2021-01-18 GC - Item 3 - Attachment 1 - Coastal Hazards Adaptation Plan for Community Consultation

Subject to the above investigation, this option could be reasonably expected to remain feasible for
Peregian to Sunrise Beach until approximately 2070, beyond which the relative frequency of
erosion (due to a recessed shoreline) will render it unfeasible. For Sunshine Beach it is unlikely
this option can be presumed feasible (due to reduced effectiveness) by 2070.

Construction of hard-engineered seawalls

This option involves buried armoured rock seawalls being built for all beach sections identified as
having high or very high erosion risks. These coastal protection works would provide the benefit of
protecting a small number of properties and public assets (relative to the whole local government
area) from damage for the foreseeable future.

The cost benefit analysis included lengths of wall at the following locations:

   -   110m at Peregian Park (Peregian Beach)
   -   410m adjacent to David Low Way (Castaways Beach)
   -   500m adjacent to David Low Way (Sunrise Beach)
   -   980m adjacent to Tingira Street (Sunrise Beach)
   -   1,960m (entirety of Sunshine Beach)

In all locations, the alignment of a wall would need to be located significantly seaward of the assets
for which protection is sought in order to mitigate impacts associated with wave run-up and
overtopping (i.e. slumping of dune landward of the structure).

The seawall is also highly likely to exacerbate erosion of the beach seaward of the structure by
slowing the replenishment of the beach. The loss of sandy beach that would be a virtually
inevitable result of this option would negatively affect recreation, tourism, scenic and ecological
values associated with the beach on a significant scale.

The cost benefit analysis found this option performed poorly with a net present value of -$2.77
billion for Peregian to Sunshine Beach and -$67 million for Teewah Beach. While the expected
property and asset benefits are high because the seawall would provide a defence from erosion,
the implementation costs would be very high.

The establishment of a physical barrier of the proportions required to reduce the risk to the built
environment would impair the natural coastal processes of sand replenishment and the natural
function of the adjacent dune systems, and thus impact scenic amenity, tourism, recreational, and
environmental attributes that are considered of high value to Noosa. These areas are currently
characterised by their natural sandy, vegetated beachfronts, uninterrupted by hard walls. The loss
of these wide sandy beaches would also impact the broader economy of Noosa.

This option is not considered feasible as the analysis found there is a 60 per cent loss in
recreational benefits to users of the beach, a 14 per cent loss in tourism expenditure and a 44 per
cent loss in non-use benefits (scenic amenity, landscape character) which is considered to
significantly outweigh the value of the private properties and public assets being protected.

The construction of a physical barrier to withstand storm waves of the size that may potentially
occur in these areas would also have a strong potential to result in adverse impacts in adjacent
locations as wave energy erosive forces are transferred to neighbouring properties that do not
have a wall in place.

The analysis also noted that the analysis did not factor in the likely interruptions to beach use and
adverse effects for adjacent properties during construction which may increase the costs of this
option. In addition, there remains uncertainty regarding material costs and construction costs, and
material supply in term of access to feasible rock supply.


Noosa Council – Coastal Hazards Adaptation Plan 2020 - 2030 (community consultation version)   Page 26