Cables Reef

Cables Reef is an artificial surfing reef off Cable Station in Perth, Western Australia. Constructed in 1999, it was cited by some as the worlds first artificial reef constructed specifically to improve surf.

The reef has received mixed reviews from surfers who appreciate the quality of the wave when it breaks but cite lack of frequency as the biggest problem. According to at least one report, it only provides good waves a handful of times each month. However, other reports claim that there are rideable waves on the reef around 150 days per year.

Design and Construction

The goal of the project was to create a more consistent surfing spot in the Perth area that offered left and right-hand waves that gently barreled. The government group behind the project, the Perth Artificial Surfing Reef Committee, also specified that the reef “surf should work with swell sizes ranging from 0.5m high to 3.5m” with a peel angle around 45º.

The process design process started in 1988 when M Crawfords studied and critiqued every Perth surf spot to identify the best site for Cables Reef (“Cables”). Andrew Pitt, founder of SurfingRamps.com.au, assisted with the plan by providing sketches that helped the project gather momentum and funding.

The Western Australia Ministry of Sport and Recreation provided funding for engineering investigations and preliminary design. The Department of Marine and Harbours and the University of Western Australia lead these studies with the help of private engineering consulting firms.

In 1994, the Committee and the Ministry engaged qualified coastal and construction engineers. The ASRC also submitted a comprehensive report to the WA government on their findings. The report summarized site selection, reef design, construction and environmental impacts.

After multiple studies and iterations, the Committee landed on the designs below.

The overall length of the reef (from north to south) was designed to be around 140 meters. The maximum width (from shallow to deep water) is 70 meters. The reef was designed to sit about 275 meters off shore in water that varied from 3 to 6 meters deep. Once installed the crest of the reef would be between 1 and 3 meters below the water surface on average tides.

Construction started in February 1999 and it was 90% complete by May 1999. It was 100% complete in December 1999.

The reef was constructed using more than 10k tons of quarried granite boulders measuring up to 3 meters in diameter. Construction, performed primarily by a company named WA Limestone, started when a barge was loaded at the local port with the granite. The rock (and the required personnel) were transported to the construction site by the barge and the stone would then be placed on the seabed according to the dimension, lines, level and slopes specified in the design. The barge would return to the port and collect more material. This cycle repeated until the reef was complete.

The reef was installed over uneven a limestone bedrock which keeps the boulders from sinking. It was originally believed that the rocks should be covered with sand, but that turned out to be unnecessary so the funds earmarked for sand were used to extend the southern side of the reef to make the right-hand wave longer.

Total cost to study, design and construct the reef was around $2 million AUD and the project was funded by the Western Australia Department of Sport and Recreation.

Results

The quality of the waves that break at Cables is rarely questioned. In a comprehensive study that monitored the reef through 1999, Stacey Bancroft reported that the the peel angles were right around 45º, as designed, which is the sweet spot for intermediate surfers. Under the right conditions, the wave provides a steep open face good for all types of turns and, occasionally, a quick head-dip is possible. When the swell is right, the right turns on and becomes one of the better surf spots in the region.

The frequency of surfable days is questionable. Stacey Bancroft monitored the reef immediately after construction in 1999 and recorded the number of days someone surfed on the reef.

The number of breaking days observed exceeded the expected value and, as seen in the images below, the reef improved the number of surfable days per year as measured in three different ways (S1, S2, S3).

A monitoring report by Charitha Pattiaratchi studied conditions from 1999 to 2001 and drew similar conclusions: the reef is performing according to its design and its performing as well or better than predicted.

However, according to and 2009 article by Andrew Pitt, lack of consistency is an issue. The number of surfable days was initially inflated due to the novelty status of the wave and the reef only provides a “few surfable days per month”. According to locals, the reef does not break when the waves are under chest high, which would mean that the reef failed to meet the design requirement of working “… from .5 meters”.

According to Andrew, reef depth and location are the primary contributors to the consistency problem. Andrew dove the reef in 2009 and found that the crest was rough 1.5 meters deep at the lowest tide. The location of the reef, in the shadow of Rottnest island and other outer reefs, limits exposure to the more common south swells.

Andrew suggested that some fine tuning could improve consistency. He recommended capping the reef to make it shallower and extending the nose of the reef seaward to draw in more swell.

The construction method of the reef, which used granite boulders up to 3 meters in diameter, has proven to be a good choice. The solid reef has proven resistant to wave attack and maintained it shape relatively well, especially compared to the common geotextile container alternatives. The design and engineering crew who built it deserve credit and respect for this success.

Many artificial and multi-purpose reefs create salients in their shadow. This has not been observed or reported. Unfortunately, Bancroft observed significant dune erosion due to access issues that cause surfers walk down the front of the cliff to access the beach and reef.

Bancroft also reports a large amount of biological activity and recolonization on the reef.

Cables is regarded by many to be the first reef constructed specifically for the improvement of surf. It was the first successful reef, however Hoppy’s Reef in Hermosa Beach CA was the first attempt to improve surf by changing the ocean floor.

Sources: Andrew Pitt, SurfingRamps.com.au, Performance Monitoring of the Cable Station Artificial Surfing Reef (Bancroft), Performance of an Artificial Surfing Reef: Cable Station, Western Australia (Pattiaratchi)