170751                                                                  Conceptual Stormwater Management Plan
115 Eumundi Noosa Road, Noosaville                                                                        Project No: K4277

         Table 10:      Peak Discharge Rate for Site (m3/s)
                                                      Q2                      Q10                         Q100


                 Pre Development                    0.104                 0.169                          0.277


         Post Development (unmitigated)             0.174                 0.280                          0.440


         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 11:      Detention Tank A Parameters
                                                                                                   2
           Detention Tank Surface Area                                                     100 m
           Detention Tank Invert Level                                                      9.14 m
           Detention Tank Height                                                            1.26 m
           Low Flow Outlet Pipe Diameter                                        300 mm @ Invert of tank
           Low Flow Orifice Diameter                                                       210 mm
           High Flow Orifice Diameter                                                      110 mm
           High Flow Outlet Pipe Invert Level                                               9.63 m
           Over Flow Outlet Diameter                                                       150 mm
           Over Flow Outlet Pipe Invert Level                                               9.95 m
                                                                                                   3
           Detention Volume                                                                126 m

         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 12 followed by the hydrograph in Figure 3 for the critical
         duration of the Q100 storm event.

         Comparison of Pre Development, Post Development and Mitigated Flow Rates for Catchment B

         Table 12:      Comparison of Pre Development, Post Development and Mitigated Flow Rates for Catchment B
                     Average Recurrence Interval                          2                     10                   100
                     DRAINS Pre Development                    3
                                                              m /s        0.104                 0.169                0.277
                     Flow Rate
                     DRAINS Post Development
                                                               3
                     Flow Rate                                m /s        0.174                 0.280                0.448
                     Catchment A Q100
                     DRAINS           Mitigated                3
                                                              m /s        0.104                 0.169                0.277
                     Development Flow Rate




K4277-0002-C                                         05 November 2018                                            Page 8 of 16