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

Noosa Shire Council Coastal Hazard Mapping                                                               33
Permanent Inundation due to Sea Level Rise




4        Permanent Inundation due to Sea Level Rise
4.1      Hazard Assessment Approach
         As discussed by BMT WBM (2017), the State EPA mapping defines permanent tidal inundation
         due to SLR at 2100 as:

         • Present-day Highest Astronomical Tide (HAT) plus 0.8 m SLR.

         The hazard area is then obtained by extrapolating the water level across land. Areas adjacent to
         tidal waters where the ground elevation falls below the threshold water level are deemed to be
         within the hazard area.

         The SLR hazard information provided by the State is useful for ‘first-pass risk screening’ only and
         does not provide sufficient information regarding likelihood and consequence to undertake a more
         detailed risk assessment. To address this issue, SLR hazard mapping including depth classification
         has been developed for the Noosa CHAP planning horizons. The adopted approach generally
         follows the State definition, whereby a threshold water level (mAHD) is defined by consideration of
         HAT plus an appropriate SLR allowance. The water level mapping assumptions are summarised in
         Table 4-1. These thresholds for different locations throughout the study area consider Maritime
         Safety Queensland published tidal planes (MSQ 2017) along the open coast and within the lower
         Noosa River. Linear interpolation of the water level between the sites has been adopted with the
         Munna Point and Tewantin levels extending into Lake Cooroibah/Cootharaba and Lake Weyba
         respectively.

                Table 4-1     Permanent inundation due to Sea Level Rise mapping assumptions

             Planning             SLR          Noosa Head HAT       Munna Point HAT      Tewantin HAT
             Horizon         allowance (m)        (mAHD)               (mAHD)              (mAHD)

            Present-day             0                 1.16               0.68                  0.55
                2040               0.2                1.36               0.88                  0.75
                2070               0.5                1.66               1.18                  1.05
                2100               0.8                1.96               1.48                  1.35




4.2      Assessment Results
         The projected impact of inundation due to SLR is presented in Appendix E and is moderate across
         the Noosa region, primarily impacting land adjacent to the lower Noosa River. Based on current
         forecasts, and in the absence of an adaptation response, this impact would be realised between
         2060 and 2080 and significantly escalate by 2100.




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