Written by Tony Malkovic Thursday, 29 July 2010 14:02
RISING sea levels could see Perth becoming the ‘Venice of the southern hemisphere’ in coming decades unless preventative action is taken.
That’s the scenario raised at a recent one-day seminar at Curtin University of Technology featuring some of Australia’s foremost sea level experts.
The City to Cape 2100 Sea Level Rise seminar looked at the likely effects of sea level rise on WA’s most populated section of coast, from Perth to Cape Naturaliste.
Several speakers warned of the need to start planning to protect coastal communities, homes and infrastructure from rising sea levels.
The Intergovernmental Panel on Climate Change (IPCC) has predicted that sea levels could rise by between 20cm and 80cm by 2100 but some scientists say it could be as much as a metre or more.
Professor Chari Pattiaratchi of the Oceans Institute at the University of WA told the seminar that records kept since 1897 showed that the sea level at Fremantle had risen an average 1.54mm a year up to 2004.
Prof. Pattiaratchi explained to the seminar that sea levels depended on the interaction between tides, storm surges and mean sea levels.
“If you have a one-metre increase by 2100, Perth will become like Venice – which will basically flood every fortnight.”
Such a dramatic rise could see suburban beaches disappear, foreshore parks submerge, and riverside roads such as Kwinana Freeway having to be raised or relocated.
He said the Swan and Canning Rivers had some 350km of shoreline and building a barrier wall could be one way of coping with such a rise in water level.
“Do we want to build a 350km wall to protect Perth?” he asked.
“Because if you want to have life as we know it now, that is the option or have a barrage (tidal barrier) but that might not be possible because of the small tidal wave.”
He said the community would have to make some hard decisions in such an eventuality.
“It’s all to do with values.
“Do we want to keep the grass foreshores, what are the economic and social values of that compared to how much it costs to protect it?
“How much is it going to cost to protect this rather than letting it go?
“We can provide the science and say this is going to happen. But the reaction to that has to be a political, local, community decision.”
Prof. Pattiaratchi said there had been an increase in extreme storm surges in WA since 1950 which exacerbated flooding and erosion.
However, it’s not just Perth that will be affected.
Homes and infrastructure in low-lying coastal communities such as Mandurah, Busselton and Rockingham would be particularly vulnerable.
Prof. Pattiaratchi showed dramatic pictures of the 16 May 2003 storm which washed away some 40m of Rockingham’s shoreline.
He said the storm resulted in the highest water level ever recorded further up the coast at Fremantle.
“At the moment, that is expected to occur once every 100 years.
“With the mean sea level rise, that could happen every year, or every few months, by 2100.
“What we might expect to happen once in a 100 years is going to happen all the time, it’s going to be the norm.”
So how much beach or foreshore could be lost due to a one metre rise in sea levels?
Quoting the Bruun Rule commonly used to calculate shore recession, Prof. Pattiaratchi said a one-metre rise in sea levels could see beaches recede some 50 to 100 metres, which would see some beaches virtually disappear.
Earlier at the seminar, the CSIRO’s Dr John Church said that satellite measuring since 1993 indicated that oceans were rising at more than 3mm per year but this was not uniform around the world due to gravitational effects and climate variability.
He said the main causes of rising sea levels are oceans expanding as they heat up, the melting of glaciers, and more recently changes in the vast ice sheets of Greenland and Antarctica.
He said sea level rise would continue in the 21st Century.
“We will need to adapt,” he said, pointing out that coastal floodings and erosion will become more frequent and there will be more severe events.
The seminar also looked at possible engineering solutions to cope with sea level rise, as well as planning considerations and legal issues involving local government and developers’ responsibilities.
The seminar was organised by the Australian Sustainable Development Institute, the Academy of Technological Sciences & Engineering, and Engineers Australia.
(See also Rising tide of concern over WA’s sea levels )
