PA3660-Coastal Hazard Assessment - 4 arakoon

                                                 Project related




           storm than the one selected for design purposes. In fact, in the most critical last
           10 years of such a planning period, there is only a 10% probability of occurrence
           of the design storm. Thus, the risk of a storm breaching the entire erosion prone
           area at some time during the 100-year period will be significantly less than 63%.”

This assessment has adopted a combination of a 100-year ARI Storm Tide level and 100-year ARI
significant wave height as the design storm event for the reassessment of erosion prone area. It should
be noted that the joint probability of a combined 100-year ARI storm tide and 100-year ARI significant
wave height is likely to be significantly greater than a 100-year ARI storm event. The design parameters
for the assessment of the short-term beach erosion are presented in Table 6-2.


Table 6-2 Design Storm Events for Short-term Beach Erosion Assessment
                                                   Storm Event
 Storm Component
                                                   100-year ARI

 Significant Wave Height                                  6.2m

 Storm Tide                                         1.74m AHD

 Sea Level Rise                                            -


An assessment of the short-term erosion associated with the design storm event presented in Table 6-2
was undertaken for the beach profile seaward of the property and ETA602 (to the south) and ETA604 (to
the north). The site profile was derived from site survey and 2011 bathymetric LiDAR data, while ETA602
and ETA604 was derived from 2015 LiDAR and 2011 LiDAR bathymetry. These profiles were analysed to
obtain an average short-term erosion.

Vellinga (1983) has been used to derive the storm erosion profile based on the design water level of
1.74m AHD. The short-term erosion distance has been measured horizontally from the current toe of the
frontal dune (refer Section 2.3) to the base of the erosion scarp predicted by Vellinga (1983). As
discussed above in Section 2.3 the current toe of frontal dune is 2.3m AHD which is higher than the
design water level (1.74m AHD).

The average of the short-term erosion values for ETA602, site and ETA604 profiles provides a
representative short-term erosion value for this compartment spanning 800 metres of Sunshine Beach.

Table 6-3 presents the predicted short-term erosion associated with the 100-year ARI design storm event
for the three profiles. This shows that an average storm erosion cut of 19m is predicted for Sunshine
Beach. The storm cut profile for ETA602, the section in front of 4-6 Arakoon Crescent, and ETA604 are
shown in Figure 6-3, Figure 6-4 and Figure 6-5 respectively.


Table 6-3 Predicted Short-term Erosion - Sunshine Beach
 Profile                           Short- Term Erosion (m)

 ETA602                                             30

 Site                                               14

 ETA604                                             13

 Average                                            19




11 April 2024         4-6 ARAKOON CRESCENT, SUNSHINE BEACH              PA3660-RHD-XX-ZZ-RP-Z-0001   28