Rudman's city: Port company knows what to do with its dredgings

By BRIAN RUDMAN

Nine years ago, Ports of Auckland's plans to dump 270,000 cu m of dredgings in the Hauraki Gulf enraged conservationists.

Protesters, including regional councillor Mike Lee who chained himself to the dredge, were arrested.

The Seafarers Union considered slapping a green ban on the boat.

Today the port company is finalising plans to dredge up to 10 times that amount and there is hardly a ripple of concern anywhere.

Even Mr Lee is relaxed about it.

For this remarkable turn of events we can thank the armistice agreement the warring parties arrived at back in November 1994.

The furore had erupted two years earlier when contaminated inner-harbour dredgings were dumped near the Noises islands, a popular fishing spot.

As a result, the Disposal Options Advisory Group was set up, chaired by former judge Dame Augusta Wallace.

All the interested parties were represented. The consensus agreement was that the best place for future dredgings was in port reclamation.

After that came deep-water marine dumping. Two sites were identified, one south of Kawau Island, the other east of Great Barrier Island.

The port company agreed to withdraw an application to dump a further 11 million cu m near the Noises and declared that "future disposals will be at depths greater than 100m."

Ports of Auckland now needs somewhere to dump up to 2.7 million cu m of fill extracted from the bottom of the Rangitoto Channel and the approaches to the Fergusson container terminal.

The dredging is necessary to allow 24-hour passage for the latest generation of container vessels.

At present, the largest container vessels berthing at Auckland carry 2900 containers. But starting next year, P&O Nedlloyd and Contship Containerlines, between them carrying 20 per cent of the port's container trade, intend to begin replacing their vessels with ships carrying 4100 containers.

The designed draught of the new vessels is 12.5m. For a certain time around high tide, these ships would be able to gain access to the port. But at low tide they would have no chance. In the Rangitoto Channel between Rangitoto Island and the North Shore, the low-tide clearance is only 11m.

The question for the port company is how deep to go with the dredging.

Doing nothing would result in delays for the new ships while they waited for suitable tidal conditions.

The delays would be of about 10 hours a voyage. Because large container vessels spend only 15 to 17 hours in port, that would not be acceptable.

Various dredging models have been drawn up, ranging from one where the average delay per voyage would be between two and five hours through to one where there would be no delays.

The minimalist approach would result in 650,000 cu m of spoil; the optimum scenario would create 2,700,000 cu m.

Costs would range accordingly. A middle-line approach would cost about $20 million.

These, of course, are commercial problems for Ports of Auckland. For those concerned about the effect on the marine environment, the big question is where the waste would go.

For this, Ports of Auckland has the ideal answer. Mix it with concrete and use it to build the expanding Fergusson container terminal.

Give or take a few buckets full, the Fergusson development can absorb about 1 million cu m of the dredgings.

For the port company, the advantages are obvious. It gives it fill it would otherwise have to pay for. It also provides a handy solution to the dumping problem.

For the environment, it avoids the problems associated with marine dumping. It also saves a scoria mountainside from being blown up to provide alternative fill.

If there are dredgings left over, then the 1994 agreement will kick into action.

It's a 24-hour tow out beyond the edge of the continental shelf, east of Great Barrier Island near Cuvier Island, but that's where Ports of Auckland will take it.

The destination will be the site of an old military munitions dump 1000m below sea level.

I guess even the staunchest environmentalist would concede that if any shells have to be covered up, it might as well be the explosive sort.