JP6688155B2 - Landification method by coral gravel deposition, permeable structure and structure therefor - Google Patents

Description

  TECHNICAL FIELD The present invention relates to a method of depositing and coralizing coral gravel, a permeable structure and a structure therefor.

  There are about 500 remote islands that are the base of Japan's territorial waters and the exclusive economic zone (EEZ), but it is necessary to strengthen conservation and management of remote islands in order to protect water bottom resources and marine resources. In remote islands, the need for conservation and utilization of coral reefs is recognized, as coral reefs surround the islands. For example, Patent Documents 1 and 2 relocate coral reefs, Patent Documents 3 and 4 multiply coral reefs, Patent Document 5 grows and protects corals, Patent Document 6 prevents scattering of coral gravel fragments, and Patent Document 7 corals. We propose technologies such as the construction of a growing structure. Patent Document 8 proposes an annular levee structure that is composed of a seawater impermeable part and a seawater permeable part and stands up from the sea floor in order to naturally accumulate coral gravel and the like.

JP 2011-125293 JP JP 2006-158218 JP JP 2008-141979 JP 2011-125347 JP JP 2014-212704 JP JP 2014-212702 JP JP 2013-165693 JP JP-A-2015-45159

  In the vicinity of remote islands where coral reefs are predominant, dead coral becomes gravel, and there are places where coral gravel forms an island and becomes land due to air-sea conditions. In addition, at the points where coastal erosion is predominant, breakwaters made of stone or blocks may be constructed for the purpose of coastal conservation, but the sandy beach behind the breakwaters may be recovered. , The area around the breakwater is often scoured. In addition, the conservation of remote islands is not limited to the current management of the island, but in addition to the conservation of the surrounding land where coral gravel has accumulated up to the surface of the water, if a new land can be formed using coral gravel, It can contribute to national land conservation.

  Although a plurality of techniques regarding coral have been proposed as in Patent Documents 1 to 7, it is not a suggestion regarding a technique for landing using coral gravel. That is, although Patent Documents 1 to 5 aim to relocate, proliferate, and protect living corals, corals live only under the surface of the water, and it is difficult to make them land by these methods. Further, the method of Patent Document 6 merely prevents the scattering of coral gravel accumulated on the bottom of the water, and the accumulation effect due to this cannot be expected. Further, the structure / method of Patent Document 7 provides a coral cultivating body by storing the coral limestone in a cage which is mesh-like and whose entire surface is substantially closed, and does not promote deposition. In addition, although the ring-shaped dam body structure of Patent Document 8 is a land landing technique, it is necessary to install concrete blocks, crushed stones, artificial foundations, and the like, and thus large-scale work is required. Furthermore, in the natural world, coral gravel may be turned into land, but there is no technique for forming land by a simple method using coral gravel at the intended place.

  Therefore, the present inventors and others have previously proposed, in Japanese Patent Application No. 2015-195733, a method of depositing coral gravel and converting it to land. According to this method for landification by coral gravel deposition, as shown in FIG. 4, a permeable structure 100 having a plurality of openings 13 capable of capturing the coral gravel 1 is installed in a direction in which a water mass can pass, and the permeable structure is formed. The coral gravel is deposited by allowing water to pass through the openings 13 of the 10 to capture the coral gravel 1. According to this land-based method of coral gravel deposition, coral gravel is promoted to be deposited on the front surface (upstream side) of the permeable structure, but during the overtopping period, coral gravel is formed on the back surface (downstream side) of the permeable structure. It may also facilitate deposition.

However, further studies and studies by the present inventors have revealed that the morphology and shape of the deposition of the permeable structure have the following problems.
(1) When the permeable structure is installed vertically, if coral gravel accumulated on the front surface (upstream side) of the permeable structure is rolled up during overtopping, it is easy to cross the top of the permeable structure and Will be deposited on the downstream side). As described above, since the source of coral gravel deposited on the back surface of the permeable structure is the coral gravel deposited on the front surface, the gravel deposition on the front surface becomes inefficient.
(2) At the time of wave overtopping, the flow velocity is relatively high on the back side of the permeable structure, which causes the coral gravel deposit shape on the back side to be wider and lower than the front side. Seen to be inefficient.

