33522 Stormwater report018-01 SWQA issued 180704 · MCU18/0001

                                                                                    CIVIL ENGINEERING PROJECT MANAGEMENT
                                                                                           SEDIMENT AND EROSION CONTROL




              FLOW CALCULATIONS


The purpose of the management plan is to ensure the current infiltration system designed for the site is
adequate to contain flows generated by the proposed development. It will also assess whether the existing
overland flow path and existing stormwater easement (Easement B SP279875) are required.

It is expected the proposed development will generate up to approximately 90% of the site with an impervious
surface (Refer Appendix A). From the initial stormwater assessment (Aquaintel Report dated 3rd July 2014)
produced for the site; and on which the stormwater infiltration system was designed and constructed, an
impervious fraction of 70% was estimated.

Calculations generated from the WBNM model in the initial stormwater quantity assessment provided peak
flows for design storm event, with the 15-minute storm being noted as the critical duration. These flows have
been reproduced and are tabulated below in Table 1.


Table 1 - Developed Scenario WBNM Peak Flows

 Catchment             1yr ARI   2yr ARI     5yr ARI       10yr ARI      20yr ARI       50yr ARI        100yr ARI
                       (m3/s)    (m3/s)      (m3/s)         (m3/s)        (m3/s)         (m3/s)          (m3/s)
    Lot 696            0.016     0.021        0.027         0.030         0.034          0.037             0.041
(Aquaintel 03.07.14)


Discussions held with Noosa Council (and documented in the Aquaintel report) indicate that any development
needs to demonstrate that all but the most extreme rainfall events would be infiltrated and that any infiltration
tanks are to be sized to cater for all design events up to and including the 1% AEP (1 in 100-year ARI design
event).
With an increase in the impervious fraction to 90%, the original WBNM model was regenerated and provided
an increase in the peak flow for a 1% AEP design storm event from 0.041m3/s to 0.043 m3/s.




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