61
The projected extent of inundation resulting from a 100 year storm tide event with 0.3m, 0.5 m and 0.88 m
of change in water level due to sea level rise and subsidence are shown in
Figures 5.5 (a-c)
. These
maps account for the impact of drainage, roads and other infrastructure on the movement of coastal
floods.
Tonkin Engineering and WBM Oceanics (2005) found that there was no statistical association between
storm surge conditions at Port Adelaide and intense rainfall events. They found that in most drainage
catchments the extent and depth of stormwater flooding was primarily influenced by the severity of the
rainfall event and not tide height. Flooding in some smaller drainage catchments and wetlands in the
‘Gillman’ area in the City of Port Adelaide Enfield would be affected by tidal conditions.
5.2.3.Coastal recession
Coastal recession, the landward retreat of a coastline, presents a significant risk to infrastructure,
beaches and natural features along the coastline such as mangroves, wetlands and dunal systems.
Coasts comprising erodible sediments (e.g. sand, mud) may recede in response to sea level rise, with the
rate of change depending on the rate of sea level rise, the coast’s resistance to erosion, longshore
sediment movement and the effectiveness of any constructed coastal defences (e.g. sea walls, groynes).
Existing sand carting schemes may also influence the extent of erosion in the Study Area´s southern
coastline.
The Bruun rule is a rule of thumb that is commonly applied to project the recession of erodible coastlines
in response to sea level rise. It estimates that for every metre of sea level rise, sandy or otherwise
erodible shores could retreat by 50 to 100m
11
. Much of the coast in the Study Area comprises sand or
mud (refer to
Figure 8.3
) and is highly erodible. Unprotected areas along the Gulf St Vincent coast are
exposed to wave action and are more likely to recede than other areas. In the absence of any control
efforts, recession in response to the upper range of plausible sea level rise scenarios could exceed
80m
12
.
An erosion study by Coastal Engineering Solutions in 2004 considered littoral drift impacts for 20, 50 and
100 years of climate change
13
. Findings suggest that over 100 years, increased storminess would impact
around 10-15% on littoral transport potential. However coupled with sea level rise, increased storminess
would significantly affect offshore sand motion and double the storm take from dunes.
11
Townsend M, Quantifying the impact of wave overtopping on the Adelaide foreshore, Department for Environment and Heritage,
Government of South Australia. The applicability of the Bruun rule in this setting is unknown. The Bruun rule should not be
considered to provide an accurate estimate of the likely extent of coastal recession resulting from sea level rise.
12
Adelaide Living Beaches Technical Report (Department for Environment and Heritage, 2005) identified that beach nourishment
could be capable of managing recession due to sea level rise, at least over its planning period to 2025.
13
Department for Environment and Heritage (2005) Adelaide’s Living Beaches” A strategy for 2005- 2015, Technical Report
