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

Option 3 is the most feasible option for the Eastern Beaches, with an NPV of $239 million. Under
option 3, property benefits and asset benefits are 50 per cent higher than under the base case. Given
the high value of properties in this location the increase in benefits over the base case is significant.
However, this option is not economically viable for Teewah due to the high implementation costs
relative to the small number of properties affected by coastal erosion prior to 2100.

The costs associated with undertaking dune augmentation ($220 million) are significant. There is also
a high level of uncertainty around these costs due to the limited information available on reliable
sediment supply and full implementation costs. However, the benefits can be significant, materially
reducing the likelihood of damage to about 48 properties at the Eastern Beaches up to 2100.
Investigation by Council of this option for the Eastern Beaches would be justified to increase
confidence in sand availability and estimated costs. Investigation into a more targeted approach to
dune augmentation at a smaller scale would also have merit, as reducing the costs while still
delivering the most effective protection may make this option more economically viable.

The direct beneficiaries of dune augmentation comprise a relatively small number of landholders.
Therefore, it is recommended that Council should consider of the equity implications of this option
prior to funding the protection of a relatively small number of properties. The broader rate-paying base
may anticipate rates to increase or services to decrease given the significant investment in this option,
from which they receive no benefit. Cost recovery for dune augmentation from affected landholders
should therefore be considered if this option is to be pursued.


5.1.3.       Option 4 - Construction of seawalls in high risk locations

Under option 4 armoured rock revetments (seawalls) are built for all beach compartments identified as
High or Very High risk by 2100. The seawall protects a small number (relative to the whole LGA) of
properties and public assets from damage indefinitely. However, the seawall causes erosion of the
beach seaward of the structure thereby negatively affecting recreation, tourism and non-use values
(including ecological and natural coastal processes) associated with the beach.

This option performs particularly poorly with NPVs of -$2.773 billion (Eastern Beaches) and -$67
million (Teewah). Property and asset benefits are the same as under option 32, and the total
implementation costs are lower at $55 million compared to $220 million for dune augmentation at the
Eastern Beaches (although there is likely to be cost uncertainty from access to feasible rock supplies
and construction costs and time). However, there is a 60 per cent loss in recreational benefits, a 14
per cent loss in tourism expenditure and a 44 per cent loss in non-use benefits which significantly
outweigh the value of the private properties and public assets being protected. This analysis has not
included any assumptions around interruptions to beach use and adjacent properties during
construction which may increase the costs of this option.

This option is therefore considered unviable from a socio-economic perspective within this timeframe.
There may however be some benefits from very highly targeted seawall protection of specific
properties or assets in locations which are not suitable for dune augmentation or dune management.




2
    This assumes that dune augmentation continues to be effective until 2100, which depends on available sand supply as
       well as continued funding for undertaking augmentation. Building a seawall may provide greater certainty
       compared to dune augmentation.



AITHER | Final Report                                                                                               17
Noosa Shire Council – Coastal Hazard Adaptation Plan