PA3660-Coastal Hazard Assessment - 4 arakoon

                                                  Project related




Figure 6-12 North Sea storm surge hydrograph (Vellinga, 1983)


6.3.8           Wave Height
BMT (2018) and RHDHV both adopted a wave height of 6.2m based on a previous study of coastal
processes on the Sunshine Coast (BMT, 2013).

6.3.9           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 meters
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 meters aligns with the evaluation conducted by BMT.

6.3.10 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). RHDHV adopted
a 100-year ARI storm tide level of 1.74m (exclusive of wave setup) from 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 6-2 above).



11 April 2024        4-6 ARAKOON CRESCENT, SUNSHINE BEACH           PA3660-RHD-XX-ZZ-RP-Z-0001    37