Multi-purpose reef

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A multi-purpose reef, also commonly known as an artificial surfing reef or surf reef, is a structure located offshore designed to induce wave breaking in a manner that creates a wave suitable for surfing or body boarding. Artificial surfing reefs can exist in many different configurations and be built from a variety of different materials. To date there have been fewer than ten attempts worldwide to build such structures .

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Artificial surfing reefs are a variation of a long existing type of coastal structure known as a submerged breakwater. Submerged breakwaters have historically been used for coastal protection. If an offshore structure is specifically designed for both the improvement of a recreational resource (i.e. wave riding) and coastal protection or stabilization, it can be classified as a multi-purpose reef.

History

Artificial reefs have been developed for several centuries in Japan where fishermen noticed that around sunken fishing vessels their catch increased. As the vessels disintegrated, the fishermen started to deliberately place man-made (artificial) structures on the seabed to attract fish to catch.

Since this time, a number of artificial reef projects have been developed and, since perhaps the 1970s the 'science' of artificial reefs has been more seriously investigated; although many still consider placing anything in the sea (or lakes for that matter) constitutes an effective artificial reef.

Artificial reefs have historically been developed for one primary function, for example habitat creation, habitat defence, recreation (e.g. surfing, diving and sports fishing), coastal defence, and research and education.

In regard to surfing reefs, in 1997, surfers from Burkitts Reef, in Bargara, Queensland participated in an effort to improve the quality of a surfing wave on a natural reef. [1] While not a structure in and of itself, the effort consisted of shifting boulders which caused the wave to break irregularly and at time dangerously over shallow rock. Work was completed using heavy equipment to move the offending rocks during the low tide when the rocks were exposed.

The first structure built specifically for the improvement of surfing was the Cable Station Reef constructed in 1999 in Perth, Western Australia. This structure was built from granite boulders placed on top of an existing limestone reef. The total volume of material placed was in the order of 3,500 m3. Monitoring of the reef indicates that it is used for surfing when wave conditions are large enough. The site is hampered by the presence of offshore islands and reefs which block a significant fraction of the wave energy before reaching the site. However, when the swell is large enough or strong enough the reef produces good quality surfing waves. [2]

Construction began on the Narrowneck or Gold Coast Reef in August 1999. This structure was much larger (70,000 m3) in size and scope than the Cable Station Reef. The reef was designed primarily as a shoreline stabilization structure with a secondary purpose as a surfing structure; as such it was the first true 'multipurpose reef' structure. The reef was built as part of the Gold Coast City Council's 'Northern Gold Coast Beach Protection Strategy' which included a large volume of beach nourishment to be placed on the beach in addition to the construction of the reef. The Gold Coast Reef was built from large, sand-filled geotextile containers ('sandbags') which were dropped into position from a split hull barge.

In terms of its stated purpose as a coastal stabilization and sand retention structure, monitoring by the University of New South Wales Water Research Laboratory suggests that the reef has achieved its goal to produce a salient (wider beach) in the shadow of the structure. Further analysis of the shoreline change [3] quantified the beach response in relation to the reef as being approximately 20 m wider than areas unaffected by the presence of the reef.

In September 2000, construction began on another artificial reef, this time along Dockweiler Beach in Los Angeles, California. The purpose of this structure was to mitigate for the loss of surfing amenities and resources resulting from the construction of rock groyne and an associated beach fill project which was completed along Dockweiler Beach in 1984. The project was named Pratte's Reef, in honor of Tom Pratte.

Like Narrowneck, Pratte's Reef was constructed from sand-filled geotextile containers. However, the containers used on Pratte's Reef were much smaller than those used on the Narrowneck Reef (~8 m3 per container at Pratte's versus 140–320 m3 per container at Narrowneck). Additionally, the total volume of the Pratte's Reef design was only 1400 m3, approximately 50 times smaller than Narrowneck.

Extensive monitoring of the Pratte's Reef project [4] showed that the reef had very little effect on the surfing conditions at Dockweiler Beach and that it had no measurable effect on the shoreline morphology. They attribute this to the very small structure volume and the instability of the reef construction units. Within two years from the initial construction, the reef had largely disintegrated. This was due to the rupture of the individual bags and due to wave scour and self-burial. The remains of the reef were removed in October 2009. [5]

The next attempt to build an artificial surfing reef came in February 2005 when construction began on the Mount Reef in Mount Maunganui on the Bay of Plenty coast in New Zealand. The reef design called for a total volume of approximately 5,000 m3 to be contained in an arrangement of large sand-filled geotextile containers. The containers and material used on Mount Reef were similar to those used at Narrowneck, however with bigger diameters and longer lengths. The reef suffered through a series of snags in the construction process attributable to weather delays and equipment failure. Construction continued throughout 2005 and into 2006. Modifications to the reef were made as recently as late 2008.

