JPS62202104A - Fence for regulating tide current - Google Patents

Abstract

PURPOSE:To permit tidal current of slow flow rate to pass as it is but the current of fast flow rate to pass at delayed flow rates by using a fence having holes of a given opening degree which is to be fixed to the seabed. CONSTITUTION:In case where the size and shape of holes are fixed, the resistance of a perforated fence 1 is reduced when the flow rate of tidal current is slow, where the flow rate of the current passing through the fence 1 is not decelerated. When the flow rate of tidal current passing through the fence 1 is so fast as to move sand, grains, the resistance of the fence 1 is greater, where the flow rate of tidal current passing through the fence 1 is greatly reduced. The resistance of the fence 1 is determined by the opening degree of the fence 1, or an opening degree of 20-95% gives rise to remarkable effects. Therefore, scouring occurs beneath the fence 1 to form sedimented areas on the front and back sides of the fence 1, and the emvironments suitable for sources of living things can thus be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a fence for regulating ocean currents suitable for protecting and breeding organisms living in the sea and river banks.

Conventional technology As shown in Figure 5, a typical conventional sand flow prevention construction method is to build a submerged embankment or detached embankment made of stone or concrete blocks piled up in a ladder-like cross-section on the oil side of the shoreline. It was a common practice to surrender the sea surface on the pressure side of the ocean and try to establish sand grains and biological resources.

Problems to be solved by the invention Sand grains in sandy areas such as coasts and rivers move under the influence of waves and currents, and the young of plants and animals that live in sandy areas move as well. He was launched into the air and died. The objective is to provide an inexpensive alternative to conventional construction methods that prevents the movement of sand grains and prevents the dissipation of biological resources. In other words, the conventional construction method is very expensive, and by completely blocking waves from offshore, it also prevents the arrival of useful biological seeds and feed brought by wave currents, which has negative effects. There is also. Furthermore, if the hinterland of the levee becomes filled with sand and mud, the levee becomes useless and loses its purpose.

Means for Solving the Problems The present invention is a perforated fence that is fixed to the seabed, and is a fence for regulating ocean currents, characterized in that the fence has an open area ratio of 20 to 95%.

The perforated fence according to the present invention utilizes resistance to ocean current flow, and as shown in Figure 1, the flow that enters the fence at a speed of V+ generates a vortex when it passes through the grid of the fence, dissipating the energy of the flow. lost, the flow velocity decreases and v2
Next, leave the fence. At this time, if the flow is continuous, vortices will also be generated continuously, and the situation that was initially shown in Figure 4 (a) will be washed away directly under the fence, as shown in Figure 4 (b). Deposition areas are formed on the front and rear sides of the area. As a result, the inside of this sedimentary area and the area behind the fence become a zone where sand grains do not move, leading to the favorable result that the biological resources existing here are not moved by waves or currents. On the other hand, if this fence were made into a flat plate rather than perforated, the resistance from currents and waves would be substantial, and the pillars shown in Figures 2 to 4 would not be able to support it, and large-scale pillars would be required. Furthermore, the degree of scour will also increase, making it difficult for biological resources to settle. The resistance of flow against the perforated fence, CI, is the Reynolds number Re
This Re corresponds to the size of ν l: Length of the object acting as resistance (m) V: Flow velocity m/see C: Kinematic viscosity coefficient of fluid 9.18X10-'rrr/sec in the case of water/seawater It is expressed as Therefore, when the hole size and hole shape are constant and the flow is slow, the resistance of the perforated fence is small and the speed of the flow passing through the perforated fence does not decrease. When this occurs, the resistance becomes large and the flow velocity that passes through the fence is significantly reduced. In other words, slow flows are allowed to pass through as they are, while fast flows are allowed to pass through slowly, a result that is very convenient for biological resources.

The resistance of this perforated fence is determined by the aperture ratio of the fence, but it has a significant effect when the aperture ratio is 20 to 95%, preferably 50 to 80%.

Here, the open area ratio refers to the ratio of the total void area to the area surrounded by the total outer edge of the fence viewed from one direction.

The fence of the present invention can not only be installed parallel to the shoreline, but also
It is effective even if installed at right angles. In addition, the hole in the fence is
The fence is not limited to a lattice-like fence, but may be a fence having the above-mentioned opening ratio, for example, by making countless holes in a flat plate.

The fence material is most preferably FRP, but may also be metal with a suitable anti-corrosion treatment, or for short term use wood or ordinary unreinforced plastic.

Example An example of the present invention will be explained with reference to the drawings.

FIG. 2 is a perspective view of the installed fence of the present invention, and FIG. 3 (al is a front view, and (b) is a side view.

Fence height 60cm, length 4m, lattice spacing 35f1, thickness of fence material 12 cranes, open area ratio 68.6%, pillar length 2.5 cm, on sandy soil with a slope of 1150, facing the open ocean at a depth of 5 m. m, diameter 100fl, all four were made of FRP, and six were installed in succession on the shoreline. As a result of observation 6 months after installation, as shown in Figure 4 (b), scour and accumulation were observed, the depth of the scour was approximately 50 cm, and the height of the pile of sediment was approximately 30 cm.
It was m. In addition, the recovery rate of glass beads with a diameter of 3 nm, which were sprinkled on the shore side of the fence at the same time as the fence was installed, was 65% within 10 m of the fence. still,
At the time of the survey six months later, there was no abnormality in the fence, seaweed was attached to the entire surface, the opening ratio was estimated to be about 20%, and there were many benthos attached and fish that feed on them. , a rich biological layer had appeared in the sandy soil.

[Brief explanation of drawings]

Figure 1 is a schematic diagram of an ocean current hitting a hole fence and creating a vortex. FIG. 2 is a perspective view of the installed fence of the present invention. FIG. 3(a) is a front view when the fence of the present invention is installed, and FIG. 3(b) is a side view. Fig. 4 (a) is a side view of the present invention (immediately after installation and before receiving ocean current); Fig. 4 (bl) is a side view (scour deposit after receiving ocean current); Fig. 5 is a block of stone or It is a sectional view of a submerged embankment made of concrete blocks. 1... Perforated fence, 2... Frame, 3...
Pillar, 4... Seabed land, GL... Seabed line, WL... Sea level. Patent applicant: Asahi Kasei Corporation: Figure 3 Figure 4 Figure 5

Claims (1)

[Claims] 1. A fence for regulating ocean currents, which is a fence with holes fixed to the seabed, the fence having an open area ratio of 20 to 95%.