PA3660-Coastal Hazard Assessment - 4 arakoon

                                             Project related




frontal dune and therefore underestimates the reserve of sand available in the dune system. RHDHV
adopted a dune height of 9m AHD which was determine over an iterative process (see Section 6.2.3).




Figure 6-11 Dune heights and beach profile


6.3.5           Depth of closure
BTM (2018) calculated the depth of closure to be around 11-12m for Noosa beaches. RHDHV adopted
12m, where BMT adopted 11.5m. This has a negligible effect on the Bunn Rule calculation.

6.3.6           Sediment size
BMT (2018) and RHDHV both adopted a median sediment grain size (D50) of 0.22mm.

6.3.7           Storm Tide
BMT (2018) stated that a 100 year ARI design storm tide level (inclusive of wave setup) for Sunshine
Beach of 2.61m AHD was adopted based on a storm tide assessment by Aurecon (2013). However, when
reviewing the assessment summary provided it appears that a design storm tide level of 2.20m AHD was
used by BMT (2018) for assessment of the short-term erosion component of the erosion prone area.
There is no clear explanation provided by BMT (2018) for the differ storm tide levels described in their
report.

Vellinga (1983) provides an empirical method for estimating beach erosion associated with a design storm
event. The input parameters for the design storm event described in Vellinga (1983) include the deep
water significant wave height (Hos) and storm surge. The description described in Vellinga (1983)
suggests that the storm surge is exclusive of wave setup which is implicitly included in the empirical
model. Figure 6-12 shows an example hydrograph of storm surge from Vellinga (1983) indicating the
surge and tide effects and no indication of wave setup. RHDHV therefore adopted a 100 year ARI storm
tide level of 1.74m (exclusive of wave setup) from Aurecon (2013).




11 April 2024         4-6 ARAKOON CRESCENT, SUNSHINE BEACH       PA3660-RHD-XX-ZZ-RP-Z-0001   36