JP3876997B2 - Crest artificial leaf - Google Patents

Description

The present invention relates to a crest-type artificial reef that is a conservation structure to be constructed for countermeasures in a coastal area of a sea or a lake that is affected by sandy beach erosion or storm surge damage due to waves or the like.

  As structures effective for coastal conservation facilities, especially for countermeasures against storm surges and erosion, offshore dikes and artificial reefs are conventionally used. The offshore dyke has a history since the Showa 40s, and as its results show that its beach conservation effect and storm surge prevention effect are very high. However, with the changing times, there are cases where the location of a coastal facility is adversely affected as a highly functional coastal facility is required. That is, as shown in FIG. 8, there are many cases where the height is several meters above the water surface, and there is a defect that the surrounding scenery is remarkably damaged. In addition, since it is a structure in which atypical blocks are densely packed, it is susceptible to scouring due to local flow, and block settlement and scattering often occur, leading to functional deterioration. In these situations, repair costs are continuously incurred and the advantages of relatively low initial construction costs are lost.

  Artificial reefs have been constructed since the 1960s as structures that relieve functional degradation due to settlement and scattering, without obstructing the landscape, which is a drawback of offshore dikes. However, this is a submerged structure and has the advantage of not obstructing the landscape at all. However, if a strong current flows toward the shore, it may cause problems in terms of conservation and use of the beach behind. That is, as shown in FIG. 9, the water level rise on the shore side is often promoted by the strong flow toward the shore after breaking. In addition, beach protection in the hinterland that should be brought about by wave reduction, that is, the offshore dike causes sand accumulation behind the wave reduction, but artificial reefs that generate strong water flow toward the shore are satisfactory. Sand function is not obtained.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to solve the problems of the prior art, and to provide a structure that has a low water level rise behind, has a sedimentation function, and does not hinder the landscape.

In order to solve the above-mentioned problem, the invention according to claim 1 is a conservation structure constructed for countermeasures in a coastal area of a sea or a lake that has been eroded by sand or storms due to waves or the like. It is an artificial reef, and a large number of concrete blocks are installed over a predetermined length and with a predetermined width along the coast so as to cover the rubble on the lower surface, and the crest is placed on the upper surface in the longitudinal direction of the concrete block body. The crest is formed of a tapered surface and a flat surface whose upper surface is inclined upward at a predetermined gradient from the offshore side to the shore side, and the tapered surface has a gradient with respect to the width of the crest. The height is about 1/3 and the area is larger than the flat surface, and the strong waves flowing toward the shore are broken by the tapered surface to reduce the wave .

  A second aspect of the present invention is characterized in that, in the first aspect, the crest is provided in a plurality of rows at a predetermined interval in the width direction on the upper surface in the length direction of the concrete block body. The invention described in claim 3 is characterized in that, in claim 1 or 2, the height of the crest is set so as to protrude about 0.5 m from the water surface at an average tide level.

According to a fourth aspect of the present invention, in any one of the first to third aspects, the crest is integrally formed on the upper surface of the concrete block.

The invention according to claim 5 is the invention according to any one of claims 1 to 4 , wherein the concrete block including the crest from the offshore side and the concrete block installed on the shore side from both sides of the crest are installed on the shore side from these concrete blocks. It is characterized in that it is larger than the concrete block to be made.

  Since the present invention is configured as described above, the flow velocity of the shoreward waves of the conventional artificial reef can be greatly reduced by the crest. Therefore, there is an effect of effectively preventing the erosion of the back by reducing the rise of the water level behind and having a sedimentation function. Crest also has less exposure on the surface of the water, so it does not hinder the landscape compared to the offshore bank. Furthermore, the present invention has a high wave extinction property, a small reflected wave, and a high possibility of becoming a good fish place with less subsidence. And since it can visually recognize, there exists an effect that the danger of ship navigation is also small.

  An embodiment of the present invention will be described with reference to the accompanying drawings.

