2021-01-18 GC - Item 3 - Attachment 4 - Cost Benefit Analysis for Noosaville Inundation Options

Table 2: Estimated costs (undiscounted)

                              2040                   2070                       2100

 Option 1

 Levee costs                   -                      $15.6 million             $24.0 million

 Stormwater                    $9.4 million           $9.4 million              $9.4 million
 modification costs

 Option 2

 Road raising                  -                      $26.8 million             $65.2 million

Source     BMT (2020)


Benefits
The benefits assessed through the CBA are described here and include benefits associated with a
range of tangible and intangible assets including:

• property protection

• public asset protection, predominantly roads and stormwater assets

• recreational use

• tourism

All data and assumptions used in the analysis have been provided in Appendix A.

Avoided road damage
Frequent low-level inundation of roads can cause damage due to:

• increased plasticity from wetting and drying of road base and surrounding soils leading to
  movement and buckling of road surface

• formation of salt crystals in road material, eventually leading to boils and cracking of top layer This
  reduces the effective lifespan of the roads, increasing the costs of maintenance for council.

Under the base case, where there is ongoing inundation of many local roads in the Noosaville area,
road maintenance, at council’s expense, will need to occur on a regular basis to overcome the damage
caused by frequent inundation.

Under the proposed adaptation options the frequency of inundation is reduced, thereby reducing the
damage to roads and reducing the costs of council road maintenance. There is a benefit from the
avoided costs of road maintenance compared to the base case. Assumptions on the expected
maintenance costs and the different lifespan of the roads under different levels of inundation have
been provided by Noosa Shire Council and are provided in Appendix A.

Avoided stormwater network damage
As with the damage to roads described above, frequent inundation of the stormwater network with
saltwater causes damage, reducing the effective lifespan of the assets and increasing the costs of
maintenance for council. Under the base case, where there is ongoing inundation of stormwater assets




REPORT | Noosa Shire Council CHAP – Phase 7                                                             5