2021-01-18 GC - Item 3 - Attachment 3 - Cost Benefit Analysis for Coastal Erosion Options

5.2.        Sensitivities
Some key assumptions in the analysis, identified through sensitivity analysis are material to the
findings.These assumptions, set out in Table 6, should be subject to further investigation prior to
implementing any project option. Further sensitivity analysis of the discount rate and other
assumptions used in the analysis is provided in Appendix C.

Table 6        Sensitivities

 Assumption           Confidence        Sensitivity    Description
                                                       The costs included in the analysis do not fully
                                                       reflect the risk to undertaking this option including:
 Cost of dune                                          • potential viability of local sand sources
                      Medium            High
 augmentation
                                                       • costs of transportation
                                                       • potential for no sand to be available

 Rock                                                  There are also implementation cost uncertainties
 availability                                          stemming from a feasible rock supply and build
 and                  Medium            High           and cost times. For example, longer haulage times
 construction                                          given limited local supply would imply greater
 of seawall                                            costs.
                                                       The analysis does not currently account for the
                                                       impact of more frequent large storms events
                                                       occurring after each augmentation. Modelling of
                                                       smaller, more frequent events and the effect this
 Storm events         Low               High
                                                       may have should also be considered further. This
                                                       could significantly change the years in which
                                                       damage would occur, or immediately remove any
                                                       benefits of dune augmentation being undertaken.
                                                       It is difficult to fully value the benefit of new open
                                                       space recreational areas particularly given the
                                                       other recreational spaces such as beaches and
 Value of new
                      Low               High           reserves already in close proximity. Community
 parks
                                                       consultation could provide further insights on the
                                                       associated benefits of increasing public open
                                                       space.
                                                       The presence of the seawall is expected to lead to
                                                       reductions in the beach width and thereby reduce
                                                       recreational values, non-use values (including
                                                       ecological) and visual amenity. However, at the
 Changes in
                      Low               High           preliminary stage there is limited confidence on the
 beach width
                                                       timing or speed of these effects. Based on real
                                                       world evidence, the analysis currently assumes
                                                       that the beach is completely eroded up to the
                                                       seawall.




AITHER | Final Report                                                                                           23
Noosa Shire Council – Coastal Hazard Adaptation Plan