JPH05195518A - Construction method for preventing beach erosion using wave absorbing structure - Google Patents

Abstract

PURPOSE:To improve wave absorbing function by installing a wave absorbing structure including therein spherical bodies having different specific gravity under the sea in floating state and fixing it to the bottom of the sea by means of a mooring cable and an anchor. CONSTITUTION:A semispherical or cylindrical frame 2 is formed from a net or a metal frame. And spherical bodies 1 having different specific gravity are put into the frame 2, in which bulk ratio of the bodies 1 is in the range of 40-70%, to form a wave absorbing structure. Further the structure is installed under the sea in floating state and fixed to the bottom of the sea by means of a mooring cable 3 and anchor 4.

Description

TECHNICAL FIELD The present invention relates to a method for preventing coastal erosion using a structure having a wave-dissipating function.

(Prior art) Methods for preventing coastal erosion include concrete jetting blocks or rocks from the seabed, such as a jetty projecting straight from the shore to the sea or a breakwater intermittently installed about 100 m away from the coast. The mainstream method is to stack rocks. Recently, an artificial reef method has been developed that stacks 1 ton or more of rocks offshore in parallel with the coastline to a depth of about 1 m from the water depth at low tide. (Problems to be solved by the invention ) However, each of the above methods for preventing coastal erosion is a method in which several tons of concrete tetrapots or rocks are piled up from the seabed, and rocks are not used in areas where there is a large tidal range and there is no quarry nearby. It can be said that it is extremely difficult to carry a car or a tetra pot, and the method is extremely limited in terms of location. In addition, if the seabed is sandy or mud geological, a large amount of foundation work is indispensable to prevent the outflow of rocks and tetrapods offshore.

(Means for Solving Problems) The method provided by the present invention is a method completely different from the conventional embankment method mainly for heavy objects such as stacking tetrapots and rocks. A floating structure with a floating structure is placed in the sea in a floating state, and fixed with mooring lines and anchors to prevent runoff and movement due to waves, so no seabed foundation work is required. In addition, this method uses the nets and metal frames that make up the wave-dissipating structure locally assembled into semi-circular, cylindrical, or cage-shaped boxes. It is possible to process with resin and other materials) and processing equipment. If these are combined, it is possible to assemble locally and even install locally.

In addition, this method can be carried out regardless of the ebb and flow of the tide, and at the time of installation, heavy machinery such as a crane ship is not required.

(Function) A semicircular or cylindrical structure composed of a metal frame and net, or various spherical bodies (diameter 15 cm to 30 cm) with a specific gravity of 0.5 to 4 in a metal cage box. If a wave-dissipating structure containing 40 to 70% of the housing is installed in the sea in a floating state, the spheres with a specific gravity of 1.5 to 2 and the spheres with a specific gravity of 3 to 4 will both float. Therefore, when receiving a wave, a floating sphere with a large specific surface area of 1.5 to 2 moves, rotates, and collides.

On the other hand, the basic principle is that a floating sphere with a specific gravity of 3-4 receives a bottom wave, is lifted, and moves and collides to convert the wave energy into the energy of a sphere. This wave-dissipating structure is installed parallel to the shoreline at a certain distance from the shore, and is installed offshore in a floating state in the sea.The wave-dissipating structure is fixed by mooring lines and anchors to prevent movement and loss. This is an erosion prevention method.

In this method, when a wave-dissipating structure installed in the sea in a floating state receives a wave coming from offshore, it is converted into the motion of a floating sphere, and the wavelength and wave height are greatly reduced. However, since 100% of the wave is not erased, part of the wave coming out of the wave-dissipating structure reaches the shore and returns to become a wave, which collides with this wave-dissipating structure again. This wave is a method of colliding with the wave that has passed through this wave and reducing the energy of the wave by the synergistic effect of mutual interference of the waves to extinguish the wave and prevent coastal erosion due to the return wave.

(Effect of the Invention) Most of the sand movement on the beach occurs underwater. It is the result of waves and streams of waves. As long as there are waves, the beach is constantly moving.

