Response to Stormwater Management Approval Conditions Letter

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    surface levels and contours of any potentially affected properties must be provided with any application for
    a Development Permit for Operational Works for earthworks and/or stormwater drainage works.

    This may require the design and construction of drainage pipes and/or an overland flow-path within the
    development site to cater for drainage from the adjoining sites for a 1% AEP design storm.


Response

    Section 3.2.6 of Report No. 16-001014-01A demonstrates that the proposed earthworks to be carried out on site will
    not adversely impact the pattern and severity of flooding downstream, as no filling is proposed within the regional
    flood extents (up to and including the regional 1% AEP climate change storm event).

Stormwater Drainage (Quantity & Quality)

61. A suitably qualified Registered Professional Engineer, specialising in hydraulics shall prepare engineering
    drawings and specifications for stormwater designs and shall be submitted in conjunction with an
    application for a Development Permit for Operational Works.

Response

    A suitably qualified Registered Professional Engineer, specialising in hydraulics, has prepared drawings and
    specifications for stormwater design and management. Refer to Operational Works Drawings for the proposed
    stormwater devices (Drawing Set No. 16-001014-400 Series) and Report No. 16-001014-01A.


62. Stormwater pipelines within the site shall cater for 10% AEP storm event and secondary flow paths shall be
    provided within the site to cater for 1% AEP storm event.

Response

    Stormwater pipelines have been designed to cater for the 10% AEP storm event and higher storm scenarios. Road
    network and secondary overland flowpaths have been designed to convey runoff from the 1% AEP storm event.
    Refer to Stage 2 Operational Works Drawing Set No. 16-001014-100 Series for details.


63. The development must not adversely impact on the existing drainage conditions on other properties. The
    applicant must demonstrate that all stormwater runoffs from the fully developed site must be maintained at
    predevelopment rates for all storm events up to and including the 1% AEP storm event.

Response

    Section 3.2.6 in Report No. 16-001014-01A demonstrates that peak flows from the site will be reduced back to or
    below existing levels for all recurrence interval storm events up to and including the 1% AEP storm. This
    demonstrates that the development will not adversely impact existing drainage conditions on other properties.

    While aerial imagery indicates that there appears to be no existing dams on downstream properties, water balance
    analysis demonstrates that the proposed Northern (Bioretention) and Central (Water Quality Control Pond) Basins
    will not deprive downstream dams of their natural stormwater runoff. Water balance analysis results indicate that the
    average annual runoff volume at each site discharge location has not been reduced. Refer to Section 3.2.6 in
    Report No. 16-001014-01A for details.

64. Stormwater runoff generated from the development must be treated to achieve the Water Quality Objectives
    as specified under Healthy Waterways Water Sensitive Urban Design – Technical Guidelines for South East
    Queensland (2006) as well as the State Planning Policy 2014 (SPP 2014) prior to release off site. For the
    purpose of this condition, treatment of waters from catchments B1 and C1 as shown on Drawing B14158.W-
    SK100 A by Calibre Consulting, dated 050/2/16 shall be considered as part of the development to determine
    mitigation requirements and load reduction targets.

    If detailed design demonstrates insufficient footprint is available for the water quality treatment devices to
    achieve the pollutant reduction targets of 80% reduction in Total Suspended Solids, 60% reduction in Total
    Phosphorous, and 45% reduction in Total Nitrogen compared to an unmitigated development, the applicant
    must increase available space to ensure the water quality objectives can be achieved.