Coastal Hazard Assessment · MCU25/0087

                                           17 The Esplanade, Sunshine Beach                              Report


5.3.8   Wave Height
BMT (2018) and M&N adopted a wave height of 6.2m based on a previous study of coastal processes
on the Sunshine Coast (BMT, 2013).
5.3.9   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
0.4 metres annually (±0.3 metres 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 10 metres aligns with the evaluation conducted by BMT.
5.3.10 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 higher 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). M&N
adopted a 100-year ARI storm tide level of 1.74m (exclusive of wave setup) (Aurecon, 2013) to
calculate short-term erosion.
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 5-2 above).
In their analysis of Sunshine Beach, BMT (2018) categorized short-term erosion into C1 and C2
components when the dune toe level fell below the storm tide level. Figure 5-15 and Figure 5-16
shows the conceptual illustration of the approach adopted by BMT (2018). Specifically for Sunshine
Beach (ETA596 and ETA 602), BMT (2018) assigned a C1 value of 21m and 52m and a C2 value of
0m for short-term erosion. It is important to highlight that BMT conducted the short-term erosion
assessment from the design water level line rather than the toe of the frontal dune, which is not
consistence with the Queensland Hazard Technical Guide (DEHP, 2013). Had BMT measured from
the dune vegetation, the short-term erosion would have been 6m (Figure 5-15) and 40m (Figure
5-16), resulting in an average C of 23m, not 37m. This 23m is similar to the 17m calculated for this
assessment. The difference of 6m is attributed to the difference in water level and the sites
proximately to Noosa Headland compared to both Section A-A and Section B-B.
M&N conducted a site-specific assessment of the short-term erosion based on Vellinga (1983). The
finalised adopted short-term erosion component was set at 17m. The site inspection and survey of the
site indicates that the toe of the frontal dune can be approximated at 2.3m AHD (refer Section 2.4).
Dividing the short-term erosion component into C1 and C2 as adopted by BMT (2018) is therefore not
applicable for this section of beach.
The main reason for the difference in short-term erosion between both studies is the design water
level used and where the short-term erosion was calculated from. Note in both studies that C2 equals
zero as the dune's toe is situated above the design water level.




                                                               252662-MN-RP-CO-0001B | 10 November 2025 | Page 34