Reference Document - Coastal Hazard Assessment - MCU24 0094 · MCU24/0094

                                 33 Ross Crescent, Sunshine Beach – Coastal Hazzard Assessment | 33 Ross Crescent Family Trust




It should be noted that the IPCC AR5 sea level rise projections are relative to 2006 mean sea level as
indicated in Figure 6-15. IPCC (2014) has estimated the mean rate of global averaged sea level rise was
3.2mm annually between 1993 to 2010 which would indicate that the mean sea level has risen by
approximately 54mm between 2006 and 2023. Both the BMT (2018) and RHDHV have adopted a 0.8m
sea level rise relative to current sea level which effectively results in adoption of a higher sea level rise
projection due to the inclusion of sea level rise that has occurred to date.




Figure 6-15 Global mean sea level rise from 2006 to 2100 (IPCC, 2014)

BMT (2018) adopted a dune height of 4.9m AHD to undertake the assessment of recession due to sea level
rise based on a profile width of 525m (ETA602) and depth of closure of 11.5m. We believe that the dune
height proposed by BMT (2018) underestimates the true dune elevation along this section of beach.
Through our calculations, we've determined that the dune height in the active beach area stands at 13
meters AHD (Section 6.2.3).

BMT (2018) calculated a recession due to SLR of 26m, whereas this assessment adopted a recession due
to SLR of 25m.
6.4.12.    Dune Slumping
BMT (2018) have adopted a conservative approach in their assessment of dune slumping based on:

    •     Calculation of the dune slumping from a scour depth of 1m below the eroded dune toe; and,
    •     Calculation of dune slumping based on the short-term erosion width including the factor of safety,
          effectively applying the factor of safety to the dune slumping component.

A schematic of the BMT (2018) approach is presented in Figure 6-12 above.

The ‘Coastal Hazards Technical Guide’ (Department of Environment and Heritage Protection, 2013)
recommends the assessment of dune slumping from the eroded toe of the dune due to short-term erosion.

RHDHV determined the dune slumping component (D) by integrating the erosion associated with both long-
term (NxR), short-term (C) and recession due to SLR (S) factors, which currently do not account for dune
slumping in their calculations.

Therefore, RHDHV derived the dune slumping factor by adding the long-term and short-term erosion
potentials from the dune toe and applying a 35-degree angle of repose for dune slumping, based on the
depth from the design water level (Figure 6-6, above).


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