JP4353347B2 - Tidal flat construction method for closed waters - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for creating a tidal flat in a closed water area, and more particularly to a method for creating a tidal flat using a bottom sediment in a closed water area.
[0002]
[Prior art]
Closed water areas 1 such as inner bays surrounded by lakes and the surrounding land have been used as fishing grounds for a long time blessed with a peaceful natural environment as shown in Fig. 4, but at the same time, exchange of water with the outside It has a characteristic that the water flow is slow and mud and organic substances accumulate easily. In recent years, especially in closed waters 1 with a hinterland of inflows of organic substances and salts due to population growth and sand mud discharge due to regional development, the biological habitat environment has deteriorated, the species and population have decreased, and the amount of catch has increased. There are problems such as a decrease in
[0003]
It is thought that one cause of the deterioration of the environment of the closed water area 1 is sludge formation of mud and organic substances (hereinafter sometimes referred to as water bottom deposits) 6 accumulated on the water bottom. Moreover, when nutrient salts elute from the bottom sediment 6, it may cause the water quality of the closed water area 1 to deteriorate. For this reason, dredging of the bottom sediment of the closed water area 1 is carried out as a purification measure for the closed water area 1.
[0004]
In addition, a plan to create an artificial tidal flat on the coast of closed water 1 has been proposed in order to actively create a habitat for living organisms in closed water 1 and increase the number of species and individuals. The tidal flat formed in the intertidal zone in nature is a place for reproduction of small animals and microorganisms that are used extensively as a place of contact between water, land and air, and not only serves as a feeding area for birds, but also purifies water in closed water areas 1. Can also be expected. For example, as shown in FIG. 3, a conventional artificial tidal flat is provided with a wall body 20 that opens toward the offshore on the coast of the closed water area 1, and the mountain sand 21 and the like are placed on the offshore side of the wall body 20 with a gentle gradient. It is common to lay down and create.
[0005]
[Problems to be solved by the invention]
However, in conventional artificial tidal flats, sand is likely to flow out by waves, and the sand may be pushed up by the waves, resulting in a steep slope and a decrease in the area of the shallow part. There is a problem that it is difficult to build diverse ecosystems. In addition, since the conventional mountain sand 21 spread on the tidal flat is different from the natural material in the closed water area 1, there is also a problem that it takes time for the organisms in the closed water area 1 to settle. In order to preserve and restore the environment of the closed water area 1 by increasing the number of species and individuals, it is desired to develop an artificial tidal flat construction method that can form diverse ecosystems close to nature.
[0006]
Accordingly, an object of the present invention is to provide a method for constructing a tidal flat in a closed water area that can establish various organisms quickly and continuously.
[0007]
[Means for Solving the Problems]
Referring to the embodiment of FIG. 1, the method for constructing a tidal flat in a closed water area according to the present invention is such that a wall body 10 that opens to the land 8 side offshore within the closed water area 1 is higher than the high water level HWL from the bottom 7. Build a groove 15 in the direction from the wall 10 to the land 8 at the bottom of the water between the wall 10 and the land 8, and trap the deposit 6 in the groove 15 at the low tide in the opening 11 of the wall 10 and tidal flats 9 are loading higher than the water level LWL, regularly is shall such to construct a flats 9 over the inner entire region of the wall 10 by or expand raised flats 9 repeated cycles of dredging and loading .
Preferably, a weir body 13 for preventing outflow of the bottom sediment 7 is provided in the opening 11 of the wall body 10.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 shows an embodiment of the present invention in which an island-shaped tidal flat 9 is constructed offshore in a closed water area 1. First, a wall body 10 having, for example, an arcuate horizontal section having an opening 11 toward the land 8 side is built up from the bottom 7 of water in the closed water area 1. In order to form the tidal flat 9 in the intertidal zone, the height of the wall 10 is made higher than the high water level HWL at high tide. Preferably, the wall body 10 has a masonry structure, and a gap such as a joint where small animals inhabit around the tidal flat 9 is formed. However, the wall 10 is not limited to a masonry structure, and may be made of, for example, concrete or a material that has little influence on the living environment.
