TORRANCE MENDEZ
Some of WA’s best beaches and waterways face severe erosion and flooding this winter because of a series of factors that could combine to create a perfect storm.
Already the mean coastal water levels around WA have risen 20cm in response to peculiar atmospheric conditions over the Pacific Ocean.
These higher water levels will combine with the biggest tides in the 19-year lunar cycle and lift mean water levels a further 15cm.
And winter storms can be expected to compound the effect by adding another 50cm to these levels, which will allow king waves to lash areas higher up the shoreline.
The scenario could see popular beaches pounded, submerged and washed away by towering tides.
Coastal oceanographer Charitha Pattiaratchi, from the University of WA, says the phenomenon has been dubbed La Nina, which is Spanish for girl child, and the meteorological opposite of El Nino, Spanish for boy child.
“Water levels in rivers and estuaries would be higher,” he predicted. “And we would get coastal flooding in low-lying areas.”
There was no safeguard and the only precaution was awareness.
La Nina happens when strong trade winds move water from east to west over the Pacific, causing water to pile up in the eastern Indian Ocean near Indonesia.
The effect has already been seen along the WA coast where water levels have risen 20cm, the change being most acute between Geraldton and Esperance. The increase is not as critical in the north, particularly around Derby which already has Australia’s biggest tides.
In addition, the 19-year cycle of astronomical tides caused by the Moon’s gravity will peak between 2006-08 to produce big seas and lift mean water levels another 15cm.
But the biggest damage will be inflicted by winter storms which could increase sea levels by another 50cm.
Low-lying Busselton will be particularly vulnerable, as will waterways in some canal developments around Mandurah.
Scientists say this year’s water levels are similar to those observed in 1999 when the most recent La Nina event caused greater coastal erosion in many beaches from Fremantle to Albany.
The good news is that La Nina usually brings higher rainfall. And larvae of western rock lobster have more chance of settling on coastal reefs with an expected bumper harvest in about four years.
The better-known El Nino phenomenon occurs when trade winds in the Pacific weaken and water moves west to east across the Pacific towards South America. Waters around Peru become warm around Christmas and cause the demise of local fisheries because of low sea levels, hence the name which equates to Christmas child.