4 minute read
Palm Beach
Gold Coast, Queensland, Australia
Constructing an artificial reef to provide coastal protection and recreational opportunities. For decades, Palm Beach, located on the Gold Coast in southeast Queensland, suffered significant erosion events that threatened beachfront infrastructure, exposing seawalls and impacting the local lifestyle due to the temporary reduction of available recreational shoreline. To find an appropriate solution to address these hazards, the City of Gold Coast developed the Palm Beach Shoreline Project, following a “design with nature approach.” After significant investigation, testing, and design, sand nourishment stabilized by an artificial reef was adopted for Palm Beach to provide coastal protection as well as recreational and surfing amenity outcomes. This option was favored for its low visual impact and the long-term retainment of nourished sand. Taking place in two phases, sand nourishment began in 2017, followed by construction of the artificial reef in 2019. Postconstruction monitoring revealed the project is achieving its objectives by sustaining an average of 370,000 cubic meters of sand above the preproject levels within the Palm Beach coastal system, creating a new surf break for the community, generating a positive impact on the local marine ecology, and transforming the site from a barren sandy bottom to a marine ecosystem flourishing with flora and fauna.
Article Cover: Constructed of large rock boulders and located approximately 270 meters offshore, the Palm Beach artificial reef has a 160-meter-long and 80-meter-wide footprint, sitting 1.5 meters below the average water level at its highest point. (Photo by City of Gold Coast)
Producing Efficiencies
During a comprehensive design process spanning several years, an initial feasibility assessment evaluated 18 management options. Each option was assessed and compared on the basis of cost, coastal protection, and impacts or benefits for a range of aspects, such as coastal processes, ecology, surfing, and beach amenity. The final detailed design phase adopted a “multiple lines of evidence” approach, involving real-world data capture, several forms of sophisticated numerical modeling, and two programs of scaled physical modeling in wave tanks. These investigation methods allowed for crosschecking and calibration between the results of the various design investigations and provided confidence in the unique design.
Using Natural Processes
During nourishment, sand was sourced from deepwater deposits and placed within the surf zone via split hopper dredge. The sand was placed in a unique noncontinuous deposition process that worked with changing bathymetries, minimized beach-user impacts, and provided temporary surfing opportunities. The artificial reef was designed to use the natural northward movement of sand, which is driven by southeast waves arriving oblique to the shoreline. The reef interacts with the waves and currents to slow the northerly sand transport near the reef, promoting an updrift buildup of a portion of the passing sand.
Broadening Benefits
The benefits of the project extend beyond coastal protection to include enhancing the local ecology, surfing culture, industry, and community on the Gold Coast. Collected surfing metrics have confirmed that the reef produces a regular rideable wave. Flora and fauna habitat was also created on the previously bare sandy habitat. Ecological monitoring has revealed the establishment of seaweed; sea turtles; several common invertebrates, such as sea squirts (Ascidiacea) and feather stars (Crinoidea); and schools of yellowtail scad (Atule mate), eastern pomfred (Schuettea scalaripinnis), bream (Abramis), tarwhine (Rhabdosargus sarb), sweetlips (Plectorhinchus), trevally (Caranx), and snapper (Lutjanidae).
Promoting Collaboration
The City of Gold Coast collaborated with a team of scientists, coastal management experts, engineers, environmental officers, dredging consultants, and maritime construction experts to find a sustainable solution to protect Palm Beach. Local residents, the surfing community, and other interest groups were also important stakeholders in the project. These groups were consulted regularly throughout the design and construction process to ensure their voices were heard and that the community received the best outcome possible. For its work, the project was twice awarded by the Institute of Public Works Engineering Australasia Queensland Excellence Awards in Innovation in 2019 and Coastal Engineering in 2020.
