Dredging sucks*

For several years now, turmoil has been brewing in Dunedin. The fate of Otago Harbour lies in the balance. Some groups claim that dredging the harbour will be a step forward for Dunedin; others say it will destroy it. Caitlyn O’Fallon looks into it.

The plan that sparked the controversy goes by the somewhat grandiose name of 'Project Next Generation'. According to Port Otago, the company planning the dredging, Port Chalmers needs to make itself available to the new, larger ships if it is to continue to grow and serve the country's supply chain. Currently, only around half of the harbour reaches the 14-metre clearance required for the largest container ships.
   To create this deeper channel, Port Otago will be dredging large parts of the harbour. Dredging involves using specially fitted-out boats to lift rock, clay, sand, and silt from the sea floor. Widening of the channel near Harrington Bend and Swinging Basin will involve blasting away the rocks. The resulting sediment will then be dumped at a site about six kilometres northeast of Taiaroa Head.
   Port Otago already carries out routine dredging to maintain the current channel. In fact, the first dredger to work in the harbour was built in 1868 for this purpose. The harbour is already a very altered environment from what it was when the first settlers arrived. As ships grow in size, the port has continuously dug deeper to keep them coming in to Dunedin. 
   What distinguishes this project is its scale. Currently, around 200 000 cubic metres of sediment per year are dumped near Aramoana. This project will involve up to 80 000 cubic metres of material per day being dumped at sea. A total of 7.2 million cubic metres may be moved in total.
   The effects of this alteration, which add up to a total of 34 million cubic metres dredged over about 135 years, are quite dramatic. Some of the effects can be clearly seen. Logan Park, for example, was Logan Lake before the land was created using the spoils of early dredging. Others are less obvious to the casual observer. The first comprehensive survey of the area in 1850 showed that the maximum clearance available to ships coming in to Dunedin was four metres. This is drastically different to the 14 metres planned after Project Next Generation.
   Clearly, dredging projects have been of great value to the port, and probably to the city as well. But the issues arise when one considers the potential ecological effects of changing the local environment to such a huge extent. Environmental groups and Port Otago have widely differing views on the potential effects of Project New Generation. Richard Reeves, the organiser of Friends of the Otago Harbour, a group opposing the alterations, claims that the dredging will “radically change” the marine environment. In an opinion piece for the local paper he said that for shellfish, the economic advantages translated to “widespread death, an underwater Pompeii.”
   Port Otago has repeatedly assured the public and interested groups that there will be no such devastation. Their claims are at least partially backed up by the research done by NIWA (the National Institute of Water and Atmospheric Research), which concluded that most of the effects were likely be short-lived and underwater life would likely recover.
   However, these conclusions can only describe what is likely to happen. There are more serious possible outcomes, and some scientists believe they are risks we should be worried about. Dr. Chris Hepburn and Associate Professor Liz Slooten, both from the University of Otago, believe that the consequences for the environment could be more serious than what NIWA predicts.
   Dr. Hepburn explained that the biggest concern, one that is shared by commercial fishers and tourism operators, is the deposition of sediment after the material that is dredged is dumped off-shore. According to the models presented by NIWA, this should be present in only low levels near the shoreline. This model has been repeatedly called into question during the consultation process. If it is wrong, then sediment from the dump site could be deposited much more heavily along the coastline from Shag Point to Warrington, smothering rocky reefs, kelp forests, and other habitats. The interconnected nature of marine environments mean that it is difficult to predict what might happen next, but it could have serious consequences for life in the harbour.
   The consultation process regarding the project has stretched out over the last three years. The consultative group involved representatives from groups as diverse as the Department of Conservation, Southern Clams, Monarch Wildlife Cruises, and the Otago Yacht Club. 
   However, critics of the plan, like Reeve, claim there has not been enough publicity or public discussion for a project of this scope. Reeve says “The process of public consultation undertaken by Port Otago has to date been underwhelming at best, at worst smoke and mirrors.” Dr. Hepburn does not take such an extreme view. “I don't think the port's the most evil company around ... they've tried but I don't know if their process was quite right. They listen but then don't do anything.”
