MCU25 0087 - Reference Document - Coastal Hazard Assessment (As Published)

                                                                     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

Document Set ID: 24631530
Version: 1, Version Date: 24/03/2026