  The present invention, in view of the problems of the prior art as described above, a landing method by coral gravel deposition for efficiently depositing coral gravel on the front surface of a permeable structure installed for coral gravel trapping, and therefore It is an object of the present invention to provide a transparent structure and a structure.

  The landing method by coral gravel deposition to achieve the above object is a method of landing by coral gravel deposition, in which a water mass can pass through a permeable structure having a plurality of openings capable of capturing coral gravel. The coral gravel is deposited by arranging the coral gravel in the vertical direction and by sloping with respect to the vertical direction, passing the water mass through the opening of the permeable structure, and capturing the coral gravel.

  According to this land-based method of coral gravel deposition, the permeable structure allows water lumps that move due to waves or tidal currents to pass therethrough, while capturing coral gravel that moves with the movement of the water lumps. The trapped coral gravel accumulates on the front surface (upstream side) of the permeable structure, but when a water mass (wave) that overwhelms the permeable structure comes, the permeable structure is vertically oriented. The slope prevents the coral gravel accumulated on the front surface from moving to the back surface, which improves the stability of the coral gravel accumulated on the front surface of the permeable structure and improves the coral gravel on the front surface of the permeable structure. Gravel can be deposited efficiently. Moreover, by inclining the transparent structure with respect to the vertical direction, it is possible to improve the stability of the transparent structure itself against waves.

  In the above-mentioned land-based method by coral gravel deposition, it is preferable that the permeable structure includes a planar trapping portion having the opening, and the trapping portion is inclined toward an upstream side in a moving direction of the water mass. . This allows coral gravel to be efficiently captured and deposited on the front surface of the permeable structure.

  Further, by providing an eaves portion projecting upstream in the moving direction of the water mass on the top end side of the permeable structure, the coral gravel accumulated on the front surface of the permeable structure is further suppressed from moving to the back surface. can do.

  Incidentally, the coral gravel existing around the planned installation position of the permeable structure is sampled, the longitudinal dimension and the lateral dimension of the collected coral gravel are measured, and the average dimension is obtained from the measurement result. It is preferable to calculate and set the size of the opening based on the average size. It is possible to obtain an average size that is close to the actual coral gravel, and it is possible to capture the coral gravel more efficiently. Further, it is preferable that the size of the opening is set to be equal to or smaller than the average length and longer than the short length.

  The permeable structure for achieving the above object is a permeable structure for accumulating coral gravel and landing it, having a plurality of openings capable of capturing coral gravel and allowing passage of water mass. Is installed in a vertical direction and inclined with respect to the vertical direction to allow the water mass to pass through the opening and capture the coral gravel.

  According to this permeable structure, a water mass that moves due to waves or tidal currents can be transmitted, while coral gravel that moves as the water mass moves can be captured. The trapped coral gravel accumulates on the front surface (upstream side) of the permeable structure, but when a water mass (wave) that overwhelms the permeable structure comes, the permeable structure is vertically oriented. The slope prevents the coral gravel accumulated on the front surface from moving to the back surface, which improves the stability of the coral gravel accumulated on the front surface of the permeable structure and improves the coral gravel on the front surface of the permeable structure. Gravel can be deposited efficiently. Moreover, by inclining the transparent structure with respect to the vertical direction, it is possible to improve the stability of the transparent structure itself against waves.

  It is preferable that the permeable structure includes a planar trapping portion having the opening, and the trapping portion is inclined toward an upstream side in a moving direction of the water mass. This allows coral gravel to be efficiently captured and deposited on the front surface of the permeable structure.

  Further, by having an eaves portion on the upper end side of the permeable structure that projects upstream in the moving direction of the water mass, it is possible to further suppress the movement of the coral gravel accumulated on the front surface of the permeable structure to the back surface. can do.

