THE REEF:
Where is the reef located?
What is the reef like?
What are the waves like?
How was the reef built?
How long did construction take?
What are the bags made of?
Will the reef wash away in a storm?
Will the reef sink into the sand?

ENVIRONMENTAL:
Will the reef harm the environment?
How do we know the reef will meet expectations?

BENEFITS:
What is the benefit?
Is the reef economically beneficial?

WORLD LEADERS:
ASR Ltd

RESEARCH...

New Zealand's environment remains one of the best in the world, but the mounting pressure on the coast due to suburbanisation means special care has to be taken to ensure the coasts are sustained. The Mount Reef is a research focus for sustainable coastal protection and marine ecology. Students study the beach and the reef to landmark and baseline this multi-purpose community facility.

REEF MAKING...

Where is the reef located?
Click here to view a map of its location or here to see live webcam images from the Mount Reef.

What is the reef like?

The original reef that was envisioned during the long resource consent process was a single-sided right-hander. The redesigned reef is now shaped like a Delta wing or classic A-frame instead of a rectangle. The re-design was undertaken because of the relatively wide range of wave directions in the Bay of Plenty to allow both the left and right to break better during different conditions. The Delta wing shape will produce fast-peeling, tubing lefts and rights during clean swell conditions once completed. Having a left and right allows more surfers on the reef at one time. The 2 metre scale model of the delta reef, shown below, was carved and shaped by hand for testing in ASR Ltd's wave pool in Raglan. 

A contour diagram of the mount reef is also shown below (waves coming from left to right). The reef has been constructed in around 4.5 metres water depth. The reef crest (shallowest point) is about 0.4 metres below lowest astronomical tide. The total volume of the reef is about 6000 m3. Click here to view map of the location.

What are the waves like?

Once completed, both the left and right will break from a single peak. Both will peel for around 50m, with either being slightly longer than the other depending on swell direction.  The reef slope has been designed to break waves at a high intensity, i.e. they will be heavy and hollow. ASR has done extensive research into the skill level required to ride various waves around the world. This knowledge has allowed the incorporation of challenging hollow waves into the Mount Reef design.

With a volume of 6000m3 the reef is relatively small. The reef is located some 250m offshore, around 4m deep. The crest depth on the reef is approximately 40 cm above the Lowest Astronomical Tides (LAT) so that it is nearly always covered with water.  This means that it is best ridden around mid-tide. The best conditions are clean, straight swells with offshore winds - in these conditions the waves are 'primed' and ready to break, with 'wobbly' swells having little time to shoal and adjust prior to breaking on the reef. Wave heights of 1-2m are optimum, a couple of hours either side of low-mid tide. During larger swells (e.g. actual wave heights of over 3m) waves break prior to the reef at low tide, meaning that the best window for surfing is later in the tidal cycle.

With a skill-level ranking on the '1-10 Skill-level Scale' of 6-7, i.e. suitable for top amateurs, the ride length will be about 50m on each side and the breaking wave will be "hollow", particularly on low tides.

Reef designer Dr Kerry Black, says the A-frame has always been one of the classic rides. 'The Mount Reef will provide the hollow A-frame type waves that can be found at Matakana during the right conditions - with a fast wave on one side and a slower wave on the other depending on swell direction.  At Matakana, waves are focused into peaks by the massive Tauranga Harbour delta - the design of the Mount Reef does this at a local scale. Surfers should be able to use the reef taking off in two directions. It will be spectacular during those clean offshore conditions that the East Coast is well known for.'

These pictures taken in the wave pool during testing using the new Delta reef model, show a fast take-off and pitching lip immediately setting up both left and right-hand barrels!

How was the reefbuilt?

The reef was made from 24 individual geotextile bags of varying sizes. The empty bags were tied onto a webbing lattice on dry land before being folded up and towed out to the reef site on a barge. The empty reef was offloaded and pulled down into position on the seabed through Manta Ray Ancor Locs. Once secured in place 6000m3 of sand was pumped into the bags to eventually fill them all up and create the shape of the reef.

