ASK twenty surfers to describe the perfect wave and you鈥檒l get twenty
different answers. It鈥檚 a personal thing. But most would settle for a curving
breaker more than 2 metres high that will catapult them along at about 10 metres
a second. With a wave like this seasoned surfers can plummet down its face,
careen through the tube created by the plunging wave or race high along the
crest. The big problem for surfers is that beaches where you can be sure to find
such waves are rare indeed, which is one reason why the dedicated few scour the
globe in search of the right surf.
But suppose you could build a reef to deliver great breakers virtually all
the time. Would the reliability of the waves at these sites make them Meccas for
surfers? Or would it make surfing boring: a travesty, perhaps, of the notion
that searching remote beaches for the best waves is part of the sport? It may
not be long before these questions are answered. Three groups of surfing
enthusiasts in Australia want to build reefs to create surfing waves to
order鈥攆or beginners and even the most brazen board riders.
The first three artificial reefs鈥攊n Western Australia, Queensland and
New South Wales鈥攁re at varying stages of planning. The most advanced is at
Cable Station, a rocky beach 15 kilometres from the centre of Perth, which could
be ready next summer. 鈥淭he testing, design and survey work has been done,鈥� says
Charitha Pattiarachi of the Centre for Water Research at the University of
Western Australia, where much of the modelling was done. 鈥淎ll we need is the
money.鈥� And that is now starting to arrive. The government of Western Australia
has pledged A$200 000 (about 拢100 000) of the estimated
A$1.5 million price tag for the scheme.
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The waves at most renowned surfing beaches break over reefs or sand bars and
the designers of artificial reefs aim to replicate this effect. As waves reach
the coast, they 鈥渇eel鈥� the rising seafloor. Their energy is compressed upwards
and the wave steepens. The water in a wave has a circular motion, and when the
velocity of water at the crest exceeds the speed of the advancing wave, it
breaks. Coastal engineers divide waves into four types: spilling, plunging,
collapsing and surging (see
Diagram). Surfers are interested only in the first
two. Spilling waves allow them to drop down the face of the wave, while plunging
waves provide high-speed rides through the tube that they form.
For plunging and spilling waves, the gradient on the seaward side of a reef
needs to be between 1 in 20 and 1 in 40. If it is any steeper, the waves surge or
collapse. It鈥檚 also known that the ratio of the depth of water to the height of
the breaking wave is about 1.3. So a 2-metre wave will break in water about 2.6
metres deep.
Height and speed
So far so good. But how do you decide on the best dimensions for a surfing
reef? The answer to this question emerged from work started by James 鈥淜emo鈥�
Walker at the University of Hawaii in the 1970s. He studied the relationship
between the speed of the surfer, the wave height and something called the peel
angle. As a wave moves towards the beach, the point on the crest that is just
beginning to break often travels from left to right or vice versa. So, over
time, this point carves out a path that not only moves forwards, but sideways as
well. The angle between this path and the wavefront is the peel angle, and the
smaller it is, the faster the breaking part travels along the wave. To keep
ahead of this advancing white water, surfers must travel at the same speed or
faster.
鈥淎 peel angle of about 30掳 is about as fast as you would want,鈥� says Ed
Couriel, a coastal engineer with Australian Water and Coastal Studies, a
Sydney-based consultancy. Walker鈥檚 research and subsequent work show that at
this angle, a beginner could handle a wave about 1.5 metres high, an
intermediate surfer would be happy with a 3.5-metre wave and an expert could
ride a 7-metre wave.
But anyone designing a reef also needs to know about the height, period and
direction of waves approaching the shore. The best swells for surfing have a
constant height and arrive at regular intervals. Then there is the tide: as the
depth of water varies, so will the height of the waves. The wind is also a
factor, with the best waves forming when the wind blows offshore. 鈥淭his is what
the critics of artificial reefs don鈥檛 seem to appreciate,鈥� says Couriel. 鈥淭hey
say an artificial reef will be too mechanical and machine-like. But the elements
are always changing. Even if you have a uniform bottom reef, you will never get
two waves exactly the same.鈥�
The generally accepted shape for artificial reefs is like a boomerang, with
the apex pointing out to sea. Incoming waves will begin to break at the apex and
peel along each arm of the boomerang. The surfers begin to ride at the apex and
can go right or left. The wave height and peel rate can be varied by changing
the size, shape and angle of the reef.
The reef at Cable Station will be boomerang-shaped. Researchers at the
University of Western Australia reckon that a 1 in 20 slope will be best for the
reef, and that its arms should approach the shore at an angle of 45掳. The reef鈥檚
apex will be 400 metres from shore, with arms stretching 80 metres one way and
60 metres the other. The team鈥檚 aim is to build up an existing limestone reef so
that it sits 1 to 3 metres below the average water level.
Sinking hundreds of tonnes of rocks will kill off the marine life of the
existing reef, says Pattiarachi. But this is mostly limited to worms. In the
long term the new reef should attract other species, including fish. 鈥淲e will
enhance the biological diversity and productivity of the area,鈥� he says. Another
bonus is that the reef will dissipate much of the incoming wave energy, leaving
a lagoon in its lee. The lower wave height here will allow a sandy beach to
form. 鈥淧eople will want to come and swim here,鈥� says Pattiarachi.
While the Western Australians want to use rock for their reef, surf
enthusiasts at Narrowneck near Surfer鈥檚 Paradise on Queensland鈥檚 Gold Coast have
another material in mind. Every year 500 000 cubic metres of sand drift away
northwards. Gold Coast city council wants to recycle the sand to form a
boomerang-shaped bar for surfing. Initially, about 2 million cubic metres of
sand would be used, with about 80 000 cubic metres a year added after that. 鈥淭he
beauty of our plan is that we have a permanent source of sand and we can create
a break where and when we want to, just by pumping more sand in the desired
location,鈥� says John McGrath, the council engineer responsible for beaches. The
plan has to be approved by the state government, but McGrath expects the bar to
be in place within two years.
Sporting pride
The third Australian reef is planned for a headland near Freshwater in
Sydney. Here, the plan is to add local sandstone or granite to a submerged rocky
reef. The reef will not be boomerang shaped, but will jut out diagonally from
one side of the headland. This plan has still to be approved by the local
council.
So far, surfers have been fairly calm about these plans, says Jack Finlay of
Surfworld, a surfing museum at Torquay in Victoria. But a wave of criticism
could break at any time. 鈥淭he sport prides itself on individuality, especially
finding your own break,鈥� he says. 鈥淎rtificial reefs are the antithesis of
迟丑补迟.鈥�
Yet supporters of artificial reefs believe they are inevitable, and some
predict that there could soon be hundreds of them around the coast, even though
no one really knows how good the reefs will be. How many days of good surfing
Cable Station will enjoy with its new reef is not clear. At the very least, says
Pattiarachi, good surf today will become brilliant surf once the reef is built,
and average surf today will be good in future. 鈥淚f one is built and it works,鈥�
says Pattiarachi, 鈥渋t will be the start of a new industry.鈥