TECHNICAL FIELD

The disclosure relates to the field of artificial reefs, and more specifically to an artificial reef, an installation, methods, and a computer program for preventing or reducing coastal or river bank erosion.

BACKGROUND

In tropical, equatorial, and subtropical regions, mangroves are productive habitats that support many functions on which depend the local biodiversity (refuge, habitat, nursery, or spawning ground) and the surrounding populations through derived services (fisheries production, raw material, or coastal protection). Through their complex root systems, mangroves modify the physico-chemical conditions of the environment. For example, mangroves participate in the oxygenation of the substrate or in the creation of a low-energy environment by dissipating part of the incident wave energy and by slowing down the currents.

These species are known for their action on sediment dynamics. Indeed, they reduce sediment resuspension and promote sediment deposition. These different effects contribute to the stability of the substrate, an essential element for the sustainability of the mangrove. Thus, the physical interactions between mangroves and the environment create positive feedback loops that generate alternative stable states: the presence of mangroves catalyzes the installation of other mangroves and thus the progression of the mangrove, and vice versa in case of disturbance or degradation of these species.

With the intensification of the effects of climate change and human activities, mangroves play an essential role for local communities as they are natural coastal protections against erosion and marine submersion. However, mangroves are subject to an alarming regression. In this context, mangrove replanting programs have been implemented during the last decades. However, the survival rates of transplants are generally low for several reasons. These reasons include the use of inadequate planting methods, an insertion or reinsertion of inappropriate species or their establishment in hydro sedimentary contexts that have evolved and are no longer favorable to them.

Within this context, there is still a need for an improved solution for preventing or reducing coastal or river bank erosion.

SUMMARY

It is therefore provided an artificial reef for preventing or reducing coastal or river bank erosion. This artificial reef may be referred to as "first type of artificial reef." The artificial reef comprises means for anchoring the artificial reef to a water bottom. The artificial reef comprises elongated elements extending at least partially upward so as to form a porous barrier extending upward from the water bottom when the artificial reef is anchored to the water bottom. The porous barrier formed by the elongated elements presents a substantially constant density vertically. The artificial reef comprises horizontal structural elements maintaining the elongated elements.

The artificial reef may comprise one or more of the following: each elongated element is maintained by at least two of the horizontal structure elements arranged at different heights when the artificial reef is anchored to the water bottom; one or more of the elongated elements are made of wood; one or more of the elongated elements are made of 3D printed concrete; the horizontal structural elements and the elongated elements have a total height greater than 1 meter; the elongated elements occupy at least 50% of the total height; each horizontal structural element has a flat shape of substantially circular circumference in a horizontal plane perpendicular to a vertical axis of the artificial reef when anchored to the water bottom; each horizontal structural element has a diameter greater than 0.8 meter and/or less than 3 meters; the circumference of each horizontal structural element comprises centimetric or pluricentimetric irregularities, including vertical notches, depressions and/or protrusions; each elongated element has two ends, each end being embedded in a respective horizontal structural element; the horizontal structural elements comprise a first horizontal structural element and a second horizontal structural element; for each elongated element, one of the two ends of the elongated element is embedded in the first horizontal structural element and another one of the two ends is embedded in the second horizontal structural element; the horizontal structural elements comprise a first pair of horizontal structural elements and a second pair of horizontal structural elements, the second pair being arranged above the first pair when the artificial reef is anchored to water bottom; the elongated elements are gathered in a first set and a second set, for each elongated element of the first set, one of the two ends of the elongated element is embedded in one of the horizontal structural elements of the first pair and another one of the two ends is embedded in another one of the horizontal structural elements of the first pair; for each elongated element of the second set, one of the two ends of the elongated element is embedded in one of the horizontal structural elements of the second pair and another one of the two ends is embedded in another one of the horizontal structural elements of the second pair; the horizontal structural elements consist in three horizontal structural elements arranged at different heights, each horizontal structural element comprising holes, each elongated elements passing through each of the horizontal structural elements via a respective one of the holes; each horizontal structural element is made of concrete; each horizontal structure element has a rectangular shape aligned in a horizontal plane perpendicular to a vertical axis of the artificial reef when anchored to the water bottom, each horizontal structure element being arranged at a respective height when the artificial reef is anchored to the water bottom, the horizontal structure elements comprising pairs of horizontal structure elements, each horizontal structural element of each pair being contained in a respective radial plane along the vertical axis of the artificial reef, each elongated element passing through each horizontal structural element of a respective pair; each horizontal structural element is made of wood; each horizontal structural element has a length greater than 0.8 meter and/or less than 2 meters; and/or the artificial reef further comprising a pillar configured for being sunk into the water bottom and thereby anchoring the artificial reef.

It is also provided an installation comprising one or more such artificial reefs. Each artificial reef is anchored to water bottom in a coastal, riverine or estuarine environment. The installation prevents or reduces coastal or river bank erosion of the coastal, riverine or estuarine environment.

The installation may comprise several artificial reefs each comprising a respective pillar. The installation may comprise one or more connection means each connecting the respective pillars of two or more artificial reefs of the several artificial reefs.

It is also provided a computer-implemented method for simulating the prevention or reduction of coastal or river bank erosion of a real-world coastal, riverine or estuarine environment with such an installation. This method for simulating the prevention or reduction of coastal or river bank erosion may be referred to as "the simulation method." The simulation is performed on specifications of the installation and specifications of the real-world coastal, riverine or estuarine environment.

