Artificial algae, system and method for controlling sand encroachment / erosion of a coastal site based on such algae

Abstract

The invention relates to an artificial seaweed (S) characterized in that it comprises: - an anchoring means (A) for anchoring the artificial seaweed (S) to a seabed (FM); - a flexible stem (T) configured to be folded by wave movements; - flexible lateral branches (B) forming projections around the stem (T), configured to be folded by wave movements; - a flotation means (B1) having a density lower than that of seawater, configured to maintain the stem (T) in a substantially vertical position. The invention further relates to a system and method for controlling siltation / erosion of a coastal site (S1, S2) based on several such seaweeds (S). Abstract figure: Fig. 2

Description

Title of the invention: Artificial algae, system and method for controlling sand encroachment / erosion of a coastal site based on such algae

[0001] The invention relates to the field of systems and methods for controlling the hydrodynamics of sediments, in particular for controlling the silting up of an outlet of a channel open to a sea, or of a pass of a sheltered port for example.

[0002] In this field, when a channel is made with an opening to the sea, in particular to facilitate various activities carried out around the channel (maritime traffic, users, sailing, etc.), the movements of the swell and currents generate a displacement of marine sediments, in particular sand and debris of marine fauna and flora, so that these sediments accumulate at the level of a channel passage.

[0003] Thus, we observe a problem of obstruction of the entrance of a pass which can lead, from the first heat, to severe eutrophication of the body of water.

[0004] It follows that the width available for passage is then very reduced and the draft shallow, making navigation perilous and limiting incoming and outgoing flows and causing confinement.

[0005] The problem is also observed in harbor entrances designed to facilitate the mooring of pleasure craft in particular. Boaters report cases of damage to their boats during maneuvers to leave or enter the harbor due to the shallow water depth.

[0006] One proposed solution to restore traffic is to carry out spot dredging operations of the accumulated sediments, restoring access temporarily, until the channel is obstructed again.

[0007] These dredging operations require environmental permits and mobilized significant and recurring equipment and funding.

[0008] Furthermore, the environmental and social context around ports, such as the port of Jaï, is complex: - a protective dike for a pass can generate a change in local sedimentary dynamics; - rapid sediment dynamics can fill in a few weeks the areas cleared by dredging, making the channel inoperative for recreational boaters and professional fishermen for a good part of the year; - in general, localized accumulations of rotting macrophytes occur, causing olfactory and ecological nuisances; - The failure of professional fishermen to comply with regulations, who discard the waste from their fishing into the basin, accentuates the dynamics of eutrophication of the internal basin of the site.

[0009] Thus, a first objective of the present invention is to propose a solution to mitigate the silting up of a coastal site, such as a channel entrance or a harbor entrance, for example of a marina, in particular by attenuating the energy of the swell and the currents.

[0010] A second objective is to limit the ecological impact of silting, particularly on aquatic fauna and flora.

[0011] To achieve these objectives, the invention proposes an artificial alga characterized in that it comprises - a means of anchoring to anchor the artificial algae in or on a seabed; - a flexible rod configured to follow the movement of the waves; - flexible lateral branches forming projections around the stem, having a density greater than that of seawater, and being configured to cause hydrodynamic dissipation, and to bend according to the movement of the waves; - a flotation means having a density lower than that of seawater, configured to maintain the rod in a substantially vertical position.

[0012] In the context of the invention, we can speak of "artificial algae" or "artificial sargassum" interchangeably, because the algae has a form similar to natural sargassum.

[0013] Advantageously, a plurality of such artificial algae makes it possible to significantly mitigate the silting up and / or erosion of a coastal site. In addition, the artificial algae is colonized by algae and constitutes a habitat for the development of juvenile fish and crustaceans.

[0014] Moreover, the suppleness and flexibility of the artificial algae allow for movements similar to those of natural algae and magnoliophytes.

[0015] Since the structure of the artificial algae is modular with separable elements, it allows for the replacement of individual elements in case of damage without having to dispose of the entire algae. Furthermore, the algae can be adapted to the depth of the installation site.

[0016] In addition, the implementation of artificial algae makes it possible to limit the frequency of dredging involving the use of construction machinery and heavy and often polluting equipment.

[0017] According to one embodiment, the anchoring means comprises a plate, preferably in the form of a disc, having a density greater than that of seawater, and configured to be buried in the seabed, the plate being fixed, preferably threaded onto the rod and attached thereto. The disc may be made of metal or concrete.

