2019-12-16 GC Agenda - Item 5 - Attachment 1 - Noosa Spit Shoreline Erosion Management Plan-Part 1

 Noosa Spit SEMP Final Report                                                                              16
 Noosa Spit Shoreline Erosion




         Stage 1 of the shoreline strategy is considered to have been partially successful in stabilising Noosa
         Spit. The remaining stages of the shoreline erosion management strategy involve an extension of
         the partially submerged groyne and the installation of two smaller conventional groynes.

         While these elements may ultimately assist in successfully retaining a beach, it is considered that:

         • The founding levels of the various structures will need to incorporate the potential for undermining
           from the southern channel (i.e. they may need to be significantly deeper and therefore larger and
           more expensive structures than originally intended); and

         • Ongoing exposure to flows in the southern channel would be expected to generate scour points
           at the structures (like those already observed), causing artificial deepening of the channel, and
           possibly encouraging natural retention or re-establishment of the southern channel in this
           location.

2.4.1    Recent Shoreline Recession
         Shoreline recession at Dog Beach is not occurring linearly and is dependent on the continued
         dominance of the southern channel. In addition, The Spit has changed shape and orientation over
         time, and artificial nourishment of the beach and within the flow channels have influenced beach
         width.

         The assessment of shoreline changes seeks to clarify the understanding of:

         • Erosion of The Spit, particularly in relation to width and vulnerability to breakthrough; and

         • Availability of a beach for recreational use.

2.4.1.1 Movement of vegetated shoreline
         To provide a reliable assessment of shoreline movements along Dog Beach, measurements of
         vegetation lines relative to a fixed location or ‘baseline’ at Hayes Island (now known as Noosa Sound)
         have been made. In addition, the narrowest part of The Spit has been measured. Note that although
         this location varied slightly from year to year, it was consistently in the same vicinity.

         Measurement locations are shown in Figure 2-4, and actual measurements are reported in Table
         2-2. The monitoring lines used in this project have deliberately not been established perpendicular
         to the shoreline as The Spit has been slowly changing shape over time – a line perpendicular to the
         2019 shoreline is not perpendicular to the shorelines from the 1980’s and 1990’s. The lines have
         therefore been established on a north-south orientation and linked to readily identifiable landmarks.
         This also reduces confusion for future measurements and supports a rapid and simple assessment
         of future changes.




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