Palm Beach Reef

Palm Beach Reef is an artificial reef that sits just off the Gold Coast of Australia. While its main purpose is shoreline protections, it’s already clear that it can improve surfing conditions.

The reef takes incoming swells that would otherwise probably close out and turns them into rights that break for up to 60m. On larger swells, the reef also creates a short, intense left. The video below shows the reef in action, and it looks incredibly fun.

Design

The project began 2013 when the city of Gold Coast decided they had to do something to protect the Palm Beach from erosion. The city awarded DHI Australia with the Concept Design Study in an open tender. Simon Mortensen, Managing Director for DHI, was the project manager and lead engineer. DHI completed that phase of the project in 2014.

In 2015, the city started the next phase of the project. This phase was focused on validating DHI’s design and investigating structural stability. The city relied primarily on Royal Haskoning DHV (RHDHV) as the principal project consultant in this phase. RHDHV engaged a number of other professional teams including DHI for numerical modeling; the Water Research Laboratory for physical modeling; and the Queensland Government Hydraulics Laboratory (QGHL) for physical modeling.

To identify the best solution, the research teams used a variety of data sources such as wave buoys, beach and hydrographic surveys, and coastal imaging. The teams also used scaled physical modeling and computer modeling to develop and refine the final solution: beach nourishment stabilized through the construction of an artificial reef.

The research resulted in some adjustments to the original design including moving the reef 50m closer to shore to save rock volume. The rock size was increased from 3 tons to 5 and 8 ton rocks..

The city started implementing the plan in 2017 when they successful completed a beach nourishment effort. The city’s contractors pumped 470,000 cubic meters of sand on to Palm Beach.

In phase two of the project, the city focused on creating a reef that would help keep the sand in place.

DHI Australia, the company that designed the reef, began by evolving an underwater submerged breakwater into a shape that refracts the wave energy toward the shallow crest. The reef design channels that energy into a continuous and predictable right-hand wave. The team designed the reef to produce waves with a ripable, open face good for intermediate and advanced surfers to work on their turns. According to Mortensen, the reef should really start working well with swells that measure 1.5m or above in the open ocean, and a low to medium tide.

Design on the left, results on the right.

The design called for installation of the reef approximately 270 m off shore. The dimensions of the reef are roughly 160m long and 80m wide. The team designed the reef to sit 1.5 m below mean sea level to help ensure the reef was still covered at low tide and continued to produce waves in most swell conditions.

Testing

To test their designs, the DHI team used the MIKE 21 SM (Shoreline Morphology) software module. The team used the software and 30 years of historical conditions to predict the Palm Beach shoreline response. They also used a detailed 3D VOF wave model OpenFoam and DHI’s inhouse surf simulation software OptiSurf to validate impact on surfing and safety conditions.  

The Queensland Government Hydraulics Laboratory (QGHL) create a scaled physical model for testing in a small wave pool as well.

Construction

The construction of Palm Beach Reef was lead by Heron Construction from New Zealand. Hall Contractors handled the rock sourcing. Construction started in April 2019. The team completed construction in September 2019, ahead of schedule.

Hall Contractors quarried the rocks from SE Queensland and loaded them onto split-hull barges in Brisbane. The rocks vary in size from 4 to 8 tons each. The barges dropped the boulder into reef area. Then, a backhoe dredger moved the rocks more accurately into place using GPS.

Results

Construction of the Palm Beach Reef cost a total cost of $18.2 million AUD ($12.5 million USD).

From a surfing perspective, the reef appears to be a success. Through refraction, incoming swells turn into long, fun right-hand rides that offer plenty of turn opportunities. The right runs for up to 60m, but they may end up running longer when a wave connects to the inside sandbars. On larger swells the left comes alive for a short, intense ride as well.

The video above shows the reef shaping an overhead swell into consistent rides, as designed. According to Mortensen, the reef should hold at least double-overhead waves if the swell direction is SE. If the waves are from the ENE, then the wave will start to close out earlier.

The local lifesavers club said the reef “went off” in July of 2019, well before construction was complete.

Mortensen is also please with the results:

Since designing multipurpose reefs had already been attempted several times in the past 15 years, there was a tremendous pressure to make sure that we could incorporate all the lessons learned from past projects, to overcome the many problems that had limited their performance. If it was not for the recent advances in advanced computer modeling in combination with our local knowledge of the location, it had probably not been possible to deliver a design that ticked all the boxes.

Simon Mortensen, MSc, CPEng, Director, DHI Australia

If you want to check out recent conditions yourself, you can find a time lapse here: http://www.livetimelapse.com.au/clients/city-of-gold-coast/palm-beach/iframe.html?displayWidth=728

Source: City of Palm Beach, Swellnet.com, DHI, SurferToday.com