WO2009108070A1

WO2009108070A1 - Improvements in and relating to coastal protection reefs

Info

Publication number: WO2009108070A1
Application number: PCT/NZ2009/000020
Authority: WO
Inventors: Kerry Peter Black
Original assignee: Kerry Peter Black
Priority date: 2008-02-22
Filing date: 2009-02-23
Publication date: 2009-09-03

Abstract

This invention relates to an improved coastal protection reef system, structure and operation. In particular, the invention is directed to an artificial reef positioned within the body of water relative to a coastline. The reef includes a reef crest, being submerged periodically during tidal cycles of the body of water, and a capture area. The reef is positioned to create predetermined currents induced by waves in the body of water breaking over the crest of the reef. The capture area includes an entrance to receive material directed there into from the bed of the body of water, and the entrance of the capture area faces substantially away from the coastline. The material accumulated in the capture area determines the level of the bed of the body of water in the capture area which in turn effects a change in the breaking characteristics of the waves over the crest of the reef. It is envisaged the invention will be applicable for use in generating surf waves, but that in doing so, the emphasis in operation is to provide coastal protection and for building coastal beach areas normally otherwise impacted on or eroded by wave action. The currents created around the reefs may also be harnessed for generation of electricity.

Description

IMPROVEMENTS IN AND RELATING TO COASTAL PROTECTION REEFS

Technical Field

This invention relates to improvements in and relating to coastal protection reefs.

In particular, this invention is directed to provide an improved coastal protection reef system, structure and operation.

It is envisaged the invention will also be applicable for use in generating surf waves, but that in doing so, the emphasis in operation is to provide coastal protection. However, the invention may have applications outside this field. For example, the invention may be applied for building coastal beach areas normally otherwise impacted on or eroded by wave action; or, the currents created around the reefs may be harnessed for generation of electricity and so forth.

Background Art

The continual impact of water against shores often causes gradual erosion of the shores over time. This erosion, caused by currents along or away from the shore gradually reduces the usable land area in the vicinity of the shoreline, as the rate of material extracted from the shore by currents exceeds the material deposited. The rate of erosion may vary widely depending on the particular characteristics of the water-to-shore interaction. In the worst cases, valuable properties are endangered due to the land between these properties and the sea being eroded away. As average temperatures continue to increase, sea levels are expected to rise, further compounding the effects of erosion.

A multi-purpose reef is a recent innovation that provides multiple benefits, particularly surfing waves and coastal protection. Other benefits may include sheltered waters inshore for safer swimming or improved marine ecology on the reef. The key purpose of the reef as detailed herein however, is coastal protection and/or surfing. A multi-purpose artificial surfing reef (MASR) is a specially shaped large offshore structure with a crest that is submerged at times during the tidal cycle. Such MASR' s have been disclosed in the prior art ( i.e. Black US Patent No. 4,997,311) and have typical dimensions of 20-1000 metres longshore and 10-300 metres cross-shore and volumes in the range of 2000- 200,000 m3. The reef is placed below the low tide line and may be hundreds of metres offshore, and well beyond the breaking wave zone.

The reef may be made of rocks or other materials such as geotextile mega-containers filled with sand. In US Patent No.4997,311, Black discloses a method of construction that provides for accurate placement and filling of the geotextile containers on the seabed.

All previous MASR's have been shaped with one of the following layouts:

• Straight (mostly shore-parallel or shore-normal)

• One or more arms joined at a point which faces out to sea. The arms may be separated by a small gap.

A reef which is cup-like in shape with the cup entrance pointing out to sea has not been disclosed in the prior art. A reef that is designed to maximise coastal protection with minimum reef volume, while still retaining the capability for improved surfing has also not been disclosed in the prior art. Whilst many structures to protect coasts have been disclosed, a reef that is multi-purpose in providing surfing waves, coastal protection, potentially sheltered waters inshore for safer swimming or improved marine ecology on the reef has not been disclosed in the prior art.

Many breakwater structures designed to break or dissipate the waves at the structure are known. Each of these have shapes (holes, irregular or sloping surfaces, curved faces) designed to maximise wave energy absorption. Some are designed to move the wave-induced water flow through the structure in a way that will bring sand onto the shoreward side of the structure and thereby help to prevent erosion.

