Engineering Response · MCU23/0094

Information Request
19.     Provide a revised Stormwater Management Plan (SMP) which addresses the following:
        a.      Provide a revised stormwater quantity analysis which identifies changes in peak flows at each of
                the three proposed discharge locations. Where peak flows are still predicated to increase post-
                mitigation, then an analysis of the downstream drainage network is required in order to show that
                the performance of the drainage network will not be detrimentally affected. In this regard:
        i.      Provide an assessment for the downstream drainage network from Point B in the 1%AEP event,
                demonstrating that the QUDM major event criteria are still achieved (refer QUDM s7.4.3);
        ii.     Provide an assessment for discharge point A, demonstrating that the QUDM major/minor event
                criteria are still achieved in Eumundi-Noosa Rd; and
        iii.    Undertake a HGL analysis for the inter-allotment drainage system downstream of discharge Point
                C, showing the AEP when the system currently surcharges and surface flows through the
                downstream lots occur. Show that the frequency of surface flows through these lots will not
                increase post-development.
        b.      Include the predicted effects of climate change by including an assessment for the 1%AEP with
                increased rainfall intensity at year 2100 for each discharge location.
        c.      The engineering plan SW1.2 has details for the outlet from bio-detention basin C which differ from
                those stated in the SWMP and the 1%AEP peak water surface level on the plan is blank. Amend
                and include 1%AEP peak water surface level at year 2100.

Response

Please refer to our revised Stormwater Management Plan attached. The revised proposal has reduced the site’s
discharge points to Headland Drive and the existing inter-allotment drainage network connection in the north east
corner of the site. The revised proposal maintains existing peak flow rates at each discharge point therefore,
assessment of Council’s existing network is not considered necessary.

The Noosa Plan does not provide design criteria for regarding climate change effects to rainfall intensity nor does
it state it as a requirement. Therefore, an assessment of the predicated effects of climate change is unable to be
verified.

Issue: Stormwater Quality

The Stormwater Management Plan (SMP) provided by SCG Consulting Engineers (Reference 33132(SWMP),
Date 19 July 2023) does not include reuse assumptions and bioretention parameters required to demonstrate
compliance with the State Planning Policy and Noosa Plan 2020.
Information Request
24.     Provide and updated SMP which addresses the following issues relating to stormwater quality:
        a.      State all reuse assumptions (rate of reuse and identification of areas to be irrigated from each
                tank)
        b.      State all bioretention parameters (filter media depth, filter media area, extended detention depth,
                hydraulic conductivity etc.) required for each bio-retention bed in Section 6.1.4 of the SMP.

Response

Please refer to our revised Stormwater Management Plan attached, which includes further design assumptions
adopted in the adopted MUSIC Model. As a conservative approach, we have removed the modelling for the
rainwater harvesting tanks. A summary is as follows: -


                                                  Bio-Retention A               Bio-Retention B
                 Filter Media Depth                   400mm                         400mm
                 Filter Media Area                     50m2                          30m2
                 Extended Detention Depth             200mm                         200mm
                 Hydraulic Conductivity               180mm/hr                      180mm/hr




SCG Consulting Engineers                            Page 2 of 5                                   SCG Ref: 33132(L1)