MNA_250215_33 Ross Crescent Sunshine Beach_00

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




Figure 6-11 North Sea storm surge hydrograph (Vellinga, 1983)


6.4.8.    Wave Height
BMT (2018), RHDHV (2024) and the assessment herein adopted an offshore significant wave height of
6.2m based on a previous study of coastal processes on the Sunshine Coast (BMT, 2013).


6.4.9.    Long-term erosion
Digital Earth Australia and CoastSat have calculated the long-term recession rates. Figure 3-9 shows that
the long-term change in shoreline position in the immediate vicinity of the site is approximately 0.4m
annually (±0.3m at 95% confidence interval).

Given the long-term stability of this section of coast a nominal 10m has been adopted in accordance with
the Department of Environment and Heritage Protection (2013). The long-term erosion of 10m aligns with
the evaluation conducted by BMT (2018).


6.4.10.   Short-term erosion
The BMT (2018) evaluation of short-term erosion was undertaken using the Vellinga method. Vellinga
(1983) presents an empirical method for estimating beach erosion associated with a designated storm
event. The required input parameters described in Vellinga (1983) involve the deep-water significant wave
height (HOS) and storm surge. The description in Vellinga (1983) implies that storm surge is distinct from
wave setup, which is implicitly encompassed in the empirical model.

BMT (2018) adopted a conservative assessment adopting a design water level of 2.11m AHD (i.e. storm
tide + wave setup). Acknowledging the inclusion of wave setup is not consistent with Vellinga (1983), they
stated, "This is considered a conservative approach since the erosion model only necessitates input of the
‘surge plus tide’ level, and the additional contribution of wave setup to the extreme water level leads to an
increase in the predicted erosion volume" (BMT, 2018). The BMT (2018) assessment also did not appear
to include the storm profile termination at a depth of 75% of the deep-water significant wave height (refer
Figure 6-1 above).

In accordance with the input parameters described in Vellinga (1983), RHDHV (2024) adopted a 100-year
ARI storm tide level of 1.74m (exclusive of wave setup). To address Noosa Shire Council’s further
information request dated 19 December 2024 this assessment adopted a storm tide level of 1.79m AHD to
reassess the erosion prone area. The minor increase in storm tide level of 0.05m has been shown to have
negligible impact on the estimated erosion profile at the site.



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