WO2023108204A1

WO2023108204A1 - Artificial reef arrangement and module for an artificial reef

Info

Publication number: WO2023108204A1
Application number: PCT/AU2022/051495
Authority: WO
Inventors: Matthew Allen; Liam MINOTTI; Marijn HOOGHOUDT; Justin GELDARD; Ryan Lowe; George ELWOOD; Scott DRAPER; Jack FRANCIS
Original assignee: MMA Subsea Services Pty Ltd
Priority date: 2021-12-14
Filing date: 2022-12-13
Publication date: 2023-06-22
Also published as: WO2023108205A1

Abstract

An artificial reef arrangement (10) including a plurality of spaced rows (12) of reef structures (14).

Description

ARTIFICIAL REEF ARRANGEMENT AND MODULE FOR AN ARTIFICIAL REEF

FIELD OF THE INVENTION

[0001] One or more applications of the present invention relates to an artificial reef arrangement, such as for wave attenuation.

[0002] One or more applications of the present invention relates to a module for use in forming an artificial reef arrangement.

[0003] In particular, but not limited to, one or more forms of the present invention relates to an artificial reef arrangement/structure including an array of spaced rows of reef structures and/or to one or modules for use in an artificial reef structure.

[0004] To provide context, the disclosed artificial reef arrangement and is suitable for deployment in a large body of water such as an ocean, sea, lake or river.

BACKGROUND TO THE INVENTION

[0005] Natural reef structures provide coastal protection from storms, erosion and flood events, as well as provide habitat for marine life. Shorelines become more exposed to rising sea levels, increasing storm intensity and erosion as natural reefs become degraded.

[0006] Artificial reef structures can provide a similar function as natural reefs and can modify the effects of prevalent waves on the coastline to reduce erosion, modify movement of coastal sediments, and increase or decrease wave height and wave run-up at a particular location. [0007] Offshore artificial reefs have been typically constructed from rubble mounds, geotextile containers or modular reef modules configured in single rows running parallel to the shoreline. For example, submerged artificial reefs have been configured as rubble mounds such as the Palm Beach Reef, geotextile sand container reefs such as Narrow Neck, or as modular precast reefs such as Mon Choisy Artificial reef.

[0008] Emergent artificial reef structures include detached offshore breakwaters such as those along the Italian Adriatic coast or modular reefs such as Stratford Point on Long Island, USA.

[0009] Multi-function artificial reef structures can perform similarly to natural reefs for coastal protection while also offering many additional benefits over conventional engineering structures.

[0010] T raditional artificial reefs built for wave attenuating tend to be very large in nature, requiring a large amount of material to be placed offshore. These emergent reefs, alternatively called detached breakwaters, are designed to break the surface at least at mean sea level. Their tall height breaks the surface of the water, creating exposed breakwaters that are unsightly. Detached breakwaters can also create issues through excessive sand accretion as they significantly disrupt the littoral processes that naturally occur in the intertidal zone and beyond.

[0011] Alternatively, the visual amenity and littoral processes may be preserved, to some extent at least, by creating a submerged or partially emergent reef. However, such submerged reefs but must be very wide in order to provide sufficient wave attenuation effect to protect the shoreline.

[0012] The typical approach to ameliorate coastal erosion is to ‘armour’ the eroded shoreline with groynes, exposed offshore breakwaters and seawalls, which destroy the visual amenity of the shoreline and its function as a beach for both people and animals.

[0013] It will be appreciated that one or more forms of the present invention advantageously provides a convenient artificial reef arrangement that addresses, ameliorates or at least provides an alternative to known artificial reef structures.

SUMMARY OF THE INVENTION

[0014] An aspect of the present invention provides an artificial reef arrangement including a plurality of spaced rows of reef structures.

[0015] The rows may be at predetermined spacings relative to one another. The artificial reef arrangement may include at least two spaced rows of the reef structures.

[0016] For an artificial reef having three or more rows of the reef structures, the spacing between a first said row and a second said row may be substantially the same as the spacing between the second row and a third said row.

[0017] At least one of the rows of the reef structures may include a plurality of modules. The modules of a said row may be arranged linear or staggered/offset configuration relative to one another.

[0018] Two or more of the modules of a row may be connected together, such as by a fastening arrangement or the modules may inter-engage together.

[0019] At least one said module may have a porous structure and/or at least one aperture into or through the module. At least one said module may include two or more said apertures of differing width/diameters relative to one another. [0020] At least one said module may have a monolithic structure, preferably of a precast material (such as concrete or including concrete).

