Download Information on sea and lake level rise

Planning for
Future Flood Risks
Information on sea and lake level rise
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Lake Macquarie City Council is committed to
providing a safe community now, and in the future.
This information sheet provides an overview of sea
level rise and how it may affect Lake Macquarie.
Who is
measuring sea level
rise in Lake Macquarie?
What causes sea level rise?
There are three water level gauges in Lake
Macquarie operated by the NSW Government,
at Swansea, Belmont and Marmong Point.
The gauges measure relative water levels.
Levels can change due to various factors such
as land subsidence or El-Niño cycles, so it is
not possible to attribute changes specifically
to sea level rise. Measurements of relative lake
level from the Belmont gauge indicate a rise
of 2.6mm a year over the last 25 years, a 6.5
centimetre rise since 1986.
Sea levels are rising due to the warming of the
atmosphere and oceans, which causes the water
in the oceans to expand. In addition, the melting
of land-based glaciers and ice sheets increase the
volume of water in the ocean.
How was the projection for
sea level rise of 0.90 metres
by 2100 calculated?
The best advice from international, national and
state scientific organisations is that sea levels on
the east coast of Australia will rise by 0.90 metres
by about 2100. This projection is based on three
components (see table below).
It is important to note that the predictions are for a
slower rise in the first half of the Century (currently
predicted, and measured, at about 3mm a year)
accelerating to over 10mm a year in the second
half of the Century. Lake Macquarie will rise by
about the same amount and at the same time as
the ocean. These projections will be reviewed as
new scientific advice becomes available.
The nearest fully calibrated gauge, at Port
Kembla and operated by the Australian Bureau of
Meteorology, shows a rise of 2.6mm a year since it
began measurements in 1991.
Why does Council need to plan
for projected sea level rise?
The NSW Government requires all Councils to
include the effects of climate change and sea level
rise in their planning for flood and coastal risks.
Council is responsible for flood planning in Lake
Macquarie City. This includes planning to reduce
risks to natural and built environments. Council
has a duty of care to ensure assets such as new
Table: Derivation of projected sea level rise on the NSW coast
1
0.59 metres by 2100
Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment
Report (2007) – global average sea level rise (excluding ice melt) - high
emissions scenario
2
0.20 metres by 2100
Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment
Report (2007) – allowance for ice melt uncertainty
3
0.14 metres by 2100
CSIRO Technical Report (2007) – calculation for local (Australian East Coast)
variation on IPCC global average sea level rise
Rounding
- 0.03 metres
TOTAL
0.90 metres
Projected lake levels and flood
levels in Lake Macquarie
houses or roads, and the communities that use
them, are safe for the life of the asset – this could
be up to 100 years.
How will projected rises
in lake levels affect f looding?
As the average ‘still-water’ level of the lake
rises, flood levels will also rise. The Lake
Macquarie flood study showed that with 0.40
metres rise in ‘still water’ lake levels, the level of
the predicted 1-in-100-year lake flood will increase
by 0.36 metres.
Also, for any given flood level, the frequency
of flooding will increase as lake levels rise.
For example, with the ‘still water’ lake level today
as a starting point, a flood level of 1.50m AHD
could be expected to occur on average once every
100 years. However, with an increase in lake ‘still
water’ level of 0.40 metres, lake flooding will reach
1.50m AHD an average of once every 15 years.
Lake flooding will reach this level an average of
once every two years with a 0.90 metre rise in
lake levels.
tides. The Lake Macquarie Waterway Flood Study
predicts that, without protection, foreshore land
below 0.50m AHD may be permanently inundated
by 2050, and land below 1.0m AHD may be
permanently inundated by 2100. The majority of
this low-lying land is managed by Council.
How will the lake foreshore and
foreshore residents be affected
by rising lake levels?
As well as increased levels for severe floods,
increased frequency for minor floods and
permanent inundation, rising lake levels may
increase foreshore erosion and cause rises in
groundwater. If the average lake level rises by
0.90 metres, the number of properties affected by
a serious (1-in-100-year) flood will increase from
about 7700 to about 9800.
What is the difference between
inundation and f looding?
Get
involved
As sea and lake levels rise, some low-lying areas
along the coast and around the lake foreshore may
be inundated. This means they are permanently
covered by rising water or regularly covered by
For more information about
planning for future flood risks:
Visit www.lakemac.com.au/future-flood-planning
Call Council on 4921 0333
Email [email protected]
PO Box 1906 Hunter Region Mail Centre 2310
How to have
your say
Online: Join our interactive
online forum http://haveyoursaylakemac.
com.au/future-flood-planning and be part of
the conversation, view flood maps, ask us
questions and help us create solutions.
Contact us: Please write or call Council
using the contact details listed.
Information Sheet #2 - Ver. 1 - Printed August 2013