The simulation method may comprise one or more of the following: the method comprises setting the specifications of the installation, including selecting a type of artificial reef between a first type of artificial reef and another type of artificial reef, depending on whether the real-world coastal, riverine or estuarine environment is not or respectively is a predominantly high swell environment; and/or the another type of artificial reef corresponds to: o a second type of artificial reef comprising:

■ means for anchoring the artificial reef to a water bottom, elongated elements extending at least partially upward from the water bottom so as to form a porous barrier when the artificial reef is anchored to the water bottom, and

■ a substantially plain base lying on the water bottom when the artificial reef is anchored to the water bottom, or o a third type of artificial reef presenting a lower part and an upper part above the lower part and comprising:

■ means for anchoring the artificial reef to a water bottom, and

■ elongated elements extending at least partially upward from the water bottom so as to form a porous barrier when the artificial reef is anchored to the water bottom, the porous barrier formed by the elongated elements presenting vertically a first density in the lower part and a second density in the upper part, the selection of the type of artificial reef between the first, second and third types further depending on whether the real-world coastal, riverine or estuarine environment is or respectively is not a predominantly high current environment.

It is also provided a method for installing such an installation in a coastal, riverine or estuarine environment to prevent or reduce coastal or river bank erosion of the coastal, riverine or estuarine environment. This method for installing an installation may be referred to as "the installing method." The installing method comprises anchoring each artificial reef of the installation to water bottom in the coastal, riverine or estuarine environment.

The installing method may comprise one or more of the following: the coastal, riverine or estuarine environment is a predominantly high swell environment; each artificial reef is anchored at a depth between 1.5 meter and 6 meters from the surface; the installation comprises artificial reefs each comprising a respective pillar, the method further comprising, for each artificial reef, driving the pillar of the artificial reef into the water bottom thereby anchoring the artificial reef; the method further comprises connecting the pillars of two or more artificial reefs of the artificial reefs; at least one of the artificial reefs comprises two pairs of horizontal structural elements, the number of pillars being lower than the number of pairs of horizontal structural elements; and/or the method comprising, prior to the installing, performing the simulation method for simulating the prevention or reduction of coastal or river bank erosion of the coastal, riverine or estuarine environment induced by the installation.

It is also provided a computer program comprising instructions for performing the simulation method.

It is also provided a device comprising a data storage medium having recorded thereon the computer program.

The device may form or serve as a non-transitory computer-readable medium, for example on a SaaS (Software as a service) or another server, or a cloud-based platform, or the like. The device may alternatively comprise a processor coupled to the data storage medium. The device may thus form a computer system in whole or in part (e.g., the device is a subsystem of the overall system). The system may further comprise a graphical user interface coupled to the processor.

BRIEF DESCRIPTION OF THE DRAWINGS

Non-limiting examples will now be described in reference to the accompanying drawings, where:

FIG.s 1 to 3 illustrate a first example of the artificial reef;

FIG.s 4 to 6 illustrate a second example of the artificial reef;

FIG.s 7 to 9 illustrate a third example of the artificial reef;

FIG.s 10 to 12 illustrate a fourth example of the artificial reef;

FIG.s 13 to 15 illustrate a fifth example of the artificial reef;

FIG.s 16 to 18 illustrate a sixth example of the artificial reef;

FIG.s 19 and 20 illustrate two examples of the installation;

FIG.s 21 to 24 illustrate examples of other types of artificial reef; and FIG. 25 shows an example of the system.

DETAILED DESCRIPTION

According to a first aspect, it is provided an artificial reef for preventing or reducing coastal or river bank erosion. This artificial reef may be referred to as "first type of artificial reef." The artificial reef comprises means for anchoring the artificial reef to a water bottom. The artificial reef comprises elongated elements extending at least partially upward so as to form a porous barrier extending upward from the water bottom when the artificial reef is anchored to the water bottom. The porous barrier formed by the elongated elements presents a substantially constant density vertically. The artificial reef comprises horizontal structural elements maintaining the elongated elements.

The artificial reef forms an improved solution for preventing or reducing coastal or river bank erosion.

Notably, the artificial reef allows imitating the role of the mangrove in the creation of a low-energy environment by dissipating a part of the incident wave energy. Indeed, the porous barrier formed by the elongated elements allows slowing down the swells, which allows preventing or reducing coastal or river bank erosion. The artificial reef dissipates the energy of the swell which passes through it and disturbs its circulation (diffraction, refraction) thus contributing to dissipate its energy. The artificial reef reduces sediment resuspension and promotes sediment deposition, thus contributing to the stability of the substrate and restoring the erosion balance.

Moreover, the artificial reef allows stopping the regression of mangrove. Indeed, the stability of the substrate induced by the artificial reef favors the installation of new mangroves, which in turn stabilizes the environment and thus favors the installation of other mangroves. The artificial reef therefore allows for the recolonization of the mangrove.

Moreover, by reproducing mangrove structural complexity, the artificial reef also supports similar ecological functionalities and ecosystem services. It supports nursery, habitat, substrate, spawning area or functions, hosts local life and helps species to settle and grow, supporting part of their lifecycle. It also supports production services, like fish or shell production. It also supports regulation services, as carbon capture and storage, by protecting soil carbon from remobilization through waves and flows, and helps mangrove settlement and growth.

Furthermore, as the porous barrier formed by the elongated elements presents a substantially constant density vertically, the structure is uniformly distributed over its height, while easy to manufacture. The artificial reef has a tower-like structure which is well-adapted to a predominantly high swell environment. Indeed, the porous barrier (and the induced occupancy of the water column along the artificial reef) provides energy dissipation on incident waves passing through the artificial reef, while supporting local biodiversity by its structural complexity.