Like Cable Station, the Mount Reef was designed purely to improve surfing wave quality. While there have been numerous documented instances of surfers using the reef and of high quality surfing waves breaking on the reef, many users complain that it does not work often enough as a surf break. Although it was not designed as a shore stabilization structure, an analysis of beach width and offshore survey data suggest that the beach in the shadow of the reef is up to 20 m wider than sections of the beach away from the reef (Weppe et al., 2009).

Boscombe Surf Reef

The most recently constructed artificial surfing reef is the Boscombe Surf Reef located in Boscombe, Bournemouth on the south coast of England. This was the first Surfing Reef to be constructed in the northern hemisphere. [6] The town of Boscombe opted to build a surfing reef to provide a unique focal point for the town's multimillion-pound waterfront redevelopment effort (Bournemouth Borough Council, 2008). According to the local council, "The reef will give Boscombe beach its own identity, raise the profile of Boscombe and attract a large number of visitors on an annual basis."

The reef which was originally suggested in the late 1990s suffered considerable delays before construction finally began in June 2008 by the New Zealand Company ASR Ltd and half was completed during the summer of that year. Construction was suspended for the winter season and resumed the following summer. The reef was officially declared open on 2 November 2009. [7] Like most of the other reefs built to date, the Boscombe Reef was built from large sand-filled geotextile containers. With a total volume of 13,000 m3, the reef was designed purely as a surfing break. Since the reef was built, there have been a few documented instances of surfers riding waves breaking on the reef. As the season changes into the more energetic winter, it is expected that the reef will break more often. This has subsequently been removed due to damage, safety fears and performance issues.

Related Research Articles

Surfing Sport of riding waves

Surfing is a surface water sport in which an individual, a surfer, uses a board to ride on the forward section, or face, of a moving wave of water, which usually carries the surfer towards the shore. Waves suitable for surfing are primarily found in the ocean, but can also be found in lakes or rivers in the form of a standing wave or tidal bore.

Beach Area of loose particles at the edge of the sea or other body of water

A beach is a landform alongside a body of water which consists of loose particles. The particles composing a beach are typically made from rock, such as sand, gravel, shingle, pebbles, etc., or biological sources, such as mollusc shells or coralline algae. Sediments settle in different densities and structures, depending on the local wave action and weather, creating different textures, colors and gradients or layers of material.

Coastal erosion The loss or displacement of land along the coastline due to the action of waves, currents, tides. wind-driven water, waterborne ice, or other impacts of storms

Coastal erosion is the loss or displacement of land, or the long-term removal of sediment and rocks along the coastline due to the action of waves, currents, tides, wind-driven water, waterborne ice, or other impacts of storms. The landward retreat of the shoreline can be measured and described over a temporal scale of tides, seasons, and other short-term cyclic processes. Coastal erosion may be caused by hydraulic action, abrasion, impact and corrosion by wind and water, and other forces, natural or unnatural.

Longshore drift Sediment moved by the longshore current

Longshore drift from longshore current is a geological process that consists of the transportation of sediments along a coast parallel to the shoreline, which is dependent on oblique incoming wave direction. Oblique incoming wind squeezes water along the coast, and so generates a water current which moves parallel to the coast. Longshore drift is simply the sediment moved by the longshore current. This current and sediment movement occur within the surf zone.

Bulkhead (barrier) Anti-flooding structure

A bulkhead is a retaining wall, such as a bulkhead within a ship or a watershed retaining wall. It may also be used in mines to contain flooding.

Beach nourishment

Beach nourishment describes a process by which sediment, usually sand, lost through longshore drift or erosion is replaced from other sources. A wider beach can reduce storm damage to coastal structures by dissipating energy across the surf zone, protecting upland structures and infrastructure from storm surges, tsunamis and unusually high tides. Beach nourishment is typically part of a larger Integrated coastal zone management aimed at coastal defense. Nourishment is typically a repetitive process since it does not remove the physical forces that cause erosion but simply mitigates their effects.

Seawall Form of coastal defence

A seawall is a form of coastal defence constructed where the sea, and associated coastal processes, impact directly upon the landforms of the coast. The purpose of a sea wall is to protect areas of human habitation, conservation and leisure activities from the action of tides, waves, or tsunamis. As a seawall is a static feature it will conflict with the dynamic nature of the coast and impede the exchange of sediment between land and sea. The shoreline is part of the coastal interface which is exposed to a wide range of erosional processes arising from flowing water sources, wind and terrestrial sources, meaning that a combination of denudational processes will work against a seawall.

Breakwater (structure) Structure constructed on coasts as part of coastal management or to protect an anchorage

Breakwaters are structures constructed near the coasts as part of coastal management or to protect an anchorage from the effects of both weather and longshore drift.