[0021] The rows may be arranged parallel to each other, such as when submerged or partially submerged in the water. The rows may be arranged straight or curved. In use, the rows of the structures may be in the water at a distance from a shoreline. The rows may be parallel to or at an angle relative to the shoreline. An upper height of the structure of one or more of the rows is provided at lowest astronomical tide (LAT), or with one or more of the rows at some distance above LAT and one or more of the rows at some distance below LAT, such that the artificial reef arrangement is partially or fully submerged during a tidal cycle.

[0022] In some embodiments, there is provided an artificial reef arrangement including a plurality of spaced rows of reef modules.

[0023] The rows may be at predetermined spacings relative to one another.

[0024] The artificial reef arrangement may include at least two spaced rows of the reef modules.

[0025] The artificial reef arrangement may include at least three spaced rows.

[0026] The spacing between a first said row and a second said row may be substantially the same as the spacing between the second row and a third row.

[0027] A virtual width of the reef may present to a wave as the overall dimensions of the multiple rows of the reef structures. [0028] The rows of the reef structures may be spaced relative to one another to maximise wave attenuation for a given reef location and/or across a range of wave frequencies.

[0029] At least one of the rows of the reef structures may include a plurality of modules.

[0030] The modules of a row may be arranged in a linear or in a staggered/offset configuration relative to one another.

[0031 ] Two or more of the modules of a row may be connected together.

[0032] At least one said module may have a porous structure.

[0033] At least one said module may have at least one aperture into or through the module.

[0034] At least one said module may include two or more apertures of differing widths relative to one another.

[0035] At least one said module may include two or more apertures of differing diameters relative to one another.

[0036] At least a portion of at least one said module may have a monolithic structure.

[0037] The at least one said module may have a monolithic structure.

[0038] The at least one module may be precast or created in situ in water. [0039] The at least one module may include material cast in situ within an inflatable shell.

[0040] The rows may be arranged parallel to each other.

[0041 ] The rows may be straight or curved.

[0042] In use, the rows of the structures may be in water at a distance from a shoreline.

[0043] The rows may be parallel to or at an angle relative to the shoreline.

[0044] An upper height of the structure of one or more of the rows may be provided at lowest astronomical tide (LAT), or with one or more of the rows at some distance above LAT and one or more of the rows at some distance below LAT, such that the artificial reef arrangement is partially or fully submerged during a tidal cycle.

[0045] A further aspect of the present invention provides a module for an artificial reef arrangement, the module having a porous structure and/or at least one aperture into or through the module.

[0046] The module or each module may include two or more said apertures of differing width/diameters relative to one another.

[0047] The respective module may have a monolithic structure, preferably of a precast material (e.g. concrete or containing concrete) or created from one or more inflatable cast in-situ modules (e.g. an inflatable shell filled with a curable/settable material, such as concrete or material containing cement or other material). [0048] A base of the module may be wider than a top of the module, preferably the module tapers form the wider base to the narrower top. The module may have a substantially flat upper surface.

[0049] An artificial reef arrangement may include multiple spaced arrays of reef structures. The arrays of the reef structures may be in rows spaced at intervals from one another e.g. rows of artificial reef structures deployed at certain spacings, to create a partially submerged (below Mean Sea Level (MSL) or fully submerged (below Lowest Astronomical Tide (LAT)) reef arrangement.

[0050] The artificial reef arrangement may have an effective width that is equivalent or near to equivalent to a traditional width submerged reef.

[0051 ] A portion of the artificial reef arrangement may include a plurality of reef modules e.g. rock, precast modules or inflatable cells, which may be provided in multiple rows/arrays, such as at a predetermined spacing relative to one another to create an effective width of the reef (the effective width being the width from a front of a foremost row/array to a rear of a rearmost row/array relative to an incident wave).

[0052] It will be appreciated that embodiments of the present invention can provide void space between rows of the artificial reef arrangement i.e. the rows are spaced and not continuous across the effective width or are not mechanically connected as part of the reef structure.

[0053] Wave height can be attenuated by the artificial reef arrangement prior to reaching the shoreline by wave reflection or cancellation, reducing the amount of wave energy reaching the shoreline.

[0054] It will be appreciated that one or more of the artificial reef arrangement of the present invention can help with one of, or a combination of two or more of, the following: reduce the amount/volume of material required to construct a reef; reduce the wave height and wave energy reaching the shoreline; reduce the wave run up at the shoreline; reduces shoreline erosion; enable large reefs to be constructed cost effectively; maintain the visual and functional amenity of the sheltered beach and dune system.

