Saturday 28 May 2016

The early effects of sea level rise in New Zealand

Eating the shore: New Zealand's shrinking coastline

28 May, 2016
Carters Airport 03Carters Airport
(2003-2015) Near Westport, a road had to be redirected as the sea inches closer to a runway at the airport. 
Erosion is eating away at New Zealand's coastline, with satellite images showing the dramatic impact of its appetite on small communities the length of the country.

It has forced people from their homes, and caused councils to relocate public infrastructure away from the encroaching sea.

But the issue is a contentious one, as shown on Thursday, when the Christchurch City Council announced the team of five experts comprising the second peer review panel to assess Tonkin and Taylor's Coastal Hazard Assessment Report. The move came after skepticism of the science behind the report, which identified 6000 properties that could be susceptible to erosion and nearly 18,000 at risk of coastal inundation over the next 50 to 100 years.
Carters Beach
(2003-2015) In Carter's Beach on the West Coast, the coastline has claimed some of the cricket field.
In the small West Coast town of Granity, the school has been engaged in a long battle with the sea, which it looks unlikely to win.

Coastal erosion claimed the school's pool when rocks were flung into it by a high tide, cracking the base. It is now bearing down on the playcentre, which is not currently at risk but will almost certainly be in the future.

Coastal erosion around the country has forced people from their homes, and caused councils to relocate public infrastructure away from the encroaching sea.

(2009-2016) In Clifton on the Hawke's Bay, the campground lost sites and roads were damaged due to erosion.

Satellite images show erosion has impacted some small communities dramatically in the space of a decade. With sea levels rising, the rate of erosion will likely increase in some parts of the country.

"It's a really big problem," said Granity principal Megan Rich.

"[Erosion] really requires a national strategy. It's not something I think councils can tackle, it's just too big. The government needs to be looking at what we need to do to absolutely preserve these areas."

Washdyke Lagoon
(2010-2016) Washdyke Lagoon near Timaru has reduced by more than 80 per cent over the last century, and will one day disappear completely.

The seawall which causes the school to jut out onto the beach has been repaired twice, at a cost of more than $200,000. For a school with a roll of 41, it does not bode well for the future.

Erosion is clear elsewhere on the West Coast: near Westport airport, a road had to be redirected from the incoming sea, and the Punakaiki camp ground faces the prospect of falling into the sea.

It's a problem which could become evident elsewhere, as sea level rises cause the rate of coastal erosion to accelerate.

Beach Road near Oamaru fell into the sea after years of coastal erosion.
Beach Road near Oamaru fell into the sea after years of coastal erosion.

Coastal erosion is a natural process which affects sand beaches and areas with soft cliff, and is caused by waves, tidal currents and wind wearing away the land. The sand and gravel stripped away is then deposited on other beaches through ocean currents, which is known as accretion.

Some beaches alternate between erosion and accretion, but cliffs can only erode.

Parliamentary commissioner for the environment Dr Jan Wright, who last year produced a report on the impact of sea-level rise, said the rate of coastal erosion would almost certainly increase.

"Where you have soft cliff, the result is very predictable – it can only go one way so erosion will go on at an accelerating rate. 

Clifton 09Clifton
(2006 - 2016) The popular Muriwai beach near Auckland moved its surf club inland and removed part of the main car park due to erosion.

"But where you have erosion generally, you would expect it to pick up speed and go faster, and where you've got accretion, you would ultimately expect that to start eroding."

She said erosion occurred in different ways, and determining which areas would be worst affected in the future was difficult to establish.

"In some places it's episodic – you might get it one time of the year while another time of year it might accrete.

St ClairSt Clair
(2015-2016) A violent storm at Ocean Beach in Dunedin last year caused sudden erosion which came near neighbouring homes.

"There's a slow chipping away in many cases, but then you can get a lot at one time when you've got a storm. Often erosion can happen in big chunks."

One such example is Ocean Beach in Dunedin, where in the space of less than a year erosion has drastically altered sand dunes near homes.

More gradual erosion has caused houses to fall into the sea in Wairarapa and Taranaki, and parking lots sacrificed in Auckland and Waikato.

Sunset BeachSunset Beach
(2010-2016) At Waikato's Sunset Beach, erosion claimed a car park and is threatening other buildings.

In Clifton on the Hawke's Bay, the motor camp lost multiple sites when they fell into the sea.

Manager Bob Pollock said the erosion had stopped in recent years, but for a time, the camp's future looked uncertain.

"We lost several sites at the front, and had problems with access and all that. Naturally it –downsized us a bit," he said.

(2001-2013) Houses were claimed by the sea at Mokau in Taranaki.

"It's narrowed the camp and narrowed the coastline all the way around to Haumoana... but it seems to have slowed down a bit."

While some areas invest heavily in costly barriers – Paekakariki on the Kapiti Coast has approved work on a $10 million seawall - it was not a viable long term option.

"The issue is, you can't build seawalls everywhere," Wright said.

"In New Zealand this is a particular problem; we've got an awful lot of coast per person. In more populated countries, they've got lots of people to pay for it... but it's going to be quite tricky for New Zealand."

She said it would take a long time for the effects of coastal erosion to become apparent, but when it did, it would reveal social and economic costs.

"People face a potential loss of property, of course, and it's going to be very hard for them. We need to think about this carefully and not rush.

"Long term, there are big issues here for central and local government, because there will be cause for compensation, and it's certainly not too early to think about how that is handled."

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