MNA_250215_33 Ross Crescent Sunshine Beach_00

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




In their analysis of Sunshine Beach, BMT (2018) categorized short-term erosion into C1 and C2
components when the dune toe level fell below the storm tide level. Figure 6-12 shows the conceptual
illustration of the approach adopted by BMT (2018). Specifically for Sunshine Beach (ETA 595 and ETA
602), BMT (2018) assigned a C1 value of 21m and 52m and a C2 value of 0m for short-term erosion. It is
important to highlight that BMT conducted the short-term erosion assessment from the design water level
line rather than the toe of the frontal dune, which is not consistence with the Queensland Hazard Technical
Guide (DEHP, 2013). Had BMT measured from the dune vegetation, the short-term erosion would have
been 6m (Figure 6-13) and 40m (Figure 6-14), resulting in an average C of 23m, not 37m. This 23m is
closer to the 20m calculated for this assessment. The difference of 3m is attributed to the difference in
water level.

RHDHV conducted a site-specific assessment of the short-term erosion based on Vellinga (1983). The
finalised adopted short-term erosion component was set at 27m. The site inspection and survey of the site
indicates that the toe of the frontal dune can be approximated at 2.3m AHD (refer Section 2.4). Dividing
the short-term erosion component into C1 and C2 as adopted by BMT (2018) is therefore not applicable for
this section of beach.

The main reason for the difference in short-term erosion between both studies is the design water level
used and where the short-term erosion was calculated from. Note in both studies that C2 equals zero as
the dune's toe is situated above the design water level.




Figure 6-12 BMT (2018) conceptual illustration of the erosion prone area components




                                                                                                                         33