US Pat No 5,536,112 issued to Oertel on July 16, 1996, discloses a plurality of individual modules including individual support platforms for cylindrical hollow core risers installed in side-by-side interlocked relationship to construct a semi-permeable barrier that is oriented approximately parallel to the shoreline. Designed as a narrow breakwater to absorb wave energy, the upper segment of the structure is always above the water line at high tide and low tide. The structure is designed to act on the waves, but does not act to capture sand.

De Vilbiss (U.S. Patent No. 1,753,776) describes a method of making a casing for making "filled concrete blocks". The concrete blocks may be used for revetment or levee work on river banks and can be filled with sand and gravel. These elements may be used for constructing a MASR.

Campbell (U.S. Patent No. 3,875,750) describes a modular unit for preventing and reversing erosion of waterfront land. The modules are elongated concrete blocks which are roughly triangular in cross-section, and have five peaks and four depressions. The central peak is the topmost with two additional peaks symmetrically located on either side of the central peak at progressively lower elevations. The blocks are designed to be placed on the beach for direct protection of land.

Weir (U.S. Patent No. 4,498,805) describes a concrete breakwater module for shoreline protection. It is roughly triangular in cross-section and has a vertical rear face, a large upwardly concave trough, and a sloping front wall. The rear wall is substantially higher than the front wall and the top and front walls have a variety of holes and passageways for redirection flow.

Schaaf et al (U.S. Patent No. 4,722,598) describe a concrete module partially submerged to dissipate the energy of waves. The module is roughly triangular in cross-section and has sloping seaward and rear faces. Openings on the front face lead to a series of passages that terminate in upwardly-directed openings on the rear face.

Brade (U.S. Patent No. 4,776,725) describes an erosion control apparatus comprised of a plurality of interconnected members. Each of the members includes the equi-angularly disposed planar panels integrally coupled to a hub. One panel is vertically disposed and the other two rest on the seafloor. Capron (U.S. Patent No. 4,801,221) describes an "Oceanwheel Breakwater" which transfers lateral loads from the sea surface to the seafloor. The wall is composed of modular concrete cylinders held together by a tension spoke.

Mouton et al (U.S. Patent No. 4,896,996) describes a series of low-profile beach cones for trapping sand on the beach face. Rows of beach cones are placed along the waters edge at low tide to eliminate the damaging effects of "undertow".

Atkinson et al (U.S. Patent No. 5,011,328) describes a permeable breakwater constructed of pre-cast concrete beams and plastic piping. The structure is roughly triangular in cross- section with an upward projecting (vertical) permeable wave wall.

Rauch (U.S. Patent No. 5,120,156) describes a submerged breakwater comprised of a plurality of modules. The modules are roughly triangular in shape. The beachward and seaward faces are gently concave upward. The top of the modules have a short vertical wall with three open channels between the seaward and landward faces. The ends of the modules have interlocking members which allow construction along a continuous axial line.

Wheeler (U.S. Patent No. 5,129,756) describes an apparatus for coastal erosion control using a massive sea-block system. The blocks are large rectangular blocks that could be filled with sand, mud, shell or concrete rip rap. Each block has a massive concrete lid.

Creter (U.S. Patent No. 5,238,326) discloses a concrete module partially submerged to dissipate the energy of waves. The module is again roughly triangular in cross-section and has sloping seaward and rear faces.

Hubbard (U.S. Patent No. 4,407,608) describes a modular structure for effecting deposits of fluid entrained alluvium which is normally placed along the shoreface but may be placed underwater.

Hall (US Patent No. 6,565,283) describes an artificial unit consisting of compartments that are adjacent to each other and when filled with material such as beach sand will support each other to form a required reef or breakwater structure on the seabed for beach protection or enhancement of marine life.

Sample (US Patent No. 4,966,491) reveals in October 30, 1990 a subsurface dune protection system which is similar to Hall's invention, making use of a wedge-shaped geotextile container with a slope to an upper wave impacting surface for dissipation of wave forces and accretion of sand on a dune surface being protected.

