PA2906-Coastal Hazard Assessment-R1 · MCU21/0212

                                                 Internal use only




6.1.3       Recession due to Sea Level Rise
As discussed in Section 5.1.2, sea levels are predicted to rise in response to climate change and the
Queensland Government have adopted a sea level rise of 0.8 metres above present day mean sea level
by the year 2100. The Department of Environment and Heritage Protection (2013) requires the shoreline
response to sea level rise be considered when assessing erosion prone area widths. An industry
standard practice for the assessment of shoreline recession due to sea level rise is to apply the ‘Bruun
Rule’ (Bruun, 1962), see Figure 18.




Figure 18 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 18. The Bruun Rule is given by:

𝑟=                Equation 2

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

The Bruun Rule assumes that the beach and dune consist of a uniform loose sand material. It is also
applicable to long straight sections of beach. The geotechnical assessment which is supported by aerial
photography from 1974 has shown the underlying soil profile includes indurated sand layers (i.e., coffee
rock) which may slow recession rates.

The assessment of recession due to sea level rise is presented in Table 6. The profile adopted has been
based on site survey supplemented with Sunshine Beach profile survey for ETA 602.0. Based on the
information available an active beach height of 40 metres has been adopted from the depth of closure of -
12m AHD to the dune height at the rear of the subject property of 28m AHD. This provides an active
beach profile width of 550 metres.
Table 6 Summary of Shoreline Recession due to Sea Level Rise


                                 Profile Width     Dune Height      Depth of Closure      2100 Shoreline Recession
             Beach
                                      (m)            (m AHD)             (m AHD)                     (m)

             Sunshine Beach           550               28                  -12                      11



15 October 2021       66 SEAVIEW TERRACE, SUNSHINE BEACH                           PA2906-RHD-ZZ-XX-RP-Z-0001        26