[0018] This allows for effective anchoring with a simplified structure. A disk in Steel at a depth of one meter can withstand 0.5 tonnes of tensile force. Another object of the invention relates to an anchoring means described in this application, for a given aquatic structure which may be algae, a net or other sediment barrier, or another structure to be anchored to the bottom of a watercourse.

[0019] According to one embodiment, the stem and / or branches are in the form of ropes. This allows for simplified production of the algae, using readily available materials. The resulting structure is very effective for controlling sand encroachment and allows for the attachment of algae and the colonization of juveniles of several species. The rope-like shape also facilitates attachment to other structures.

[0020] According to one variant, the branches extend over a stem length greater than 1 m or even 2.5 m, preferably less than 3.5 m, more preferably about 3 m. This allows for a length sufficient to obstruct the movement of sediments towards the coastal site.

[0021] According to one embodiment, the flotation device comprises a float attached to the rod. This allows for simplified manufacturing based on readily available materials. The float also improves visibility and the ability to avoid ships and other vessels.

[0022] The invention further relates to a system for controlling siltation / erosion at a coastal site, in particular for limiting siltation at a channel entrance, a section of coastline, or a harbor entrance. The control system comprises a plurality of artificial algae according to the invention, configured to be arranged in a wave field oriented towards the coastal site. In particular, the algae are arranged judiciously, taking into account the hydrodynamic conditions of the site.

[0023] According to one variant, the control system may include, depending on the site requirements, at least ten, possibly fewer than 500 (or more) artificial seaweed units; depending on the circumstances, more than 16, and possibly fewer than 300, artificial seaweed units may be considered. This significantly improves the impact on strong swells and the corresponding sediment transport. The number of artificial seaweed units is adjusted according to the coastal site, the swell, and the currents to be attenuated / dissipated. For large areas, depending on the hydrodynamics, the use of more than 500 artificial seaweed units may be considered.

[0024] According to one variant, the control system includes at least one underwater fence barrier. This improves the effectiveness of sand encroachment / erosion control in shallow seabed areas by reducing sediment transport.

[0025] According to one variant, the control system includes at least one net forming a sediment barrier. This makes it possible to limit the movement of large sediments such as shells towards the coastal site.

[0026] The invention further relates to a method for controlling siltation / erosion of a coastal site, in particular for limiting siltation of a channel entrance, a section of coastline, or a harbor entrance. The control method comprises at least a first step for deploying a plurality of artificial seaweed in a wave current directed towards the coastal site. Each artificial seaweed comprises an anchoring means; a flexible stem that bends under the effect of wave movements; flexible lateral branches that bend under the effect of wave movements; and a flotation means. The first step comprises substeps for - anchor the anchoring devices to the seabed; and - arrange the means of flotation so as to maintain the rod in a substantially vertical position.

[0027] Preferably, the control method further includes at least one step to put in place at least one underwater wattle barrier in the wave current; and / or at least one step to put in place at least one sediment screen net in the wave current.

[0028] The invention will be further detailed by describing non-limiting embodiments, and based on the accompanying figures, among which: - [Fig.1] illustrates a side view of an artificial algae module according to a preferred variant of the invention; - [Fig.2] illustrates the adaptability of artificial algae according to [Fig.1] to different depths of seabed; - [Fig.3] illustrates an arrangement of several artificial algae according to [Fig.1] with pressure sensors; - [Fig.4] illustrates an aerial view of a first site for the invention, which is a channel inlet; - [Fig.5] illustrates an aerial view of a second site for the invention, which is a harbor entrance of a marina; - [Fig. 6] illustrates a side view of a chestnut paling fence of a sand encroachment / erosion control system according to a preferred variant; and - [Fig.7] a side view of a net forming a sedimentary screen for a sand encroachment / erosion control system according to a preferred variant.

[0029] The invention relates to a system for controlling silting / erosion of a coastal site SI or S2. This is for example an entrance SI of a channel CM; or an S2 pass of a sheltered port of a marina; or another site presenting the disadvantages already discussed.

[0030] The system of the invention makes it possible to limit the silting up of said site, namely in particular the entrance of channel SI or the passage of port-abri S2 of a marina.

[0031] According to the invention, the control system comprises a plurality of artificial algae S configured to be arranged in a wave field or CV wave current. The CV wave current is oriented towards the coastal site SI, S2.

[0032] The artificial algae S each comprise a flexible stem T configured to be bent by wave movements. They further comprise lateral branches B (also called fronds B) attached along the stem T, so as to form projections around the stem T. The lateral branches B are preferably flexible in the same way as the stem T. They have a density greater than that of seawater. In addition, they are configured to be bent by wave movements.