The means of anchoring the artificial reef to the water bottom may comprise a pillar configured for being sunk into the water bottom. When sunk into the water bottom, the pillar may anchor the artificial reef into the water bottom. The pillar may pass through each of the horizontal structure elements. The horizontal structural elements may be arranged at different heights along the pillar when the pillar is sunk into the water bottom. The pillar allows ensuring the stability of the artificial reef in energetic contexts, an economy of materials and a reduction of the compromise on performance due to stability needs. In examples, the pillar may be connected (e.g., bound) to one or more other pillars (e.g., one or more pillars each of another respective artificial reef). It allows optimizing the stability of a whole work made of several artificial reefs (i.e., the artificial reef and each another respective artificial reef to which it is bound) or to change its mechanical response to hydrodynamic forcings. This connection may be done at the top or at the bottom of the pillar, and may bound two or more pillars together (i.e., the pillar of the artificial reef and the one or more other pillars of each another respective artificial reef to which it is bound).

Additionally, the artificial reef may be further anchored to the water bottom by its own mass (also referred to as "weight" in the following). The mass of the artificial reef may be higher than 30 kilograms. For example, the means for anchoring the artificial reef to the water bottom may include the horizontal structural elements. The mass of the horizontal structural elements may constitute at least 50% of the whole mass of the artificial reef.

Each horizontal structural element may be made of a material with a density large enough to sink into water, e.g., such that the position of the artificial reef remains constant with respect to the water bottom. For example, each horizontal structural element may be made of concrete material, from locally available concrete, possibly rudimentary, to technical ones as porous concrete, 3D printed or stamped concrete and/or concrete with inclusions like shell fragments. The use of concrete allows for an efficient local and sustainable manufacture of the artificial reef. The use of concrete also provides strength to the artificial reef. When the artificial reef comprises a pillar, the horizontal structural elements made of concrete may hold the elongated elements along the pillar.

Each elongated element extends at least partially upward. Each elongated element may extend substantially from the water bottom, or from a certain height above the water bottom. The water bottom may be a sea bottom when the artificial reef is anchored in a coastal sea environment. Alternatively, the water bottom may be a lake bottom when the artificial reef is anchored in a coastal lake environment. Alternatively yet, the water bottom may be a river bottom (e.g., a river bank) when the artificial reef is anchored in a riverine or estuarine environment. Each elongated element may be directed in a direction close to a direction perpendicularto the water bottom. For example, the horizontal structural elements may each define a respective parallel plane and the planes may be substantially parallel. The parallel planes may also be substantially parallel to the water bottom when the artificial reef is anchored to the water bottom. Each elongated element may be positioned relatively to the horizontal structural elements such the elongated element forms an acute angle with a direction normal to the parallel planes. The acute angle may be less than 45 degrees (e.g., less than 20 degrees). Each elongated element may be positioned vertically to the water bottom. In this case, the acute angle may be close to zero, for example less than 2 degrees. The elongated elements may be positioned parallel to each other. The elongated elements may occupy at least 60% of the total height of the artificial reef (i.e., of the height between the upper horizontal structure element and the lower horizontal structure element).

The porous barrier formed by the elongated elements presents a substantially constant density vertically. The density may be a density of elongated elements per unit area (e.g., per unit horizontal area). For each height along a vertical axis, the density of elongated elements per unit horizontal area may be substantially constant. For example, the number of elongated elements passing through each horizontal plane along the vertical axis may be constant. Alternatively or additionally, the elongated elements may be spaced apart from each other and the spacing between the elongated elements may be substantially constant. For example, the spacing may be less than a minimum distance, for example so that the swell is reduced when passing through the artificial reef. The spacing between two adjacent elements may be higher than 5 and/or lower than 50 centimeters. This spacing allows the passage of local fauna (e.g., fishes) while dissipating small waves. The porous barrier may occupy entirely the water column. The porous barrier allows redirecting the flows on the sides of the artificial reef, which allows an easier flow than at the level of the artificial reef.

The elongated elements may be made of wood (e.g., the elongated elements may comprise rods) or may be made of concrete (e.g., 3D printed concrete). The elongated elements may have a regular shaped cross-section (e.g., rectangular, or circular cross-section) or the circumference of the cross-section may comprise irregularities.

Each horizontal structural element may have a flat shape of substantially circular circumference in a horizontal plane perpendicular to a vertical axis of the artificial reef when anchored to the water bottom. The diameter of the circumference may be greater than 0.8 meter and/or less than 3 meter. The circumference may comprise irregularities (e.g., vertical notches, depressions and/or protrusions) or may be smooth.

Each elongated element may be maintained by at least two of the horizontal structure elements. For example, each elongated element may have two ends and each end may be attached to a respective horizontal structural element. Each end may represent a portion of the elongated element and said portion may be embedded in a respective horizontal structural element. For example, each horizontal structural element may have been obtained by pouring concrete into a mold, and inserting a portion of the elongated elements thereinto before hardening of the concrete, such that after hardening the concrete fixedly embeds said portion of the elongated elements. Alternatively, the ends of each elongated element may be fixed/anchored to a respective horizontal structural element, for example after hardening of the concrete. For example, each horizontal structural element may comprise, for each elongated element, a respective spike protruding upward out of the horizontal structural element and inserted into the end of the elongated element so as to attach the elongated element to the horizontal structural element. In yet another example, each horizontal structural element may comprise holes and the elongated elements may be press-fitted inside the holes.

With reference to FIG.s 1 to 3, a first example of an artificial reef 100 of the first type is now discussed. FIG.s 2 and 3 are top and side views of the artificial reef 100 shown in FIG. 1.