The bags were laid out with the smallest bags at the front or seaward side of the reef, i.e. bags numbered 17, 18, 19, and 20. These bags are about 1m high and 35m long. The bags gradually get bigger as they go towards the back of the reef with bags 3 and 4 being the biggest - 3.5m high, 50m long and each holding 660m3 of sand! A smaller geo-textile tube ("scour tube") was alsoattached to the back of the reef to prevent sand being scoured from under the two big bags.

The above diagram shows the right hand side of the reef viewed from the seabed. The waves come from left to right with the beach being 250m away on the right hand side. Bag 19 is about 1m high, bag 3 is about 3.5m high - just under the water at low tide.

The bags were tied onto the webbing lattice (red lines in above diagram) on dry land before being taken out to sea. The empty reef was thenpulled down onto the seabed through the 20 numbered Manta Ray Ancor Loc points that were installed earlier at the site. Once secured in place on the seabed the bags were pumped full of sand one at a time until the reef was completed.

This picture is of the left hand side of the webbing lattice in a local park andgives a better idea of the size of the reef.The two guys at the front of the reef from Unique Covers and Tarps Ltd (they sewed it together!) are at point 1 in the diagram above. The truck in the background is at point 14 about 70m away! The white bag on the webbing lattice is one of the smallest bag in the reef, bag number 1.

How long did construction take?

This wasdependanton the waves and weather asdead flat conditions were needed to work in. We initially had hopedto be able to complete construction within one month, however the weather and various technical difficulties stretched this out to over a year!

What are the bags made of?

The bags are made from highly durable Terrafix non-woven staple fibre geo-textile, which provides the best possible resistance to vandalism, abrasion, damage, while providing a superior platform for the growth of marine organisms. This UV stabilised polyester material with a life of over 20 years, allows for simple yet very effective patching of the bags should they get damaged.

The Terrafix 1209R is about 5.7 mm thick and comes in 4 m wide rolls.

The Terrafix 1209RP is a composite polyester and polypropylene material which is about 9.5 mm thick and comes in 4.7 m wide rolls. This material has the added advantage of being able to trap sand within the 'hairy' outer brown layer of the geotextile which significantly improves its puncture resistance and gives marine life a better surface to latch on to.

Geo-textiles are commonly used on roads, land construction and were fully tested on the Gold Coast surfing reef which has been in place for a over 7 years now.

Will the reef sink into the sand?

A'geomat' was laid under the first 25m of the nose or 'focus' of the reef to ensure this critical section, which sets up the wave, does not sink over time. The rest will most likely sink by about 0.5m over the first year but this has been taken into account in the design.

BENEFITS...

What is the benefit?

The multi-purpose reef will provide world-class surfing, wind surfing, kite surfing, body boarding, snorkelling, a marine habitat for fish and other marine life and coastal protection. The reef will also be the focus for research into the multi-purpose benefits of artificial reefs.

Is the reef economically beneficial?

Yes, national and international studies show that multi-purpose reefs bring 20-70 times their full construction cost back to the community through visitor spending over time. The Mount Reef will return more than 30 times its cost.Just one 3-day contest with 100 competitors could bring at least $100,000 into the district in food, accommodation, travel and other spin offs.

WORLD LEADERS...

ASR Ltd is a Marine and Freshwater Consultancy and Numerical Modelling 'House', with a diverse range of research and consulting experience.ASR Ltd is the world leader in Artificial Surfing Reef Design, supported by unique real-world measurements and proven numerical modelling.

ASR Ltd was formed to unify multi-disciplinary professionals in marine science, consulting and engineering. University, Institute and science funding links placeASR Ltd at the forefront of research and industry applications.

Innovative solutions are sought to match modern environmental awareness. Through computer modelling and modern instruments,ASR Ltd provides a niche resource, by underpinning less technical groups with high-quality advice and provision of skills.