JPH07113216A - Tsunami breakwater - Google Patents

Abstract

PURPOSE:To damp tsunami energy by notching part of the upper surface of a levee body to provide an overflow opening in which tsunami is partially passed, at the same time, forming a roughness surface on the circumference thereof, and installing the levee body in the shallow sea area of a bay section. CONSTITUTION:When tsunami surges against a tsumani breakwater 10 in the direction of the arrow to raise wave height, surface current of the tsunami partially flows in an overflow opening to pass through the breakwater 10. Then, at that time, a roughness surface 21 such as a sawtooth-shape, etc., is formed at least partially on the upper surface, etc., of the opening 20, so that the overflow sea water passing on the surface 21 consumes moving energy in the case of the passing. After that, the overflow sea water falls to the surface of the water from the rear end section 10b of the breakwater 10, and energy carrying capacity is further reduced. According to the constitution, tsunami energy can be efficiently damped in the shallow sea area and, at the same time, the arrival of tsunami energy to the coastline can be greatly controlled, and large scale damage caused by tsunami coming up to the land and going back to the sea can be prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tsunami breakwater, and more particularly to a tsunami breakwater that is installed in a shallow sea area and that attenuates the energy of the tsunami to minimize coastal tsunami damage.

[0002]

2. Description of the Related Art Japan is an island nation that is located in an earthquake-prone region on a global scale and is surrounded on all sides by the sea. For this reason, in the past history, in addition to direct damage caused by earthquakes, damage caused by tsunami has been repeated in coastal areas. By the way, the tsunami causes vertical displacement of the seafloor plate due to crustal movements such as earthquakes and eruptions on the seafloor, causing a shift.
The deviation is transmitted to the seawater between the sea floor and the sea surface, and a long wavelength wave is generated on the sea surface.The wave propagates in all directions from the generation point to the land area. The wave height increases, and it goes up to the land with huge energy. This phenomenon is called "run-up," and in areas where the tsunami has run up, houses and other buildings built on low land near the coastline are overwhelmed by the force of the tsunami. At the same time as the run-up reaches the peak and the power weakens, the tsunami (seawater) that rushes pulls with tremendous force. It has been reported that many people, cars on the streets, and destroyed houses were kidnapped by the sea along with seawater at the time of this "pull", leaving nothing behind on the land after pulling. As described above, although the tsunami has a low frequency of occurrence, the damage at the time of occurrence is great. Therefore, comprehensive tsunami countermeasures have been taken to eliminate the damage caused by the tsunami.

Construction of various tsunami countermeasure facilities is underway in coastal areas where there is a risk of a tsunami. The tsunami breakwater is one of them. The tsunami breakwater was constructed at the entrance of the bay where the tsunami entered, and delayed the arrival time of the tsunami by diminishing the tsunami height and current, and changing the shape of the bay to change the natural oscillation cycle of the bay water, and It is designed so that the bay water does not resonate with the periodic component and the tsunami wave height does not increase abnormally. As a result, the height of the tsunami reaching the bay is suppressed and the run up to the land is minimized.

As an example of the construction of such a tsunami breakwater in Japan, the Ofunato Bay mouth tsunami breakwater is known, and the one currently under construction is the Kamaishi Bay mouth tsunami breakwater. The Ofunato Bay mouth tsunami breakwater that has been completed is a long breakwater of about 740 m long constructed at the mouth of the bay with a width of about 700 m and a maximum depth of about 38 m. L-1
A 6 m opening is provided. This opening has a part of the long breakwater as a submerged structure, and its purpose is to secure the shipping route of the ship at normal times and to limit the inflow of seawater into the bay at the time of the tsunami. On the other hand, the Kamaishi Bay mouth tsunami breakwater has a width of about 2100 m and a water depth of about 60 m, as shown in FIGS.
At the mouth of the bay reaching, the north dike 50 (L = 990m) and the south dike 5
1 (L = 670 m) is constructed to block the bay mouth 52. The tsunami breakwater at a water depth of -60 m has a structure in which a rubble mound 53 having a crown height of 35 m is constructed and a caisson 55 having a wave-dissipating slit 54 is installed thereon, as shown in FIG. ing.

[0005]

However, there is a problem that a huge construction cost and a long construction period are required to construct the huge tsunami breakwater as described above. Moreover, when such a huge structure is actually constructed, there is a possibility that a big change may occur in the environment such as the tide of the neighboring port and the ecosystem of the surrounding sea area. In addition, tsunamis can occur in any sea area, and the terrain of the coastline reached by tsunamis is diverse.
Therefore, a tsunami breakwater that is effective in a coastal area with a narrow bay opening, such as Ofunato Bay and Kamaishi Bay (see Fig. 7), has little effect elsewhere, or the construction of the tsunami breakwater itself There is also a drawback that you cannot do it.