The artificial reef 100 is shown as it would be anchored to a water bottom. The artificial reef 100 comprises elongated elements 103, 104 extending at least partially upward from the water bottom so as to form a porous barrier when the artificial reef is anchored to the water bottom. The elongated elements 103, 104 are arranged parallel to each other, at least substantially. The artificial reef 100 comprises two horizontal structural elements 101 and 102. Each elongated elements 103, 104 is maintained by the two horizontal structural elements 101.

The artificial reef 100 comprises a pillar 107. The pillar 107 is configured for being sunk into the water bottom and thereby anchoring the artificial reef 100. Once anchored, the pillar 107 is vertical to the water bottom. The two horizontal structure elements 101, 102 are arranged at different heights along the pillar 107. The height of the horizontal structure element 102 with respect to the water bottom is greater than 120 millimeters and/or less than 250 millimeters. The height between the two horizontal structure elements 101, 102 is greater than 1 meter. The height may be comprised between 1.5 meter and 2.5 meters.

The elongated elements 103 are all arranged parallel to the pillar 107, at least substantially. Each elongated element 103, 104 comprises two ends. One of the two ends is near one of the two horizontal structure elements and the other one of the two ends is near the other one of the two horizontal structure elements. The elongated elements 103 occupy at least 80% of the total height of the artificial reef 10 (i.e., the height between the two horizontal structure elements 101, 102). In other words, the thicknesses of the horizontal structure elements 101, 102 represent less than 20% of the total height of the artificial reef 100.

The porous barrier formed by the elongated elements presents a substantially constant density vertically. The density of elongated elements is substantially constant along the vertical axis of the artificial reef 100 between the two horizontal structure elements 101, 102. The density of elongated elements is substantially constant in each plane perpendicular to the vertical axis. The density refers to the number of elongated elements per unit area.

The artificial reef 100 comprises two types of elongated elements 103, 104. The elongated elements 103 are made of wood and have a rectangular cross-section. The elongated elements 104 are made of concrete and have a circular cross-section. The elongated elements 103 may have an apparent diameter between 60 millimeters and 160 millimeters. The elongated elements 104 allows reinforcing the structure of the artificial reef 100 and maintain vertically the horizontal structure element 101 with respect to the horizontal structure element 102.

The pillar 107 passes through each horizontal structure elements 101, 102. Each horizontal structure elements 101, 102 comprises a hole 108, through which the pillar 107 passes. The pillar may have a circular cross-section. The pillar may be made of concrete, wood or steel. The diameter of the pillar may be greater than 120 millimeters and/or less than 250 millimeters. The diameter of the hole 108 is greater than the diameter of the pillar.

Each elongated element 104 is maintained by the horizontal structure element 101 by means of a respective rod 105. The rod 105 may pass through the horizontal structure element 101 and the elongated element 104, thereby holding the horizontal structure element 101 and the elongated element 104 fixed relative to each other. Each elongated element 104 is also maintained by the horizontal structure element 102. For example, each elongated element 104 may be bonded to (or may be integral with) the horizontal structure element 102. The horizontal structure element 101 and the horizontal structure element 102 also maintain each elongated element 103. For example, each of the horizontal structure element 101 and the horizontal structure element 102 may comprise spikes 110, and the two ends of each elongated element 103 may be configured to be held on one spike of the horizontal structure element 101 and another spike of the horizontal structure element 102. For example, each end may comprise a hole and the spike may be inserted in the hole. Alternatively, each end may be pushed onto the spike. The spikes 105 may be sealed, embed or screwed into the elements 101, 102 or 103. The spikes 105 and may be either exposed to external environment through a space between 103 and 101 or 102, or insulated from external environment if there is no remaining space between 103 and 101/102.

Each horizontal structural element 101, 102 may have a flat shape of substantially circular circumference in a horizontal plane perpendicularto the vertical axis of the artificial reef. The diameter of the circular circumference may be greater than 0.8 meter and/or less than 3 meter. The circular circumference of each horizontal structural element may comprise irregularities 106. The irregularities 106 may include vertical notches, depressions and/or protrusions. The irregularities 106 may be centimetric or pluricentimetric. The irregularities create roughness which increases friction and therefore the performance of the artificial reef in dissipating incident wave energy. Moreover, the irregularities promote micro-complexity and thus promote ecological performance through the fixation of fixed fauna and the creation of habitat for small organisms.

The horizontal structural elements 101, 102 may have substantially the same thickness. The thickness of the horizontal structural elements 101, 102 may be greater than 120 millimeter and/or lower than 250 millimeters.

The artificial reef 100 allows preventing coastal or river bank erosion and reproducing the mangrove when installed in a coastal, riverine or estuarine environment. The term "erosion" refers to the erosion of coasts, banks or other boundaries between land and water of the coastal sea or coastal lake or riverine environment. For example, the method may comprise installing the artificial reefs in one or more coasts of a sea or lake. In that case, the erosion may be the coastal erosion of the one or more coasts on which the artificial reefs are installed. Alternatively, the method may comprise installing the artificial reefs in one or more banks of a river. In that case, the erosion may be a river bank erosion of the one or more banks on which the artificial reefs are installed.

With reference to FIG. s 4 to 6, a second example of artificial reef 200 of the first type is now discussed. FIG.s 5 and 6 are top and side views of the artificial reef 200 shown in FIG. 4.