  FIG. 1 is a longitudinal side view of a crest-type artificial leaf, and FIG. 2 is a plan view thereof. Reference numeral 1 denotes a crest-type artificial reef, which is installed at an offshore position at a predetermined distance from the coast along the coast where the beach is eroded or damaged by storm surges. Usually, the sea bottom is a sandy beach that is gradually inclined from the coast (land side) toward the offshore side, but on this sandy beach, a large number of rubble 2 is in the range where the artificial reef 1 is installed, over a predetermined length, And it is laid with a predetermined width. A large number of concrete blocks 3 are installed on the rubble 2 so as to cover the rubble.

  The crests 5a and 5b are arranged in a row at predetermined intervals in the width direction on the upper surface in the width direction of the concrete block body made of a large number of concrete blocks 3 in the width direction. It is provided integrally with the concrete block 3. The distance between the crests 5a and 5b is preferably about 10 m. Moreover, it is preferable that the crests 5a and 5b have their top heights set so as to protrude about 0.5 m from the water surface at an average tide level. HHWL, which shows the tide level in Fig. 1, is the highest tide level among the highest tide levels during the statistical period, HWL is the long-term average value of the high tide level at the tide (plastic desired average high tide level), and LWL is the long-term low tide level at the tide. Mean value (plastic desired mean low tide level), MWL is mean tide level, and TP is mean sea level (land surface altitude reference plane). The above-mentioned 0.5 m is obtained as the crest heights of the crests 5 a and 5 b of 0.657 m−average tide level 0.157 m.

  The crests 5a and 5b are formed of a tapered surface 6 and a flat surface 7 whose upper surfaces are inclined upward at a predetermined gradient from the offshore side to the shore side. The slope of the taper surface 6 is preferably set to 1 when the width of the crests 5a and 5b is 3 (1: 3). The tapered surface 6 is formed on the upper surfaces of the crests 5a and 5b for effective breaking. When the tapered surface is not formed, it becomes like a breakwater and it is easy to receive strong waves directly. However, if the tapered surface has the gradient as described above, it can be expected that even strong waves are reduced. The tapered surface having the above-described gradient is formed not only in the crests 5a and 5b but also in the concrete block 3 as shown in FIG.

  The concrete block 3 including the crests 5a and 5b from the offshore side and the concrete block 3 installed on the shore side from both sides of the crests 5a and 5b are formed larger than the concrete blocks installed on the shore side from these concrete blocks. Yes. This is because the offshore concrete block receives strong waves from the offshore, so we want to be able to cope with it. Therefore, since the land side protected by the crests 5a and 5b is less likely to receive strong waves, a small concrete block may be used.

  In the crest-type artificial leaf 1, the crests 5a and 5b are provided on the upper surface of the concrete block body so as to protrude from the water surface as described above, so that even if there is a strong wave flow toward the shore, the crest 5a , 5b makes it possible to break the waves and calm the shore-side flow. Therefore, there is no accumulation of sand on the back beach, and the water level rise on the shore side does not become extremely high. Moreover, although crest 5a, 5b is provided, since it protrudes very slightly from the water surface, a landscape is not inhibited.

That is, this will be explained by a hydraulic experiment based on a schematic diagram (field scale) of the experimental case shown in FIG.
(1) Examination of crest effect by hydraulic model experiment A model of a sandy beach and five offshore dikes was created in a plane test tank, and a hydraulic experiment was conducted to compare the changes of the beach behind the waves. Moving bed experiment). The experimental cases are 8 cases shown in Table 1 below and FIG. As a result of experiments, it was found that conventional artificial reefs are difficult to preserve the beach terrain behind and need to be crested, and that two crests with low crest are most effective (Fig. 4). FIG. 4 shows a comparison of the terrain change behind the artificial reef. According to this, it can be seen that in the case of two low crest rows in case B3, the soil volume change rate exceeds 1.02 and is the largest. In other words, if the soil volume at the beginning of the experiment is 1.0, the soil volume moves to somewhere in the cases A2 and A3 after the experiment and is extremely small, but the soil volume is maintained in the case B3. On the contrary, you can see that it has increased a little.