[0033] In particular, the rod T and the branches B are in the form of ropes. These are in particular ropes used as accessories, especially in nautical activities.

[0034] The central cord forming the stem T can have a diameter of approximately 30 mm. The peripheral cord forming the branches B can have a diameter of approximately 16 mm.

[0035] Ropes such as those from Socomap and / or Technical Ship Supplies may be used.

[0036] The fronds B are attached along the stem T, for a horizontal span of approximately 80 cm (DI = 80 cm in [Fig. 1]). The fronds B can be spaced from 5 to 30 cm apart, for example.

[0037] The S algae can have a length, excluding the float, of 4 m (H = 4 m in [Fig. 1]). They can be deployed at a depth of 2 to 3 m (h = 2.5 m in [Fig. 1]). Furthermore, the S algae can be adapted to the depth of the installation site, as illustrated in [Fig. 2].

[0038] The anchoring distance can be from 60 cm to 1 m.

[0039] The artificial algae S further include an anchoring means A for anchoring the algae S in a seabed FM (or a watercourse).

[0040] Preferably, the anchoring means A comprises a platform that can have a given shape, in particular with a density greater than that of seawater, so as to sink to the seabed. Preferably, said platform is in the form of a disc, for example, a metal or concrete disc. The platform or disc is configured to be buried in the seabed and attached to the rod T. For example, one or more holes are provided for passing the rope forming the rod T or a link, which may be made of stainless steel, to secure the disc A to the rod T.

[0041] The disc is preferably anchored in the sediments via a high-pressure water jet (or “jetting” in English).

[0042] Of course, within the framework of the invention, one can consider an anchoring means of any shape, such as an anchor, resting on the seabed.

[0043] The lowest B fronds can touch the seabed FM, but they rise preferably above the seabed to limit desilting via the phenomenon of scouring, which would affect the anchoring strength of the S algae.

[0044] Indeed, studies seem to show that when the B fronds do not touch the bottom, the maximum scour calculated under most hydrodynamic conditions would be 4 cm.

[0045] The flexibility of the algae further improves their anchoring in the soil because the scour study model is based on a rigid structure. The flexible and foldable structure of the S algae probably results in less scour.

[0046] The artificial seaweed S further comprises a flotation means Bl. The flotation means Bl is configured to float on the surface of the sea SM. Furthermore, it is configured to maintain the rod T in a substantially vertical position. For this purpose, the flotation means Bl, which is preferably a buoy, is fixed, in particular attached, to the rod T in the illustrated variant.

[0047] The flotation means Bl may be a float, or other buoy, for example of the known type, with sufficient buoyancy to keep the rod T substantially vertical at the installation site. In the preferred variant, EVA (ethylene-vinyl acetate) floats with a buoyancy of 5000 g, such as those from Technorope, may be used.

[0048] The flotation means Bl can be attached to the rod T using a link L1, for example made of stainless steel. Links L1 such as those marketed by Etigo can be used.

[0049] The control system can comprise about ten S algae and up to approximately 300 artificial S algae, or even more depending on the hydrodynamic conditions of the coastal site considered. The S algae can be aligned in a geometric block, for example polygonal as illustrated in [Fig. 4]; or in a star shape with concentric alignment as illustrated in [Fig. 5]. In Figures 4 and 5, the white area represents the sea. Depending on the case, one can speak in terms of a module for a single artificial alga, or of a forest for several artificial algae, which can have different geometries (square, round, staggered, etc.) depending on the requirements and local hydrodynamics.

[0050] In the variant of [Fig. 4], the system comprises 16 algae S arranged in a square. The square is positioned so that it follows the edge of the constructed dike BD. Each structure is spaced 1 m apart and has been anchored by jetting.

[0051] In the variant of [Fig.5], the system comprises about sixty S algae.

[0052] In a variant such as that illustrated in [Fig. 5], the system further comprises at least one underwater chestnut palisade barrier G. The chestnut palisades are illustrated in detail in [Fig.6].

[0053] The S algae are preferably not implanted in excessively shallow depths. It It appears more advantageous to use a system of underwater G-shaped wattle fences to act as shock absorbers / slow-down barriers and create sediment settling chambers for transported sediments. This role will be all the more effective the more significant the epibiosis. Tests have shown that the potential is very high.

