SWMP change reps

       PFR A          (+1)     (-17)      (-13)        (-1)         (-9)         (-19)         (0)

      Mitigated        29       37         45           56           65           82           90

       PFR B          (+2)      (-2)       (-7)        (-3)         (-4)         (--1)        (-1)

  (PFR – Peak Flow Rate)

As shown in Table 6.6 the proposed OSD facilities have demonstrated the proposed mitigated peak
discharge flow rates will not exceed the total pre-development flows for all design storms above 2 year
ARI, up to and including the 1% AEP Design Storm. We note that there is a marginal increase in the
mitigated developed peak flow rate for the Q1 (1EY) storm event of 2L/s. However, as the increase in
stormwater discharge is considered very minor and below the design ARI for the minor stormwater
drainage system, the effect on the downstream network is considered to be insignificant and negligible.



Further, all stormwater discharging site in the developed case will discharge to the bio-retention basins
which both have an extended detention depth of 200mm prior to the allocated detention zone. This
equates to approximately 6kL of additional detention storage which has not been considered in the
calculation of peak stormwater discharge rates for the developed site. The peak stormwater discharge
values are therefore considered to be conservative and are expected to be less than the existing site. We
consider the developed site will not have a non-worsening effect on surrounding properties and
downstream network, with regard to stormwater discharge.

The proposed stormwater detention system is therefore considered to be adequate for the development.

6.2       Proposed Drainage
The proposed site drainage is detailed in drawings SCG 33132 - SW1.1 - SW1.4 (Appendix D) and is
discussed below.

As defined in the Noosa Plan 2020 stormwater drainage must be designed in accordance with QUDM
2017, therefore the following design storms were adopted: -

          1.      Minor Drainage System      -      10% AEP ARI (Q10 Storm)
          2.      Major Drainage System      -       1% AEP ARI (Q100 Storm)

6.3       Downstream Infrastructure Consideration
The mitigated peak flow rates for both discharge points will be less than existing peak flow rates
discharging to the existing drainage infrastructure located in Lot 108 on SP106085, No.6 Starboard
Avenue, & the existing stormwater drainage infrastructure located within Headland Drive, as discussed



SCG Consulting Engineers                  Page 22                            SCG Ref: 33132(SWMP).RevC