   Dunedin advertises itself as the nature capital of New Zealand. The validity of that claim is inextricably intertwined with the wellbeing of Otago Harbour. The ocean around Dunedin is an important habitat for conservation. A 2003 survey carried out by the Ministry for Agriculture and Fisheries identified 275 different species in the harbour. Rocky reefs and kelp forests stretch along the coastline. A huge variety of fish and other creatures live here and further out to sea, including scallops, starfish, sea sponges, and tubeworms.
   There are also many species of bird that make their home on our coast. The Yellow-eyed Penguin is one of the rarest species of penguin on the planet, making the breeding colony on Otago Peninsula important for both research and conservation. The albatross colony at Taiaroa Head is the only mainland breeding site for any albatross species in the southern hemisphere. The Stewart Island shag, pied oystercatcher, bar-tailed godwit, and banded dotterel are some of the other vulnerable bird species that inhabit the area.
   Hooker's Sea Lion is also among the most endangered of its kind. They had been hunted almost to extinction, by both Maori and European settlers, when they gained protected status in the 1890s. A colony is established on Otago Peninsula, and once again this is the only place where these magnificent animals breed on the mainland. New Zealand Fur Seals are another resident with a similar story of near-extinction by hunters after their pelts. They also became protected in the late nineteenth century.
   A group of about 20 Hector's dolphins, unique to New Zealand and under serious threat of extinction, live in the area around Blueskin Bay, the very area that may be affected if sediment is pulled in-shore.
   Dr. Slooten, whose research interests include marine conservation biology and marine mammal biology, stated at a public meeting in July that these sediments could affect the dolphins, as well as fish and seabirds. Hector's dolphins forage for food near the shore, and would be disrupted by the presence of cloudy sediments.
   According to NIWA's assessment, seabirds are unlikely to be affected. Several species, like the albatross and penguins, travel many kilometres in search of food and will simply avoid the dredging and dump sites. Other birds forage in waters nearer to home, and the models predict that the sediment reaching these areas will not be enough to affect these birds. However, if these models are wrong, increased levels of sediment will drive fish away from the area, and those that are left would be difficult to find in the murky water. Birds that would be harmed if this happened include rare species of gull, shag, and tern.
   Another threat to birds is loss of roost sites. A large variety of birds roost on sand islands opposite the port at high tide. Some of these islands may be removed by the dredging process. NIWA recommended replacing any lost habitat by creating new islands with the spoils from dredging.
   As well as hosting important conservation sites and eco-tourist attractions, Dunedin is also popular with fishers, both commercial and recreational. Tarakihi, sole, elephant fish, lobsters, clams, paua, and squid are some of the species harvested in the area around the harbour. According to the East Otago Taiatupere Management Committee, which is responsible for managing fisheries along the coastline, marine life in the area is already under threat from over-fishing, and will be even more threatened by the dredging project.
   The Port Chalmers Fishermen's Co-operative Society has expressed concern that the dump site and resulting “plume” of silt and other material might damage fishing.
   Another group with an interest in maintaining the harbour in its current state is the surfing community. The Otago Peninsula offers some of the best surfing around, albeit some of the coldest. Local surfing groups South Coast Boardriders and the Surfbreak Protection Society are concerned that the dumping of large quantities of sediment off the coast might negatively impact surfbreaks around Dunedin. They say that past dredging has already impacted breaks; and this dredging is on a scale that has never been done before in the area.
   So, what will happen?
   Dunedin is not the first city to object to modifications to its harbour. Melbourne had a similar controversy in the lead-up to the Port Phillip Channel Deepening Project that was scheduled to begin in 2008. Opponents claimed that the impact on sensitive marine habitats in one of the most diverse and valuable areas in Victoria would be catastrophically and possibly irreparably damaged by the process. So what happened?
   Work on the harbour was completed late last year. The company behind the project declared it a complete success. Certainly, there have been none of the predicted algal blooms and dead zones. But the original opponents point to increased erosion, higher swells, decreased fish populations, and the disappearance of certain rare sea sponges, and say that this should never have happened. It could be years before the full impact can be observed.
   In Dunedin, it seems very likely that Project New Generation will be going ahead as planned. If its opponents fail to force substantial changes to the project, then the best we can hope for is that Port Otago was right, and our precious harbour is safe.
   *They're using suction dredges to do the work

Posted 5:20am Monday 23rd August 2010 by Caitlyn O’Fallon.