Residents of Great Barrier island don’t want the dredgings from Auckland’s port and marinas near their island, but marinas say it has nowhere else affordable to go, reports Eloise Gibson.

Auckland’s ports and marinas are all silted up with nowhere to take the sediment – apart from a remote dumping spot 25km east of Great Barrier Island, the Environmental Protection Authority (EPA) has been told. 

Works to ready the waterfront for the 36th America’s Cup alone are projected to create 70,000 m3 in sludge that needs to go somewhere.

All told material from dredging marinas around Auckland and, possibly, from Ports of Auckland, will create an estimated 500 percent increase in the amount of silt and sediment needing to be dropped in waters beyond the Hauraki Gulf Marine Park over the next decade, the EPA heard.

Auckland Council’s coastal rules make it difficult to get permission to discharge sediment inside the region’s waters, so barges travel all night and into the next day to reach a dump zone with a 1.5km-radius in New Zealand’s exclusive economic zone. That zone is under the jurisdiction of the EPA.

One company, Coastal Resources Limited (CRL), currently has the only marine dumping permit for the Auckland region, which it has used it to allow marinas and ports to dispose of 223,000m3 of material over the last five years.

Now CRL wants the EPA to increase its limit fivefold so that 250,000 m3 could be dumped each year for the next 35 years instead of 50,000 m3 a year.

Great Barrier’s local board says locals don’t want the waste in waters near their island. In a submission, it admonished Auckland for having an “out of sight, out of mind” attitude.

Other opponents, including the Department of Conservation (DOC), fear the barges will carry invasive species such as Mediterranean fanworms to the waters off Great Barrier, as well as creating more noise for dolphins and whales, and – possibly – smothering protected creatures, like stony corals. (So far no protected corals have been found in the area but DOC wants better exploration of the habitat).

Auckland’s marinas, on the other hand, say there’s nowhere else to take their dredged-up stuff, because disposing of it on land would be too costly and difficult and the days of big coastal reclamations (like Fergusson port, which used marine sludge as fill) appear to be over.

Waste used to be dumped at another site in the EEZ – the Auckland Area Explosives Dumping Ground, east of Cuvier Island. But that had to stop as the water was too deep to allow the effects to be properly monitored, as well as a risk of unexploded ordinances.

Bayswater marina said in its submission to the EPA that, without regular dredging, silt would build up and, within a decade, yachts wouldn’t be able to use the marina. Eventually passenger ferries would also be ousted. Moving the material somewhere on land by truck would require 1428 truck trips along an already-congested route, Lake Rd, the marina said.

CRL doesn’t do the dredging itself; it administers access to the dump zone for barges carrying sludge excavated by diggers from marinas. Over the next decade it says its customers, including Bayswater, Pine Harbour, Hobsonville, Sandspit and Whitianga marinas, will want to dispose of hundreds of thousands of tonnes more dredged material, including an estimated 70,000 m3 from preparations for the 36th America’s Cup.

On Wednesday CRL told the EPA’s hearings panel that Ports of Auckland would apply for its own dumping permit, but CRL had agreed to take its material if the port’s bid failed.

CRL says regular dredging already makes up about half the cost of berthing at places like Pine Harbour marina, so not being able to dump in the EEZ would drive up berth costs for yachties. It estimated the current cost for transport and disposal of material once loaded into a barge was about $50 per m3.

Unwanted intrusion 

The slow barge journey from Auckland travels through the Hauraki Gulf before dropping the sludge through the hull into the sea where it settles on the ocean floor.

CRL has facilitated more than 500 trips in the past five years to dump a total of about 200,000 m3 – still less than the yearly limit it wants to take to the zone from now on.

Twice, a barge has suffered a mechanical problem and had to drop its load on the way to the dump site.

Of the 76 submissions to the EPA, 31 were from people on Great Barrier Island. Most – 63 of the 76 – were opposed to the plan.

The Aotea Great Barrier Local Board says its community fears bio-security risks from the boats and that contaminants like heavy metals will escape from the sediment. “Our islands and waters are largely pest-free and the dredged material comes from highly infested locations,” says the board’s submission. “The measures to prevent infestation do not adequately provide safeguards of catastrophic risks for the environment … As humans we should take responsibility for managing and minimising our waste and not subscribe to a philosophy of ‘out of sight is out of mind’.”

The Hauraki Gulf Forum is also against the plan, citing opposition from tangata whenua and other locals. The forum is worried that ocean currents might carry contaminated sediment from the dump site into the Hauraki Gulf Marine Park.

The Department of Conservation, another submitter, says the proposed conditions on the permit aren’t strict enough to stop barges disturbing marine mammals and seabirds and that there’s a risk to creatures near the dump zone itself, like filter-feeding sponges, which it says don’t cope well with sediment. Like the local board, DOC has raised worries about barges carrying invasive species, such as the Mediterranean fanworm, to the area on their hulls.

Experts working for CRL studied samples of the sea-floor in the dump zone to find out what creatures would likely be harmed.

CRL acknowledges that the dumped material smothers and kills little creatures like worms, molluscs and sponges that live immediately under the drop spot, however it says the vast majority of the damage is confined to immediately under the mound.

But DOC’s Clinton Duffy said in a written statement for the panel that the sampling process wasn’t good enough to fully tell what kinds of bottom-dwelling creatures and ecology the dumping might disturb.

A review of CRL’s evidence by NIWA also found shortcomings in the sampling methods, and said that, although there was unlikely to be a large population of protected species in the dump zone, there might be protected stony corals inside the area. (CRL says there’s no viable way to be certain, but it’s unlikely the corals are there and it wouldn’t be reasonable to require total certainty.)

“These delicate and immobile species would have little chance of surviving being smothered in dredge spoils. A further consideration is the smothering effect of the sediment plume on benthic organisms such as corals, sponges, and bryozoans that live down-current,” read NIWA’s report to the panel.

Then there are whales and other marine mammals around and en route to the area.

Under the dumping permit, barge operators are supposed to look out for marine mammals and wait until they leave the area before discharging their load.

But the Auckland Conservation Board is worried that untrained operators won’t spot dolphins and whales, especially if they arrive in the dark.

CRL’s biologist admits that the 545 trips to the dump site so far have added 10,000 hours of underwater noise to the Hauraki Gulf Marine Park, noise that can have impacts on some animals’ hunting and other behaviour.

But he also said that even the maximum number of trips that barges would be able to make per year would still be less than 1 percent of the total boat traffic in the Hauraki Gulf.

CRL wants permission for two barge trips a day.

CRL’s experts have told the EPA that there are few if any effects on species like fin-fish, dolphins, whales and endangered seabirds and no known vulnerable ecosystems or habitats inside the dump zone.

Most of the dredged sludge lands on the seafloor in a mound, but about 5 percent of the sediment will stay suspended in the water, and currents may carry some of it outside the dump zone. But it won’t be at high enough concentrations to cause any serious effects, says CRL.

Thoroughly cleaning the barge’s hulls would manage the risk of bringing in invasive species from the inner harbour, said the company’s experts, and any unwanted creatures in the sediment itself would likely die from the unexpectedly deep cold water they were being dropped in.

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