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

Noosa Shire Council Coastal Hazard Mapping                                                                    4
Storm Tide Hazard Assessment




2        Storm Tide Hazard Assessment
2.1      Background
         The Noosa CHAP Scoping Study Report (BMT WBM 2017) discusses the three ‘categories’ of
         storm tide hazard that have been considered as part of previous local government scale
         assessments:

         (1)    ‘Open coast storm tide’ which can lead to inundation of nearshore areas adjacent to
                beaches. For these locations the combination of tide, surge and wave breaking processes
                contribute to the observed water level.

         (2)    ‘Lower Noosa River catchment storm tide’ which can lead to flooding of areas within the tidal
                extent of the lower river system. For these locations and in the absence of significant rainfall
                and catchment flooding, the combination of tide and surge contribute to the observed water
                level.

         (3)    ‘Coincident catchment flooding and storm tide’ which can lead to flooding of areas within the
                tidal extent of the lower river system. For these locations the combination of river flow, tide
                and surge contribute to the observed water level.

         Aurecon (2013) assessed ‘storm tide only’ (i.e. categories 1 and 2 above) for the present-day and
         2100 planning horizons and range of exceedance probabilities. The other planning horizons
         relevant to the CHAP (2040 and 2070) were not previously assessed. The method for producing
         outputs for the other planning horizons of interest is summarised in Table 2-1 and further described
         in Section 2.2. Table 2-1 also indicates the sea-level rise (SLR) allowance adopted for the Noosa
         CHAP. Further details regarding the Noosa CHAP SLR assumptions are provided in BMT WBM
         (2017).

         The likelihood of peak storm tide conditions coinciding with peak catchment flooding (storm tide
         category 3) within the lower Noosa River is expected to be a rare event, that whilst valuable to
         understand, would be an extreme event and not preferred as a basis for making planning
         decisions. The coincident rainfall, river flooding and storm tide hazard was recently assessed by
         WMA Water (2017a) for the present-day and 2100 planning horizons. The 2040 and 2070 planning
         horizons were subsequently assessed to provide the additional hazard information required for the
         CHAP (WMA Water 2017b).




G:\Admin\B22613.g.mpb.Noosa_CHAS\R.B22613.002.04.NSC_CHAP_Mapping.docx