Especially, when the waves approaching the beach are small, the sand on the seabed moves toward the shore along with the trajectory of water molecules. On the other hand, when the waves are large and high, the waves carry sand away from the shore and carry it offshore.

If there is a steep shallow water such as a sandbar, the waves will break there, so the sandbar acts as a filter. In addition, the sand that is moved by the significant turbulence due to the waves has a structure that prevents the waves, and accumulates wherever the action of the waves is weakened.

The present invention is a method of preventing coastal erosion using a wave-dissipating structure devised based on such a natural phenomenon.

Spheres with different specific gravities are accommodated in a semicircular or circular structure using a net reinforced with an iron frame or a cage made of metal in the range of 40 to 70% depending on the height of waves. This wave-dissipating structure will be floated in the sea by 50 cm to 1 m above the sea floor and set up alongside the coastline. Since this whole wave-dissipating structure is floating, it is fixed by mooring lines and anchors to prevent erosion and erosion due to waves.

When waves rushing from offshore hit this coastal erosion preventive body, among the floating spheres contained in the wave-dissipating structure, the floating spheres with a large specific surface area of 1.5 to 2 rotate and move up and down, left and right, and between the spheres. It becomes a motion to collide with each other. On the other hand, a heavy sphere with a specific gravity of 3 or more receives the bottom wave of the waves and moves up. Most of the waves are converted into spherical motion of the wave-dissipating structure and its energy is reduced, but some of them are pushed toward the shore. When this wave returns to the wave-dissipating structure and returns to the wave-dissipating structure, it becomes the kinetic energy of the floating sphere again, or collides with the next wave inside and outside the structure, and both the wave and the wave return energy. Are offset.

In this way, the wave-dissipating structure attenuates large high waves from offshore by its spherical movement, but the wave-dissipating structure reduces the storage density of the storage spheres so that seawater can move freely. Therefore, the water has a space to flow freely. This structure enables the wave-dissipating structure not only to move the sphere, but also to reduce and cancel waves by collisions of waves of return waves and return waves. As a result, it is possible to prevent coastal erosion by extinguishing waves with large wavelengths and wave heights, and to apply it to the restoration of beaches that have already been eroded by waves.

[Brief description of drawings]

Figure 1 shows the overall view of coastal erosion prevention by the wave-dissipating structure of the invention. Is a sphere is an iron frame is a mooring line is an anchor Figure 2 shows the shape of a wave-dissipating structure ~ is a wave-dissipating structure that is a combination of a net and a frame. Is a sphere b. Is Netha. Is a frame

Claims (2)

[Claims] 1. A net or a metal frame is formed into a semicircular or cylindrical structure, or a cage-shaped box, in which spheres having different specific gravities are accommodated in a volume ratio of 40 to 70%, A wave-dissipating structure that has the function of converting wave energy into the kinetic energy of this sphere, and this wave-dissipating structure is installed in a floating state in the sea offshore along the sandy beach along the coastline where wave erosion is prominent. To do. The coastal erosion prevention method is fixed to mooring lines and anchors to prevent the wave-dissipating structure from flowing away due to waves. 2. The net used for the wave-dissipating structure may be made of metal, resin, or synthetic resin. The net and frame are used to make a circular or semi-circular structure or a metal cage box. The spheres housed in the body structure have a specific gravity to add buoyancy to the wave-dissipating structure.
0,5 to 0,7 hollow spheres, and those with a structure that maximizes the surface area of the sphere to have a wave-dissipating function, such as circular holes in the vertical direction and fan-shaped openings at the top and bottom In addition, the structure is such that a line is attached from one side of the fan-shaped hole toward the center, so that the specific gravity of the sphere is 1.5 to 2 and the specific gravity of 3 to 4 in order to have a wave canceling function for the bottom wave. The solid spheres are stored in the bottom of the wave-dissipating structure, and the diameters of the three spheres with different specific gravities are 15CM to 30cm, and the collection rate of each sphere is 40 to 70% depending on the strength of the waves. The method for preventing coastal erosion as described in the first paragraph, which is a wave-dissipating structure by determining within the range.