Shonky Sediment Science

Trans Tasman Resources’ (TTR) wants to strip 50 million tonnes of seabed from the South Taranaki Bight every year for 20 years. They’ve already got the mining consent but have struggled to convince regulators to let them discharge the 45 million tonnes of waste the mining will produce back into our moana. Now, under the National-led Government’s Fast Track, they’re hoping to dodge the scrutiny a proper process would allow.

Dumping seabed waste doesn’t make it vanish. It creates something called a sediment plume, a dirty cloud that hangs in the water and spreads through the ocean. That much is undeniable, and even TTR admits it.

What they don’t admit is the scale of the problem. They claim the plume will quickly sink and stay “localised,” but the evidence presented to the Environmental Protection Authority hearings in 2024 shows that’s simply not true.

The Dirty Cloud

Suspended sediment isn’t just harmless dirty water. It poses real risks to ocean life.

Image: WWF

Some sediment enters the South Taranaki Bight naturally for example from rivers, erosion, and storms. TTR points to this to argue their mining waste won’t make much difference. But that doesn’t stack up. Natural deposits of sediment are short-lived, and marine life can recover once they pass. Just like coughing your way through a cloud of smoke. Technically possible, but that doesn’t mean you could live in one! 

What TTR proposes is very different: a constant source of waste, day after day for 20 years. And that difference matters because suspended sediment can:

• Block sunlight needed by phytoplankton, the base of the food web.

• Smother filter-feeders like mussels and krill that pygmy blue whales and fish rely on.

• Disrupt visual hunters like kororā (little blue penguins) and fish.

• Carry trace metals and toxins through the food chain.

As marine biologist Shaw Mead put it back in 2017, there's a big difference between the 'pulse' events marine life has evolved with, versus the continuous 'press' of industrial waste - something they've never had to deal with. 

Occasional sediment already entering the Bight does not justify dumping millions of tonnes more, all the time.

Far From ‘Bog Standard’

Image: Project Reef

We’re still discovering what lives in the South Taranaki Bight. Sunlight reaches down to banks, shoals, and reefs around the coast, creating ‘goldilocks zones’ where marine life thrives. Project Reef has been documenting this richness, and a 2022 Taranaki Regional Council survey found that “subtidal reefs are in fact common on Pātea Bank, with many more awaiting discovery.”

That’s a big deal. As oceanographer Dougal Greer explained, “it will not be possible for the numerical modellers to provide information for all reefs in the area since many remain undiscovered.”

While these reefs aren’t inside the mining zone, they sit in the path of the sediment plume. TTR’s models can’t account for ecosystems we haven’t found yet — which means they can’t honestly predict the impacts of their operation.

They want to dump millions of tonnes of waste into waters where we don’t yet know the extent of what’s at stake.

Flawed Modelling

Because no project like this has ever been attempted, TTR relies on computer models to predict how their waste will spread. Modelling isn’t a problem in and of itself, but it’s only as good as the data you feed into it. In this case, it’s garbage in, garbage out.

The problems start with the basics. To represent a 66 square kilometre mining area — about half the size of Hamilton City — TTR tested just three sediment samples. As oceanographer Dougal Greer pointed out, “It would be expected that these values would vary throughout the mining region.”

Those limited samples then fed into flawed assumptions. TTR’s models claim less than 4% of the seabed affected by their mining is ‘fines’ (materials like mud, silt, or clay). Yet samples with up to 70% ‘fines’ have already been collected from within the mining zone. As coastal engineer Joris Jorissen warned, “There are likely to be major, unknown releases of fine material during the operation.”

Fine sediment floats longer, spreads further, and causes the greatest harm to marine life. TTR’s picture of a “localised” plume simply doesn’t stack up.

Wrong Waves, Wrong Results

The problems don’t stop there. TTR’s modelling overlooked major ocean processes like upwellings and downwellings, and used wave data that simply wasn’t realistic. Their plume model tested wave periods of just 7–11 seconds, when the South Taranaki Bight regularly sees long swells of 13–18 seconds.

As Dougal Greer explained: “The reason this place is a surf mecca is because of all that high period swell …. I can categorically say that the use of the seven second wave period was incorrect in the modelling.” Longer wave periods mean more turbulence, and stronger waves which keep sediment floating longer and spreading further.

Photo: Cory Scott

That error becomes critical when you’re talking about 20 years of continuous discharge. The models were too short-term to show how sediment builds up year after year. Professor Luick warned that fine particles drifting into the mid-Bight could “remain in suspension for many months, accumulating over time” to levels that “pose a threat to marine mammals.”

At the March 2024 EPA hearing, Greer concluded that TTR’s plume models were “not fit for purpose” and “do not favour caution and environmental protection.” He recommended running new models spanning the full 20 years of mining, with accurate wave data, climate change inputs, and independent review. The EPA panel  was preparing to commission further expert advice on TTR’s assumptions and limitations.

But before that scrutiny could happen, TTR pulled out of the hearing. Their 2025 Fast Track application simply recycles the same flawed 2017 models, hoping this process won’t dig too deeply…

We can’t trust the seabed miners

TTR’s plume models aren’t reliable science — they’re built on limited samples and assumptions that downplay the real risks. They’re asking us to gamble 20 years of ocean health on “close enough” modelling. That’s not something Kiwis will accept.

The company is counting on complicated reports to hide the flaws. But the truth is simple: their predictions are based on poor science. We can’t let seabed miners pose as the voice of reason when they haven’t done the work.

Our ocean is too precious to gamble. Let’s stop seabed mining before it starts.

Visit KASM.org.nz/take-action to see a list of ways you can help stop Trans Tasman Resources from getting approval to mine the South Taranaki Bight.