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

2.          Expected coastal erosion impacts and
            project options

2.1.        Coastal erosion impacts
The socio-economic analysis has investigated the effects of coastal erosion over the period 2020 to
2100. Modelling undertaken in Phase 3 of the CHAP shows that coastal erosion events will encroach
progressively landwards as sea levels rise (relative to present day extents) at the Eastern Beaches
and Teewah. If no management activities are undertaken, the risk to assets at these locations
progressively increases, though not uniformly due to differences at the local scale. Estimated effects
are based on geo-spatial analysis of the erosion prone area. These effects have previously been
assessed at nominal timeframes of 2020, 2040, 2070 and 2100 selected to align with increases in sea
level of 0m, 0.2m, 0.4m and 0.8m respectively. The key identified effects of coastal erosion are
damage to public and private assets and to the beach itself (i.e. vegetated and un-vegetated dunes).
A range of potential options for managing these impacts have been developed and are tested through
this analysis. These options are set out in Section 2.2.


2.1.1.      Impacts to public and private assets

Under the base case there are a number of private properties at both locations that will potentially be
affected as a result of coastal erosion. For the purposes of this study, properties considered likely to
be affected are those where a portion of the current main building falls within the coastal erosion
prone area in a specified time period.

In addition to private assets, a large number of publicly owned assets are likely to be affected by
coastal erosion in future. These include roads and parking areas, stormwater drainage and sewerage
networks, beach accesses, energy systems, streetlighting, parklands/greenspace and surf lifesaving
clubs.


2.1.2.      Impacts on beach width

The overall beach width in any given year is a function of a range of factors. These include offshore
and inshore sand supply, erosion events, and natural accretion processes, as well as human factors
such as active beach nourishment and the existence of any hard structures (e.g. seawalls or
groynes). Under the base case of ‘do nothing’, the beach and frontal dune is expected to migrate
landwards as sea levels rise, infringing on existing land-uses (residential and other). Where no hard
protection is constructed the beach is assumed to move landwards with the lower beach width
remaining consistent with its present-day width. However, the width of the vegetated dune zone may
decrease leading to a potential loss of environmental and aesthetic values.

Where a seawall is constructed, over time the beach seaward of the wall is expected to erode up to
the base of the wall. This erosion will occur on a permanent or semi-permanent basis, thereby
reducing the sustainable beach width. This will cause reductions in recreational, environmental and
aesthetic values due to the loss of beach, presence of exposed wall, and effects on existing
ecological processes.




AITHER | Final Report                                                                                      7
Noosa Shire Council – Coastal Hazard Adaptation Plan