Artificial reef A human-made underwater structure.which functions as a reef

An artificial reef is a human-created underwater structure, typically built to promote marine life in areas with a generally featureless bottom, to control erosion, block ship passage, block the use of trawling nets, or improve surfing.

Coastal morphodynamics refers to the study of the interaction and adjustment of the seafloor topography and fluid hydrodynamic processes, seafloor morphologies and sequences of change dynamics involving the motion of sediment. Hydrodynamic processes include those of waves, tides and wind-induced currents.

Geotextile Textile material used in ground stabilization and construction

Geotextiles are permeable fabrics which, when used in association with soil, have the ability to separate, filter, reinforce, protect, or drain. Typically made from polypropylene or polyester, geotextile fabrics come in three basic forms: woven, needle punched, or heat bonded.

Coastal management Preventing flooding and erosion of shorelines

Coastal management is defence against flooding and erosion, and techniques that stop erosion to claim lands. Protection against rising sea levels in the 21st century is crucial, as sea level rise accelerates due to climate change. Changes in sea level damage beaches and coastal systems are expected to rise at an increasing rate, causing coastal sediments to be disturbed by tidal energy.

Beach evolution occurs at the shoreline where sea, lake or river water is eroding the land. Beaches exist where sand accumulated from centuries-old, recurrent processes that erode rocky and sedimentary material into sand deposits. River deltas deposit silt from upriver, accreting at the river's outlet to extend lake or ocean shorelines. Catastrophic events such as tsunamis, hurricanes, and storm surges accelerate beach erosion.

The Gold Coast Shoreline Management Plan (GCSMP) is an ICZM plan to manage the coastal resources of City of Gold Coast. The EPA encourages the City Council's to produce shoreline management plans for coastlines and tidal waterways within the local authority area.

Narrow Neck is the name of an isthmus that separates the anabranch of the Nerang River from the southern end of Main Beach and the northern end of Surfers Paradise beach.

Chevron Reef

Chevron Reef, also known as Pratte's Reef, was an artificial reef constructed in 2000 in Santa Monica Bay, offshore from Dockweiler State Beach. It is the first artificial surfing reef in the United States and was the second to be built worldwide.

Surf break A permanent obstruction on the seabed which causes waves to break

A surf break is a permanent obstruction such as a coral reef, rock, shoal, or headland that causes a wave to break, forming a barreling wave or other wave that can be surfed, before it eventually collapses. The topography of the seabed determines the shape of the wave and type of break. Since shoals can change size and location, affecting the break, it takes commitment and skill to find good breaks. Some surf breaks are quite dangerous, since the surfer can collide with a reef or rocks below the water.

Boscombe Surf Reef

Boscombe Surf Reef was an artificial reef built to enhance surfing conditions at Boscombe in Dorset, England.

Living shorelines

Living shorelines are a relatively new approach for addressing shoreline erosion and protecting marsh areas. Unlike traditional structures such as bulkheads or seawalls that worsen erosion, living shorelines incorporate as many natural elements as possible which create more effective buffers in absorbing wave energy and protecting against shoreline erosion. The process of creating a living shoreline is referred to as soft engineering, which utilizes techniques that incorporate ecological principles in shoreline stabilization. The natural materials used in the construction of living shorelines create and maintain valuable habitats. Structural and organic materials commonly used in the construction of living shorelines include sand, wetland plants, sand fill, oyster reefs, submerged aquatic vegetation, stones and coir fiber logs.

Dynamic revetment

Dynamic revetment, also known as a "cobble berm", uses gravel or cobble-sized rocks to mimic a natural cobble storm beach for the purpose of reducing wave energy and stopping or slowing coastal erosion. Unlike seawalls, dynamic revetment is designed to allow wave action to rearrange the stones into an equilibrium profile, disrupting wave action and dissipating wave energy as the cobbles move. This can reduce the wave reflection which often contributes to beach scouring.

References

  1. ↑ "The world's first formal renovation of a surfing reef, Burkitts Reef Bargara". Surfingramps.com.au. 2009-12-02. Retrieved 2010-03-22.
  2. ↑ Wannasurf.com Ltd. "Artificial reef". Wannasurf.com. Retrieved 2010-03-22.
  3. ↑ Turner, I.L. (2006) Discriminating Modes of Shoreline Response to Offshore-Detached Structures, Journal of Waterway Port, Coastal and Ocean Engineering
  4. ↑ Borrero J.C.
  5. ↑ Fontaine, E (2009) "SandbaggedAfter years of unspectacular closeouts, Pratte's Reef is removed from El Segundo", Surfline.com
  6. ↑ "Surf reef could be ready in 2008". BBC News. 2007-10-09. Retrieved 2010-03-22.
  7. ↑ "Optimism at Boscombe surf reef's opening day (From Bournemouth Echo)". Bournemouthecho.co.uk. 2009-11-03. Retrieved 2010-03-22.
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