2019-07-09 P&E Agenda - Item 10 - Attachment 1 - Coastal Hazards Risk, Vulnerability and Adaptation Assessment

Noosa Shire Council Coastal Hazard Mapping                                                                  11
Erosion Prone Area Assessment




         erosion has occurred. The following relationship was originally used by the former Beach
         Protection Authority (BPA) for determining erosion hazard area widths throughout Queensland.
         This formula continues to be recognised by DEHP (2013) as a reasonable method of assessing the
         erosion hazard on sandy coastlines.

         𝐸 = [(𝑁 × 𝑅 ) + 𝐶 + 𝑆] × (1 + 𝐹) + 𝐷
         Equation 3-1

         Where     E = Calculated erosion distance or width (metres)
                   N = planning period (years)
                   R = rate of long term erosion (metres per year)
                   C = short term erosion from the design storm event (metres)
                   S = erosion due to sea level rise (metres)
                   F = factor of safety
                   D = dune scarp component

         In the assessments for the Noosa region described in this Section, the values of C, S and D have
         been determined for individual beach compartments using existing beach profile survey data, site
         specific modelling and SLR projections adopted for the CHAP (refer BMT WBM 2017). As
         described below in Section 3.4, insufficient data is available to accurately assess R on an individual
         beach basis. Previous studies and the limited data that is available suggests that most beaches
         within the region are ‘dynamically stable’ and are not displaying trends of long term recession that
         can be linked to a deficit in sand supply. The notable exceptions are Noosa Main Beach and Dog
         Beach, where coastal structures and an ongoing sand replenishment program (via back-passing
         using a sand shifter or dredging) are used to maintain the beach profile. The localised erosion
         issues at Dog Beach are related to channel migration (rather than sand supply) and appear to be
         linked to the dynamic morphology of the Noosa River entrance. For the CHAP, the potential for
         channel migration is accounted for through the State-defined EPA erosion component 1 (i.e. 40 m
         buffer on present-day HAT). This buffer is applied consistently across all planning horizons.

         The open coast calculated erosion distance has been assessed at 25 existing beach and offshore
         profile locations indicated in Figure 3-1. These monitoring locations, commonly known as ‘ETA’
         profiles, were originally established by the former BPA and surveyed at semi-regular intervals
         between 1970s and early 2000s. The assessments described in this Chapter focus on the locations
         shown in Figure 3-1.




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