Attachment C_R.B23636.001.02.SEMP_final_lowres

Noosa Spit SEMP Final Report                                                                                  3
Noosa Spit Shoreline Erosion




2       Noosa Spit Shoreline Erosion
2.1     Introduction
        The findings from an analysis of historical shoreline movements in the mouth of the Noosa River are
        presented in this section, including:

        • An update to the conceptual understanding of shoreline recession at The Spit and Dog Beach
          based on recent observations;

        • An evaluation of the current shoreline erosion management strategy;

        • The estimated rate of shoreline recession at Dog Beach and the potential timeframe for a
          breakthrough event if left untreated; and

        • Identification of potential entrance configuration scenarios to be assessed with the numerical
          modelling developed for the SEMP and presented in Chapter 3.

2.2     Previous Assessments
        The Noosa Spit area was largely established by the construction of the Noosa River training wall,
        starting in 1978. The historical movements of the channels and sand shoals in the mouth of the
        Noosa River have previously been described by Tomlinson and Chamberlain (2006). That study
        qualitatively considered aerial imagery captured between May 1972 and January 2002.

        Migration of the river channels occurs in response to tidal flows and weather conditions, dominant
        seasonal wind directions and catchment rainfall contributing to riverine flows. Tomlinson and
        Chamberlain (2006) indicate that prior to the late 1960’s, the Noosa River channel entrance tended
        to re-establish following storm or flood events in a “more direct south-eastern channel and migration
        of the entrance to a more easterly position” (i.e. the approximate vicinity of Noosa Woods). Historical
        imagery only captures the internal channels downstream of Munna Point running close to the
        northern bank, although the lack of vegetation on the extensive sand shoals elsewhere in the river
        mouth indicates highly mobile sand deposits.

        The continual movement and re-establishment of the channel close to the centre of the historical
        river mouth opening reflects the complexity of combined impacts of flood and tidal flows, along with
        longshore sediment transport continually supplying sand to the area.

        The formalisation of Hayes Island in the early 1970’s and the subsequent construction of the Noosa
        River training wall in 1978 now restricts the channel to the northern half of the historical river mouth.

        An assessment of erosion at The Spit was made by International Coastal Management (ICM) in 2010
        (ICM 2010a). That assessment included observations of manual interference to restrict channel
        movements, such as the placement of dredged sand to close the channel immediately adjacent to
        the spit prior to 2005 (see Figure 2-1). It is unclear how frequently this dredging was undertaken, or
        the source of the dredged sand.

        In addition, several structures have been installed to mitigate erosion, including an extension of the
        southern training wall, and two geofabric sand container structures (one submerged) at each end of
        Dog Beach. These are described and considered further in Section 2.4.




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