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

 Noosa Spit SEMP Final Report                                                                                 i
 Executive Summary




Executive Summary
The Noosa Spit at Dog Beach has been identified as an erosion hot-spot, with narrowing of the man-made
peninsular presenting a risk of a future breakthrough. Primarily, this erosion is caused by natural migration of
the channel, driven by sand infilling of the river mouth, while boat traffic adjacent to the Dog Beach is a
secondary cause of bank erosion. Works completed in 2013 were successful in stabilising the western extent
of Dog Beach; however, the rate of shoreline recession in the middle section has since increased, prompting
the need for this investigation.

Avoiding a breakthrough at Noosa Spit is important for maintaining the multiple attributes that the community
currently values. The consequences of a breakthrough include:

• Reduced attenuation of the ocean tide and increases to peak high tide water levels in the lower Noosa
  River. This reduces the freeboard for waterfront development and therefore increases the likelihood of
  flooding driven by coastal and/or fluvial processes.

• Rapid and unpredictable morphological change following a breakthrough and further loss of coastal land
  and open space that shelters existing development.

Within this projects, various shoreline erosion management options were considered for Dog Beach. A key
objective was to identify ways to reduce the risk of a breakthrough while maintaining or enhancing the
recreational, social and environmental values attributed to Dog Beach. The promoted management strategy
focuses on relocating sand from adjacent channels and shoals to replenish the Dog Beach shoreline. The
strategy seeks to provide protection from the risk of breakthrough by delivering a shoreline position equivalent
to the condition in 2013 with the following triggers for management action:

(1)   The first trigger occurs when the recreational width at Dog Beach is lost. At this time beach nourishment
      and the construction of ‘sand plugs’ to reduce the flow in the adjacent channel is to occur. These works
      would be undertaken by a small cutter suction dredge, using a mobile pipeline to deliver the sand to the
      placement locations. It is anticipated that the works would be repeated several times between now and
      2040.

(2)   The second trigger is represented by significant narrowing of The Spit width at Dog Beach (to ~20 m)
      and signals that the shoreline replenishment and channel flow reduction strategy is not performing as
      intended and/or the frequency of works is unsustainable. The notional 20 m width of land above the high
      water mark represents the likely minimum development footprint required for land-based construction of
      a seawall or similar shoreline protection structure.

The trigger-based approach is designed to avoid a seawall for as long as possible and only calls for
consideration of a seawall if the sand relocation works are unable to maintain the risk of a breakthrough at an
acceptable level. Ongoing resilience building actions, including revegetation and habitat management, are
expected to continue as part of routine maintenance.

The shoreline condition in 2019 suggests that the first trigger has been reached and therefore the shoreline
nourishment works proposed as part of the strategy could commence immediately.




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