  A structure for achieving the above object is a structure for depositing coral gravel and landing it, and includes a plurality of the above-mentioned permeable structures.

  According to this structure, by installing a plurality of permeable structures, it is possible to expect landification due to the accumulation of coral gravel in a wider range.

  A first structure as the above structure is a structure for accumulating coral gravel and landing, and includes a plurality of the above-mentioned permeable structures, and the plurality of permeable structures are arranged in a row in a lateral direction. It was installed side by side. According to this structure, it can be expected that landification will occur due to the accumulation of coral gravel in a wider range.

  Similarly, the second structure is a structure for depositing and coralizing coral gravel, and includes a plurality of the permeable structures described above, and the plurality of permeable structures are separated from each other in the moving direction of the water mass. It was installed. According to this structure, when the permeable structure is installed alone or in a plurality of rows, if the movement direction of the water body is uniform, the deposition is promoted, but the movement of the water body becomes the opposite direction depending on the period. In this case, it is expected that the accumulated coral gravel will be destroyed. Therefore, by installing multiple permeable structures away from each other in the movement direction of the water mass, even if the movement of the water mass is in the opposite direction, the coral gravel can be captured in the space between the permeable structures. It will be possible.

  Similarly, the third structure is a structure for accumulating and coralizing coral gravel, and includes a plurality of the above-mentioned permeable structures, and the plurality of the permeable structures are arranged side by side in a row. Further, a plurality of the permeable structures are installed side by side in a row in the lateral direction so as to be apart from each other in the moving direction of the water mass, and the plurality of rows are installed apart from each other in the moving direction. According to this structure, it is possible to expect landfall due to the accumulation of coral gravel in a wider range, and it is possible to capture coral gravel in the space between each row even if the movement of water mass is in the opposite direction. Become.

  In the second and third structures, the permeable structures that are installed apart from each other in the moving direction have their top heights sequentially increased from the upstream side to the downstream side in the moving direction. It is preferable to be configured as follows. Even if the water mass moves in the opposite direction, the permeability is reduced by decreasing the crown height on the upstream side of the water mass moving direction and increasing the crown height on the downstream side of the moving direction. The capture of coral gravel in the space between the structures becomes more efficient.

  Similarly, the fourth structure is a structure for accumulating coral gravel and landing, and is provided with a plurality of the permeable structures described above, and the plurality of permeable structures are installed so as to surround one region. Further, the plurality of permeable structures are installed so as to surround the plurality of permeable structures surrounding the one region. Examples of planar installation shapes of such structures include concentric circles, squares, rectangles, polygons, and oval shapes.

  In the fourth structure, it is preferable that the permeable structures are configured such that the top heights of the permeable structures gradually decrease from the inner side of the one region toward the outer side.

  In each of the above structures, it is preferable that the permeable structure is fixed to the water bottom so as not to move.

  According to the present invention, a landing method by coral gravel deposition for efficiently depositing coral gravel on the front surface of a permeable structure installed for coral gravel capture, a permeable structure and a structure therefor are provided. can do.

It is a perspective view showing the basic composition of the permeable structure by a 1st embodiment. 1 is a side view of the permeable structure 10 of FIG. 1 installed on the water floor, schematically showing the processes (a) to (d) in which coral gravel is trapped and deposited. It is a side view which shows the transparent structure by 2nd Embodiment roughly. It is a perspective view which shows the basic composition of the permeable structure in a prior application (Japanese Patent Application No. 2015-195733). It is a principal part top view (a) (b) which shows the modification of the capture part 12 of FIG.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings.

[First Embodiment]
FIG. 1 is a perspective view showing the basic structure of a transparent structure according to the first embodiment. Note that, in FIG. 1 and the like, the openings and the coral gravel are exaggerated for convenience of description.

  As shown in FIG. 1, the permeable structure 10 according to the present embodiment includes a bottom plate portion 11 and a capturing portion 12 provided on the bottom plate portion 11. The capturing portion 12 is configured in a flat shape or a flat shape, and has a large number of openings 13 formed in the flat surface. As shown in FIG. 1, the capturing portion 12 is inclined by an inclination angle θ with respect to a virtual vertical plane V (shown by a broken line) that is virtually formed so as to spread in the vertical direction.

