Sea level rise and coastal impacts

Sea level rise and its impacts

Of all the impacts from climate change, the projected rise in mean sea level is one of the most significant concerns for management of the coastal zone.

Analysis of global tide gauge records indicates that:

• the rate of sea level rise increased from the 19th to 20th century; and
• the total 20th century rise was estimated to be 17 ± 5 cm.

Along the Australian coastline, the change in relative mean sea level between 1920 and 2000 was about 1.2 mm/year (Church et al. 2006). Since late 1992, satellite altimeters have been monitoring the world’s oceans and measured global average rates of sea level rise of around 3 mm/year.

The main component of sea level rise is thermal expansion – as the water warms, it expands. Other contributing components of sea level rise include:

• melting of glaciers and ice caps
• melting of the Greenland and Antarctic ice sheets
• runoff from thawing of permafrost; and
• changes in the amount of water stored in the terrestrial environment, such as groundwater or surface lakes and reservoirs.

The potential implications of sea level rise include:

• Higher projected storm surge and inundation levels.
• Landward recession of sandy shorelines. Depending on the rate and scale of sea level rise, the environmental, social and economic consequences of recession within low lying inter-tidal areas, in particular, are expected to be significant.
• Salt water intrusion and landward advance of tidal limits within estuaries. This will have significant implications for freshwater and saltwater ecosystems and development margins, particularly building structures and foundation systems within close proximity to the shoreline.
• Existing coastal gravity drainage, stormwater infrastructure and sewerage systems may become compromised over time as mean sea level rises.
• Sea level rise will influence the entrance opening regimes for intermittently closed and open lakes and lagoons (ICOLLs) and alter catchment flood behaviour.
• The level of protection provided by existing seawalls and other hard engineering structures will decrease over time due to the increasing threat from larger storm surges and inundation at higher projected water levels.

Coastal impacts research

Awareness of climate change impacts on the coastal zone is growing; however more work could be done on climate change impacts on the NSW coastline and estuaries.

OEH is undertaking research that takes an initial step towards addressing this knowledge gap. The overarching objective of the research is to assess the environmental impact of potential coastal erosion, coastal inundation and degradation of estuaries due to climate change in coastal NSW. This will be undertaken by:

• defining climate change driven environmental impact events at two representative NSW estuary/beach systems for both 25 and 75 year planning horizons
• quantitatively estimating the coastal and estuarine impacts (e.g. coastal erosion, coastal inundation, estuarine flushing, eutrophication, modification of estuary entrances) due to climate change driven low-, mid-, high-, and probable maximum level impact events at the two representative study sites; and
• using the information generated to develop adaptation policy responses for the NSW coastal zone.

The first stage of this has been completed and comprises two complementary reports. The first report Climate change projections for the Wooli Wooli Estuary and Bateman's Bay (WooliBatemans.pdf; 1.06 MB) draws on existing literature to provide information on changes in climate variables likely to impact the Wooli Wooli Estuary and Batemans Bay for the 2030 and 2070 planning horizons. The second report Projected changes in climatological forcing for coastal erosion in NSW (nswdnrreportv1020070824.pdf; 832 kB) described projected changes in environmental variables that influence coastal erosion for the same two locations and planning horizons.

Historical and future impacts of East coast 'lows'

East coast 'lows' (ECLs) are amongst the most dangerous meteorological events affecting Australia, and certainly the most significant for coastal eastern Australia. They frequently have severe consequences in terms of flash flooding, wind damage, storm surge, and heavy and damaging seas. They are also responsible for heavy rainfall events that contribute significantly to total rainfall and runoff along the Australian East Coast.

The coarse resolution of the global climate models means they are currently unable to adequately model ECLs due to their relatively small spatial extent and short life span. Consequently, it is difficult to project how climate change will impact on this weather phenomenon.

OEH received $750,000 over three years from the Environmental Trust to better understand the historical and future impacts of East coast lows and other major weather patterns on the eastern seaboard.

For more information

NSW Sea level rise policy statement (2009) (09708sealevrisepolicy.pdf; 349kB)

A Snapshot of Future Sea Levels: Photographing the King Tide (2009) (09722KingTide.pdf; 2.62MB)

For additional technical information "Fort Denison Sea Level Rise Vulnerability Study"  (09698FortDenSeaLevRiseStudy.pdf; 1.26MB)