New battleground?

where sand has been pumped aboard barges for nearly 30 years.

And 76,000m3 can be taken a year in water 5 to 10 metres deep in the Mangawhai-pakiri embayment in the northern Hauraki Gulf.

Coastal permits allowing the company Mccallum Brothers to dredge at Pakiri were extended in 2009, when the High Court upheld an Environment Court decision that natural sand replenishment would compensate for sand taken.

The science is still being argued.

Pakiri is a finite sand system, according to Jim Dahm, who has worked as a coastal scientist for more than 40 years.

‘‘It’s got all the sand that it’s pretty much ever going to get, and anything you draw is going to be replaced ultimately, in the long term, by erosion of the dunes.’’

The beach sands moved onshore at the mining site after sea level rose to its current elevation about 7500 years ago, after the last glaciation, but that net onshore supply has now largely ceased, the Thamesbased consultant says.

If shell content from dying organisms was coming into the beach system at a rate of nearly 100,000m3 a year, as argued by some, the beach system would be far bigger than it is, Dahm says.

While sand is being replenished in the ‘‘humungously large sand system’’ at Kaipara Harbour on the west coast of the upper North Island, drawing sand from east coast beaches is ‘‘nuts’’ in the face of sea-level rise.

‘‘For east coast beaches, the figures generally vary between the potential for 20m to 50m erosion with 1m sea-level rise, and we’re expecting 1m or 2m as a minimum.

‘‘So the last thing you want to be doing is sucking sand out of it.’’

Mccallum Brothers declined to comment, referring to the Environment Court decision and resource consent requirements.

A lot of the damaging sand mining in New Zealand, however, is a thing of the past, Dahm says.

‘‘Generally in New Zealand, we became aware of the issues of sand mining in the 1960s and 70s.

‘‘There was a lot of sand mining done in New Zealand in the early 1900s, around Manukau Harbour, Thames coast, Coromandel beaches, Auckland beaches, a lot of irreplaceable sand was removed.

‘‘So most of our really bad sand mining is historical.’’

Iron sand, meanwhile, has been mined onshore for more than 40 years.

The black sand contains the mineral iron ore, which is extracted to make steel.

The Taharoa Ironsands mine in Waikato has been reported to export more than $150m worth of sand a year, mostly for use in factories in Asia.

When the mine opened in 1973, it gained access to an estimated 300m tonnes of iron sand concentrate. In 2013, it was forecast to have another 15 years to run.

The Waikato North Head mine produces up to 1.2m tonnes of iron sand a year, for use in the New Zealand Steel mill at Glenbrook. The deposit is estimated to contain more than 150m tonnes.

Information about Vince Beiser’s book, ‘The World in a Grain: The Story of Sand and How It Transformed Civilization’, can be found at https://www.penguin randomhouse.com/books/ 537681/the-world-in-a-grain-byvince-beiser/