Swmp

Peak flow rates determined for each 3 cases are outlined in Table 6.6.

                                 Table 6.6 – Comparison of Peak Flows (L/s)

   AEP Storm          Q1        Q2          Q5           Q10           Q20       Q50        Q100
                     (1EY)    (0.5EY)     (0.2EY)    (10%AEP)       (5%AEP)    (2%AEP)    (1%AEP)

      Existing        110       160        216           251           295       352        391
        PFR

      Mitigated       105       159        204           248           293       349        386

  (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, up to and
including the 1% AEP Design Storm.

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, SW1.2 & SW1.3 & 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
To determine if the existing lawful points of discharge for Catchment B is capable to safely convey the
post development mitigated flow we have modelled the existing drainage infrastructure as discussed in
Section 4.1 using the software PC DRAINS. The modelling has demonstrated that all post development
mitigated peak will be below existing flow rates and can be safely contained within the existing 375m2
diameter stormwater line traversing the rear of Lots 75-77 RP 71151 & Lot 3 SP 208257.

Proposed Catchment B will be connected to the existing stormwater drainage infrastructure within
Headland Drive, via a new 375 diameter RCP branch into the site.

This will increase flows within a length of the pipes within Headland Drive.

The below figure 6.2 shows the pipe run in question: -



SCG Consulting Engineers                   Page 19                               SCG Ref: 33132(SWMP)