Lucky low tide keeps Chch safe

Last updated 05:00 01/03/2010
Lyttelton Harbour, tide out
CHRIS RUDGE

SUDDENLY STRANGE: Boats sit on the seabed after tsunami surges drained Cass Bay in Lyttelton Harbour.

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A "hell of a lucky" low tide saved Christchurch from damage after tsunami surges triggered by a massive earthquake in Chile hit yesterday, scientists say.

New Zealand was on high alert yesterday as oceanographers and Civil Defence watched waves move across the Pacific from South America after Saturday's magnitude 8.8 quake left more than 300 people dead.

Three large surges struck the Canterbury coast yesterday with one breaching the shores of Lyttelton Harbour, flooding paddocks, submerging jetties, washing across a road and filling the car park of a country hotel.

Ports including Lyttelton and Auckland closed for the day and evacuated ships out to sea.

The Marsden Point Oil Refinery was briefly put in an emergency shutdown and events nationwide such as a fishing competition at the Rakaia River mouth were called off.

Residents in some low-lying areas of the Banks Peninsula coast were advised to be ready to evacuate and campers were moved to higher ground.

Civil Defence warned that people should stay away from the coast and river mouths for the next few days.

The first surge in Canterbury, between midday and 1pm, was "a big one" that raised the sea level in the harbour 2.2 metres in less than an hour, coastal geographer Bob Kirk said.

Fortunately, it was low tide when the wave arrived, averting major damage.

Two further surges were recorded an hour either side of the 5pm high tide.

A reported one-metre wave hit the Chatham Islands about 8am yesterday. About 11am water dramatically sucked out from several Canterbury beaches. Yachts were left grounded when the water disappeared from Cass Bay on Banks Peninsula. Similar dramatic surges were seen at beaches in Northland, East Cape, Otago and Chatham Islands.

Lyttelton Harbour tidal gauges showed a surge raising the sea level 2.2 metres in the hour between 11.45am and 12.45.

Press reporter Martin van Beynen was almost caught by the returning surge at Purau Bay on Banks Peninsula when he went onto the beach to investigate fish stranded by the earlier outflow.

The 4pm surge submerged the jetty at Governors Bay and caused a stream beside the Wheatsheaf Tavern in Teddington to burst its banks.

Patrons at the tavern, which was flooded in the 1960 tsunami, rushed outside as water started flowing through the car park.

All the vehicles escaped serious damage. The surging tide carried on past the pub to flood a paddock.

Farmed salt marshland on the east side of the Teddington road was also flooded.

Wheatsheaf owner Susan Hamilton said she was at an outside table when the car park started filling with water.

"We weren't shocked. It was more, `Wow, we are going to see something'," she said. "The water gushed in and then went out again before coming back."

Guy Goddard, a Teddington farm manager, said he was running his dogs about 800 metres from the pub when he saw the surge about 4pm.

"I drove in [to the pub car park] as it was coming through. It was about six inches (15cm) deep. It was like an extra high tide. Nothing dramatic but definitely worth watching."

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Fulton and Hogan's Paul Dumbleton said the Teddington road had flooded on one corner in the 4pm surge but it was not necessary to close it.

He and other staff remained in Teddington until about 6pm. A surge due around 5pm with the high tide swelled Teddington waterways again but peaked below the previous surge.

Kirk said low tide had again intervened to avert damage.

"As in 1960, we are hell of a lucky it's occurred at low tide. That first wave is not chicken feed at all, that's a big one," he said.

Civil Defence yesterday afternoon downgraded the threat to the country but warned that Lyttelton Harbour and the long bays of Banks Peninsula could continue to experience tsunamis and that people should stay away from the coast and river mouths.

It would take a while for the Pacific Ocean and Canterbury waters to recover from the Chile earthquake, Kirk said. "What happens with something as big as that is you get excited water motions on the continental shelf, so it is a bit like water slopping around in the bathtub – once they're going it takes time to get them to die out."

CHILE EARTHQUAKE

Magnitude: 8.8

Strikes: 3.34am Saturday (7.34pm, NZ time)

Centred: 115km northeast of Concepcion, 325km southwest of Santiago

Depth: 35km

Death toll: 300 (expected to rise)

Homes damaged: 1.5 million

- The Press

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