Atmosphere
Page 134
The project’s study area covers approximately 10,000 hectares, and
predominantly lies below the highest astronomical tide level. Sea walls and
other flood mitigation measures protect some sections of the banks of the Port
River currently.
To compound the risk, studies have found that the Port Adelaide area has a
history of land subsidence (sinking), which is believed to be largely the result of
wetland reclamation and groundwater extraction from the local aquifers. The
combined impacts of local land subsidence and contemporary sea-level rise
have led to net land subsidence of around 2.1mm/yr within the study area.
The study involved analysis of the 100 year storm tide level and simulation of
inundation from three future scenarios of sea-level rise and land subsidence
(refer to table 24 below).
Upper and lower estimates were modelled for each scenario, with the difference
being the extent of water storage capacity in the non-tidal areas.
For instance, if a non-tidal area has been exposed to rainfall before the storm
tide event, there is a reduced capacity to store incoming inundation waters and
so could lead to greater inundation (upper case).
Table 24:
Future scenarios of sea-level rise and land subsidence used in the
study
Scenario
Sea-Level
Rise
(metres)
Period
of
land
subsidence
(years)
Description
S0
-
-
Existing case – no sea-level rise or subsidence
S1
0.30
50
Complies with current requirements for infill
development
S3
0.50
100
Based on IPCC projections for sea-level rise using
medium values in the IPCC range +subsidence
S4
0.88
100
Based on IPCC projections for sea-level rise using high
end values in the IPCC range +subsidence
Figure 26
below indicates the extent of flooding for a current 1-in-100 year
storm tide event (Scenario S0 - blue shades), as well as the predicted extent of
inundation for each of the upper case scenarios (S1–S4). The area of
inundation increases to affect larger areas of residential and commercial
buildings and roads. The estimated damage costs rise significantly with each
scenario. The study suggests that damage costs from a 1-in-100 year storm tide
could increase from an estimated $8–28 million for a current day event to $180–
310 million with future scenarios of sea-level rise and land subsidence.
The study explored a range of abatement options, particularly sea defence
measures. For example, a concept design involving the construction of a
