West Coast waste will end up in deep sea canyon, scientist warns

Tuesday, 9 April 2019

Some of the rubbish spilling out into the Tasman Sea from an old rubbish dump on the West Coast will not be able to be collected, scientists say.

Heavy rainfall and flooding caused the historic Fox Glacier landfill to become exposed last month, with rubbish spilling out into the wider environment. Rubbish has spread along about 300 kilometres of the coast from Okarito to Martins Bay in Fiordland.

Associate Minister for the Environment Eugenie Sage has said she will investigate old landfills around the country if they are in danger of erosion.

A close up of rubbish that has spilled out onto beaches from an old landfill near Fox Glacier.

NIWA marine geological processes programme leader Joshu Mountjoy said while some of the rubbish had washed up on beaches, a large amount would have floated offshore and be out of sight beneath the ocean surface.

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'Directly offshore [from] Fox River, the Cook Canyon comes to within at least 4km of the shoreline and is a major pathway for transporting sediment from rivers to the deep ocean. The end of the canyon has not been found but is deeper than 4000 metres.

Rubbish has spread about 300 kilometres along the West Coast from Okarito to Martins Bay in Fiordland.

'We know from recent studies that sediment from rivers is actively being moved into canyons on the West Coast and it is likely that a component of the Fox River landfill waste will end up in the deep ocean by the same processes.'

A recent study on canyons off the coast of Sicily, published in the Scientific Reports journal, found flash flooding caused huge amounts of rubbish to end up in water up to 1km deep.

The 170-metre Waiho Bridge was washed away during heavy rain on March 26.

'We need to do a lot more to understand if rubbish is being transported into the Cook Canyon or other canyons around New Zealand,' Mountjoy said.

The canyons were key marine ecosystems, hosting 'some of the most concentrated biomass on earth and supporting important fisheries'.

AUT Build Environment Engineering senior lecturer Jeff Seadon said once waste got into the environment, it was very hard to clean it up and its effects could last for generations.

'When it gets into the oceans, currents can carry it thousands of kilometres from its origin as we have seen with plastics in the marine environment. By the time it gets back to shore, beachcombing is really the only way to clean it up.

'These wastes can be hazardous, so cleaning them up requires specialised knowledge and equipment to avoid injury or adverse health effects,' he said.

Modern landfills in New Zealand captured a high percentage of methane emissions and had liners to prevent leaching, but old landfills had no methane collection, proper cover or liners.

'However, in the past, landfills could best be described as dumps … [They] allowed water to pass through, creating more leachate that spilled into the environment … [and] were often located by the seaside or near waterways,' he said.

'Storm events, like the recent one at Fox Glacier on the West Coast, can uncover these dumps and the waste then flows away, often to the nearest marine environment. From there it can be carried out to sea or along the coast to wash up wherever the currents carry it.'

Volunteer co-ordinator Mike Bidoleau said volunteers travelled in 11 helicopters on Tuesday to focus on the coastline between Karangarua and Okarito.

Specialists were dealing with potentially hazardous waste in the Fox River and near the rivermouth.

'We've had flat seas, very little wind, so we don't know how much is being washed up or how much has gone out to sea,' Bidoleau said.

The new bailey bridge across the Waiho River, between Fox Glacier and Franz Josef, is expected to open on Friday.

New Zealand Defence Force engineers and contractors working for the NZ Transport Agency are helping rebuild the bridge.

'We will have a rest day [on Wednesday] because we are due some bad weather and after that we'll see how much has been churned up and how much more washes up.

'At the moment, we've got the beaches looking pretty stable; it looks way better than it was.'

PLANS TO REOPEN BRIDGE ON FRIDAY

Meanwhile, the NZ Transport Agency (NZTA) and New Zealand Defence Force (NZDF) engineers hope to reopen the washed-out Waiho Bridge on Friday.

The State Highway 6 bridge, between Fox Glacier and Franz Josef, was destroyed by flooding on March 26.

Westland mayor Bruce Smith said in a statement that the road closure was costing Westland $3 million a day in lost tourism income.

The NZDF sent a team of army engineers to help NZTA and construction company Downer install in a new bailey bridge across the river.

Bailey bridges are a type of portable, pre-fabricated truss bridge developed for military use during World War II.

'The support of the NZDF and contractors has been a huge morale boost for our community – no question about that,' Smith said.