2019-07-09 P&E Agenda - Item 10 - Attachment 1 - Coastal Hazards Risk, Vulnerability and Adaptation Assessment

Noosa Shire Council Coastal Hazard Mapping                                                                 18
Erosion Prone Area Assessment




         east Queensland beaches; however, it is noted that the Vellinga model is relatively sensitive to the
         assumed sediment grain size with the erosion volume and setback distance increasing with
         decreasing grain size.

         The pre-storm upper beach profile for the assessments was obtained from topographic LiDAR
         survey acquired in 2016 and provided by Council. The upper beach profile data typically extended
         offshore to an elevation between 0 and -1.0 m Australian Height Datum (AHD). Below this
         elevation, the nearshore and offshore beach profile information used in this assessment was
         extracted from a bathymetric LiDAR survey captured in 2011 (Queensland Government, 2012).

         The combined 100 year ARI ‘surge plus tide’ level, wave height and wave setup allowance that
         define the ‘design event’ for the Noosa CHAP short term storm erosion assessments are
         summarised in Table 3-2.

         It is noted that the likelihood of the 100 year ARI storm tide event coinciding with the 100 year ARI
         wave conditions throughout the Noosa region remains uncertain however is considered a rare
         event and appropriate for planning periods of at least 100 years.

3.5.1.2 Design Erosion Events Modelling Results
         The predicted storm erosion profile at each assessment location is provided in Appendix C and the
         model inputs and assessment results are summarised in Table 3-2.

         An example storm erosion modelling result at North Shore beach is presented in Figure 3-3. The
         position of the design water level and the DNRM coastline on the surveyed beach profile is also
         shown in Figure 3-3. As discussed in Section 3.2.1.1and illustrated conceptually in Figure 3-2, the
         DNRM coastline definition has been used to estimate the dune frontal toe position and is the
         seaward reference for the storm erosion assessment and the overall open coast calculated erosion
         distance (E in Equation 3-2). Both the C1 and C2 components of the short term erosion are
         provided in Table 3-2. In situations where the DNRM coastline reference is landward of the design
         water level, the C2 term has been set to zero.

         The short-term setback distances varied significantly throughout the region, with the range between
         7 m and 63 m (n = 25, mean = 25 m, SD = 16 m) relative to the seaward toe of the frontal dune.
         The variation is primarily due to differences in the height and volume of the coastal barrier and the
         nearshore slope. Relatively subtle changes in the design storm characteristics also contribute to
         alongshore variation in the erosion estimates.

         It is also important to note that the Vellinga storm erosion estimates do not account for erosion
         controls, such as the presence of bedrock behind the beach or man-made coastal erosion
         protection structures. Consideration of the seawall at Noosa Main Beach is discussed further in
         Section 3.9.




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