Rising sea levels to erode Sydney beaches - study

Rising sea levels as a result of climate change will erode Sydney's iconic beaches by 2050, with some at risk of disappearing, and threaten beachfront homes and commercial properties, a new climate change study said.

Sea levels along Sydney's coast are expected to rise by up to 40 cm above 1990 levels by 2050 and by 90 cm by 2100, with each one centimetre of rise resulting in one metre of erosion on low-lying beaches, said the Sydney climate change impact report.

"The Sydney region has a heavy density of residential and commercial beachfront developments that may be threatened by either ocean inundation or sea level rise-induced recession," said the report by the NSW Department of Climate Change.

"Rising sea levels may exacerbate flood risk in coastal rivers," said the report received yesterday.

The report said further study was needed to determine the extent of coastal erosion in particular locations.

But low-lying Sydney beaches such as Collaroy and Narrabeen, which have already been severely eroded by storm seas, and Dee Why and Curl Curl, are most at risk.

Beaches which have a hard promenade, such as Manly, Bondi and Coogee, will shrink as sand is washed away and may need sand deposits in order to survive in further decades.

"In general we expect a recession of the coastline of a sandy beach of about one metre for every centimetre rise in sea level," said Simon Smith, deputy director-general with the department. "The coastline will move inward. What is now currently a vegetated dune may become the beach," Mr Smith said yesterday.

"It depends on the beach and the coastal area. Some coastal areas have a rocky foreshore and 40 cm does not make much difference. Some beaches are very deep and high so the beach line will retreat, other beaches are very low-lying and they are up against higher landforms behind them, they will become narrower."