[0055] Wave transmission across submerged artificial reefs depends on a variety of parameters, including the incident wave height (Hi), wave period (T), water depth (d), acceleration due to gravity (g), structure height (h), crest width of the structure (B), and the freeboard of the structure (F=h-d). A dimensional analysis using the parameters above provides four dimensionless groups which influence wave attenuation: (i) relative free board (F/Hi), (ii) relative reef width (B/gT²), (iii) degree of submergence (d/h) and (iv) wave steepness (Hi/gT²).

[0056] It has been realised that an increase in wave steepness and relative reef width (B/gT²) can increase attenuation; whereas an increase in relative freeboard and degree of submergence were shown to reduce attenuation.

[0057] Unlike submerged rubble mound breakwaters, artificial reefs formed of modules/units are much more porous and complex in shape. Wave transmission across such artificial reefs depends on additional parameters of the structure (e.g. spacing between structures/modules). For example, wave attenuation over rows of abutting artificial reef modules can increase with the addition of more rows, changing the structural ratio of reef width B which was occupied by void space between rows.

[0058] Embodiments include a method of creating an artificial reef to attenuate waves includes providing or creating a plurality of rows of artificial reef structures in a depth of water subject to prevailing waves, the rows spaced from one another such that the waves encounter consecutive said rows. [0059] Embodiments include providing at least three spaced rows of said artificial reef structures including a front row, a rear row, and at least one intermediate row between the front and rear rows, wherein a distance between the front row and the rear row relative to prevailing waves provides an effective artificial reef width attenuating the waves.

[0060] Embodiments include a method of attenuating a wave includes providing a plurality of rows of artificial reef structures, the rows spaced from one another, such that a distance between a front row and a rear row provides an effective artificial reef width attenuating the waves.

[0061] An example of artificial reef arrangement of the present invention includes at least one row between 50 and 100m, preferably 75m, from shore, between 1 ,5m and 3m height, preferably 2.0m height, structures/rows, in a water depth between 1 ,0m and 2.0m, preferably 1 .5m, LAT, with preferably between 3m and 5m, preferably 4m, row width, with preferably between 10m and 15m, preferably 12m, row spacing, and preferably between 50m and 150m, preferably 100m, row length.

BRIEF DESCRIPTION OF THE DRAWINGS

[0062] One or more embodiments of the present invention will hereinafter be described with reference to the accompanying Figures, in which:

[0063] Figure 1 shows an application of an artificial reef arrangement in situ according to an embodiment of the present invention.

[0064] Figure 2 shows an alternative artificial reef arrangement in situ according to an embodiment of the present invention. [0065] Figure 3A shows a front view of a reef module according to an embodiment of the present invention.

[0066] Figures 3B and 3C show alternative rotated views of a reef module according to an embodiment of the present invention.

[0067] Figures 4A to 4D show plan views of alternative layouts of reef arrangements according to various embodiments of the present invention.

[0068] Figure 5 shows an artificial reef arrangement according to an embodiment of the present invention. The incident waves are travelling from the right to the left.

[0069] Figure 6A shows an example of an artificial reef in situ off a shoreline according to an embodiment of the present invention. Figure 6B shows detail of the artificial reef shown in Figure 6A.

[0070] Figure 7A shows an artificial reef arrangement according to an alternative embodiment of the present invention. Figure 7B shows detail of the artificial reef shown in Figure 7A.

[0071] Figure 8A shows an artificial reef arrangement according to an alternative embodiment of the present invention. Figure 8B shows detail of the artificial reef shown in Figure 8A.

[0072] Figure 9 shows a plot of variation of transmission coefficient with relative reef width for reef layouts 3 and 4 (Figures 4C and 4D).

[0073] Figure 10 shows a plot for layouts 1 -4 (see Figures 4A-4D) over the relative freeboard range (-0.75<F//-//<-1 .5) showing that better transmission coefficients (Kt) are achieved for a given number of modules by spacing them apart to increase the relative freeboard (B/gT²).

DESCRIPTION OF PREFERRED EMBODIMENT(S)

[0074] It is to be appreciated that each of the embodiments is specifically described and that the present invention is not to be construed as being limited to any specific feature or module of any one of the embodiments. Neither is the present invention to be construed as being limited to any feature of a number of the embodiments or variations described in relation to the embodiments.

