SCG 31131(SWM).RevA

6.4      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 flows up to Q100 can be safely contained within the existing 375m2 diameter stormwater
line traversing the rear of Lot 101 on SP106085. The pipe longitudinal sections and calculations have
been exported and are shown in Appendix D.



Catchment A will result in a increased discharge to the Eumundi Noosa Road kerb and channel, however
this has been limited to a Q10 flow rate of 25Lt/s at each kerb adaptor location as per Noosa Council
requirements. The net total discharge from the proposed site will remain below pre development flows
for all storms from Q1 up to Q100.



6.5      Climate Change Analysis for 1% AEP Storm Event at Year 2100


A climate change analysis has been undertaken to determine the impact for a 1% AEP storm event at
year 2100. This includes a 20% increase in rainfall intensity to allow for climate change. As part of the
Climate change analysis, Catchment A (rational method calculations) runoff flows were increased by a
factor of 1.2. For catchment B post development mitigated peak median flow rates were calculated using
PC DRAINS incorporating a 20% increase to rainfall intensity. Table 6.7 below displays the results for
the 1% AEP storm event for each catchment.



                           Table 6.7 – Post Development Mitigated Peak Flows at Year 2100

           Design               RATIONAL METHOD                          DRAINS CATCHMENT
            Storm                  CATCHMENT A                             MITIGATED POST
                           POST DEVELOPMENT FLOWS                       DEVELOPMENT FLOWS
                                          (m3/S)                                   (m3/S)

             Q100                         0.126                                     0.180




                                                                      0.180
SCG Consulting Engineers                       Page 22                               SCG Ref: 31131(SWMP).RevA