PA3660-Coastal Hazard Assessment - 4 arakoon

                                                  Project related




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 6-13 shows the conceptual
illustration of the approach adopted by BMT (2018). Specifically for Sunshine Beach (ETA595 and ETA
602), BMT (2018) assigned a C1 value of 21m and 52m and a C2 value of 0m for short-term erosion. It's
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 6-14) and 40m (Figure 6-15), resulting in an average C of 23m, not 37m.
This 23m is similar to the 19m calculated for this assessment. The difference of 4m is attributed to the
difference in water level and the sites proximately to Noosa Headland compared to both ETA595 and
ETA602.

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 19m. The site inspection and site survey
indicates that the toe of the frontal dune can be approximated at 2.2 m 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 6-13 BMT (2018) conceptual illustration of the erosion prone area components




11 April 2024        4-6 ARAKOON CRESCENT, SUNSHINE BEACH                        PA3660-RHD-XX-ZZ-RP-Z-0001   38