  The size of the opening 13 is equal to or less than the longitudinal dimension of the typical dimension of the coral gravel and equal to or more than the lateral dimension thereof. Thereby, the coral gravel can be efficiently captured while passing the water mass through the large number of openings 13 provided in the capturing unit 12. Here, the representative dimension is an average longitudinal direction calculated by statistical processing by collecting the coral gravel existing around the planned installation position of the permeable structure 10 and measuring the dimensions in the longitudinal direction and the lateral direction. And the length in the lateral direction. Note that, for example, the size of the opening may be set based on past data regarding the size of coral gravel.

  The capturing unit 12 can be formed of, for example, a flat plate-shaped mesh member, and the multiple openings 13 are formed of the mesh of the mesh member, and the size of the opening 13 corresponds to the mesh size of the mesh member. In the above example, the mesh size is selected such that the average size of the coral gravel is equal to or smaller than the longitudinal size and equal to or larger than the lateral size.

  In the permeable structure 10 of FIG. 1, a bottom plate portion 11 is installed on a water bottom G, and a flat or flat trap portion 12 having a large number of openings 13 is provided in a direction opposite to a moving direction x of a water body from a virtual vertical plane V. It is configured to stand at an inclination angle θ toward ax. The capturing unit 12 is positioned so that the virtual vertical plane V is orthogonal to the moving direction x of a water body such as a wave or tidal current. That is, the permeable structure 10 is installed so that the trapping section 12 is orthogonal to the moving direction x of the water mass when the slanting trapping section 12 is viewed from above. Further, the permeable structure 10 is fixed to the water bottom G by a fixing means (not shown) such as an anchor at the bottom plate portion 11 so as not to move. It should be noted that instead of such fixing means, gravity type fixing in which the bottom plate portion 11 is fixed by gravity may be used.

  Further, the inclination angle θ of the capturing portion 12 of the permeable structure 10 shown in FIG. 1 from the vertical plane V is preferably more than 0 degrees and 45 degrees or less.

  Next, the function and effect of the permeable structure 10 of FIG. 1 will be described with reference to FIG. FIG. 2 is a side view of the permeable structure 10 of FIG. 1 installed at the bottom of the water, and schematically shows processes (a) to (d) in which coral gravel is captured and accumulated.

  As shown in FIG. 2A, a water mass moving due to waves or tidal currents flows in the moving direction x so as to be substantially orthogonal to the trapping portion 12 of the permeable structure 10 (when viewed from the top), and a large number of openings are formed. 13 is transmitted. The coral gravel 1 that has moved in the water along with the movement of the water mass is captured by the multiple openings 13, and the captured coral gravel 1 is the front surface (upstream side) of the permeable structure 10 as shown in FIG. 2A. At the right side of the figure, the bottom plate 11 and its surroundings start to be deposited.

  Due to the permeability of the accumulated coral gravel, the water mass continues to act on the large number of openings 13 until a certain amount of accumulated thickness is reached, and subsequently the coral gravel 1 moves with the water mass and is trapped and accumulated on the large number of openings 13. Then, as shown in FIG. 2B, the accumulated thickness of the coral gravel 1 increases, and the accumulated coral gravel 1 becomes the coral gravel deposit 2.

  When the coral gravel deposit 2 has a certain thickness, the permeability of the coral gravel deposit 2 is lowered to form a new ground of the bottom of the water, and the height of the flowing water mass is higher than that of the upper surface of the coral gravel deposit 2. As a result, as shown in FIG. 2C, the coral gravel 1 is sequentially deposited at a higher position, and the upper surface of the coral gravel deposit 2 rises. As shown in FIG. 2C, even if a wave that overwhelms the permeable structure 10 comes in and the deposited coral gravel 1a is rolled up, the capturing part 12 of the permeable structure 10 moves in the moving direction of the water mass. Since it is inclined from the vertical plane V on the upstream side of x, it is difficult to cross the top end of the permeable structure 10. As a result, the coral gravel 1 deposited on the front surface (upstream side) of the permeable structure 10 is suppressed from moving to the back surface (downstream side) (left side in the drawing). Therefore, the coral gravel 1 is efficiently deposited on the front surface side of the permeable structure.