The artificial reef 200 comprises elongated elements 203, 204 extending upward from the water bottom and forming a porous barrier. The elongated elements 203, 204 are arranged parallel to each other. In this example, the artificial reef 200 comprises a pillar 207 and three horizontal structural elements 201, 202 and 202'. Each of the horizontal structural elements 201, 202 and 202' has a flat shape of circular circumference in a horizontal plane perpendicular to the vertical axis of the artificial reef 200. The pillar 207 passes through each of the horizontal structure elements 201, 202 and 202'. The horizontal structural elements 201, 202 and 202' are arranged at different heights along the pillar 207 when the pillar 207 is sunk into the water bottom. The height between the upper horizontal structure element 201 and the lower horizontal structure element 202' is greater than 1 meter. The height may be greater than 1.5 meter and/or lower than 2.5 meters.

The artificial reef 200 comprises two types of elongated elements 203, 204. The elongated elements 203 are made of wood and the elongated elements 204 are made of concrete. Each of the elongated elements 203, 204 has a circular crosssection. The elongated elements 203 made of wood have substantially the same length and the same diameter. The length of the elongated elements 203 may be greater than 1.5 meter and/or lower than 2.5 meters. The diameter of the elongated elements 203 may be greater than 60 millimeters and/or lower than 160 millimeters. The diameter of the elongated elements 204 may be greater than 120 millimeters and/or lower than 250 millimeters.

The horizontal structural elements 201, 202 and 202' maintain the elongated elements 203, 204. Regarding the elongated element 203 made of wood, each of the horizontal structural elements 201, 202 and 202' comprises first holes and each of the elongated elements 203 passes through each of the horizontal structural elements via a respective one of the first holes. Each of the elongated elements 203 is thus maintained by each of the horizontal structural elements. This allows the installation and replacement of the elongated elements 203, which may be inserted in the horizontal structural elements 201, 202 and 202', without replacing the whole artificial reef. Regarding the elongated elements 204 made of concrete, each horizontal structural element comprises second holes 210 aligned with the elongated elements 204 and the artificial reef 200 comprises rods 206 which maintain the elongated elements 204 by passing through the second holes 210 and the elongated elements 205. These rods may also support handling of the artificial reefs. Each of the elongated elements 204 is maintained by two of the horizontal structural elements 201, 202 and 202'.

The porous barrier formed by the elongated elements 203, 204 presents a substantially constant density vertically. The density of elongated elements is substantially constant along the vertical axis of the artificial reef 200, i.e., between the horizontal structure element 201 and the horizontal structure element 203. In each plane perpendicular to the vertical axis, the number of elongated elements passing through the plane is constant. Additionally, the elongated elements may be evenly spaced from each other and the density of elongated elements passing through the plane is thus substantially homogeneous on the plane. The porous barrier allows regulating the flow of water through the artificial reef 200, which reduces the swell at the artificial reef 200.

With reference to FIG.s 7 to 9, a third example of artificial reef 300 of the first type is now discussed. FIG.s 8 and 9 are top and side views of the artificial reef 300 shown in FIG. 7. The artificial reef 300 comprises a pillar 307 and several pairs of horizontal structure elements (a first pair 301, 302 and a second pair 301', 302'). Each horizontal structure element passes through the pillar 307 and is at a respective height along the pillar when the artificial reef 300 is anchored. The second pair is arranged above the first pair in the vertical axis of the artificial reef 300. In this example, the artificial reef 300 comprises two pairs of horizontal structure elements. In other examples, the artificial reef 300 may comprise another number of pairs of horizontal structure elements (e.g., three or more pairs). The pairs of horizontal structure elements may be arranged one above the other along the pillar. The height between the two horizontal structure elements of each pair is greater than 0.8 meter and/or lower than 1.2 meter. The height of the porous barrier may therefore be greater than 1.6 meter.

The artificial reef 300 comprises a respective set of elongated elements for each pair (the set of elongated elements 303, 304 for the first pair and the set of elongated elements 303', 304' for the second pair). Each elongated element of the first set comprises two ends. One of the two ends is embedded in one of the horizontal structural elements of the first pair (e.g., 301) and another one of the two ends is embedded in another one of the horizontal structural elements of the first pair (e.g., 302). Similarly, regarding the second set, each elongated element of the second set has one end embedded in one of the horizontal structural elements of the second pair and another end embedded in another one of the horizontal structural elements of the second pair. The elongated elements 303, 303' are made of wood and the elongated elements 304, 304' are made of concrete. The pairs of horizontal structural elements form two floors (i.e., levels) and the elongated elements each belong to one of these two floors. Unlike the first and second examples, this third example of artificial reef therefore comprises two floors. In other examples, the artificial reef may comprise any other number of floors.

With reference to FIG.s 10 to 12, a fourth example of artificial reef 400 of the first type is now discussed. FIG.s 11 and 12 are top and side views of the artificial reef 400 shown in FIG. 10. The artificial reef 400 comprises a pillar 407 and two horizontal structural elements 401, 402 each having a flat shape of substantially circular circumference. The circular circumferences of the horizontal structural elements 401, 402 are irregular and comprise undulations 410. The irregularity of the circular circumference creates roughness which increases friction and therefore the performance of the artificial reef in dissipating incident wave energy. Moreover, it promotes micro-complexity and thus ecological performance. The horizontal structural elements 401 and 402 may be made with porous material, creating microholes to enhance the settlement and growth of larvaes and spores. The elongated elements 403 are made of wood and have either a rectangular or circular cross section. Each elongated element 403 has two ends, one embedded in the horizontal structural element 401 and another one embedded in the horizontal structural element 402. The horizontal structural elements 401, 402 maintain the elongated elements 403 vertically and spaced apart from each other so as to form a porous barrier for water flowing through the artificial reef 400. The height between the upper horizontal structure element 401 and the lower horizontal structure element 402 is greater than 1 meter. The height may be greater than 1.5 meter and/or lower than 2.5 meters.