Many such coastal protection devices reveal a design of elements that are used for coastal protection. Most involve the formation of concrete or other resilient material blocks shaped in a particular form so as to dissipate the wave energy (e.g. Oertel). The inventions of Sample and Hall describe a method of construction of a reef element using large containers.

Some devices have been known to protect the land, but exacerbate erosion of the beach offshore. There is no prior art directed to describing a structure which uses the currents caused by breaking waves to direct sand into a capture zone that is specially incorporated into the constructed reef. There is no prior art directed to describing ways to use the captured sand to improve the coastal protection resulting from the presence of the structure. No-one has described an MASR reef shape that is cup-like, with the entrance to the cup facing offshore.

Black, previously disclosed a reef which was not designed to reduce the wave energy or to collect sediment around the structure itself. Instead, the reef was designed to be sufficiently substantial to induce a rotation of the wave crests offshore of the surf zone. These re-oriented waves, when they subsequently break in the natural surf zone inshore, then alter the longshore currents along the beach. By changing the orientation of the waves at the offshore reef, the waves after passing over the structure then approach the beach at a pre-selected angle to reduce the longshore currents in the natural surf zone that are the primary cause of erosion at many sites worldwide. The structure is able to be constructed of various materials including possibly adopting the containers revealed by Hall and Sample.

The problems with the previous inventions however as described in the prior art are that: • No solution has been provided to minimise the volume of the reef while still retaining the full coastal protection benefits; and

• Wave breaking induces currents around the reef, but these current are not beneficially used; and • The arms of the reef need to be wide (in the order of 30-50 metres) across, to enable quality breaking for surfing and to ensure that waves break for coastal protection. Waves can pass across narrower submerged reefs without breaking, or the energy loss will be less than over a wider reef; and

• Reefs have to be constructed with high precision to prevent bumps in the reef face which will reduce the quality of the surfing ride; and

• Little regard has been had for the potential to maximize use of the currents created and harness such energy — to, for example, generate electricity.

The current invention describes methods, applications and configurations adapted to overcome these problems. In addition, it is anticipated to be used in seas, lakes, rivers and any other applicable water body.

While the present invention has a number of potentially realisable applications, it is in relation to problems associated with existing artificial reefs and breakwater systems that the present invention was developed. More specifically, it was with regard to the issues of providing a system capable of creating surfing waves and yet at the same time providing benefits of coastal protection using an artificial reef system, that the present invention was developed. Additionally, it was having regard to the need to provide a system that would optimise the outcomes for both a surfer and the environment. Finally, it was having regard to the potential to utilise currents associated with the reef as a means for electricity generation that the present invention was also developed.

It would be useful therefore, to have an artificial reef system that offered at least some, if not all, of the potential advantages of the above proposed system. It is therefore an object of the present invention to consider the above problems and provide at least one solution which addresses a plurality of these problems. It is also another object of the present invention to at least provide the public with a useful choice or alternative system.

Further aspects and advantages of the present invention will become apparent from the ensuing description which is given by way of example only. It should be appreciated that variations to the described embodiments are possible and would fall within the scope of the present invention.

Disclosure of Invention

The present invention relates to a multi-purpose artificial surfing reef (MASR) specifically tailored to achieve improved coastal protection, whilst also providing improved surfing conditions. The invention is also directed to reducing strong alongshore currents for safer bathing or natural habitats and to providing system able to be adapted for generating electricity.

The present invention is a specially shaped, large, offshore structure with a crest that is submerged at times during the tidal cycle. If the reef crest is emerged above sea level at all times, it is typically called a breakwater, not a reef. To distinguish the two main types of structure, the term breakwater is used herein to denote a structure that penetrates the water surface and thereby blocks the waves. The term reef is used herein to denote a structure which is underwater and lies on the floor of a body of water, whether sea, lake, manmade or otherwise.

In relation to the current invention, a sub-tidal reef is described herein which is designed to capture sediment and thereby greatly reduce the construction volume of the artificial reef.