  As shown in FIGS. 2C and 2D, as the accumulation of coral gravel 1 progresses, the upper surface of the coral gravel deposit 2 gradually rises, and the lower portion of the coral gravel deposit 2 becomes wider and the upper portion becomes narrower. A foreshore slope is formed, so that the moving direction of the water mass gradually changes to the obliquely upward direction x ′. As shown in FIG. 2D, when the top end of the permeable structure 10 is located higher than the surface of the water, the coral gravel 1 is washed up and deposited on the surface of the water, resulting in coral gravel deposition. The upper surface of the object 2 comes to be exposed from the water surface.

  As shown in FIGS. 2A to 2D, the movement of the coral gravel 1 from the front surface to the back surface of the permeable structure 10 cannot be completely suppressed, and a slight movement at the time of overtopping can be avoided. However, the coral gravel 1 deposited on the front surface slightly moves to the back surface, but the movement of the coral gravel is suppressed compared to the case where the permeable structure stands vertically, and the deposition of coral gravel 1 on the front surface is more efficient. Is done in a regular manner.

  In the case of a vertical permeable structure, coral gravel accumulated on the front surface of the permeable structure is easily moved to the back surface of the permeable structure during overtopping, whereas according to the present embodiment, By inclining, the effect of suppressing the movement of the coral gravel can be expected, and the stability of the coral gravel deposited on the front surface of the permeable structure can be improved. In addition, the inclination can be expected to improve the stability of the transparent structure itself against waves.

  As described above, in the area where the permeable structure 10 is installed, the coral gravel 1 that moves in the water together with the water mass is captured and efficiently deposited on the front surface (upstream side) of the permeable structure 10 by land. Can be efficiently realized. That is, only by installing the permeable structure 10, the natural external force is utilized to promote the landing by the coral gravel 1 and the conservation of the remote island is achieved.

[Second Embodiment]
Next, a second embodiment of the transparent structure will be described with reference to FIG. FIG. 3 is a side view showing the basic structure of the transparent structure according to the second embodiment. As shown in FIG. 3, in addition to the configuration of FIG. 1, the permeable structure 20 is provided at the top end of the capturing unit 12 that is inclined at an inclination angle θ from the vertical plane V on the upstream side in the moving direction x of the water mass. The eaves portion 15 is provided. The eaves portion 15 has an opening 13 (FIG. 1) like the capturing portion 12.

  It is desirable that the length L of the eaves portion 15 is equal to or longer than the average length of the coral gravel in the longitudinal direction measured as described above and equal to or smaller than the water depth H at the time of high tide at the installation position. Further, the eaves portion 15 extends in the horizontal direction on the upstream side in the moving direction x of the water mass, but it may be inclined vertically from the horizontal direction, and is preferably within ± 45 ° with respect to the horizontal direction. .

  According to the permeable structure 20 of FIG. 3, the capturing part 12 is inclined from the vertical plane V at an inclination angle θ to the upstream side in the moving direction x of the water mass, and at the top end thereof in the moving direction x of the water mass. Since the eaves portion 15 that extends in the horizontal direction is provided on the side, even if the coral gravel accumulated on the front surface (upstream side) of the permeable structure 20 is rolled up at the time of overtopping, it is more difficult to exceed the top end of the permeable structure 20. Become. Therefore, the coral gravel accumulated on the front surface (upstream side) of the permeable structure 20 is further suppressed from moving to the back surface (downstream side). Therefore, coral gravel can be efficiently deposited on the front surface side of the permeable structure.

