Sea level rise would affect us, says study

The draft Brisbane Water Foreshore Flood Study has found that "almost all the low-lying areas in foreshore towns like ... Ettalong, Umina and Woy Woy are affected by potential water level rises ... as a result of greenhouse-related climate change".

However, consultants Cardno-Lawson Treloar who produced the study say that estimates of sea-level rise vary considerably and the study has allowed only 300mm over the next 100 years, based on Intergovernmental Panel figures.

"There is some uncertainty associated with this parameter ... and it should be re-assessed every decade.

"Should a rise greater than 300mm occur in the longer term, there will be ample time to undertake design modifications," the draft report states.

The study found that 100-year peak water levels would be 1.59m above mean sea level at Ettalong and Woy Woy, with five-year peaks of around 1.3m.

The "probable maximum flood" level was found to be 1.85m at Ettalong and 1.94m at Woy Woy, equivalent to a 10,000-year peak.

The 100-year peak would only increase to about 1.9m with a 300mm sea level rise.

The consultants stated that, to date, planners have assumed a 1.95m 100-year flood level based on data from the May 1974 flood.

It was a purpose of the study to provide more reliability to the flood level data.

The study said that the combination of factors that caused this flood was rare.

These included a high astronomical tide, an inverse barometric effect, wind setup, wave setup, and possible propagation of coastal trapped waves and ocean basin effects.

"The average recurrence interval of an event like the May 1974 storm is considered to be greater than 100 years."

The study found that severe ocean storms caused the highest foreshore water levels, rather than catchment flooding.

The draft report on the Brisbane Water Flood Study has been released for comment and is available at Peninsula libraries and from the council's website.

The closing date for comments is February 15.

Peninsula Residents' Association secretary Ms Sheelagh Noonan said she was a member of the council's floodplain risk management committee and was available to ask questions on behalf of residents.

Draft report, 21 Jan 2008 Sheelagh Noonan, Peninsula Residents' Association