[0009]
The bottom sediment 6 between the wall 10 and the land 8 is dredged and loaded into the opening 11 of the wall 10 from the back side. When much water in the drowned bottom sediment 6 tends to collapse, as shown in FIG. 1 (B), a weir body 13 is provided in the opening 11 of the wall body 10 so as to face the wall inner surface from the water bottom. The bottom sediment 6 is embedded between the weir body 13. By constructing the weir body 13 having voids using masonry, wooden piles, rough sledges, etc., it is possible to prevent the bottom sediment 6 from flowing out while allowing water to enter and exit. Moreover, since the opening 11 of the wall body 10 faces the land 8 side, and the ingress of waves from offshore can be suppressed by the wall body 10, the loaded bottom sediment 6 is not directly hit by the waves, so the outflow is also suppressed. it can.
[0010]
The loading height of the bottom sediment 6 is set higher than the low tide level LWL, and the portion higher than the low tide level LWL is defined as a tidal flat. Preferably, as shown in the figure, the bottom sediment 6 is piled on the back side of the wall 10 higher than the high tide level HWL, and gradually from the back side to the opening 11 side between the high tide and low tide line. A descending slope is formed. Establishing diverse biological habitats such as non-flooded areas, sandy areas that are flooded, mud areas that are flooded but well drained, mud areas that are well drained, etc. it can.
[0011]
Even after dredging the bottom sediment 6 from the bottom between the wall 10 and the land 8, mud and organic substances accumulate again on the bottom of the closed water area 1 over time. The bottom sediment 6 accumulated again on the bottom between the wall 10 and the land 8 is dredged at appropriate intervals and loaded into the opening 11 of the wall 10 to raise the tidal flat and further expand the area. be able to. For example, a bottom sediment can be stacked on an existing tidal flat, or a bottom sediment can be loaded adjacent to the existing tidal flat to expand the area of the tidal flat. By repeating the dredging and loading of the bottom sediment 6, a tidal flat over the entire inner side of the wall body 10 can be created.
[0012]
Since the tidal flat according to the present invention is constructed using the bottom sediment 6 in the closed water area 1, it is expected that organisms in the closed water area 1 will settle early compared to the conventional method using mountain sand or the like. it can. In addition, since the tidal flat according to the present invention is sand mud in which the bottom sediment 6 contains a large amount of silt, living organisms that have a silt habitat that has not been established in conventional artificial tidal flats, such as sandworms, tiger crab, etc.・ Establishment of sand crabs such as rice crabs and rock crabs, fish such as mahaze using eels and mud flats, crustaceans such as prawns and crabs, and bivalves such as clams.
[0013]
Within the tidal flat, various biological habitats such as sandy parts with a lot of sand and mud parts with a lot of mud are formed naturally by the flow of water, and the establishment of various creatures can be achieved. The mud portion can be a habitat for organisms that like the silt, the sandy portion can be a habitat for clams such as clams suitable for sand, and the portion higher than the high tide water level can be a habitat for plants such as reeds. In addition, by setting the walls as masonry structures and forming gaps such as joints around the tidal flat, it is possible to expect the establishment of more diverse organisms. The crevice between masonry can be a habitat for sea crabs, sea crabs, crabs, etc., and the wall part higher than the water level at high tide can be a habitat for land crabs such as sea bream crabs and acate crabs. The masonry gap can be a habitat for fish that prefer holes such as eel. In addition, since the present invention forms a tidal flat in the wall body with the opening directed to the land side, it is possible to suppress the outflow of sand and mud due to waves, and to continuously establish various creatures close to nature.
[0015]
As shown in the embodiment of FIG. 1, enclosed the water bottom 7 of the body of water 1 bored in the direction of grooves 15 extending from the land 8 to the wall 10, wall deposits 6 of the groove 15 periodically dredged to construct a tidal 9 by repeating the cycle loading in 10 opening 11. As shown by the arrows in the figure, the surrounding bottom sediment 6 falls into the groove 15 after dredging the sediment due to waves, tides, etc., and the gentle bottom is recovered over time. For example, the groove 15 is cut every two to three years, and the bottom sediment 6 is loaded into the opening 11 of the wall body 10. According to this method, the efficiency of dredging work can be improved as compared with the method of dredging from the entire bottom of the water between the land 8 and the wall 10. For example, when the length of the groove 15 in the direction from the land 8 toward the wall 10 is 50 m, the width of the groove 15 can be about 20 m and the depth can be about 3 m.
