Sandbags on horizon for coastal residents

By JO-MARIE BROWN

Parts of the coastline may one day need dykes to protect low-lying land against rising sea levels caused by global climate change.

Experts say a United Nations report on global warming predicting a 1m rise in sea level by 2100 means that flat coastal areas may require defences against encroaching tides.

Ports may need higher wharfs, which would require huge investment.

The prediction of a 1m rise in the sea level comes from the UN's Intergovernmental Panel on Climate Change.

The panel's conclusions have left local scientists and coastal experts contemplating the impact on New Zealand's landscape, marine life and populated areas.

But although tiny South Pacific atolls could be inundated if the predictions of the UN scientists prove correct, a leading coastal scientist says New Zealand's coastline is unlikely to change dramatically.

Waikato University coastal scientist Professor Terry Healy said Ninety Mile Beach would probably shrink by around 100m on either side and sand dunes around the country would erode over time.

But New Zealand's geological makeup and high sedimentation rate should ensure that sand and mud were deposited in most places around the coastline at a rate greater than that of erosion.

Flooding would become a problem for low-lying areas in places such as the Coromandel as big storms flooded more places than at present.

Thames, Whitianga and parts of the Kaipara and Waitemata harbours might have to build dykes or other sea defences to keep water out during bad weather.

"Places like Thames already have a sea wall but obviously that is not going to be sufficient should the water come up by another metre," said Professor Healy.

Coastline Consultants director Jim Dahm said many settlements around the Firth of Thames were only 1 to 2m above sea level.

"This raises serious concerns about the extent to which these settlements should be allowed to intensify."

Serious erosion would also occur on the eastern Coromandel, where housing developments had already destroyed natural sand dunes.

Other difficulties Professor Healy foresaw included the need to raise low-lying roads and wharves at the country's main ports.

"Some of them may be too low to take an extra metre of water over the high spring tide.

"That would be serious because to construct a new wharf costs millions."

Ports of Auckland hydrographer Dave Hoskins confirmed that a 1m sea-level rise would create problems.

The wharves now stood 1.6m above the average high spring tide but redevelopment plans would have to take into account the predicted sea level.

Mr Hoskins said: "If it suddenly rose by one metre at the moment we would probably have to issue gumboots to everyone."

Herald Online feature: Climate change

Intergovernmental Panel on Climate Change

* Draft summary: Climate Change 2001

  (requires Adobe Acrobat Reader)

United Nations Environment Program

World Meteorological Organisation

Framework Convention on Climate Change