The method uses wave induced currents to drive sand into a reef with a novel shape. The

. captured sand then helps to protect the coast by effecting breaking of the waves in the shallower water caused by the elevation of the seabed level due to the captured sand. Reefs which use natural processes to fill a region with sand using currents generated by the reef have not previously been described. Therefore, in one embodiment, the invention uses the energy in waves beneficially to create a coast protection reef filled naturally with sand. Traditional methods of protecting a shoreline from erosion have achieved varying success. They have involved reflecting or absorbing the wave energy, either by providing a solid structure at the water to shore boundary, or by inducing breaking offshore to reduce the energy of the waves as they contact the shoreline. Man-made protection structures are commonly observed at beaches that are either oriented along the shoreline or placed across the beach. Sea walls on the beach are designed to either protect the land from erosion, while groynes or jetties are designed to stop the longshore drift of sand along the beach by blocking the currents.

Many structures have also been built offshore, with one of the most common being a breakwater that may protect a port or a beach by blocking the wave energy. Such structures project above the water surface to ensure that the waves are essentially eradicated in the lee of the structure for boat and shipping safety.

According to one embodiment of the present invention, there is provided a method of shore protection including positioning an artificial submerged and/or inter-tidal reef adapted to create preferred currents induced by waves breaking - over the crest thereof; said reef incorporating a capture area to receive seabed material by natural processes.

Preferably, the reef will be placed on a mobile seabed, possibly sand.

Preferably, the reef will consist of 2 or more arms linked by a joining segment.

Preferably, the arms and joining segments shall be essentially linear or curved in plan.

Preferably, the arms and joining segment shall project up from the natural seabed to the reef crest by at least 1 m.

Preferably, the reef will be greater than 20 m long and the crest will be underwater at some stages of the tide and sufficiently shallow to induce wave breaking at the site when sufficiently large waves are present. According to another aspect of the present invention, there is provided a method substantially as described above wherein the capture area includes a substantially concave region. The capture area may be U-shaped/cup-shaped.

According to another aspect of the present invention, there is provided a method substantially as described above wherein the capture area is partially or totally filled with seabed material thereby greatly reducing the volume of material needed to construct the reef. Preferably, the capture area is sufficiently large so that the volume of sand captured by the reef exceeds 200 m³ and could be as much as several hundred thousand m³.

Preferably, the crest height will be determined by the tidal range and wave climate at the site in question using oceanographic data analysis methods and expert knowledge.

Preferably, the joining segment shall be at the inshore end of the arms thereby putting the joining segment into shallower water and reducing the construction volume.

Preferably, the segments shall be joined to form a continuous barrier.

Preferably, there may be some gaps in the continuous barrier which would allow sand to leak out of the structure. This may be an option where computer design modeling shows this to be a benefit for the surfing, coastal protection or other reasons.

Preferably, the sand will build up against the barrier in places to a level where the waves will break on the sand as well as the barrier, thereby helping to dissipate wave energy and protect the coast.

Preferably, the arms and joining segment will be sufficiently robust to trap sand in the capture area zone.

Preferably, the reef will be designed with an orientation of the arms so that the waves breaking on the build up of sand are suitable for surfing and thereby reduce the need for a broad reef crest with high vertical precision. Preferably, the arms serve the purposes of one or more of (1) breaking the waves; (2) acting as a barrier to capture sand,(3) providing a suitable shape to cause waves to break in a fashion suitable for surfing and (4) breaking the waves to create a wave height shadow inshore. Preferably, the arms are oriented so as to enhance surfing on the breaking waves.

Preferably, once the capture area is sufficiently filled, sand will spill over the reef crest, so that the reef does not permanently stop the natural movement of sand.

Preferably, the currents over the reef crest and in the capture area are directed shorewards which will direct sand inshore to deposit on the beaches.

Preferably, the capture area entrance will be aligned partially offshore and into the waves.

Preferably, the at least two arms may be of different lengths and the structure may not be symmetrical. One example of a non-symmetrical shape is a "hook" or "j" plan shape with the reef oriented such that the rounded section is placed inshore.

In some embodiments of the present invention, the reef may or may not be used for either or both surfing and coastal protection. In some embodiments, the reef may be positioned and adapted to take advantage of water currents that traverse the reef, for other purposes.

