Stormwater Management Plan

Good Shepherd Lutheran College                                                                        Odyssey Consulting Group
Proposed Unit Development                                                              Conceptual Stormwater Management Plan
Lot 30 on SP170751                                                                                           Project No: K4277
115 EUMUNDI NOOSA ROAD, NOOSAVILLE

        Table 8:      External Catchment

                                                                                   Time of concentration

                          Catchment           Catchment                                Concentrated
          Catchment               2                             Overland flow              flow
                           Area (m )          Properties                                                       Total tc
                                                               Friend’s Equation       QUDM Figure
                                                                                          4.09

                                               Open             Horton’s (n) =
                                           Space/parks –             0.035
              A              449            Light cover            L = 31 m                 n/a               11.04 min
                                          bushland / poor       Slope = 4.38%
                                            grass cover         t = 11.04 min



3.4.4   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 9.

        Table 9:      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          0.042      0.042         0.042       0.042        0.042
          Average Rainfall Intensity (mm/h)         I          121.1      149.7         166.0       188.6        240.5
          Peak Flow Rate (m3/s)                     Q          0.008      0.012         0.014       0.016        0.024



3.4.5   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 eastern boundary. For details and locations of the
        proposed field inlet refer to Odyssey Consulting Group, Stormwater Management Plan (Ref:
        K4277/P007/A) 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.




K4277-0002                                              14 March 2018                                             Page 7 of 16