2021-01-18 GC - Item 3 - Attachment 2 - Phase 7 Project Summary Coastal Hazards Adaptation Plan

 Noosa Shire Council Coastal Hazard Adaptation Plan: Project Summary                                    18
 Findings




3.1.3    Gap Analysis
         The scoping study identified that two pieces of further technical work would be required to support
         the CHAP. These were:

         • Development of storm tide hazard mapping for the CHAP planning horizons (present-day, 2040,
           2070 and 2100); and

         • Coastal erosion prone area assessment and mapping for the CHAP planning horizons.

3.2      Phase 3: Hazard Mapping
         Hazard maps for the Noosa Council boundary are provided in Appendix A. The key findings of the
         coastal hazard assessment were:

         • Permanent inundation due to sea-level rise: the area subject to tidal inundation due to sea-level
           rise is considered moderate in extent (i.e. relative to stormtide) across the study area and is
            primarily constrained to areas of land adjacent to the Noosa River.

         • Storm tide: due to the topography of the study area, the vast majority of locations subject to
            inundation during the design storm tide event are located adjacent to the Noosa River.
            Comparatively, only a small area of land in open coast areas would be exposed to storm tide
            inundation.

         • Erosion: the alongshore variation is primarily due to differences in the height and volume of the
           coastal barrier and the nearshore slope. The short term erosion component and the natural
            shoreline response to sea-level rise account for approximately 30% and 35% of the defined 2100
            erosion prone area, respectively.

         A comparison was conducted of the modelled hazard extents for planning horizon 2100 for 1% AEP
         storm tide and 1% AEP rainfall event, with both incorporating a projected relative sea-level rise
         component of 0.8m. The comparison revealed that within the Noosa River estuary 1% AEP
         catchment flooding is likely to be more severe than inundation during a 1% AEP storm tide event.

3.2.1    Erosion Hazard Areas
         In line with the methodology described in Section 5, the extent of the erosion hazard areas were
         mapped for open coast sections of the shoreline i.e. eastern beaches and Noosa Main Beach.

         It should be noted that the calculated erosion distances do not account for local erosion controls,
         such as the engineered coastal protection structures or erosion resistant bedrock slopes. Properly
         designed and maintained seawalls are expected to limit the landward extent of the erosion. The
         design standard of the Noosa Main Beach seawall, concealed within the sand dune, remains
         uncertain. It has been assumed the existing structure may not withstand a design storm event but
         would be sufficient to limit long term recession and the shoreline response to sea level rise. This
         assumption has been incorporated to the coastal hazard mapping that was produced for Noosa Main
         Beach.