Storm Water management plan · MCU12/0133.03

Noosa Council documents


                  Bligh Tanner Consulting Engineers                                                                           Page 15
                  Noosa Flexi Learning Centre Stormwater Management Plan
                  August 2012



                  impervious has been conservatively adopted at 20% (the actual ground level impervious
                  area, including the full area of the carpark, is about 10%).

                  Table 7 Rational method estimates of peak flows
                                               Predeveloped                                   Developed
                  Area                         0.8 ha                                         0.8 ha
                  Frequency factor (Fy)        1.2                                            1.2
                  Fraction Impervious (Fi)     0%                                             20%*
                  C10                          0.53                                           0.74
                  Time of concentration                            10 minutes                 10 minutes
                  I (mm/hr)                                        250                        250
                  Peak Flows
                  Q2 (m3/s)                                           0.1                     0.2
                  Q10 (m3/s)                                          0.2                     0.3
                  Q100 (m3/s)                                         0.4                     0.5
                  *
                                              0.60

                                                     Predevelopment
                                              0.50
                                                     Post-development
                      Peak discharge (m³/s)




                                              0.40


                                              0.30


                                              0.20


                                              0.10


                                                -
                                                         2                      10                    100
                                                                 Average Recurrence Interval (yrs)

                  Figure 6 Comparison of pre and post developed peak flows (without mitigation). The
                  increase in peak flow for the Q100 is about 140 litres per second.

                  The increase in the Q100 flow as a result of the development, in absolute terms, is about 140
                  litres per second.

                  The detention size, in accordance with initial sizing method outlined in chapter 5.05 of
                  QUDM, has been estimated at 1 m³ (being the average of QUDM equations 5.01, 5.02, 5.03
                  and 5.04).

                  This flood detention is particularly small and could be considered immaterial particularly in
                  light of
                      • the limited infrastructure between the site and the receiving environment (being
                           raised classrooms and sporting facilities)
                      • the small increase in peak flow is unlikely to have a significant impact on the erosivity
                           of flows in Burgess Creek given it has a far larger catchment

                  Nonetheless the small volume will be easily provided for as follows (in order of preference):
                     • in the infiltration depressions beneath the buildings



                                                                                                            Print Date: 2 March 2020, 2:19 PM