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

Noosa Shire Council Coastal Hazard Mapping                                                                  9
Erosion Prone Area Assessment




3        Erosion Prone Area Assessment
3.1      Background
         These assessments have been undertaken with the key objective of developing maps suitable for
         the Noosa CHAP and to better understand the erosion hazard and associated risk to assets and
         values within the local government area in order to progress consultation with the community about
         the consequences of these risks. In addition to the CHAP, the outcomes of these assessments
         may be used to support an amendment to the State-declared erosion prone area plans, if desired.
         Details of the State-declared erosion prone areas for Noosa are provided in BMT WBM (2017).

3.1.1    Erosion Prone Area Definition & Mapping
         The State Erosion Prone Area plans are intended to assist development assessment and to inform
         the preparation of planning instruments, such as planning schemes and regional plans under the
         Planning Act 2016.

         Erosion prone areas have been declared for all coastal local government areas in Queensland. The
         Noosa Shire Plan NOS3A is available online via DEHP website:

         https://www.ehp.qld.gov.au/coastal/development/assessment/pdf/noosa-erosion-prone-area-
         plan.pdf

         The EPAs apply to land subject to inundation by the Highest Astronomical Tide (HAT) by the year
         2100 or at risk from sea erosion. On land adjacent to tidal water the EPA is defined by whichever of
         the following methods gives the greatest width:

         (1)    40 m buffer from the present-day HAT contour

         (2)    Calculated erosion distance shown in Table 1 of the statutory plan

         (3)    Permanent inundation due to SLR in 2100 (defined by present-day HAT plus 0.8 m).

         The 40 m buffer from present-day HAT (component 1) generally applies within estuarine areas not
         exposed to open coast processes. This approximate method is intended to account for the
         migration of channels within tidal waterways with natural (undeveloped) shorelines.

         The calculated erosion distance (component 2) is intended to cater for the potential loss of land for
         open coast locations. Both short term (storm-related) and longer term (gradual) trends are included
         in the assessment together with an allowance for potential sea level rise associated with climate
         change. Provision is also included for a factor of safety on the estimates and an allowance made
         for slumping of the dune scarp that is often observed after significant storm erosion has occurred.
         For the Noosa CHAP this component has been reassessed and is discussed further in Section 3.2.

         The Noosa Shire Plan NOS3A (NOS3A, Table 1) provides a summary of the calculated erosion
         distance for open coast locations. Consideration of the potential presence of bedrock is included
         however it is noted that the State plans do not capture all local-scale natural and/or manmade
         features that may limit the landward extent of shoreline erosion.

         The permanent inundation due to SLR (component 3) represents the HAT coastline (or elevation
         contour) in 2100 in the absence of any adaptation response to treat the risk, such as filling land to


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