[0075] Figure 1 shows an application of an artificial reef arrangement 10 according to an embodiment of the present invention.

[0076] The artificial reef arrangement 10 comprises a number of artificial reef modules 14. Throughout this description, the term “reef module” may be used interchangeably with “reef structure”. Rows 12 of the artificial reef modules 14 are positioned to form the artificial reef arrangement 10 to receive incoming waves form a general direction of wave propagation 20 prior to the shoreline 16 of a shore 18.

[0077] The term ‘reef’ on its own can hereinafter be used to refer to the whole artificial reef arrangement 10 (such as including the rows of reef modules). The reef 10 may consist of two or more rows 12 of continuous reef modules of a combination of individual reef modules 14 positioned side by side or connected side by side to form the respective row.

[0078] Dimension S is the distance between rows 12 of reef modules 14. Dimension Y is the width of an individual row 12 of the reef modules 14.

Dimension h is the height of the reef modules forming the rows 14. Dimension L is the transverse/lateral length of the row(s) of the reef. Dimension B is the effective width (or depth front to rear) of the reef. LAT is the lowest astronomical tide.

[0079] The reef modules 14 are the building block of the modular reef and may be of rock, precast modules or containers that can be filled or inflated with sand, dredge spoil or stabilised aggregates such as concretes or geopolymers, or a combination of any two or more thereof.

[0080] It will be appreciated that each row 12 of the reef modules 14 may include a plurality of the reef modules arranged to form the respective row. Each row 12 may be straight or curved. The reef 10 may include a combination of straight and curved rows 12 of the reef modules 14.

[0081] Each row may be oriented to be in the water 22 parallel to the shoreline 16 or oriented to be in the water 22 at an angle to the shoreline 16 such as to attenuate best the prevailing wave climate.

[0082] The distance (‘S’) between the rows of the reef modules can be determined to optimise wave attenuation for a given site.

[0083] The height h of the rows 12 of the modules 14 from the seabed 24 or from the mean water level is preferably the same for all rows of the reef arrangement.

[0084] Dimensions of a module 14 of the reef can be between 1 .5 and 2.0m tall/high 28, upper width/diameter 30 can be between 1 .2 and 1 .8m wide, lower width/diameter 32 can be between 1 .8 and 2.5m wide and a wall thickness 34 can be between 0.12 and 0.25m thick.

[0085] The upper surface 36 can include one or more apertures 38 therein or therethrough. [0086] Figure 3 shows a front view of a reef module 14 according to an embodiment of the present invention.

[0087] One or more reef modules 14 of the present invention can include one or more apertures 26 (26A, 26B, 26C, 26D, 26E...26_n) into or through the module.

[0088] One or more of the reef modules can be positioned in the respective row with a chosen aperture arrangement facing the prevailing wave front to act to attenuate a portion of the wave in a required way to suit the required performance of the reef arrangementl 0.

[0089] Four alternative embodiments of layouts of reef arrangements are shown in Figures 4A to 4D. These show plan view schematics of different module layouts. In the plan view schematics, the reef crest width (B) is indicated in terms of the module base diameter (D).

[0090] Rows of the reef modules (reef modules) 14 can have different reef crest widths (8) and reef module row spacings (S, such as Si, S2).

[0091] The reef arrangement can preferably be provided in prototype water depths (d) of 1 .5m to 5.0m, more preferably 1 .6m to 3.0m, yet more preferably 1 .8m to 3.0m. The reef arrangement can preferably be provided in prototype water depths (d) of 1 .8m (i.e. d/h = 1 , top of the module representing a prototype low tide), 2.7 m (i.e. d/h = 1 .5, representing a prototype high tide) and 2.3 m (i.e. d/h = 1 .25, an intermediate water depth).

[0092] It will be appreciated that one or more of the part reef modules 14 (such as half modules) can be incorporated in one or more rows 12. For example, two of the modules may be halves such as in for Layouts 3 and 4 to ensure that a desired reef length/width is created. [0093] The geometry of each module 14 need not be symmetric (see Figure 3) e.g. may be asymmetric. Reef modules 14 can be individually rotated to ensure a randomised orientation relative to the incident wave direction. This is preferable for how the modules are expected to be deployed in practice.

[0094] Scale tests conducted in a wave tank on artificial reefs arrangements

10 with row spacing are shown in Figures 4A to 4D. The tests were conducted in a 54-m long and 1 .5 m wide wave on 1 /6^th scale modules at scale water depths (d) of 0.32m (top of the module representing a prototype low tide) representing an equivalent 1 :1 depth of 1 ,92m, 0.47m (1 .5 times the module height representing a prototype high tide) representing a 1 :1 depth of 2.82m, and 0.39m (an intermediate water depth) representing a 1 :1 depth of 2.34m.