According to another embodiment of the present invention, there is provided a method of positioning an artificial submerged and/or inter-tidal reef adapted to create preferred currents induced by waves breaking over the crest thereof; said reef incorporating a capture area to oppose natural coastline currents in the region of a surf zone.

In such embodiments, the currents passing over the reef are still utilised. However, instead of using the currents to capture sand in a cup like capture area, the currents are used to oppose the natural currents that travel along the coast in surf zones. These natural longshore currents lead to erosion of beaches. Therefore, the reef is placed in the stream of current with an orientation such that the currents passing over the reef crest are heading in the opposite direction to the natural longshore currents. The reef may be a straight line or more complex shape - oriented between 10 and 80 degrees to the incoming waves. However, it is the ability to use the currents passing over the crest of the reef to impact on the energy and direction of the natural currents which is significant, rather than the shape of the reef per se.

Preferably, in some cases of, say, strong longshore currents, the capture area entrance is aligned such that the water currents over the reef crest act to oppose the strong longshore currents which typically carry sand away and caused beach erosion.

Preferably, in cases of strong longshore currents, the reef may be of simpler shape with just one or two arms oriented so that wave-induced currents over the crest oppose the longshore currents that cause sand to be swept away.

In yet further embodiments, there exists the opportunity to locate energy generating devices, such as turbines, around the reef to generate electricity and thereby beneficially use the currents (redirected or otherwise) as an alternative to or in addition to using them for beach protection.

Preferably, the currents on or around the reef are directed by suitable placement of and configuration of the reef, so as to generate electricity using turbines.

It will be appreciated that the invention broadly consists in the parts, elements and features described in this specification, and is deemed to include any equivalents known in the art which, if substituted for the prescribed integers, would not materially alter the substance of the invention.

Variations to the invention may be desirable depending on the applications with which it is to be used. Regard would of course be had to at least effecting the desired shape of the reef and capture area to maximise the benefits afforded by captured seabed material, the preferred orientation and shape of the reef to effect the preferred currents in the lee of the reef for energy generation and/or affecting natural shoreline currents, and the desired wave formation over the crest and the consequent desired affect on surf wave creation and beach shoreline

Il protection. The present invention is differentiated from existing systems by virtue of the shape and orientation of the reef, the capture area, and the effect of the reef on water currents, and so forth.

Whilst some varying embodiments of the present invention have been described above and are to be yet exampled, it should further be appreciated different embodiments, uses, and applications of the present invention also exist. Further embodiments of the present invention will now be given by way of example only, to help better describe and define the present invention. However, describing the specified embodiments should not be seen as limiting the scope of this invention.

Brief Description of Drawings

Further aspects of the present invention will become apparent from the following description, given by way of example only and with reference to the accompanying drawings in which: Figure 1 is a top plan representation illustrating a cup-shaped "capture" reef in accordance with one embodiment of the present invention; and Figures 2a, b illustrate variations to the cup-shaped capture reef, in accordance with another embodiment of the present invention; and Figure 3 illustrates a typical pattern of currents and wave heights around the capture reef depicted in Figure 1; and

Figure 4 illustrates currents around the reef of Figure 2a with currents running shorewards in the sand capture area, in accordance with one embodiment of the present invention; and Figure 5 illustrates wave height associated with the reef of Figure 2b, showing big waves offshore and small waves in the lee of the structure, in accordance with one embodiment of the present invention; and Figure 6 illustrates a top plan representation illustrating a cup-shaped "capture" reef, in accordance with one embodiment of the present invention; and Figure 7 illustrates the reef of Figure 6 with the wave driven currents around the reef, in accordance with one embodiment of the present invention; and Figure 8 illustrates the reef of Figure 6 with the waves breaking on the shallow reef, in accordance with one embodiment of the present invention; and Figure 9 illustrates an obliquely oriented shallow reef, in accordance with another embodiment of the present invention; and Figures lOa-c illustrate energy generation device placement and the direction of strong wave driven currents over the reef, in accordance with other embodiments of the present invention. Best Modes for Carrying Out the Invention

With reference to the figures by way of example only, there is provided an improved artificial reef system (generally indicated by arrow 1). The reef is an artificial submerged and/or inter- tidal reef adapted to create preferred currents induced by waves breaking over the crest thereof. The reef includes a capture area 2 to receive seabed material deposited therein by natural processes. The deposited seabed material contributes to the creation, stability and operation of the reef.