[0016]
2 (A) and 2 (B) show an embodiment in which the groove 15 formed in the water bottom 7 of the closed water area 1 has a terrace structure deepened in a step shape. Although the example of illustration shows the groove | channel 15 which has the three steps terrace structure 16a, 16b, 16c, the number and shape of a terrace are not limited to the example of illustration. The bottom sediment 6 that has fallen into the terrace 16a in the groove 15 due to waves, tides, etc., further falls from the deeper terrace 16b to the deepest terrace 16c due to waves, tides, etc., and is collected in the deepest terrace 16c. That is, the deepest terrace 16c having a terrace structure serves as an aggregation site for the depressed bottom sediment 6. According to the method of dredging the bottom sediment 6 from the deepest terrace 16c, the dredging work can be made more efficient than the method of dripping the entire groove 15 as shown in FIG. 2 (C), for example. .
Thus, it is possible to achieve the object of the present invention, “a method for constructing a tidal flat in a closed water area capable of quickly and continuously establishing various organisms”.
[0017]
【The invention's effect】
As described above, the method for constructing a tidal flat in a closed water area according to the present invention is to build a wall with a horizontal cross-section that opens to the land side offshore in a closed water area, higher than the water level at the time of high tide from the bottom of the water. bored the water bottom in the direction of the groove extending from the wall to the land between the land, and tidal flats are loading higher than low tide water level in the opening of the wall by dredging deposits of the groove, the dredging and stowage By periodically repeating the cycle to raise or expand the tidal flat , the tidal flat covering the entire inner side of the wall body is created.
[0018]
(B) In addition to purifying the closed water area by dredging the bottom sediment, the formation of tidal flats using the bottom sediment helps to settle various organisms in the closed water area and contribute to the improvement of the environment of the closed water area.
(B) Since a tidal flat is formed in the wall with the opening facing the land, it is possible to suppress the outflow of sand and mud due to waves and to sustain the establishment of various organisms.
(C) Since tidal flats are constructed using bottom sediments in closed waters, early settlement of organisms in closed waters can be expected.
(D) Since tidal flats are constructed using bottom sediments that contain a large amount of silt, the establishment of organisms that have silt habitat can be expected.
(E) The method of dredging from the groove formed in the bottom of the closed water area can improve the efficiency of dredging of the bottom sediment compared to the method of dredging from the entire bottom of the water bottom.
(F) It is possible to further improve the efficiency of dredging of the bottom sediment by drilling a stepped deep groove in the bottom of the closed water area.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram of an embodiment of the present invention.
FIG. 2 is an explanatory diagram of a dredging method for bottom sediment.
FIG. 3 is an explanatory view of a conventional tidal flat creation method.
FIG. 4 is an explanatory diagram of a closed water area.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Closed water area 2 ... Lake 3 ... Closed water area 4 ... Outer sea 6 ... Submarine sediment 7 ... Water bottom 8 ... Land 9 ... Artificial tidal flat
10 ... wall 11 ... opening
13 ... Weir body 15 ... Groove
16 ... terrace 20 ... wall
21 ... mountain sand

Claims (5)

A wall body that opens toward the land side offshore in a closed water area is built higher than the water level at the time of high tide from the bottom of the water, and a groove in the direction from the wall body to the land is drilled in the bottom of the water between the wall body and the land. The inside of the wall body is piled up and expanded by periodically repeating the dredging and loading cycle by dredging the deposits inside the wall and loading it into the opening of the wall higher than the water level at low tide to make a tidal flat. A method for creating a tidal flat in a closed water area. The method for creating a tidal flat in a closed water area according to claim 1, wherein a weir body for preventing the outflow of the bottom sediment is provided in the opening of the wall. 3. The method of constructing a tidal flat according to claim 1 or 2, wherein the bottom sediment is loaded into the opening of the wall body higher than a high tide level, and gradually falls toward the opening between a high tide line and a low tide line. A tidal flat construction method for closed waters formed by slopes. The tidal flat formation method in any one of Claim 1 to 3 WHEREIN: The tidal flat formation method of the closed water area which becomes the terrace structure which deepens the said groove | channel in the step shape. 5. The tidal flat creation method according to claim 1 , wherein the wall body is a masonry structure.

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