Coastal Hazard Assessment · MCU25/0087

                                              17 The Esplanade, Sunshine Beach                              Report




Figure 5-2: (Vellinga, 1983) shows a conceptual representation of the profiles of the erosion and accretion zones
                                            associated with storm.


The Department provides the following recommendation in relation to defining a storm event:
    “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%.”
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 5-2.




                                                                  252662-MN-RP-CO-0001B | 10 November 2025 | Page 24