(2) Examination of crest height and interval by numerical calculation The crest height and the interval in the case of two rows were examined by numerical simulation. Waves entering from offshore are crushed and attenuated by artificial reefs. At this time, strong waves flow toward the shore and erodes the beach. Item. The calculation result is the ratio of the flow velocity when no crest (conventional artificial leaf) is set to 1, but the effect of reducing the flow velocity is small even if the crest height is 1.0 m or more above the water surface from FIG. It was found that the maximum flow velocity and the average flow velocity are balanced (ratio is 1.0 or less) when the height is about 5 m. In addition, it was found from FIG. 6 that the interval between the two rows of crests is 10 m, which is the most effective because both the maximum flow rate and the average flow rate are reduced (ratio is 1.0 or less).

(3) Examination of crest height and tide level by numerical calculation The relationship between the existence / height of crest and the tide level was examined by numerical simulation (Fig. 7). The effect of crest on the suppression of the rise of the water level behind is large, and changes in the tide level have little effect. Since there is almost no difference in the height of the crest, it was found that the low crest two-row format is advantageous. The change in tide level has an effect on the wave height transmitted to the back, but if there is a crest, the increase in transmission rate can be suppressed. Again, there was no significant difference in crest height, indicating that two lower crest rows are effective.

  In the above-described embodiment, an example in which the crest-type artificial reef 1 is installed exclusively along the coast has been shown. However, this is only an example, and the crest-type artificial reef 1 may be installed in a lake that has been eroded by sand or the like. Moreover, the shape of the crests 5a and 5b of the concrete block 3 is only a preferable example, and the present invention can be variously changed and modified when implemented within the technical scope described in the claims. .

It is a vertical side view of the crest type artificial leaf which shows one embodiment of this invention. It is a top view same as the above. It is a schematic diagram of an experiment case. It is a graph which shows the comparison of the terrain change behind an artificial leaf. It is a graph which shows the comparison of the height of a leaf crest. It is a graph which shows the comparison of the space | interval of two leaf crests. It is a graph which shows the examination result of a tide level change, the existence of crest, and height. It is the installation schematic diagram of the conventional breakwater. It is the installation schematic diagram of the conventional artificial leaf.

Explanation of symbols

1 Crest-type artificial leaf 2 Rubble 3 Concrete blocks 5a, 5b Crest

Claims (5)

An artificial reef that is a conservation structure to be constructed for countermeasures in the coastal area of the sea or lake where sandy beach erosion or storm surge damage is caused by waves, etc.
A large number of concrete blocks are installed over a predetermined length along the coast so as to cover the rubble on the lower surface, and with a predetermined width, and crests are provided on the upper surface in the length direction of the concrete block body so as to protrude from the water surface . The crest is formed of a tapered surface and a flat surface whose upper surface is inclined upward with a predetermined gradient from the offshore side toward the shore side, and the tapered surface has a height that is 1/3 of the width of the crest. A crest-type artificial reef characterized by having an area larger than that of a flat surface and reducing the wave by breaking a strong wave flowing toward the shore with a tapered surface . The crest type artificial leaf according to claim 1, wherein the crest is provided in a plurality of rows on the upper surface in the length direction of the concrete block body at a predetermined interval in the width direction. The crest-type artificial leaf according to claim 1 or 2, wherein the height of the crest is set so as to protrude about 0.5 m from the water surface at an average tide level. The crest type artificial leaf according to any one of claims 1 to 3 , wherein the crest is integrally formed on an upper surface of the concrete block. Concrete block installed on shore side from offshore from both sides of the concrete blocks and crest containing crest, according to any one of claims 1 to 4 from these concrete block is large than concrete block installed on the shore side Crest type artificial leaf .

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