JP2005002737A - Sand depositing construction method in seashore - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem of being unable to actively cure the eroded seashore, since such a conventional technology is an erosion preventing construction method and a seashore stabilizing construction method, though a main civil engineering structure conventionally performed as a seashore sand depositing work is a jetty, an off-shore bank, and a head land control. <P>SOLUTION: A permeable structure is continuously constructed in parallel to a shoreline, and sand and pebbles floating by being carried by waves, are precipitated and deposited before and behind the structure. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a coastal sedimentation method for restoring an eroded beach.
[0002]
[Prior art]
On sandy beaches, the main civil engineering structures conventionally used as wave-dissipating structures are jetty, breakwater, headland control, etc., which prevent erosion caused by the impact of waves, During the wave extinction process, gravel may gradually accumulate over the years inside these civil structures.
[0003]
[Problems to be solved by the invention]
Therefore, such a prior art is an erosion prevention method, and the eroded beach cannot be actively restored.
[0004]
[Means for Solving the Problems]
Therefore, in the present invention, a permeable structure is constructed in parallel with the shoreline, and the floating gravel carried by the waves is sedimented before and after the structure by being provided in the surf zone. By this, when the wave that hits the shore begins to break naturally or ends and transforms into a flow, the wave energy is weakened, and the wave after breaking breaks through or passes through the structure. The eroded beaches by slowing the speed of the waves, increasing the float time of the gravel carried by the waves and allowing the gravel to settle down before and after the structure. It is something to restore.
[0005]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is an explanatory diagram, and the structure 1 of the present sand construction method is constructed as a bank-like body in parallel with the coastline of the coast to be deposited as shown in the figure. As shown in the figure, the dam-like body of the structure 1 generally has a substantially trapezoidal cross-sectional shape. However, it is not always necessary to have such a shape, and is appropriately determined according to local conditions. Is done.
[0006]
Moreover, it is good for the installation location to make it the wave condition of the incident state in which a structure exists in a wave breaking zone, and, by doing so, most of the incident waves become a wave during wave breaking or after wave breaking.
The incident angle of the wave is preferably perpendicular to the shoreline. However, although this condition is determined by the situation at the site, it is desirable that the construction should be performed so as to satisfy this condition.
[0007]
The term “continuous” as used herein refers to the construction of offshore dikes in the conventional construction method. ) Is not provided, but no opening is provided (excluding the entrance of a small boat).
) Therefore, the structure 1 is continuous in series, and as described above, even if there is an entrance / exit of a small boat, it is a concept of a continuous state.
[0008]
When such an opening is provided, although not shown, a straight line is provided on the sea side of the opening so as to face the opening at a distance that does not interfere with the entry / exit of the boat from the opening. It is advisable to install a shielding wall bent in the shape of an arc or arc so that waves do not enter the back (land side) directly from the structure 1.
[0009]
In addition, the term “parallel” refers to any shape such as when the back of the structure 1 (land side) is a natural sandy beach, a forest zone, a cliff-like coast, or a coastal dike or tide revetment. Even on the coast, in principle, it should be built in parallel with the shoreline.
However, there are many cases where the natural situation is not suitable for such a construction, and in such a case, the construction is made as close to parallel as possible within a possible range. Therefore, the present invention (including claims) including all these states is referred to as parallel.
[0010]
The construction material of the structure 1 uses a wave-dissipating atypical block in the present embodiment, but does not necessarily need to be a wave-dissipating atypical block, and is used because it is a readily available material. The other material examples may be wood, natural stone, natural rock, blocks made of clay, or the like. The wave-dissipating atypical block damages the landscape. Ideally, it should be a material that disappears over time, such as sandstone, and a material that helps improve the environment should be used.
[0011]
In addition, if a block or the like is installed directly on the sandy beach, it will cause a settlement over time. Under such circumstances, the effect cannot be exerted, so it is advisable to install an anti-sagging material such as a gabion or a futon wall on the installation ground. Ideally, it should be 1 meter or more.
[0012]
Furthermore, since the gravel is settled and deposited in the land-side inner area of the structure 1, the top height of the structure 1 must be a height that generates some overtopping and overflowing of the incident wave.
Therefore, the ceiling height is lower than that of the wave breaker and the offshore bank.
Moreover, the fact that it is a permeation bank is an element that affects the sedimentation effect. Therefore, the floor width and the cross section of the top end are designed to be smaller than the cross section of the wave breaker.
[0013]
As a result, both the action of transporting gravel when the wave after collision with the structure 1 permeates behind the structure 1 and the action of sedimentation and sedimentation after the overcast water mass is transported behind the structure 1 Sand can be used (see FIG. 2).
In addition to that, on the sea front side of the structure 1, the gravel in the seawater that passes through the gap between the structure 1 when the gravel that breaks and breaks and the seawater that has entered the back of the structure 1 is drawn. Settles and deposits are obtained (see FIG. 2). In the figure, the one-dot chain line indicates the state of the beach before erosion.
[0014]
According to experiments, the following conditions were found to be optimal conditions.
That is, when the seabed slope is 1/20 to 1/30, and the offshore wave slope is 0.025 to 0.040, the bottom of the structure 1 seems to be within 3.0 to 5.0m from the shoreline of sandy beach etc. The best results were obtained when constructed. The waveform gradient is represented by wave height / wavelength.
[0015]
The above is the optimum condition obtained experimentally. Actually, the natural condition in the field is not necessarily applicable, but as described above, a better effect can be obtained by approaching the condition.
In this way, sediment is obtained before and after the structure, but in order to obtain sediment in a wider area, as shown in FIG. By installing it, it is possible to restore and restore the foreshore by sequentially depositing sand.
[0016]
【The invention's effect】
According to the present invention described in detail above, by constructing a permeable structure that is continuous in parallel with the shoreline, the wave after breaking can be suppressed in its moving speed, and is carried by the wave and floats. The action is to deposit the gravel that has been transported when it has permeated behind the structure by increasing the floating time of the gravel, and by the action of the water mass overtopping the structure causing sedimentation of the gravel behind the structure. The effect of depositing and restoring gravel behind the continuous structure is obtained.
[0017]
Furthermore, even on the front surface of a continuous structure, it floats in the seawater when it passes through the gap between the structures when gravel floats along with breaking waves and the seawater that enters the back of the structure pulls. The gravel is settled and the sediment is obtained, and the effect of restoring is obtained.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram showing an accumulation state. FIG. 3 is an explanatory diagram of a sedimentation method for advancing a foreshore.
1 structure

Claims (4)

A coastal sedimentation method characterized in that a permeable structure is constructed in parallel to the shoreline, and sand and gravel carried by waves are settling before and after the structure. The coast according to claim 1, wherein the structure is provided in a surf zone, and the floating time of the gravel carried by the waves is increased and the gravel is sedimented before and after the structure. Sedimentation method. 2. The top height of the structure according to claim 1, wherein the top of the structure is a height that generates an overtopping or overflow of the incident wave, and the floating time of the gravel carried by the waves is increased to increase the gravel before and after the structure. Coastal sedimentation method characterized by sedimentation of sand. 2. The coastal sedimentation method according to claim 1, wherein the structure is provided so that an incident angle of the wave is close to a right angle with the shoreline.

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