With reference to FIG.s 13 to 15, a fifth example of artificial reef 500 of the first type is now discussed. FIG.s 14 and 15 are top and side views of the artificial reef 500 shown in FIG. 13. The artificial reef 500 comprises a pillar 507 and two horizontal structural elements 501, 502 each having a flat shape of substantially circular circumference. This fifth example of artificial reef 500 differs from the fourth example in that the elongated elements 503 are made of 3D printed concrete. The elongated elements 503 have an unregular shaped cross-section. The circumference of the cross-section of each elongated element 503 comprises irregularities. These irregularities are formed by undulations along the circumference, which form vertical niches 510 along the elongated elements 503. These vertical niches 510 increase the structural complexity of the artificial reef 500, which promotes local biodiversity. They also create additional complexity which increases the ability of the artificial reef to dissipate flows and waves energy.

With reference to FIG.s 16 to 18, a sixth example of artificial reef 600 of the first type is now discussed. FIG.s 17 and 18 are top and side views of the artificial reef 600 shown in FIG. 17. The artificial reef 600 comprises a pillar 607 and several horizontal structure elements 601, 602 arranged at different heights along the pillar 607. The pillar 607 may be made of wood and may have a circular cross-section. The circular cross-section of the pillar 607 may have a diameter between 80 millimeters and 250 millimeters. Each horizontal structure element 601, 602 may be made of wood and has a rectangular shape aligned in a horizontal plane perpendicular to a vertical axis of the artificial reef when anchored to the water bottom. The horizontal structural elements 601, 602 may have substantially the same length. The length of the horizontal structural elements 601, 602 may be greater than 0.8 meter and/or lower than 2 meters.

The horizontal structure elements comprise three pairs of horizontal structure elements (e.g., the pair 601 and 602). Each horizontal structural element of each pair is contained in a respective radial plane along the vertical axis of the artificial reef. As illustrated in the figure, the pair 601 and 602 is contained in the same radial plane. The same applies for the pair 601' and 602', which are also contained in a same radial plane. The pairs of horizontal structural elements are arranged in evenly spaced radial planes along the vertical axis as shown in FIG. 18.

Each elongated element passing through the horizontal structural elements of a same pair. For example, each of the elongated elements 603 passes through the horizontal structural elements 601' and 602' of the pair 601' and 602'. The height between the lower horizontal structure element 610 and the upper horizontal structure element 611 is greater than 1 meter and/or lower than 1.5 meter. Each elongated element has a length greater than 1.5 meter and/or lower than 2.5 meters. It is also provided an installation comprising one or more artificial reefs. Each artificial reef is anchored to water bottom in a coastal, riverine or estuarine environment. The coastal environment may be a coastal sea environment or a coastal lake environment. When the installation comprises several artificial reefs, the artificial reefs may be positioned relative to each other to form a pattern on the water bottom. For example, the artificial reefs may be associated and aligned to form lines or patches and the pattern may comprise one or more lines of adjacent artificial reefs. When the artificial reefs of the installation each comprises a respective pilar, the installation may comprise one or more connection means each connecting the respective pillars of two or more artificial reefs of the installation. For examples, the connection means may bound the pillars of the two or more artificial reefs together (e.g., the top or bottom of the pillars). The association of several artificial reefs next to each other allows building a whole porous swell attenuation work to protect coastline against erosion and/or flooding risks.

FIG.s 19 and 20 illustrate two examples of such installations each comprising several artificial reefs 650, 650'. The artificial reefs are aligned next to each other, thereby forming a pattern along the sea shore. The installation illustrates in FIG. 20 comprises artificial reefs of the third example of FIG. 7. Each artificial reef comprises two floors. Each floor comprises a pair of horizontal structural elements. During installation, the installing method may comprise driving the pillars of each artificial reef and then, at each pillar, installing the two floors of the artificial reef comprising the pillar. In the installation, the number of pillars is lower than the number of floors to be installed (i.e., the number of pairs of horizontal structural elements). Indeed, each artificial reef comprises a single pillar and two floors. This is also true in other examples of installations, when the installation comprises at least one artificial reef comprising two floors. This facilitates the installation.

According to a second aspect, a second type of artificial reef is provided. The artificial reef of the second type comprises means for anchoring the artificial reef to a water bottom. The artificial reef of the second type comprises elongated elements extending at least partially upward from the water bottom so as to form a porous barrier when the artificial reef is anchored to the water bottom. The artificial reef of the second type comprises a substantially plain base lying on the water bottom when the artificial reef is anchored to the water bottom. The artificial reef of the second type may be according to the artificial reef described in the PCT application entitled "preventing or reducing coastal or river bank erosion with bush-like artificial reefs", filed on the same day, by the same Applicants, with the same inventors, and which is incorporated herein by reference. The artificial reef of the second type may be according to each embodiment described in this PCT application. FIG. 21 illustrate an example of an artificial reef 700 of the second type. The artificial reef 700 comprises a substantially plain base 720 lying on the water bottom when the artificial reef is anchored to the water bottom. The artificial reef 700 further comprises elongated elements 710 embedded in the base 720. Each elongated element 710 is maintained by the base 720 and extends at least partially upward from the water bottom so as to form a porous barrier.

According to a third aspect, a third type of artificial reef is now discussed. The third type of artificial reef combines properties of the first type and of the second type. The artificial reef of the third type comprises means for anchoring the artificial reef to water bottom and elongated elements extending at least partially upward from the water bottom so as to form a porous barrier when the artificial reef is anchored to water bottom. The artificial reef of the third type presents a lower part in contact with the water bottom when the artificial reef is anchored to the water bottom and an upper part above the lower part. The porous barrier formed by the elongated elements presents vertically a first density in the lower part and a second density in the upper part. The first density is higher than the second density.

