Attachment 6 - Stormwater Management Plan and Engineering Response. · 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 within
                Covenant J and is ultimately conveyed through 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 to the
                stormwater drainage system 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;

            −   The interactive mapping system within the 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 Eenie Creek; and

            −   A local flood assessment of the are was undertaken to determine water levels within the natural drainage channel
                through the environmental zone in Covenant J along the western boundary of Lot 3. Further details of this study
                can be found in Section 4.1 below.




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