Shifting sands

Lorenzo Canal, left, and Stephen Priestley on their man-made headland at Kohimarama. Picture / Kenny Rodger

The two men standing on a rocky outcrop at the far end of St Heliers beach, their hair flattening in the harsh northerly, are smiling, pointing, enjoying the chance to show off their creamy brown baby that sprawls out into the water like your usual sandstone headland.

"See the darker colour? How it matches the cliffs over there," says one. The other nods thoughtfully. "Yes, a pretty perfect match. Just wait until the rocks are colonised ..."

It's only when they turn towards the city that you notice the rusty old container full of sand dredged from 4km off the Pakiri coast, the sand-pumping pontoon parked out in the bay, the mountain of sand waiting to be smoothed and the labyrinth of orange barriers diverting traffic away from the beach frontage, and realise that this headland, with its pancake-stacked sandstone and rock pools just waiting for periwinkles, is totally man-made. Fake. And proud of it.

Two of the main brains behind the transformation of Mission Bay, Kohimarama and now St Heliers beaches are these men: engineer Stephen Priestley of Beca Carter Hollings & Ferner, and project manager for the Kohi and St Heliers projects, Lorenzo Canal of Urban Solutions.

Canal, who was hired by the Auckland City Council to manage the project, is responsible for helping win both the council and the public over to the idea of replenishing Kohimarama beach by adding a 50,000cu m sweep of pristine, pale gold sand, littered with tiny deep-sea shells, plus rocky outcrops, boardwalks, and wide concrete paths to the beach.

As he says, the council was faced with a dilemma. Either repair the sea wall which was about to collapse and threaten Tamaki Dr, which would have been cheaper, or rebuild the beach, as they'd done at Mission Bay. "And then we did the comparison between the sea wall cost and the sand cost. The difference was $4 million for the sea wall - and you had to chop down all the pohutukawa trees and change the complete character of the area - and $6 million for the beach - and you solve the road problem and also get a public amenity."

The 800m Kohimarama Beach, opened by then-mayor John Banks in September 2004, gobbled up 50,000cu m of sand which meant roughly 120 trips of Kaipara Ltd's barge. And says Priestley, "there are already barnacles growing on the headlands. There'll be fish by November."

Ena Hutchinson, of MoaTrek, which designs tours round New Zealand for both local and international travellers, and has lived in Kohi most of her life, says that getting the beach back is "just wonderful".

"My father, Phil, a harbour engineer, had lived in Kohi for 50 years and scanned the beach most days of his life. Around 20 years ago he noticed the rapid erosion of the beach," she says. "He took photos, thought about it, and after a while decided that the big beach cleaners the council were using at the time, may have been responsible because they broke up the sand."

"Now the sand comes right up to the stone walls, people walk on the beach. It's made a huge difference."

The projects have been so successful the Auckland City Council and its various contractors have plans to recreate seven more city beaches over the next five years - Pt Chevalier, Pt England, Blockhouse Bay, Taylors Reserve in Hillsborough, Herne Bay, Home Bay and Sentinel Reserve.

The idea was controversial. Conservationists worried that moving sand from one side of the Hauraki Gulf to another would upset its delicate ecology. Surfers complained - and still do - that the surf at Pakiri has been flattened by the dredging of sand from the beach. Others just grumbled that the new sand would be swept away by the first decent northerly to hit Mission Bay.

"They were wrong," says the rather poetically spoken Priestley. "We found a deposit [of sand to match that of the inner-city beaches] about 4km from Pakiri Beach, in 35m-62m of water."

What has confused people, he explains, is the constant mining of much larger quantities of sand from the actual beach, which is sold to the construction business. To try and distance themselves from the mix-up Priestley and Canal don't even refer to their sand as from Pakiri any more, but as from the Hauraki Gulf site.

Priestley does, however, stress that the project had to go through rigorous planning and resource management procedures. "It was subject to external peer review, public scrutiny and the regulatory authority, so you can't be glib about it."

Architect Nick Malloy, who's had a bach at Pakiri for 30 years, doesn't think they should be taking sand from Pakiri. On the other hand he recognises most of it is going into building: plaster, concrete, glass - "a huge lot of things" - rather than beach replenishment. "They dredge it. It's organised by satellite over a really large area, mainly from Mangawhai north of us. Although the rocks get more uncovered each year, it's really hard to see whether it's having an effect. The surfies think it's altering the waves though. I think the onus of proof, that the resource is not being depleted, should be on those people who are dredging it."

