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

Options and costs
The cost benefit analysis assesses the net change in the costs and benefits of each adaptation option
relative to the base case. The base case and two separate options considered are:

• Base case: No additional coastal adaptation or risk mitigation efforts are undertaken

• Option 1: Protect (Levees with Stormwater infrastructure modifications)

• Option 2: Accommodate (Road Raising)

Under the base case, with no additional coastal adaptation or risk mitigation efforts being undertaken,
low-level inundation continues to affect the Noosaville area. Over time there is an increase in areas
being affected, and the inundation occurs more regularly and for longer durations. Under the base
case there is increasing damage to roads and stormwater assets from increased inundation, and
properties are at increased risk of salinity damage. Local recreational areas are increasingly
inaccessible to the local population during inundation, and tourism is likely to decrease over time as
access to important areas such as the foreshore and jetties are inundated more often.

Under option 1, levees or barriers are constructed around the river, creek, or lake frontages of the
area. Different structural forms of differing heights (earth bunds, revetment extensions or clear glass
vertical panels) have been specifically selected and costed for each location. This option also includes
modifications to the stormwater network involving three different types of devices to prevent the
egress of tidal water into the network (e.g. tide flap, duckbill valve or inline check valve). Under this
option the stormwater infrastructure modifications occur from 2040, whilst the levees are not
constructed until 2070.

Under option 2 all roads that experience some level of inundation are raised, to prevent flooding of
the roads. It is worth noting that the road raising option can potentially cause significant
inconvenience to the local community, both during construction and once complete. Additional costs
associated with substantial modifications required to address matters such as driveway crossovers,
grading of intersections, pedestrian movements, and other issues, have not been included in the
analysis at this stage. Under this option the road raising takes place from 2070.

The management costs included in the CBA are set out in Table 2. These costs have been provided by
BMT and include high-level assessments of the potential costs of undertaking the relevant adaptation
options. These costs only include the estimated construction costs and do not include any
maintenance costs associated with future damage.




REPORT | Noosa Shire Council CHAP – Phase 7                                                                 4