  In addition, although the permeable structures 10 and 20 according to the present embodiment may be independently installed on the water bottom, the present invention is not limited to this, and a plurality of permeable structures may be installed, so that the coral gravel is more efficiently provided. It can be landed by deposition. For example, a plurality of transparent structures may be installed in a line in the vertical direction, or may be installed in a row or in a row in the horizontal direction.

  Further, the permeable structure may have a configuration in which the bottom plate portion 11 of FIG. 1 is omitted and a supporting member is provided so as to project orthogonally to the capturing portion 12 at the lower ends of both ends of the capturing portion 12. Alternatively, the bottom plate portion 11 of FIG. 1 may be omitted, and vertical piles may be driven on the water bottom on both sides of the capturing portion, and the capturing portion 12 may be fixed to and supported by the vertical piles at both ends thereof.

  Further, a large number of permeable structures 10 and 20 may be arranged and installed in a square shape, a concentric shape, a rectangular shape, a polygonal shape, an oval shape or the like so as to surround a predetermined area.

  Although the embodiments for carrying out the present invention have been described above, the present invention is not limited to these, and various modifications can be made within the scope of the technical idea of the present invention. For example, in FIG. 1, the capturing portion 12 having the plurality of openings 13 is configured in a flat plate shape or a flat surface shape, but the present invention is not limited to this and may be a planar shape, and as a planar capturing portion. , Not only a flat plate-shaped one or a flat one, but also a V-shaped trapping portion 12A in FIG. 5A or a corrugated trapping portion 12B in FIG. 5B. Also includes those configured in a shape.

  When the capturing part is made of, for example, a flat plate made of a steel material, expanded metal, or the like, it has a certain degree of rigidity so that it retains a substantially flat shape during service, but it may be made of a resin material or wire mesh, for example. When it is made of a flexible material in a planar shape, it may be deformed into a curved shape due to movement of a water mass during service.

  Further, the capturing unit 12 in FIG. 1 is positioned so that the virtual vertical plane V is orthogonal to the moving direction x of the water body such as a wave or a tidal current, but the present invention is not limited to this, and the water body serves as the capturing unit. It only needs to pass.

  The coral gravel in the present specification is derived from a coral reef, and in many cases, it has a shape like a tree branch or a table-like shape.

  According to the present invention, it is possible to provide a method of accumulating coral gravel for landification, a permeable structure and a structure that can be used therefor, and thus it is possible to create a new island.

1 Coral gravel 2 Coral gravel deposits 10, 20 Permeable structure 11 Bottom plate 12 Capture part 13 Opening 15 Eaves θ Angle of inclination L Length of eaves H Water depth G Water bottom V Virtual vertical plane, vertical plane x moving direction
ax reverse direction

Claims (7)

A method of depositing coral gravel and converting it to land,
A permeable structure having a plurality of openings capable of capturing coral gravel is installed in a direction in which a water mass can pass, and is installed so as to be inclined with respect to the vertical direction,
A method of landification by coral gravel deposition, which deposits the coral gravel by passing the water mass through the opening of the permeable structure and capturing the coral gravel.   The landing method by coral gravel deposition according to claim 1, wherein the permeable structure includes a planar trapping portion having the opening, and the trapping portion is inclined toward an upstream side in a moving direction of the water mass. .   The method for landification by coral gravel deposition according to claim 1 or 2, wherein an eaves portion is provided on the top end side of the permeable structure, the eaves portion projecting upstream in the moving direction of the water mass. A permeable structure for accumulating and coralizing coral gravel,
Having multiple openings that can capture coral gravel,
A permeable structure for allowing the water mass to pass through and slanting with respect to the vertical direction so as to allow the water mass to pass through the opening to capture the coral gravel. A planar trap having the opening,
The permeable structure according to claim 4, wherein the trapping portion is inclined upstream in the moving direction of the water mass.   The permeable structure according to claim 4 or 5, which has an eaves portion that protrudes toward the upstream side in the moving direction of the water mass on the top end side of the permeable structure. A structure for depositing coral gravel and converting it to land,
A structure comprising a plurality of the permeable structures according to any one of claims 4 to 6.

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