Attachment 5 - Servicability Report · MCU23/0078

2.3     TOPOGRAPHY AND CATCHMENT CHARACTERISTICS

        The topography and catchment characteristics for the development site, broken down between both Lot 3 and Lot 7, are
        discussed below:


2.3.1   Lot 3 – Western Lot

            −    The high point of the existing site is RL 9.47m AHD located on the eastern side of the site;

            −    The development falls from the high point at an approximate grade of 2.5% to a low point of RL 3.88m AHD in the
                 south-western corner;

            −    During both minor and major storm events, runoff from the site discharges as overland flow over the western
                 boundary of the development site and onto the environmental zone and natural drainage channel, and is ultimately
                 conveyed through existing culverts below Hofmann Drive to Eenie Creek and Lake Weyba;

            −    As the roadways surrounding the site have been built assuming a fully developed catchment, there is no external
                 catchment.

2.3.2   Lot 7 – Eastern Lot

            −    The high point of the existing site is RL 10.63m AHD located on eastern side of the site;

            −    The development falls from the high point at an approximate grade of 1% to a low point of RL 9.2m AHD in the
                 south-west corner;

            −    During both minor and major storm events, runoff from the site discharges as overland flow over the western
                 boundary of the development site and onto the private access roadway, and is ultimately conveyed via the existing
                 stormwater drainage network along the access roadway to Eenie Creek and Lake Weyba;

            −    Lot 7 is split into two sub-catchments, with a high-point located midway along the private access road frontage,
                 with flows directed either towards the north-west onto the private access road and around Lot 3 to the
                 environmental zone and natural drainage channel, or towards the south-west onto the private access roads; and

            −    As the roadways surrounding the site have been built assuming a fully developed catchment, there is no external
                 catchment.

        See the survey plan in Appendix C for more information.


2.4     EXISTING FLOODING CONDITIONS

        The Noosa Shire Council Plan Interactive Mapping Flood Extents have been obtained for the site and states the following:

            −    No flood levels or flags for building development purposes exist for the development site; and

            −    The interactive mapping system within Noosa Shire Council Plan confirms that the development site is clear of the
                 mapped flood hazard overlay extents of Eenie Creek, and the site is expected to be at low risk of flood inundation
                 from Ennie Creek.

        A local flood assessment of the area was undertaken to determine water levels within the natural drainage channel through
        the environmental zone bounding Lot 3 under existing conditions for the 1% AEP storm event (with increased rainfall
        intensities for the year 2100). The results of this study were used to ensure any openings along the basement wall on the Lot
        3 western boundary were set at a level to be adequately protected from water inundation within the drainage channel.
        Further details on this study can be found in Bornhorst and Ward’s Stormwater Management Plan.




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