Therefore, an object of the present invention is to solve the problems of the above-mentioned conventional techniques and to reduce the wave energy of the tsunami in shallow water near the coastline to effectively prevent tsunami damage. To provide.

[0007]

In order to achieve the above-mentioned object, the present invention provides an overflow opening notched at a predetermined position on the top surface of a levee body to allow a part of a tsunami to overflow, and the peripheral surface of the overflow opening. Is characterized in that a roughness surface is formed on at least a part of the ridge and the levee body is installed in a shallow sea area of a bay where there is a risk of a tsunami.

[0008]

According to the present invention, an overflow opening for notifying a part of the tsunami is provided by notching a predetermined position on the top surface of the dam body, and a roughness surface is formed on at least a part of the peripheral surface of the overflow opening. Since the levee body was installed in the shallow sea area of the bay where there is a risk of a tsunami, the wave energy of the tsunami is converted into flow energy and the turbulence is generated by passing through the specified roughness surface. The energy is attenuated so that it does not reach the land portion, or the run-up behavior can be minimized even when it reaches the land portion.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the tsunami breakwater according to the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a schematic perspective view showing an example of a tsunami breakwater according to the present invention constructed in a shallow sea area near a coastline. This tsunami breakwater 10 has a length of 20 to 4
It is a breakwater type tsunami breakwater set to about 0 m. It consists of a structure in which a reinforced concrete caisson is placed on a seabed foundation formed by laying foundation rubble (not shown), and it is almost in the center of the breakwater crown 10a. An overflow opening 20 is formed at the position. As for the overflow opening 20, the opening width (a) facing the outside of the bay is the opening width (b) inside the bay as shown in FIG.
The larger planar shape has a notch structure with a substantially trapezoidal shape. Therefore, as shown in FIG. 1, the tsunami rushes to the tsunami breakwater 10 as indicated by the arrow, and when the wave height rises, a part of the surface current flows into the overflow opening 20 and passes through the tsunami breakwater portion. At that time, a roughness (roughness) surface 21 as a water control work is formed on the top end surface of the overflow opening 20, and the overflow seawater passing on this roughness surface consumes moving energy during passage, Tsunami breakwater 10
The retained energy is further reduced by the "step down" that falls from the rear end portion 10b to the water surface.

The height of the tsunami breakwater 10 is shown in FIG. 2 (b).
As shown in, the height is set higher than the planned high tide (H.H.W.L.). Specifically, the highest tide level during the tsunami with a return period of 10 years is used. Overflow opening 20
The height of the crown is set to be approximately equal to the high tide level (H.W.L.), and the wave height at this time is set to a high wave that will occur with a probability of 50 years. Further, the average sea level (MWL) can be set to the top height of the overflow opening 20 depending on the condition of the sea area. In this way, the wave height of the tsunami changes significantly when it reaches the shallow sea area in the bay, in relation to the shape of the bay and the natural oscillation period of the bay water. It is preferable to set it based on characteristics and ocean data.

Further, the contraction rate as the flow of the tsunami flowing over the overflow opening 20 is shown in FIG. 2 (a).
The opening ratio (a / a) between the opening front end 20a and the opening rear end 20b of 0
It can be specified in b). Although the value varies depending on the roughness of the top of the overflow section, it is preferable that a / b> 2 or more. Also, the rear end opening width (b) is b from the viewpoint of overflow efficiency.
It is preferably> 1 m.

FIG. 3 shows, as a modification, a tsunami breakwater 10 in which the side surface 22 of the overflow opening 20 is finished in a stepped shape. According to this modification, the moving energy can be further attenuated as the water level of the tsunami passing over this portion changes. In addition, since it has a staircase shape, it is possible to walk on the top end portion of the tsunami breakwater 10, and it is possible to ensure work safety during maintenance work.