Nigel Hutchinson, 26, son of Ena from Kohi, has been surfing at Pakiri since he was 18, and has noticed a huge difference over the past four years. "Pakiri's almost unsurfable now. Dredging has totally depleted the sand banks 100m off-shore. The waves are fatter, they break all at once instead of peeling along like they used to when I arrived back from Aussie in early 2002. Now we surf at Te Arai and Forestry about 45 minutes along a dirt road from Pakiri."

Certainly the Auckland University and Auckland Regional Council environment committee have recommended that dredging is banned. However all objections were quashed in June 2006 when Environment Court judge, David Sheppard dismissed environmental objections and allowed white sand dredging for a further 14 years. His comment: no link between sand extraction and coastal damage had been shown.

But, counters Priestley, in the context of the huge sand deposit their contractors, Kaipara Sand, are dredging from, 50,000cu m is quite small. It's a long way off-shore. Also they are careful to scrape the sand off the sea bed a little like peeling the top layer of an onion. "Certainly you're unlikely to change any swell patterns by taking a metre or two off that particular part."

As for the idea that the ecology would be upset, Priestley points to history. The relic sand of what he calls Auckland's "pocket" beaches was deposited by the Waikato River "which used to wander up through the Firth of Thames and into the Hauraki Gulf." The sand, which they found in the deep sea in the Hauraki Gulf, has a different mineralogy and "quite large" grain size that was never destined to end up on Pakiri beach.

On the other hand, says Priestley, it was as near to the original Mission Bay and Kohi sand as they could get. "The whole thing with beaches is that the kind of sand you use dictates the shape of the beach."

Lastly, the sand used to replenish Mission Bay beach did not get washed away with the first wild northerly. Twelve years on, council monitoring proves the sand, and the beach, is still there.

First the engineers had to figure out why the beaches had eroded in the first place. The construction of Tamaki Dr, in the 1930s, did much of the damage, cutting through some beaches including St Heliers and Kohimarama, damaging others with the extra rock needed to support the road, even minimising the possibility of new sediment which would naturally have replenished the sand over time. Next, the stormwater, both from the road and an ever-increasing number of people, cars and concrete on the hills behind, started eating away at the beaches.

Then there are the other causes, including loosening up of the sand through cleaning processes and ferry wakes. But, says Priestley, "they're very minor and it's difficult to prove [they've eroded the beach]".

Especially compared to the stormwater problem. "What happens when you discharge stormwater onto the beach?" asks Priestley. "The beach has no choice but to lower itself to that level."

By the the time Priestley and Canal got involved at Kohi, beach replenishment had been going on in the United States for 50 years. The idea that made the difference - and which is unique to the New Zealand developments - was the creation of headlands at the end of each beach which as well as looking right in the New Zealand context, would also "capture" the beach and help hold the sand in place. The brainwave goes back to George Farrant, heritage manager at Auckland City Council, who suggested using natural-looking reefs rather than concrete sea walls to contain the beaches, and Neill Forgie, his project sponsor colleague. Forgie used the headland at Tamaki Bay Yacht Club as an example of what could be done, floated it at a public open day, and got the kind of buy-in the council needed.

Priestley pulls out his old-fashioned fountain pen and sketches a diagram, showing how the waves hit these bays from both directions, causing each beach to curve and work itself into what he calls a "dynamic equilibrium".

"Storms and currents happen all the time," he says. "It's a natural process that causes the crescent shaping of the beach. We tried to understand how each beach wanted to survive, then mimicked that."

The headlands also helped solve the stormwater problem. You can see the main drain heading into the partly constructed headland at St Heliers. It's big, around 4sq m, made of concrete, sits well above beach level - and will soon be covered by an ingenious mix of what they call sandcrete. Because it spills onto the headland it will also discharge its dirty water as far out to sea as possible.

Building the headlands, which are meant to last at least 50 years, is a major mission. First step is to build a resin model which details all aspects of the structure. Next come the big concrete blocks which are used to form a temporary framework. They are then pumped full of sandcrete - which is left to set between tides, then removed - and restacked to form the basic shape. "It's amazing what you can do with a big digger," says Canal.

Next comes the plastic mesh which is hammered into place and finally a top layer of high strength gunite (a form of concrete) which is sprayed onto the shape under pressure and sculpted into a headland that looks as though it's been there for decades.

The arty part of the process comes from a team of special effects people headed by the white-bearded Peter Mahony of Maco. His CV includes the tiger enclosure at Auckland Zoo and Kelly Tarlton's Antarctic Encounter, and his team uses brooms, spades, teaspoons, whatever it takes to shape the fine detail. "They have to do everything between tides - that's the challenge," says Canal. "The risk was it would look like Disneyland."

And Disneyland it certainly ain't. Even after two years the headlands look as though they've been there for centuries. These days the ladies of Kohi worry so much about slipping on the sandstone rocks they've almost forgotten they're man-made.