The reef may be used to generate improved surf waves, redirect and/or dampen natural shoreline surf zone currents which _.otherwise are instrumental in beach shoreline erosion, enable sand deposits to build up beach shorelines in the lee of the reef, and/or direct wave generated currents towards appropriately located turbines in the vicinity of the lee of the reef for electricity generation purposes.

The reef system is typically oriented such that the capture area 2 is facing the open sea and/or the direction of incoming waves. The lee of the reef is adjacent or closer to the beach shoreline. The figures illustrate varying embodiments and practical applications of the reef and reef system.

Figure 1 illustrates an example of a cup-shaped "capture" reef, with the entrance of the cup facing essentially out to sea. The dark colours show shallower water and the black is the shoreline. The numbers on the contours show depths in metres. In this case, the reef is placed at 2 metre depth and the crest of the reef is at the low tide level. The waves come from the ocean and travel from left to right. In cases of strong, longshore currents, the capture reef may be simplified with just 1 or 2 arms or segments which are aligned so that the currents coming over the reef crest partially oppose and block the longshore currents that cause erosion.

Figures 2a and 2b illustrate two cup reef variations. In Figure 2a the cup reef has a single compartment. In Figure 2b the reef has an overall cup shape, but the structure includes 3 sub- compartments. It should be appreciated that the shape of the reef may vary according to where it is used and its application.

Figure 3 illustrates a typical pattern of currents and wave heights around the capture reef depicted in Figure 1 via use of a numerical computer model. The area designated A shows large waves and the area designated B shows small waves. In this image, the waves have been forced to break in the shallow water over the reef crest. This induces a current over the crest from the ocean side to the lee side. Water and sand stirred up by the waves is then drawn into the cup-shaped capture zone, i.e. the compartment constrained by the surrounding geobags. The waves are smaller in the lee of the reef (area B).

Figure 4 illustrates currents around the cup with currents running shorewards in the sand capture area. Figure 5 illustrates wave height, showing big waves offshore and small waves in the lee of the structure. It should be appreciated that the arms of the reef must be sufficiently wide to cause wave breaking. In turn, wave breaking induces currents to flow through the capture area and over the reef crest. In combination with the waves stirring up the sand, the currents carry the sand into the capture area where it is trapped.

In Figure 6 and 7 one embodiment of a cup-shaped reef 1 is provided. Wave driven currents 3 are directed around the reef and as a result, wave height is low in the lee of the reef (at 4) and the beach 5 is correspondingly widened as sand is deposited and/or not eroded in this "protected" region.

In Figure 8 the waves 6 break on the shallow reef 1. Sand is captured in the offshore capture area 2. Low wave heights are created in the lee of the reef (at 4) and consequently, the beach is widened in the lee of the reef as illustrated at 5. The embodiment illustrated in Figure 9 demonstrates currents 3 being re-directed by an obliquely oriented shallow reef 1. The location of the reef impacts on the strength of the alongshore currents, being stronger at 7 and weaker at 8. At 9 it can be seen that the strong alongshore currents are weakened and reversed, with a corresponding widening of the beach in the lee of the reef, at 5.

Figures 10a- 10c all illustrate varying embodiments and orientations of the artificial reef of the present invention. In each embodiment, energy generating devices, such as turbines 10 are positioned to take advantage of the wave driven currents associated with and around the reef.

When referring to the description of the present invention, it should also be understood that the term "comprise" where used herein is not to be considered to be used in a limiting sense. Accordingly, 'comprise' does not represent nor define an exclusive set of items, but includes the possibility of other components and items being added to the list.

This specification is also based on the understanding of the inventor regarding the prior art. The prior art description should therefore not be regarded as being an authoritative disclosure of the true state of the prior art, but rather as referring to considerations in and brought to the mind and attention of the inventor when developing this invention.

Aspects of the present invention have been described by way of example only and it should be appreciated that modifications and additions may be made thereto without departing from the scope thereof, as defined in the appended claims.

