Coastal Hazard Assessment · MCU25/0087

                                           17 The Esplanade, Sunshine Beach                              Report


particular stretch of beach. Through our calculations, we have determined that the dune height in the
active beach area stands at 15 meters AHD (Section 5.2.3).
BMT calculated a recession due to SLR of 26m, whereas M&N adopted a recession due to SLR of
15m.
5.3.12 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 5-14 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.
M&N 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, M&N 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 5-8, above).
BMT calculated a dune slumping factor of 16m, and M&N computed a factor of 25m.

5.4     Comparison summary
Comparison of the BMT (2018) and M&N erosion prone area assessment has identified that the
primary differences are related to the beach profiles, dune heights, storm tide levels adopted, where
the short-term erosion is measured from and the method used to calculate dune slumping. The
assessment undertaken by BMT (2018) was a broader scale assessment to determine the erosion
prone area at a beach compartment level. In comparison, the assessment presented in this report is a
site-specific assessment.
It is recommended that the erosion prone area assessment undertaken for this report is
representative of the current erosion vulnerability for the subject properties and is consistent with the
‘Coastal Hazards Technical Guide’ (Department of Environment and Heritage Protection, 2013).




                                                               252662-MN-RP-CO-0001B | 10 November 2025 | Page 37