ECM_22343537_v1_Coastal Hazard Assessment · 132000.200173.1

                                                               Internal use only




              6.1.3       Recession due to Sea Level Rise (S)
              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 21.




              Figure 21 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 21. 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) 0.8
              D=     vertical height of the active beach profile (m)

              The Bruun Rule assumes that:

                   1. the beach and dune consist of a uniform and loose sand material. It cannot be applied to rocky
                      headlands or hard coasts;
                   2. the beach responds to an elevated sea level such that an equilibrium profile is always attained;
                   3. 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,
                   4. all the eroded sediment is redistributed along the profile in the cross-shore direction.

              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.
              Further, as discussed in Section 5.3, net northerly sediment transport is observed along this section of the
              coastline and Noosa Head is a control feature that blocks the northern passage of sand.

              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 bathymetry survey captured in 2020 as part of the Great Barrier


              13 February 2023         2 ARAKOON CRESCENT, SUNSHINE BEACH                                      PA3303   29


Document Set ID: 22343537
Version: 1, Version Date: 16/03/2023