In the upper part and in the lower part, the elongated elements may comprise curved elongated elements made of concrete and presenting a circular cross-section. In the lower part, the artificial reef of the third type may also comprises a substantially circular base made of concrete and straight elongated elements made of wood attached to the circular base (e.g., embedded in the circular base).

The artificial reef of the third type allows imitating the role of the mangrove in a coastal, riverine or estuarine environment. The lower part may be used by marine fauna (e.g., as a refuge) and may reduce the currents flowing through the artificial reef. The upper part may reduce wave energy and thus reduce swell. The artificial reef of the third type reproduces more faithfully mangrove roots geometry than the artificial reefs of the first and second types, focusing on a biomimicry approach. It helps increasing environmental integration and supporting appropriate habitat functionalities.

FIG.s 22 to 24 illustrate three examples of an artificial reef of the third type.

FIG. 22 illustrates the first example 800 which presents a lower part 810 in contact with the water bottom when the artificial reef 800 is anchored to the water bottom and an upper part 811 above the lower part 810. The porous barrier formed by the elongated elements 820 presents vertically a first density in the lower part and a second density in the upper part. The first density is higher than the second density. In the upper part 810 and in the lower part 811, the elongated elements 820 comprise curved elongated elements made of concrete and presenting a circular cross-section. In the lower part 811, the artificial reef 800 also comprises a substantially circular base 831 made of concrete and straight elongated elements 830 made of wood embedded in the circular base 831. This first example 800 truly mimics mangroves and is optimal for wildlife.

FIG. 23 illustrates the second example of artificial reef 801 which differs from the first example 800 in that the elongated elements 821 are all made of concrete and present a polygonal cross-section. Additionally, the artificial reef 801 does not comprise a substantially circular base and elongated elements made of wood embedded in the base.

FIG. 24 illustrates the third example of artificial reef 802 which differs from the second example 801 in that the elongated elements 822 are all straight. The examples of FIG.s 23 and 24 are particularly simple to manufacture.

It is also provided a computer-implemented method for simulating the prevention or reduction of coastal or river bank erosion of a real-world coastal, riverine or estuarine environment with the installation (referred to as "the simulation method"). The simulation is performed on specifications of the installation and specifications of the real-world coastal, riverine or estuarine environment. The specifications of the installation may comprise the number of artificial reefs of the installation, the tpe of each artificial reef, the respective position of each artificial reef (e.g., the pattern formed) or specifications of each artificial reef (e.g., the width or height of the artificial reef or the number/density of elongated elements).The specifications of the real-world coastal, riverine or estuarine environment may comprise quantities distributed on a surface representing the real-world coastal, riverine or estuarine environment (e.g., water height, soil type and/or gradient values or swell values).

The simulation method may comprise setting the specifications of the installation, including selecting a type of artificial reef between the first type of artificial reef, or another type of artificial reef (e.g., the second type of artificial reef or the third type of artificial reef). The selection may depend on whether the real- world coastal, riverine or estuarine environment is a swell-dominated or a flow- dominated environment. For example, the simulation method may comprise selecting the first type when the real-world coastal, riverine or estuarine environment is a predominantly swell-dominated environment (or when also the real-world coastal, riverine or estuarine environment is not a predominantly high current environment). The simulation method may also comprise selecting another type of artificial reef otherwise. For example, the simulation method may also comprise selecting the second type of artificial reef when the real-world coastal, riverine or estuarine environment is a predominantly high current environment (and not a predominantly high swell environment) or selecting the third type of artificial reef or a combination of the first and second type of artificial reefs when the real- world coastal, riverine or estuarine environment is both a predominantly high swell and current environment.

The selection may depend on the effects induced by each type of artificial reef. For example, the second type of artificial reef provides a reduction of the constraint exerted by the flow close to the bottom, whereas the first type occupies a greater part (e.g., the whole) of water column, dissipating the energy of the incident waves and flows through friction and diffraction / refraction mechanisms, and horizontally offsetting the current when the artificial reef occupies the whole water column. In a predominantly high current environment, the mass of water flowing is constant. The selection may depend on whether the type of artificial reef channels these flows to preferential flow areas in such predominantly high current environment. The simulation method may thus select the second type of artificial reef in such predominantly high current environment. In cases with a high water level, the simulation method may also select the first type of artificial reef. Indeed, the first type provides strong protection needs (e.g., bank reinforcement). In a predominantly high swell environment, the energy induced by the swell is mainly concentrated near the surface. The simulation method may thus select the first type in such predominantly high swell environment. The second type also brings an interesting complement in the fight against the bottom currents. When the environment is both a predominantly high swell and current environment, the simulation method may select the third type of artificial reef, or a combination if the artificial reefs of the first and second type. Indeed, the third type of artificial reef is effective against both swell and currents. The selection may also depend on the manufacturing facilities, local skills and material availabilities. For example, the simulation method may select the third type of artificial reef when those manufacturing facilities permit, and the first and second types may be selected when those manufacturing facilities are limited.

The simulation method may also comprise setting one or more design parameters of the artificial reef (e.g., the density of the porous barrier). This allows an optimization of the performance of the installation according to the implementation context.

