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

                          Design Flow Rates
                          Design storm flow rates have been calculated for standard storms with an ARI of 2, 10, 20 and 100
                          years for the external catchments using design rainfall intensities from the Bureau of Meteorology.
                          The Rational Method (Q = 2.78 x 10-3 CIA) has been used to calculate the design flow rates.

                          The peak flows for the external catchments are presented in Table 12.

                          Table 12:       External Catchment A Peak Flow Rates
                              Average Recurrence Interval            ARI       2        5         10         20           100
                              Coefficient of Runoff                  C         0.60     0.67      0.70       0.74         0.84
                              Area of Catchment (ha)                 A         0.045    0.045     0.045      0.045        0.045
                              Average Rainfall Intensity (mm/h)      I         121.1    149.7     166.0      188.6        240.5
                              Peak Flow Rate (m3/s)                  Q         0.009    0.012     0.015      0.017        0.025


                          External Catchment Channel Conveyance
                          External Catchment A
                          External Catchment A currently discharges stormwater through the site. Flows from External
                          Catchment A will be captured in a field inlet in the subject site’s north eastern corner and conveyed to
                          Council stormwater infrastructure on the north western boundary. For details and locations of the
                          proposed field inlet refer to Odyssey Consulting Group, Stormwater Management Plan (Ref:
                          K4277/P007/G) included as Appendix F.



                 4.0 STORMWATER DETENTION
                          The development of land will potentially increase peak flow rates from the subject site due to
                          increased impervious areas and a reduced critical time of concentration. The following section
                          provides preliminary details of an onsite detention system ensuring there will be no adverse impacts
                          associated with the increased runoff rate on downstream properties and infrastructure.

                 4.1      Objective
                          In accordance with Urban Stormwater Quality Planning Guidelines 2010 (DERM USQG) the following
                          objective has been set for stormwater discharge from the site and proposed development:
                                 No net increase in peak flows from the subject site for all events up to the Q100 storm event
                                  during the post developed condition.

                          This objective shall be achieved by detaining site runoff within a detention tank located within the
                          development.

                 4.2      Hydraulic Model
                          A calculation of the required detention volume to mitigate any increase in total site discharge rates
                          has been made using the DRAINS software programme.

                          DRAINS modelling has been adopted at the preliminary planning stage to ensure that the detention
                          tank volume is estimated with a higher degree of confidence. As finished site levels and internal pipe
                          levels are still approximate, this initial calculation is an estimate but is accurate enough to progress
                          the design with confidence.

                          The DRAINS model comprised of three post development Catchments. Catchment A and B flows shall
                          be directed towards existing stormwater infrastructure located in Walter Hay Drive via a detention
                          tank. Catchment C will remain unchanged and will discharge flows towards existing stormwater
                          infrastructure located in Walter Hay Drive.




                 K4277-0002-E                                            18 June 2019                                      Page 7 of 14
Document Set ID: 20894174
Version: 1, Version Date: 03/07/2019