Flooding and Mercury – a Toxic Mix For Coromandel Harbour Project

Government Minister Shane Jones recently announced government funding for a feasibility study into improved wharf and harbour facilities at Coromandel town as part of the Provincial Growth Fund initiative. But sea level rise flooding of land beside the wharf/harbour has not been properly considered, and a series of previous studies showing high concentrations of mercury and arsenic toxins in the mud suggest the project should not proceed. 

Land Beside Harbour Will Flood From Sea

It appears that no attention has been paid to the exposure to sea level rise and coastal hazards of land-based infrastructure and businesses immediately adjacent to the Coromandel wharf/harbour.  It may be possible to design a wharf to cope with rising seas, but it another thing entirely to fully protect land-based businesses from a rising tide.  

To illustrate these concerns here is an indicative potential future coastal flooding map taken from the Waikato Regional Council’s coastal inundation tool The coastal flooding map illustrates a 0.5 m of sea level rise plus a mid-range storm surge but does not include wave effects.

2.80 m 0.5 slr plus mid storm surge

Under this scenario, there would be extensive coastal inundation of the coastal land beside the harbour/wharf on which essential marine infrastructure and businesses associated with the Coromandel Marine Gateway proposal would be located.  With this flooding threat looming the government must reconsider whether the whole proposed project is still viable, and worthy of tapayer funds. 

The project will only be able to meet its intended purpose and function effectively if extensive and expensive coastal protection works are also constructed to prevent coastal flooding of this adjacent land.  Are sea walls or other protection measures feasible in Coromandel and/or affordable, when every other city,  town, and small settlement in NZ will be demanding that THEIR place is protected?

These same coastal flooding issues arise for land-based marine services businesses proposed near the proposed wharf upgrade at Kopu which is also mooted for Provincial Growth funds.   This map is taken from the inundation tool and also shows a 0.5m sea level rise and mid-range storm surge.

3.2 kopu

Mercury Rising

Forest and Bird say there are environmental risks associated with the Coromandel Marine Gateway proposal and a similar proposal had already been rejected in the past.

Regional Manager Dr Rebecca Stirnemann said past mining activity in the area had left behind mercury and arsenic in the seabed.

“It seems ludicrous for the government to be funding a further feasibility study [when] the issues are all out there and they were well canvassed 20 years ago when the previous marina development proposal was rejected,” she said.

“It just seems the most inappropriate use of public funds.”

Coromandel resident Mike Donoghue points out that since the earlier proposal was rejected in 2001, the Thames Coromandel District Council has commissioned two scientific reports into the harbour which have both shown contamination of sediments at levels that could affect marine life.

“One of the studies by Pattle-Delamore Partners Limited found that some concentrations of mercury were in the high-risk category with three of six samples exceeding a level at which adverse impacts on aquatic life could be expected,” he said.

“Levels of arsenic were also found to be generally above the low-risk category.  The study concluded the sediments may be considered hazardous under Waikato Regional Council rules.   At the moment the highest concentrations of heavy metals are effectively sealed off because there are buried deep in the sediment where they cannot be released.  But dredging may expose these deeper sediments and release mercury and arsenic into Coromandel harbour”.

Rebecca Stirnemann said that the government should not be backing the project.

According to local scientist Thomas Everth“Mercury concentration in our harbour sediments in many samples was found to be above 3mg/kg. This is a level that puts the contamination at up to 20 times higher than the New Zealand and Australian guidelines “low” level above which species in the aquatic environment become affected.  Some samples had concentrations 3 times higher than the ANZECC Guidelines “High”, above which severe contamination must be assumed!”

everth data mercury

Before either of these projects are advanced any further and more government funds are committed, the Ministers for the Environment and of Conservation must insist that coastal flooding issues and potential associated costs and mercury toxins in the harbour mud must be thoroughly investigated.

Here is the position of the Royal Forest and Bird Society on the proposed Provincial Growth funding of the Coromandel Gateway Project :-


The Forest &Bird Protection Society today urged careful consideration of environmental impacts that might arise from the Provincial Growth Fund, citing the recent announcement of the Fund’s support for a feasibility study for the Coromandel Gateway Proposal. This controversial project would involve the removal of 100,000 cubic metres of the margins of Coromandel Harbour to create a marina basin for 12 permanent berths, a terminal for a daily ferry from Auckland as well as apartments, car parks, and a boat stacker.

“Forest & Bird supports the establishment of a government fund to support sustainable
development in rural communities, but not at the price of the environment,” said  Regional Manager, Rebecca Stirnemann

“The Coromandel Gateway proposal is similar to a marina proposal by the same developer that was rejected at the consent stage in 2001, because of its impacts on the Harbour margins, especially a nearby Area of Special Conservation Value. We do not agree with the developer or the local Mayor that this project has overwhelming local support, and we have grave concerns for the potential release of heavy metals from the Harbour sediments and its potential impacts on the shellfish industry.”

The Thames-Coromandel District Council has commissioned several studies of the heavy metal content in the seabed of Coromandel Harbour, all of which have concluded that the contamination levels for mercury and arsenic are high, in some cases exceeding international standards.

“Because of past mining activity, the seabed of Coromandel Harbour is one of the most
contaminated of all the rural harbours in New Zealand”, says local resident Mike Donoghue.

“Fortunately, most of the mercury and arsenic is currently safely bound up in deep sediments, and it seems to be the height of folly to risk its release, especially given the importance of mussel and oyster farming to the local economy. The developers had intended to press ahead with this project without conducting a sampling programme to ascertain heavy metal levels in the proposed marina basin and the 1.8 km dredged channel into the Harbour, but Forest & Bird insisted six months ago that this take place. We are still awaiting the results of that programme.”

“Forest & Bird supports sustainable development in Coromandel, but is concerned that Government money is being used to support a project that is ecologically fraught for the questionable benefit of having a daily ferry service from Auckland that will not able to run daily because of weather constraints, especially in the winter months. The ferry is currently operating from a perfectly adequate jetty a ten-minute bus ride from Coromandel Town,” Dr Stirnemann says.

“Given what we now know about the likely consequences and impacts of sea level rise and climate change, and the potential release of contaminants into the marine environment, this proposal is a totally inappropriate candidate for support from the Provincial Growth Fund.”