2019-06-11 Services & Organisation Committee Agenda

SERVICES & ORGANISATION COMMITTEE MEETING AGENDA                                                    11 JUNE 2019


    East and south-easterly wind and wave conditions (January to September) transport sand
      along the Main Beach, which collects at the Spit groyne until such time that no more
      storage is possible and bypassing occurs. This bypassing creates a shoal anchored to the
      southern shore in front of the north-shore-anchored shoal and reinforces the north-south
      orientation that also increases erosion at Noosa Spit.
    Without rainfall, the river mouth will naturally increase the volume of sand over time due to
      a combination of tide, wind and wave effects.
    With rainfall, the river mouth will decrease in sand volume, with high rainfall events able to
      overtop the northern and southern connected shoals and re-establish a straighter, central
      river alignment, reducing erosive pressure on the Noosa Spit.
Further to these findings, Griffith University have been conducting an investigation into the Noosa
river mouth dynamics as part of a broader south-east Queensland project that is set to be
presented later this year at a coastal conference. Discussions with the research team at Griffith
indicate that their findings are generally supportive of the observations of BMT-WBM.




 Figure 1: River Mouth July 2017 (left) and March 2019 (right). The left image clearly shows the shoal features and
north-south alignment, while the right image shows the most recent river alignment with a sustained middle channel
                                              due to increased rainfall.

3. Erosion Update
As can be seen in Figure 1, there is a development and stabilisation of the middle channel
between 2017 and present. An analysis of aerial photography across this time period has shown
that this has resulted in a considerable reduction in the rate of erosion at Noosa Spit. While in
2017 the Spit was receding at approximately 9m per year, this rate has reduced to approximately
2m per year as of the latest image in March 2019. Earlier erosion rates were enhanced by a river
alignment that was ideal for erosion as well as strong storm systems with a northerly wind
aspect, including Tropical Cyclone Debbie.
Over the past year, major storm systems provided east and south easterly wind aspects which
have limited erosive influence on the Spit, while the river alignment has been less problematic for
Noosa Spit. As a consequence the current reduced erosion rate is relieving timing pressures
around the SEMP project and is providing more time to adequately understand this system and
deliver suitable solutions, however, it should be noted that this favourable outcome could reverse
if rainfall through winter and spring is insufficient to maintain the current river alignment.




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