FIG. 4 shows the shape of the roughness surface 21 formed on the top end surface of the overflow opening 20. Same figure (a) ~
(C) shows an example of the roughness surface 21 formed on the surface of the upper concrete integrally cast on the caisson lid concrete, and FIG. 1 (a) shows the saw shown in FIG. The roughness surface 21 is formed in a wavy shape, and when seawater flowing from the direction of the arrow passes through this portion, the flow is disturbed, so that part of the energy of the tsunami is efficiently consumed. FIG. 6B shows an example in which a roughness surface 21 having a continuous trapezoidal cross section is formed as a modification. This roughness surface 21
Has an advantage that the energy damping effect is great because the formwork at the time of construction is easy and the fine step-down portions are formed continuously. FIG. 4C shows the roughness surface 21 in which the flat prismatic protrusions 24 are formed in a staggered shape in a plane, and two-dimensional turbulence is generated with respect to the flow of the tsunami flowing along the base surface. Can be made. Note that (a) to (c)
The roughness surface 21 shown in 1 may be formed by cast-in-place concrete, or the precast concrete manufactured may be brought into the site and firmly fixed on the caisson. In the same figure (d), large-sized crushed stones 25 are packed in a concrete frame body (not shown) formed on the upper surface of the caisson in a dense state, and filled concrete 26 is poured up to about half the height of the crushed stones. This is a modified example in which the void portion is solidified to form the roughness surface 21 by the exposed portion of the calculus. The roughness surface 21 made of such natural stone has an advantage of excellent durability.

Next, an example of a small fishing port to which the above-mentioned tsunami breakwater 10 is applied will be described with reference to FIGS. Fig. 5 shows an example of a tsunami breakwater 10 constructed near the entrance of a fishing port with a boat stay 30 surrounded by breakwaters. A plurality of tsunami breakwaters 10 are arranged. In this example, three tsunami breakwaters 10 are arranged at a predetermined interval in front of the tsunami so that they are almost in line with each other so that the tsunami passing through the tsunami breakwaters 10 in the first row can be received. Second tsunami breakwater 10 away from the rear position
Are arranged. At this time, the first stage tsunami breakwater 10
It is also preferable to construct the tsunami diversion dam 31 on land along the tsunami flow that is expected to prevent the flow deflected by the sideways from escaping to the side and going up to the private houses 32 and the like along the coastline. As shown in the figure, the tsunami dike 31 is constructed so as to deflect the direction of the tsunami that has run up to the land, and the tsunami that collides with the tsunami dike 31 changes its direction so that it will flow back into the sea. Returned to sea. As a result, it is possible to prevent the buildings and the like from being uprooted due to the rising and pulling of the tsunami to the ground.

FIG. 6 is a schematic plan view showing an example of a tsunami breakwater 10 having a relatively long dike length constructed in shallow water. As shown in FIG. 6, it is possible to construct the tsunami breakwater 10 that secures the route 33 to the fishing port 30 and blocks the tsunami from reaching the coastline in the bay over the entire area. In this case, the above-mentioned overflow openings 20 are formed at a predetermined interval on the top end of the tsunami breakwater 10 that is extended, and normally it is preferable to be formed at an interval of about 20 m.

Furthermore, in order to attenuate the tsunami energy after the overtopping against the tsunami that overwhelms the tsunami breakwater 10, a wave-dissipating block 35 as shown in FIGS. It is preferable. In particular, when the tsunami reaches shallow water and changes in the seabed causes it to break into waves and run into the coastline as step waves, the wave-dissipating effect is fully exerted.

[0017]

As is apparent from the above description, according to the present invention, the energy of the tsunami can be efficiently attenuated in the shallow sea area, so that the arrival at the shoreline can be significantly reduced and the landline can be greatly reduced. This has the effect of preventing damage to land areas due to run-ups and pulls.

[Brief description of drawings]

FIG. 1 is a schematic perspective view showing an embodiment of a tsunami breakwater according to the present invention.

FIG. 2 is a plan view and a sectional view showing an example of the tsunami breakwater of the present invention.

FIG. 3 is a front view and a plan view showing a modified example of an overflow opening of a tsunami breakwater.

FIG. 4 is a partially enlarged perspective view showing examples of various roughness surfaces.

FIG. 5 is a schematic plan view showing an example of installation of a tsunami breakwater.

FIG. 6 is a schematic plan layout showing an example of installation of a tsunami breakwater.

FIG. 7 is a schematic plan layout showing an example of installation of a conventional tsunami breakwater.

FIG. 8 is a schematic partial cross-sectional view showing an example of the structure of a conventional tsunami breakwater.

[Explanation of symbols]

 10 Tsunami breakwater 20 Overflow opening 21 Roughness surface

Claims (1)

[Claims] 1. An overflow opening for notifying a part of a tsunami is provided by notching a predetermined position on the top surface of the cutoff body, and a roughness surface is formed on at least a part of the peripheral surface of the overflow body. The tsunami breakwater is characterized by being installed in a shallow sea area of the bay where there is a risk of a tsunami.