[0095] The range of model scale wave conditions tested (period and height). Multiple wave heights were tested at two fixed periods in addition to multiple periods being tested at two fixed wave heights (Table 1 ). This approach investigated trends of attenuation with both wave height and period, respectively.

[0096] In the tests, the incident and reflected components of waves were measured at the offshore and onshore locations were decomposed via directional separation. The transmission coefficient (Kt = Ht⁺/Hi⁺), representing the ratio of the incident (shoreward⁺) propagating component of the wave heights onshore (Ht) and offshore (H) of the reef structure, were calculated to quantify the wave attenuating performance of the artificial reef. The influence of relative freeboard, relative reef width and module layout on attenuation is discussed further below.

[0097] The variation of the transmission coefficient with relative reef width for Layouts 3 and 4 is shown in Figure 9. The data is shown organised into five subcategories of relative freeboard to better understand the influence of relative reef width.

[0098] The results plotted in figure 9 for layouts 3 and 4 show that relative reef width (B/gT²) approximately linearly decreases the transmission coefficient (Kt) at different relative freeboards (F/Hi) . A reduction in the transmission coefficient with relative reef width occurs across all of the relative freeboards tested. This trend identifies that shorter period waves are more attenuated for a given reef width. A larger reef width is required to achieve a similar degree of attenuation of longer period waves. The vertical scatter in the magnitude of Kt in Figure 9 can be accounted for through differences in the relative freeboard F/Hi. Shallower relative freeboards are associated with a reduction in wave transmission due to a combination of both wave dissipation and reflection (not shown).

[0099] The variation in transmission coefficient with relative reef width for Layouts 3 and 4 are independently plotted in Figure 10 for a representative relative freeboard (-0.75<F//-/?<-1 .5). Both layouts show the same negative trend between transmission and relative reef width but at slightly different magnitudes. The broader reef width of Layout 4 (5 adjacent rows) extends the range of relative reef widths available into regions of lower transmission for a given wavelength.

[00100] Figure 10 shows a plot for layouts 1 -4 over the relative freeboard range (-0.75<F//-//<-1 .5) showing that better transmission coefficients (Kt) are achieved for a given number of modules by spacing them apart to increase the relative freeboard (B/gT²). Variation in transmission coefficient with relative reef width for Layout 1 has also been included in Figure 10. Layout 1 is designed to have the same number of rows and modules as layout 3, however the rows are evenly spaced to achieve the same reef width as layout 4 (see Figures 4A-4D). As seen in Figure 10, layout 1 has a similar reduction in wave transmission with B/L as seen for layout 3; however, the performance has improved with the range of relative reef widths available extending into regions of lower transmission for a given wavelength.

[00101] The increased attenuation with module spacing, and consequently relative reef width, is apparent. Flow separation around widely spaced modules can potentially enhance drag forces on the individual modules that, through the work done by the drag forces, could enhance rates of drag dissipation. The increased spacing of the rows can also lead to a greater contribution of energy loss through wave reflection at multiple points within the array, or alternatively cause waves to resonate at the reef unit spacing which may potentially cause increased reflection.

[00102] The variation in transmission coefficient with relative reef width for layout 2 plotted in Figure 10 further highlights the impact of module/row spacing. The performance of three rows forming the reef (e.g. 3 rows of the modules) to attenuate wave energy is further improved by increasing the spacing to occupy a slightly larger reef width B than layout 4.

[00103] As a result, similar transmission coefficients appear in comparison to layout 4, an array with 67% more material.

[00104] It will be appreciated that one or more of the modules can be porous, in the sense that either, or both, of the structure of the module(s) can have one or more apertures to a hollow interior or the material of the structure can be porous. The tests conducted included waves, velocities and mean water levels measured over a range of equivalent offshore wave conditions to quantify wave transformation and directional energy fluxes (transmission, reflection and dissipation) for different reef configurations. [00105] The capability of embodiments of the artificial reef arrangements of the present invention to attenuate surface waves is dependent on their configuration (reef width, free board and row spacing). The tests demonstrate that an increase in the relative reef width improves wave attenuation, as can reducing the relative freeboard. The spacing between rows (e.g. rows of the modules) within the reef arrangement (e.g. array of rows or rows of modules) also significantly improves reef performance in comparison to arrangements with additional modules at reduced spacings.

