RFI - ATTACHMENT A - SBSMP - Rev 2

                                                                                      20169 - SBSMP/2
                                                                                               Page 11




The detention basin will be designed to contain all flows up to a Q20 storm event. Storm events
exceeding Q20 will be expected to sheet flow across the boundaries at or less than pre development
flows.

Refer to Appendix F for the Concept Site Levels and Drainage Plan which details the proposed on-
site detention system.

5.4.4 Comparison of Peak Flows at Lawful Point of Discharge
The pre-development and post-development mitigated peak mean/median flow rates were
compared for the catchment and are shown in Table 5-5 below.

                                      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          Flows          Flows
           (m3/s)        (m3/s)          (m3/s)                (m3/s)         (m3/s)         (m3/s)
   1         0.035            0.033            0.021            0.000         0.026          0.029

   2         0.043            0.038            0.026            0.000         0.029          0.033

   5         0.068            0.052            0.041            0.000         0.039          0.044

  10         0.087            0.058            0.052            0.000         0.047          0.050

  20         0.107            0.066            0.064            0.000         0.056          0.056

  50         0.128            0.099            0.077            0.018         0.066          0.056

  100        0.145            0.123            0.085            0.034         0.075          0.056


The XPSTORM hydraulic modelling has demonstrated that the proposed mitigation implemented will
maintain pre-development flows (or less) for all design storms at the LPD located within Lot 46 and
62 on SP132578, southeast 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.

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.




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