MNA_250215_33 Ross Crescent Sunshine Beach_00

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



       “For a tide-dominated coast where storm tide levels can be large, the parameters adopted
       for the minimum design storm are:
        • storm tide level corresponding to an average recurrence interval of 1-in-100 years; and,
        • wave height for a moderate storm using the 1-in-20-year significant wave height (Hs).

       However, for wave-dominated coastlines where extreme storm tide levels can be relatively
       minor, such as the Gold Coast, the significant wave height and duration of the storm event
       are major factors influencing short-term erosion, rather than storm tide. Hence it may be
       necessary to consider a larger wave event (for example, a storm event with a 1-in-100 ARI)
       and a moderate storm tide level. Decisions on appropriate parameters to be used must be
       based on local conditions and the experience of the coastal engineer undertaking the
       assessment.”

In relation to the probability of such an event occurring the Department of Environment and Heritage
Protection (2013) states:

       “Although the abovementioned probability of occurrence may appear to be fairly high, it is
       considered that this choice is reasonable when considered in conjunction with the method
       used to determine erosion prone area widths. This method implies that the erosion prone
       area has sufficient width to accommodate the design storm erosion in 100 years’ time,
       when all of the estimated long-term erosion has occurred. Therefore, it also follows that for
       much of the 100-year planning period, the erosion prone area is sufficient to accommodate
       a larger 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%.”

The RHDHV (2024) assessment 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 (refer
Table 6-2). 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. Noosa
Shire Council have requested that the short-term erosion also be assessed based on a storm tide level of
1.79m AHD, which is approximately a 300-year ARI 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 Component               Storm Event (100-year ARI)
                            RHDHV (2024)         M&N (2025)
 Significant Wave Height        6.2m                 6.2m
 Storm Tide Level            1.74m AHD           1.79m AHD
 Sea Level Rise                   -                    -



An assessment of the short-term erosion associated with the event presented in Table 6-2 was undertaken
for the beach profile seaward of the property and ETA596 (to the south) and ETA602 (to the north). The
site profile was derived from site survey and 2011 bathymetric LiDAR data, while ETA596 and ETA602 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 storm events
presented in Table 6-2. The short-term erosion distance has been measured horizontally from the current


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