The big dig of 1991 has gone down in the ledgers of Mangawhai folklore.

On February 11, 1991, about 30 diggers and locals armed with shovels mounted a dawn raid on the northern end of their beach to try to unblock its silted-up entrance.

Since 1978, the harbour's traditional inlet had slowly closed over with sand blown in by successive storms. About 1.5km further south, another inlet, hazardous for navigation, formed after storms breached the sand dunes.


Unable to be flushed by tides, the northern end had become a stagnant, putrid pool of water.

Despite strong opposition from the Northland Regional Council and the Department of Conservation which administered the spit, the locals went ahead with that and subsequent attempts.

Richard Bull, the chairman of the Mangawhai Harbour Restoration Society, said the Big Dig marked a turning point for the community, a triumph of common sense over red tape.

The effort and various subsequent attempts at clearing it failed but, fuelled by the intoxication of rebellion, the locals set up the Mangawhai Harbour Restoration Society on April 1.

Within three years, the group had used a $980,000 loan from the Kaipara District Council, paid off by instalments on residents' rates bills, to get a plan for the harbour from coastal consultants Andre La Bonte and Florida University Professor Bob Dean.

They got resource consents and Department of Conservation support before using two dredges to close off the southern breach, and building a protective bund.

In 1996, they reopened the northern inlet. A nursery was built for dune plants to hold the sand.

The gutsy coastal town spent over a decade working to resuscitate its harbour. Now, $1.8 million, 1.2 million pingao plants and thousands of hours of voluntary labour later, the group fears it will be left to pay the price of demands for sand from Auckland's burgeoning construction industry.

Graham Mackenzie, a semi-retired businessman who splits his time between Auckland and Mangawhai Heads, can see his nemesis from his window - a sand mining barge working inside the inlet dividing the sensitive sand spit from the mainland.

Mackenzie got involved in 2000, after the society ran out of money and Jim Wintle decided it was time to call on another of Mangawhai's resources - its Aucklanders. A further $680,000 was raised. Their money was never meant to be spent on fighting sand mining.

But yesterday, a hearing began to decide if Norsand and Sea Tow will get replacement consents to continue mining Mangawhai's harbour entrance for sand destined for Auckland's construction market.

The initial consent, granted in 1993, was for 10 years. The companies could each take 5000cu m of sand in any month, and up to 25,000 in any 12-month period.

The renewed consent they seek is for 20 years, with 27,000cu m of sand being taken by each company over 12 months. If mined to this extent, a total of 1,080,000 will be taken from just over 24ha of seabed in the harbour mouth area.

Sand mining at Mangawhai has gone on since 1953.

Yet the spit, which is protected in both Northland Regional Council policies and the Department of Conservation, is home to the highly endangered fairy tern, NZ dotterels and the caspian tern.

Of 243 submissions against the consents, 145 noted they had observed the sand dunes had dramatically reduced and believed it was because of the sand mining.

Northland Regional Council monitoring from 2003 to 2004 showed a small build-up of sand over Seatow's mining area over the past year, but a loss of 103,333cu m in Norsand's area closer to shore, within the inlet.

Richard Bull was once the owner of the spit, handed down to him as part of his family's farm.

It was he who made the decision to sell it to the Crown for the Department of Conservation to look after.

He said a survey commissioned by the harbour society found there was 1,333,000cu m of sand on the spit.

"Now these people are asking to take 1,080,000. That doesn't leave a lot for the spit does it?"

Environmental consultant for the mining companies Stephen Westgate agrees there is erosion at the northern end of the spit, where the companies mine.

However, he said such erosion would be caused by the spit settling itself down following the reopening of the inlet.

He acknowledged there were changes taking place but said it was because of nature rather than the sand mining companies.

Studies commissioned to determine the effects of the sand mining have uncovered only possibilities and uncertainties.

A Niwa study, released in 1998, on the Mangawhai to Pakiri sand resources is generally relied on as the best information available.

It warned that long-term near-shore mining would cause erosion, but because there was so much movement caused by waves and wind, it was impossible to detect any harm caused by sand mining.

A subsequent 2002 Niwa report found "sand extraction is probably having a greater detrimental effect in the beach over and above natural erosion" but again could not quantify it. A report prepared for the consent applications by the council coastal consents leader Allan Richards and Niwa consultant Douglas Ramsay was based on Niwa reports and subsequent council monitoring.

It came to a similar conclusion, unable to find any actual harm by the mining but recommending mining be phased out in five years to prevent long-term damage.

What the study did find was that no new sand was flowing into Mangawhai to replace the sand taken by miners.

It also said that as a general rule, near-shore sand mining does contribute to beach erosion, though it was difficult to say how long it would take, or how bad the damage would be.

Ramsay and Richards' report acknowledged the same in recommending the mining be phased out.

That was reason enough to stop the mining for the society.

Worried its spit will collapse, the society has marshalled its own group of experts to contest the findings of the report.

Engineer Peter Riley said 750,902cu m had been taken from Mangawhai's harbour entrance since 1953.

Erosion from this was evident at the northern tip. Further erosion would mean waves could sweep into the harbour and over the dunes, affecting the foreshore properties the spit protected.

The society also paid for Professor Emeritus Bob Dean to revisit the area and make his own submission.

Dr Dean says the damage caused by mining near-shore is so well documented that New Zealand is the only developed country he knows of that allows commercial extraction. Of Mangawhai, he said the effects of erosion were already evident given its failure to recover after the repair of the breach in 1996.

He said further extraction would weaken the beach's defences against storms and eventually destabilise the spit.

The consent applications are opposed by some heavyweight names. Northland MP John Carter and Kaipara's mayor Graham Ramsay both object to the mining.

Northland Regional Council chairman and Mangawhai resident Mark Farnsworth has withdrawn from council deliberations on the matter after publicly opposing it.

"To say that just because no quantifiable effect can be found is to first totally ignore the Omaha experience where the sand spit collapsed. I do not believe just because Auckland wants a stable supply of sand, that that is any reason to allow sand mining," he said.

The society also wants the miners to either go further offshore, or to another area, such as Kaipara, which Seatow and Norsand have acknowledged "may be shown to be a more sustainable resource than the east coast".

Richards' report has recommended mining be phased out at Mangawhai, but that a consent for five years at present levels be granted to give them time to relocate and so the supply of sand for Auckland's building industry was not interrupted.

This does not wash with Mr Bull, who said the mining needed to stop now.

Both Mackenzie and Bull say if the mining did cause the dunes to slump again, the society could not afford to repair it.

Richards and Ramsay's report considers whether a bond is appropriate.

Mr Bull says he finds this disgusting, given the society had to pay a $100,000 bond for its efforts to fix the harbour.

"If it was slumping so low that it breached again, who is going to repair it and where will the money come from? Are they just expecting the community to pick up the tab?

"It's a shame such a small community has to bring so much money to a battle for land owned by the Crown."