[00106] It is to be understood that, if any prior art is referred to herein, such reference does not constitute an admission that the prior art forms a part of the common general knowledge in the art, in Australia or any other country. In the claims which follow and in the preceding description of the invention, except where the context requires otherwise due to express language or necessary implication, the word “comprise” or variations such as “comprises” or “comprising” is used in an inclusive sense, i.e. to specify the presence of the stated features but not to preclude the presence or addition of further features in various embodiments of the invention.

Claims

CLAIMS:

1 . An artificial reef arrangement including a plurality of spaced rows of reef structures.

2. The artificial reef arrangement of claim 1 , wherein the rows are at predetermined spacings relative to one another.

3. The artificial reef arrangement of claim 1 or claim 2, including at least two spaced rows of the reef structures.

4. The artificial reef arrangement of claim 3, including at least three spaced rows, wherein the spacing between a first said row and a second said row is substantially the same as the spacing between the second row and a third row.

5. The artificial reef of any one of the preceding claims, wherein a virtual width of the reef presents to a wave as the overall dimensions of the multiple rows of the reef structures.

6. The artificial reef of any one of the preceding claims, wherein the rows of the reef structures are spaced relative to one another to maximise wave attenuation for a given reef location and/or across a range of wave frequencies.

7. The artificial reef arrangement of any one of the preceding claims, wherein at least one of the rows of the reef structures includes a plurality of modules.

8. The artificial reef arrangement of claim 7, wherein the modules of a said row arranged linear or staggered/offset configuration relative to one another.

9. The artificial reef arrangement of claim 7 or claim 8, wherein two or more of the modules of a row are connected together.

10. The artificial reef arrangement of any one of claims 7 to 9, wherein at least one said module has a porous structure and/or at least one aperture into or through the module.

11 . The artificial reef arrangement of claim 10, wherein at least one said module includes two or more apertures of differing width/diameters relative to one another.

12. The artificial reef arrangement of any one of claims 7 to 11 , wherein at least a portion of at least one said module has a monolithic structure.

13. The artificial reef arrangement of claim 12, wherein the at least one said module has a monolithic structure.

14. The artificial reef arrangement of any one of claims 7 to 13, wherein the at least one module is precast or created in situ in water.

15. The artificial reef arrangement of claim 14, wherein the at least one module includes material cast in situ within an inflatable shell.

16. The artificial reef arrangement of any one of the preceding claims, wherein the rows are arranged parallel to each other.

17. The artificial reef arrangement of any one of the preceding claims, wherein the rows are straight or curved.

18. The artificial reef arrangement of any one of the preceding claims, wherein, in use, the rows of the structures are in water at a distance from a shoreline.

19. The artificial reef of claim 18, wherein the rows are parallel to or at an angle relative to the shoreline.

20. The artificial reef arrangement of any one of the preceding claims, wherein an upper height of the structure of one or more of the rows is provided at lowest astronomical tide (LAT), or with one or more of the rows at some distance above LAT and one or more of the rows at some distance below LAT, such that the artificial reef arrangement is partially or fully submerged during a tidal cycle.

21 . A module for an artificial reef arrangement, the module having a porous structure and/or at least one aperture into or through the module.

22. The module of claim 21 , including two or more said apertures of differing width/diameters relative to one another.

23. The module of claim 21 or 22, including a monolithic structure.

24. The module of claim 23, wherein the monolithic structure is precast or cast in situ in water.

25. The module of claim 24, wherein the cast in situ structure is cast within an inflatable shell.

26. The module of any one of claims 21 to 25, wherein a base of the module is wider than a top of the module, preferably the module tapers form the wider base to the narrower top.

27. The module of any one of claims 21 to 26, wherein the module has a substantially flat upper surface. 21

28. A method of creating an artificial reef to attenuate waves includes providing or creating a plurality of rows of artificial reef structures in a depth of water subject to prevailing waves, the rows spaced from one another such that the waves encounter consecutive said rows.

29. The method of claim 28, including providing at least three spaced rows of said artificial reef structures including a front row, a rear row, and at least one intermediate row between the front and rear rows, wherein a distance between the front row and the rear row relative to prevailing waves provides an effective artificial reef width attenuating the waves.

30. A method of attenuating a wave includes providing a plurality of rows of artificial reef structures, the rows spaced from on another, such that a distance between a front row and a rear row provides an effective artificial reef width attenuating the waves.