The simulation method is computer-implemented. This means that steps (or substantially all the steps) of the simulation method are executed by at least one computer, or any system alike. Thus, steps of the simulation method are performed by the computer, possibly fully automatically, or, semi-automatically. In examples, the triggering of at least some of the steps of the simulation method may be performed through user-computer interaction. The level of user-computer interaction required may depend on the level of automatism foreseen and put in balance with the need to implement user's wishes. In examples, this level may be user-defined and/or pre-defined. A typical example of computer-implementation of a simulation method is to perform the simulation method with a system adapted for this purpose. The system may comprise a processor coupled to a memory and a graphical user interface (GUI), the memory having recorded thereon a computer program comprising instructions for performing the simulation method. The memory may also store a database. The memory is any hardware adapted for such storage, possibly comprising several physical distinct parts (e.g., one for the program, and possibly one for the database).

FIG. 25 shows an example of the system, wherein the system is a client computer system, e.g., a workstation of a user.

The client computer of the example comprises a central processing unit (CPU) 1010 connected to an internal communication BUS 1000, a random-access memory (RAM) 1070 also connected to the BUS. The client computer is further provided with a graphical processing unit (GPU) 1110 which is associated with a video random access memory 1100 connected to the BUS. Video RAM 1100 is also known in the art as frame buffer. A mass storage device controller 1020 manages accesses to a mass memory device, such as hard drive 1030. Mass memory devices suitable for tangibly embodying computer program instructions and data include all forms of nonvolatile memory, including by way of example semiconductor memory devices, such as EPROM, EEPROM, and flash memory devices; magnetic disks such as internal hard disks and removable disks; magneto-optical disks. Any of the foregoing may be supplemented by, or incorporated in, specially designed ASICs (application-specific integrated circuits). A network adapter 1050 manages accesses to a network 1060. The client computer may also include a haptic device 1090 such as cursor control device, a keyboard, or the like. A cursor control device is used in the client computer to permit the user to selectively position a cursor at any desired location on display 1080. In addition, the cursor control device allows the user to select various commands, and input control signals. The cursor control device includes a number of signal generation devices for input control signals to system. Typically, a cursor control device may be a mouse, the button of the mouse being used to generate the signals. Alternatively or additionally, the client computer system may comprise a sensitive pad, and/or a sensitive screen. The computer program may comprise instructions executable by a computer, the instructions comprising means for causing the above system to perform the simulation method. The program may be recordable on any data storage medium, including the memory of the system. The program may for example be implemented in digital electronic circuitry, or in computer hardware, firmware, software, or in combinations of them. The program may be implemented as an apparatus, for example a product tangibly embodied in a machine-readable storage device for execution by a programmable processor. The steps of the simulation method may be performed by a programmable processor executing a program of instructions to perform functions of the simulation method by operating on input data and generating output. The processor may thus be programmable and coupled to receive data and instructions from, and to transmit data and instructions to, a data storage system, at least one input device, and at least one output device. The application program may be implemented in a high-level procedural or object-oriented programming language, or in assembly or machine language if desired. In any case, the language may be a compiled or interpreted language. The program may be a full installation program or an update program. Application of the program on the system results in any case in instructions for performing the simulation method. The computer program may alternatively be stored and executed on a server of a cloud computing environment, the server being in communication across a network with one or more clients. In such a case a processing unit executes the instructions comprised by the program, thereby causing the simulation method to be performed on the cloud computing environment.

It is also provided a method for installing the installation in a coastal, riverine or estuarine environment to prevent or reduce coastal or river bank erosion of the coastal, riverine or estuarine environment (referred to as the installing method). The coastal, riverine or estuarine environment may be a typical mangrove environment, i.e. a littoral in which the mangrove is disappearing, or a coastal or riverine area impacted by erosive processes. The installation may prevent the disappearance of the mangrove, lower sediment remobilization and help sediment deposition. The installing method comprises anchoring each artificial reef of the installation to water bottom in the coastal, riverine or estuarine environment. For example, the installing method may comprise positioning the one or more artificial reefs relative to each other to form the pattern on the water bottom (e.g., so as to form one or more lines of adjacent artificial reefs).

The coastal, riverine or estuarine environment may be a predominantly high swell environment. For example, the swell may be higher than 1 meter or more, according to the considered timeframe . Each artificial reef may be anchored at a depth between 1.5 meter and 6 meters from the surface. The distance from the shore of the artificial reef may depend on the slope of the water bottom.

When the installation comprises one or more artificial reefs comprising a pillar, the installing method may comprise, for each of the one or more artificial reefs comprising a pillar, driving the pillar of the artificial reef into the water bottom. After the driving of the pillar, the installing method may comprise passing the horizontal structural elements maintaining the elongated elements through the pillar. In examples, the method may further comprises connecting (or binding) the pillars of two or more artificial reefs of the installation. For example, the method may comprise positioning one or more links each connecting the top or bottom of two pillars. The method may comprise selecting the pillars of the two or more artificial reefs to be connected, e.g., according to local hydrodynamics and geologic constraints. The binding of the pillars helps reducing their height to reach stable conditions, which is particularly relevant for environments with thin superficial sediment layers.

The installing method may further comprise, prior to the installing, performing the simulation method for simulating the prevention or reduction of coastal or river bank erosion of the coastal, riverine or estuarine environment induced by the installation. The performing of the simulation method may set the specifications of the installation to be installed, including selecting a type of artificial reef between the first type of artificial reef and the second type of artificial reef for the installation. The selection may depend on whether the real-world coastal, riverine or estuarine environment is or respectively is not a predominantly high swell environment. The performing of the simulation method may also set other specifications of the installation. For example, the performing of the simulation method may set the number of artificial reef of the installation, the respective position of each artificial reef and/or the specifications of each artificial reef.