MNA_250215_33 Ross Crescent Sunshine Beach_00

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



for the assessment of shoreline recession due to sea level rise is to apply the ‘Bruun Rule’ (Bruun, 1962),
see Figure 6-5.




Figure 6-5 Conceptualisation of recession due to sea level rise due to Bruun Rule (Bruun, 1962)

The Bruun Rule assumes an equilibrium beach profile is maintained with rising sea level resulting in an
elevation and landward movement of the profile, as shown in Figure 6-5. The Bruun Rule is given by:


r=


Where:
 =        shoreline recession due to sea level rise (m)
 =        horizontal distance of the active beach profile (m)
 =        rise in mean sea level (m)
 =        vertical height of the active beach profile (m)

The Bruun Rule assumes that:

     •   the beach and dune consist of a uniform and loose sand material. It cannot be applied to rocky
         headlands or hard coasts;
     •   the beach responds to an elevated sea level such that an equilibrium profile is always attained;
     •   the beach is stable in the long term (i.e. there is no net accretion or recession). Gradients in
         longshore sediment transport are ignored; and,
     •   all the eroded sediment is redistributed along the profile in the cross-shore direction.

The geotechnical assessments conducted in the nearby vicinity of the site has shown the underlying soil
profile includes indurated sand layers (i.e., coffee rock), which may slow recession rates.

Recent research undertaken by Geoscience Australia (2021) indicates that 76% of the north-eastern coast
of Australia has been stable from 1988 to present with 11.3% retreating by more than 0.3m/year and 12.8%
accreting by more 0.3m/year. Similar trends are observed at all locations around Australia, except for the
western coast and north-western coast. During this period, sea level rise is reported to be approximately 2-
3mm/yr (5-10cm from 1988 to present). The observations from Geoscience Australia does not match to
hypothesis of long-term recession due to sea level rise predicted by the Brunn rule. Therefore, there is
uncertainty and potentially conservatism in this approach and is consistent with the Department of
Environment and Heritage Protection (2013) requirements.



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