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

 Noosa Spit SEMP Final Report                                                                               91
 Shoreline Erosion Mitigation Options




4.3.5    Option 4: three new groynes
         Figure 4-14 illustrates the model representation of the three new groynes. Key features of the option
         include:

         • The groyne crest elevation at 0 mAHD (approximately mean sea level)

         The impacts to peak tidal current figures show:

         • A local reduction to peak flood and ebbs currents in the vicinity of the three groynes suggesting
           small sections of beach could be maintained in these locations.

         • An increase in current magnitude at the head of the small groynes suggesting local scour potential
           that the design would need to be account for. A dominant channel would be expected to form and
           consolidate in the area of increased current magnitude.

         The whole of life cost estimate for this option is $1.3M with annualised costs around $70,000/year.
         This estimate is based on the costs to construct small groynes at Munna Point, with adjustments for
         inflation. This includes beach nourishment as part of the capital costs.

         The potential for impact to environmental values is primarily related to the construction phase. There
         would also be an impact to visual amenity associated with the three groynes.

         The social benefits are primarily related to stabilising a longer section of shoreline and providing a
         width of beach for recreational opportunities. It is noted that the groyne field is not expected to
         stabilise the entire length of shoreline and therefore additional management actions and costs may
         be required toward the eastern extent of the Dog Beach shoreline.

         Like Option 2, the risks to Council are generally low to medium and manageable. The exception
         being the slip and submerged hazards which could result in injury. Similar risks are associated with
         the existing training wall and groynes at Munna Point, so the groyne field does not represent a
         significant change in risk profile. Full details of the risk assessment results are provided in Appendix
         D.




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