Claims

5 TPIE CLAIMS DEFINING THE INVENTION ARE:

1. An artificial reef for a body of water, said artificial reef being positioned within the body of water relative to a coastline and said reef including a crest, said crest being submerged periodically during tidal cycles of the body of water, and said

10 positioning of the reef facilitating creation of predetermined currents induced by waves in the body of water breaking over the crest of the reef; and said reef including a capture area, said capture area including an entrance to receive material directed there into from the bed of the body of water, and said entrance of the capture area facing substantially away from the coastline.

1.5

2. An artificial reef as claimed in Claim 1 wherein the capture area and entrance are substantially oriented toward the waves in the body of water.

3. An artificial reef as claimed in Claim 2 wherein the capture area is defined by at 20 least two arms linked by a j oining segment.

4. An artificial reef as claimed in Claim 3 wherein the capture area includes a substantially concave region.

25 5. An artificial reef as claimed in Claim 4 wherein the capture area is substantially U-shaped or cup-shaped.

6. An artificial reef being as claimed in Claim 5 wherein the capture area accumulates material from the bed of the body of water which in turn contributes

30 to the construction volume of the reef.

7. An artificial reef as claimed in Claim 6 wherein the material accumulated in the capture area of the artificial reef substantially determines the level of the bed of the body of water in the capture area which in turn effects a change in the

35 breaking characteristics of the waves over the crest of the reef.

8. An artificial reef as claimed in Claim 7 wherein the wave breaking characteristics of the waves over the crest of the reef contribute to at least one or more from the following list: a) protection against the effects of waves breaking along the coastline in a region associated with the artificial reef. b) a reduction in strong alongshore currents enabling safer bathing c) a reduction in strong alongshore currents to minimise damage to natural habitats. d) surfing waves.

9. A method of coastline protection using an artificial reef positioned within a body of water relative to said coastline and said reef including a crest, said crest being submerged periodically during tidal cycles of the body of water, and said positioning of the reef facilitating creation of predetermined currents induced by waves in the body of water breaking over the crest of the reef; and said reef including a capture area, said capture area including an entrance to receive material directed there into from the bed of the body of water, said method including the steps of: a) positioning said artificial reef on the bed of the body of water, such that the entrance of the capture area faces away from the coastline; and wherein b) the capture area is partially or totally filled with material from the bed of the body of water entering the capture area; and wherein c) the material accumulated in the capture area determining the level of the bed of the body of water in the capture area and effecting a change in the breaking characteristics of the waves over the crest of the reef.

10. A method of coastline protection as claimed in Claim 9 wherein the artificial reef includes at least two arms linked by a joining segment to create a barrier with at least one capture area of predetermined configuration.

11. A method of coastline protection as claimed in Claim 10 wherein, the arms contribute to one or more of: a) providing a barrier to capture material in the capture area, b) effecting breaking of waves for surfing and c) effecting breaking of waves to create a wave height shadow inshore thereby helping to dissipate wave energy and protect the relevant coastline.

12. A method of coastline protection as claimed in Claim 11 wherein once the capture area is filled, the reef is adapted to enable material to spill over the reef crest.

13. A method of coastline protection as claimed in Claim 12 wherein the reef is also adapted to enable material from the capture area to pass through gaps in the barrier defined by the arms and the joining segment.

14. A method of coastline protection as claimed in Claim 13 wherein material spilling over and from the capture area is directed via the currents induced by waves in the body of water breaking over the crest of the reef to be deposited on the shore.

15. A method of positioning an artificial submerged and/or inter-tidal reef adapted to create predetermined currents induced by waves breaking over the crest thereof; said reef incorporating a capture area to oppose natural alongshore coastline currents in the region of a surf zone.

16.. A method of positioning an artificial submerged and/or inter-tidal reef adapted to create preferred currents induced by waves breaking over the crest thereof as claimed in Claim 15, wherein the reef is positioned in the stream of current with an orientation such that the currents passing over the crest of the reef are applied to oppose the direction of the natural alongshore currents, impacting on their direction and wave energy.

7. A method as claimed in Claim 16 wherein preferred currents on or around the reef are directed by suitable placement of and configuration of the reef, so as to generate electricity using turbines.