The IoS/Bradt guide travel-writing competition: Competition winner Simon Duncan relives childhood adventures playing chicken with New Zealand's wild and changing tides

'Oops," he says. I laugh at my brother.

We are in his car which is now perched on top of a mound of black sand. "OK, try again," he says, slamming the car into reverse and throwing us back down towards the tarmac road. He revs the engine and points us squarely at the goal. The car roars as we leap over the hill and on to the empty beach. "There!" he announces triumphantly.

You can drive on certain beaches in New Zealand. We're on one of these "beach highways" on a stretch of the west coast from Muriwai to Kaipara Harbour, a vast natural and empty inlet surrounded by forest, dunes and a few batches of summer homes that peer down from the hills.

"The same driving rules apply on here as on the roads," he tells me as we set off.

"Even speed limits?"

"Yeah, I think it's 60."

I glance over at the speedometer. We're doing double that but the wide beach is deserted in early autumn. To our left the Tasman Sea laps calmly at the shore. The trick is to drive near the water's edge where the sand is harder and the tyres have more grip. We tease the waves with our wheels. On our right a desert of dunes loom, and behind those, the dark dense forest hides all manner of imaginings.

As we head north the volcanic sand fades into the familiar gold of postcard pictures. It is quiet, just the slosh of tyres and the smell of the sea. We have the freedom of the open beach. On inland roads this journey would take nearly three hours; the beach highway cuts it to 40 minutes.

We reach the harbour and leave the car. From a distance the car looks even more incongruous; a lonely metal blob marring the landscape. The harbour is renowned for wrecks. Over the centuries sandbars have lurked beneath the surface to topple unsuspecting explorers. They are exposed by the low tide and we hop from one to another ... kings of soft small islands. We nudge the trapped fish with our toes and irritate the flitting colours.

We are intrepid explorers again, an echo of our childhood holidays. We reminisce and exchange news from our lands half a world apart; we poke and prod around, renewing our bond. He is tanned from a summer spent outdoors. We compare arms and he sniggers at my bleached skin. His hair has been made golden by the sun; mine is as dark as English winter.

Clouds begin to brew and move in from the west. It is not long before the first fat drops of rain fall. We retreat to the car to feast on the stash of food and drink. The rain beats out its tune on the roof.

"The tide is turning," my brother announces through his sandwich.

"Really? Already?" I peer out on the rain and grey.

"The sandbars have gone." He points and I follow his finger. There is now only water in front and, I notice, around us. At high tide, he tells me, the beach is wholly submerged.

We make our escape. As we drive I notice the beach is narrower and the waves begin to nibble at our wheels. Shallow trenches have formed and we slow down to ride over the softening sand.

"So what happens if the water cuts us off?" I ask.

"We'll have to drive as far as we can up the dune and sit it out."

"For how long?"

"About 12 hours," he says nonchalantly. "But we'll be fine." He jerks the wheel and we skid away from another encroaching wave. I'm unconvinced; there is no beer in the car, for a start. It would be a long night. We cannot get trapped. The race is on.

We try to keep a constant speed. We cannot slow too much in case the car begins to sink. The tide presses in, pushing us towards soft sand on which the tyres cannot grip. More water slaps the wheels but the dunes recede, giving more space, and we outwit the water with speed. We reach the gap in the dunes and spin around in the surrounding pools to rid the sand from the wheels. My brother takes aim at the hill.

"I want to do it!" The petulant child rises in me. We swap seats and I prepare a long run-up.

"Right then, you need to ...."

But I already have the pedal to the floor and I don't let up, though the hill looks like a solid wall. We whoop like cowboys, flying over the sand, away from the disappearing beach.

Prize Winners

Simon Duncan was named as the winner of the 2011 Independent on Sunday/Bradt Travel-Writing Competition at an awards ceremony at Stanfords' travel bookshop in London's Covent Garden.

He received the top prize for his tale from New Zealand, entitled "The Disappearing Beach", about a wild drive he took with his brother along North Island's black sand coast. His story was selected as the overall winner by the competition's main judge, the writer and broadcaster Matthew Parris, who announced his decision at the awards event on 19 July.

Simon is usually a train traveller and has journeyed by rail throughout Europe, Asia and the Far East sharing carriages with a variety of people and livestock. He enjoyed seeing New Zealand by car. "Having a car gave us access to remote beaches ... and it meant we could also get off them quickly too!" Simon currently lives by the beach, in Brighton, Sussex, and works as a project manager for a health insurance firm.

Jonathan Lorie, director of Travellers' Tales, announced the winner of the unpublished category. That award went to Dawn Curtis for her meditative tale, "The Art of Stillness". Dawn, from Middlesbrough, is currently working in Nicaragua.

Simon wins a trip to eastern Turkey and will write a story for these pages about his experience. Dawn wins a place on the next Travellers' Tales course, taking place in Dubrovnik, Croatia, from 7 to 10 October, led by Jonathan Lorie and Dan Linstead, editor of Wanderlust magazine.