Development plans for Coromandel Harbour stirring up resistance

Forest and Bird’s Upper Coromandel Branch is leading the local opposition to a controversial development currently being promoted by the Thames-Coromandel District Council (TCDC), to excavate 23 hectares of the foreshore of Coromandel Harbour to create a basin for a marina and an adjacent fast ferry terminal.

Like many bays in the Hauraki Gulf, the Harbour is very tidal, and at low tide, large areas of mudflat and seagrass are exposed.  Even the town’s main wharf is only able to be used for an hour or two either side of high tide.  For the marina to proceed, a huge amount of mudflat will need to be removed and a channel approximately one kilometre long is planned to connect the marina to a constant supply of sea water at low tide.  Unfortunately, the sediments of Coromandel Harbour are highly toxic, and their excavation runs the risk of damaging its marine life.

Over the past 25 years, four separate reputable studies have been carried out on the Harbour sediments in various locations around the site of the proposed marina. Each study has reached the same conclusion – that the levels of mercury and arsenic in the sediments are elevated; and that considerably higher levels of contamination exist in sediments deeper than 30 cm.  The studies agree that the mercury and arsenic in many locations exceed the levels at which some adverse effects on marine life would be expected.  Several samples had such high levels that they would be considered to be hazardous waste under the Waikato Regional Council’s Coastal Management Plan.

Coromandel was the site of New Zealand’s first gold rush in the Nineteenth Century, and the gold and silver found in the hills are often associated with elements with a high atomic mass, such as cadmium and mercury. The sediments of Coromandel Harbour contain elevated levels of heavy metals, mostly released from the rock and gold ore extracted around 150 years go and washed into the Harbour.

Relatively small amounts of heavy metals can severely affect the reproductive ability of marine species and can cause a range of abnormalities. Shellfish that daily pump large volumes of water across their gills may be particularly susceptible to poisoning, because they can absorb these toxins against the concentration gradient (i.e. when there is a higher concentration in their body tissues than in the surrounding water).

Exposure to mercury from the consumption of contaminated seafood can also have severe impacts on human health, such as Minamata Disease, caused by eating fish contaminated with methyl mercury. Globally, there is a considerable sensitivity to the amount of pollution in marine foods, and even the perception of elevated levels of heavy metals in Coromandel Harbour could be sufficient to lose long-established overseas markets for the mussel and oyster farming industries, and deter recreational fishers from using Coromandel Harbour and surrounding seas.

Because burrowing marine organisms generally only penetrate the top 200-300 mm of the seabed, it is likely that most of the mud containing the most elevated levels of heavy metal from gold-mining days is currently contained within an anoxic (oxygen-free) environment, and is effectively unavailable for uptake by marine organisms. Dredging up this mud, however, could mobilize the heavy metals currently contained within sediments deeper than 300 mm.

Interestingly, this is the second time around for the marina proposal. A similar scheme was abandoned in the face of local opposition almost two decades ago, before most people were aware of climate change and the vital importance of mangroves and seagrass beds in carbon sequestration. At a recent meeting, a senior TCDC official said that the mangroves near the channel would need to be removed to allow the channel to be widened.

Since the first meeting in 2014 of a Harbour Working Party set up by the TCDC, Forest & Bird’s Upper Coromandel Branch has raised the same concerns about the inherent risks of digging out a marina basin and concerns about where the toxic dredgings would be dumped.

We have yet to receive a satisfactory explanation of how this could be carried out safely, but we have been accused of standing in the way of progress. Our concern is progress at what price and who benefits?  Forest and Bird’s Upper Coromandel Branch believes that not only is the marina basin an environmental risk that we don’t need to take, but also that the facilities created would be mainly for the benefit of non-locals, while the local population would lose their current public access to the foreshore, as well as potentially losing biologically significant areas of mangroves and seagrass. Additionally, as the TCDC concedes, dredging will need to be carried out on a regular basis, as cyclonic rain events generate run-off into the sea and the proposed channel silts up.  This is likely to be an increasingly regular phenomenon in an era of climate change and more powerful cyclones.

Forest and Bird’s Upper Coromandel Branch is currently awaiting the release of the TCDC’s Business Plan for the Marina and Fast Ferry Terminal development, and we have already received some offers of professional advice.  We would gratefully receive further offers of expert technical support.