[0054] Alignments of piles, for example made of wood, are therefore used from the shore down to a bathymetric depth of 50 cm for example, but they can be placed deeper if necessary.

[0055] To avoid a possible barrier effect due to clogging by the epibiotic coating on the stakes, gaps of, for example, 50 cm are created. Observations also showed that the test area was frequented by juvenile mullet and whitefish, which are very common species in certain ponds. The G-shaped wattle fences therefore serve as support for sessile species and as habitat for young fish.

[0056] The implementation is carried out by jetting in a closed chamber with a curtain to prevent suspended matter from entering the chamber. This method is rapid, inexpensive, and reversible. The materials used are neutral and biodegradable.

[0057] Thus, in the variant illustrated in [Fig. 5], the system further comprises at least one net F which forms a sedimentary screen. The net is illustrated in detail in [Fig. 7].

[0058] The net F is designed to stop almost all of the residual sediment transport. In the preferred variant, it is positioned along the drop-off formed by the channel. Parallel to the protective dike in the variant of [Fig. 5], it acts as a counter-dike.

[0059] It can have a mesh thickness of 15 mm. For example, it is anchored at the foot of the slope of the pass, covering the drop created by the dredging and which is again anchored at the top of the slope along the entire length of the pass.

[0060] Thus, given the sediment's rich composition in mollusc shells and its highly heterogeneous grain size, the netting fully performs its role in stabilizing the slope. The 15 mm mesh is sufficient to allow water to pass through the screen, but with a significant loss of its residual energy, which is already largely attenuated by the system of successive partitions.

[0061] Net F is designed to withstand biofouling, and in particular to support, depending on the site, in addition to macrophyte algae, a significant amount of mussel capture. Its buoyancy is therefore designed accordingly to support the weight of the biofouling. A system of floats sufficient to provide 5 kg of buoyancy per meter is preferably chosen, but this can be adapted as needed.

[0062] The L2 toe anchor line may comprise a 10 mm chain, i.e., 2.25 kg / m, and embedded using jetting. The top anchor line may comprise a series of small screw anchors connected to a rope every 2 m, for a total of 16 anchors for a length of 30 meters.

[0063] The net F naturally reaches the surface and is therefore perfectly visible to users. The net F can be configured to prevent tangling in propellers, due to the mesh size and its robust, rigid construction. The net does not crease; the cut is adapted to the contours of the area, thus avoiding unwanted twists and turns.

[0064] The net F allows the channeling of the channel, the channeling of flows maintaining self-cleaning by the passage of ships, the maintenance of the slope, and the prevention of the filling of the channel.

[0065] The F net is preferably lightweight, neutral, non-polluting, modular and perfectly reversible. It can also provide a support for sessile life capable of increasing habitat diversity.

[0066] Its sheltered position at the breakwater and its very robust construction give it good durability if there are no acts of deliberate damage.

[0067] The F nets used are preferably special nets, their small mesh and the stiffness of the sheet make it impossible to accidentally snag as could happen with conventional fishing nets.

[0068] It may include aquaculture-type multifilament polyamide mats with 15 mm mesh (side) in 210 / 180 yarn (2.5 mm diameter).

[0069] The invention further relates to a method based on a system as described above.

[0070] The control method includes initial steps for deploying a plurality of artificial algae S, in particular as described above, in said wave current CV. To this end, the method includes substeps for anchoring the anchoring means A to a seabed FM. The method further includes substeps for arranging the flotation means B1 on the sea surface SM so as to maintain the rod T in a substantially vertical position.

[0071] The method further comprises second steps for installing at least one underwater fence barrier G in the wave current CV. These are in particular fences G such as those described previously.

[0072] Alternatively or in combination with the second steps, the method further comprises third steps for installing at least one net F forming a sedimentary screen in said wave current CV. This is in particular a net F as described above.

[0073] The order of the steps and substeps can be reversed, or they can be implemented substantially at the same time.

[0074] In the implementation of the invention illustrated in [Fig. 4], the results are very encouraging and conclusive with regard to the deployment objectives. Indeed, during the dif Despite frequent winter storms and heavy rainfall events typical of the Cévennes region, the structures withstood extreme hydrodynamic conditions. Only two algae are believed to have been lost during the entire testing period. It is possible that the hydrodynamic conditions exacerbated the erosion around the structures, which were subsequently torn from the seabed by the swell.

[0075] Furthermore, no problems or damage have been reported from the test port. This shows that the selected area will not impact maritime traffic and the various economic activities present.

