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

    Noosa Spit SEMP Final Report                                                                               13
    Noosa Spit Shoreline Erosion




2.4           Current Shoreline Erosion Strategy
              The current erosion management strategy at Dog Beach consists of several elements originally
              proposed by ICM (2010a) and illustrated in Figure 2-2. Construction of Stage 1 of the strategy was
              completed in 2013, and consisted of:

              • A training wall comprised of geofabric sand containers and rock seawall at the western end of
                Dog Beach;

              • A partially submerged breakwater constructed with geofabric sand containers at the eastern end
                of Dog Beach; and

              • Beach nourishment and sand deposition in the southern channel (associated with construction of
                the structures).

              The training wall and seawall have fixed the position of the western end of The Spit, and the training
              wall has acted as a groyne to intercept sediments carried upstream on the flood tide. Since
              construction works were undertaken, the western most 140 m of the beach has progressively
              accreted immediately east of the training wall. A large and near-permanently deep scour hole to
              approximately -9 mAHD has formed at the north-western tip of the structure, which also acts as a
              control point for the southern channel. However, in the centre of Dog Beach, southward channel
              migration has continued relatively unimpeded. It is noted that the scour depth is 3.1 m below the
              founding level indicated on the design drawings (ICM, 2010b) and may ultimately lead to a slumping
              failure of the structure1.

              At the eastern end of the channel, the submerged breakwater was largely buried by sand following
              construction, but since late 2017 is clearly fully visible in aerial imagery, and a scour pocket to -7
              mAHD has developed on the northern side of the groyne. This scour depth is 1.2 m below the
              founding level of the submerged breakwater indicated on the design drawings (ICM, 2010b) and has
              caused slumping, with the breakwater crest also approximately 1 m below the design level. This
              observation would suggest that the structure is not performing as intended. Aside from minor
              localised changes around the time of construction in the immediate vicinity of the main beach access
              point, there has been minimal change in shoreline position since 2011.

              While Stage 1 of the shoreline strategy appears to have been successful in stabilising the shoreline
              at the eastern and western ends of Dog Beach, it must be noted that the period from construction
              (2013) to 2017 coincided with non-dominance of the southern channel. Since the southern channel
              reasserted dominance in 2017, the nourishment material has been lost from the beach and erosion
              of established vegetation is now re-occurring (refer Figure 2-3).




1
    A structural integrity assessment of the training wall has not been undertaken as part of the SEMP.


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