RFI - Stormwater Mgm Plan 20169 - SBSMP - Rev 4 (2)

                                                                                         20169 - SBSMP/4
                                                                                                    Page 13




                                       Table 5-5 - Comparison of Peak Flows
         XPSTORM       XPSTORM         XPSTORM       XPSTORM         XPSTORM                  XPSTORM
        Catchment A   Catchment A     Catchment B   Catchment B     Catchment C              Catchment C
  ARI       Pre-         Post-            Pre-         Post-            Pre-                    Post-
(years) development   development     development   development     development              development
           Flows    Flows (Mitigated)    Flows    Flows (Mitigated)    Flows                    Flows
           (m3/s)        (m3/s)          (m3/s)        (m3/s)          (m3/s)                   (m3/s)
   1         0.036             0.032           0.058            0.046            0.027          0.016

   2         0.043             0.038           0.071            0.056            0.030          0.018

   5         0.068             0.052           0.112            0.084            0.041          0.024

   10        0.087             0.060           0.142            0.102            0.050          0.027

   20        0.107             0.067           0.175            0.120            0.060          0.031

   50        0.129             0.084           0.210            0.137            0.070          0.031

  100        0.146             0.106           0.240            0.157            0.080          0.031


The XPSTORM hydraulic modelling has demonstrated that the proposed mitigation implemented will
maintain pre-development flows (or less) for all design storms at the LPDs located within Lot 46
and 62 on SP132578, southeast of the site, and Lot 79 on SP138388, northeast of the site. The
modelling has also demonstrated that post-development mitigated flows up to Q20 can be conveyed
through the 225 to 450mm diameter stormwater line traversing the rear of Lots 45, 46 and 62 on
SP132578 and Lots 42-44 on SP144002 and the existing 300mm diameter stormwater line within the
driveway of Lot 79 on SP138388.

Refer to Appendix H for the pre-development XPSTORM results, Appendix I for the post-
development XPSTORM results and Appendix J for the XPSTORM post-development mitigated
results.

5.4.5 Sensitivity Analysis for 1% AEP Storm Event at end of Planning Period 2100
A sensitivity analysis has been undertaken to determine the impact from a 1% AEP storm event at
end of planning period 2100 takes into account a 20% increase in rainfall intensity for climate
change. As part of the sensitivity analysis, post-development mitigated peak mean/median flow
rates were calculated in XPSTORM as a result of incorporating the 20% increase in rainfall intensity
for the catchment and are shown in Table 5-6 below for a 1% AEP storm event.

                       Table 5-6 – 2100 Post Development Mitigated Peak Flows
          XPSTORM Catchment A                XPSTORM Catchment B           XPSTORM Catchment C
 AEP
     Post-development Flows (Mitigated) Post-development Flows (Mitigated) Post-development Flows
 (%)
                  (m3/s)                             (m3/s)                        (m3/s)
   1                   0.142                                 0.201                          0.037


The XPSTORM hydraulic modelling shows that the water level exceeds the emergency weir level in
the southern basin by approximately 36mm. However, as can be seen when comparing flows
between Table 5-5 and Table 5-6, pre-development flows are still maintained for Catchment A.
There is also a 300mm wide gap between the boundary and the basin wall where emergency
overflow will fall onto natural ground level prior to sheet flowing across the boundary. Therefore,
pre-development drainage conditions are not expected to be worsened for the downstream
properties within Lot 46 and 62 on SP132578, southeast of the site.

Site Based Stormwater Management Plan
Proposed Townhouse Development at 99, 101 & 105 Eumundi Noosa Road, Noosaville