Holding back the rising tide, naturally

Mass planting of spinifex and pingao in Riversdale dunes on the east coast.

Mass planting of spinifex and pingao in Riversdale dunes on the east coast.

Thousands of homes and billions of dollars of public assets are at risk from rising sea levels and we should be strengthening our natural defences now, experts say.

A leaked government draft report on Coastal Hazards and Climate Change concluded that $19 billion worth of buildings, 43,000 homes, and 2000 kilometres could be inundated by rising sea levels.

The greater Wellington region faces a double-whammy of rising seas and sinking land, meaning it will have the highest relative rise in New Zealand, but planners said they were "ahead of the game" compared with other areas. 

Riversdale in the early 1960s. An era when marram grass, lupin and iceplant were mainly used to combat erosion.

Riversdale in the early 1960s. An era when marram grass, lupin and iceplant were mainly used to combat erosion.

Greater Wellington Regional Council natural hazards analyst Dr Iain Dawe said  not enough was being done nationally to prepare for the coastal impacts of climate change, but Wellington was the first to have a natural hazards plan in place.

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 One of the biggest challenges was dealing with existing developments. 

Local councils have had a tough time imposing new conditions on coastal developments due to the resistance they faced because of the possible impact to property prices.

"A lot of the areas have been heavily developed for private property because they are attractive places to live along coastlines, but it's extremely difficult dealing with existing use rights," he said.

Another challenge was funding. Hard engineering solutions such as seawalls to prevent erosion were very expensive and places like the Kapiti Coast were already having to delay projects because they didn't have the money. 

Often the cheapest and most effective way of preventing coastal erosion was targeted dune restoration which was also a fraction of the cost.

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Whenever a major storm had an impact on a part of the coast, there was pressure from the public to build a seawall, Dawe said.

"The reason why we only use that as a last resort is because it interferes with sand or gravel accumulating on the beach naturally and you can get enhanced scouring and erosion at the front and at the ends of that structure," he said.

Many dune projects were already under way throughout the Wellington region including Kapiti Coast, Porirua, Wellington City, Petone and Wairarapa's east coast.

Ecologist and coastal restoration specialist Greg Jenks promotes innovative approaches such as the reintroduction of salt-tolerant native species such as pingao and spinifex instead of using exotics such as marram grass and lupin.

"Any other solution offered today for beating coastal erosion is simply not reliable and excessively expensive. Diligent coastal dune restoration is demonstrably more successful and enduring than building seawalls and importantly costs less than 1 per cent of normal sea wall expenses," Jenks said.

 - Stuff

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