[0076] Furthermore, the system of the invention plays an important role on local biodiversity. At each intervention carried out on site, a large number of post-larvae and juveniles of fish and crustaceans, of different species, were present.

[0077] In the implementation of the invention illustrated in [Fig. 5], the presence of algae is observed, including a limited quantity of green algae on the bottom FM, consisting mainly of sea lettuce (Ulva sp.), as well as filamentous brown algae caught in the structures. This presence of macrophytes, unavoidable even with a barrier net, is not problematic in any way since it helps to dampen hydrodynamic agitation. The artificial algae S, the wattle fences G, and the net F have also been colonized by algae.

[0078] The elements of the system generated a development of schools of juvenile fish.

[0079] Furthermore, the structures were well preserved for several months. No loss or damage was observed to the floats or the anchors.

[0080] A study based on sounding stakes shows that the soundings exhibiting progressive siltation are mostly located near the bank. The soundings placed offshore and those near the channel (before the sediment barrier F) do not show any variation in level.

[0081] It appears that the PL beach is accreting more rapidly than the rest of the area. The system leads to fairly rapid sedimentation of the transported sediment, since the level remains stable at the 'end of the journey', just before the channel.

[0082] After three years of monitoring, the following observation is made: the port entrance channel is usable; it has not silted up. The experimental project has worked; the operation is a success.

[0083] Analysis of sedimentation, using sounding stakes, reveals a specific evolution. The coastal fringe shows signs of siltation, the rest of the area is stable, or even slightly eroded.

[0084] In initial analysis, the system acted as a sufficiently effective decelerator so that the sediment-laden drift current merely passed in front of the system. It would therefore be a hydrodynamic microcell acting as a "bumper" which deflects problematic sedimentary inputs.

[0085] However, the channel did not become silted up at all.

Claims

Claims

1. Artificial seaweed (S) comprising - anchoring means (A) for anchoring the artificial seaweed (S) in or on a seabed (FM); - a flexible rod (T) configured to follow the movement of the waves; - flexible lateral branches (B) forming projections around the rod (T), having a density greater than that of seawater, and being configured to cause hydrodynamic dissipations, and to bend according to the movement of the waves; - a flotation means (Bl) having a density lower than that of seawater, characterized in that the flotation means (Bl) is configured to float on the surface of the sea (SM) and to maintain the rod (T) in a substantially vertical position.

2. Artificial algae (S) according to the preceding claim, characterized in that the anchoring means (A) comprises a plate, preferably in the form of a disc, having a density greater than that of sea water, and being configured to be buried in the seabed, the plate being fixed, preferably threaded onto the rod (T) and attached to it.

3. Artificial algae (S) according to one of the preceding claims, characterized in that the stem (T) and / or the branches (B) are in the form of ropes.

4. Artificial algae (S) according to one of the preceding claims, characterized in that the branches (B) extend over a stem length (T) greater than 1 m or even 2.5 m, preferably less than 3.5 m, more preferably approximately 3 m.

5. Artificial algae (S) according to one of the preceding claims, characterized in that the flotation means (Bl) comprises a float attached to the rod (T).

6. System for controlling silting / erosion of a coastal site (SI, S2), in particular for limiting the silting of a channel entrance (SI), a part of the coast, or a sheltered harbor pass (S2), the control system comprising a plurality of artificial algae (S) according to one of the preceding claims, configured to be arranged in a wave field (CV) oriented towards the coastal site (SI, S2).

7. Control system according to one of the preceding claims, characterized in that it further comprises - at least one underwater ridge barrier (G); and / or - at least one net forming a sedimentary screen (F).

8. Method for controlling silting / erosion of a coastal site (SI, S2), in particular for limiting the silting of a channel entrance (SI), a part of the coast, or a sheltered harbor pass (S2), the control method comprising at least a first step for placing a plurality of artificial algae (S) according to one of claims 1 to 5, in a wave current (CV) oriented towards the coastal site (SI, S2), the artificial algae (S) each comprising an anchoring means (A); a flexible rod (T) foldable under the effect of wave movements; flexible lateral branches (B), foldable under the effect of wave movements; and a flotation means (B1), the first step comprising sub-steps for - anchor the anchoring means (A) in a seabed; and - arrange the flotation means (Bl) so as to maintain the rod (T) in a substantially vertical position.

9. Control method according to the preceding claim, characterized in that it further comprises at least one step for placing at least one underwater ledge barrier (G) in the wave current (CV); and / or at least one step for placing at least one net forming a sedimentary screen (F) in the wave current (CV).

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