JP7480643B2 - River levee overflow control structure - Google Patents

Description

The present invention relates to a river levee overflow control structure installed on an existing levee or a newly constructed levee.

River levees, which are earth structures, are constructed from seepage-resistant soil materials so that they do not become unstable due to rainfall or seepage by river water. In addition, their structure takes sufficient consideration of overflow and seepage, such as by ensuring a height that includes a margin above the planned high water level and a cross-sectional shape that can withstand seepage.

However, in cases where recent climate change has caused an increase in precipitation that exceeds the capacity of the facilities, or where river levees have been built on soft ground and have caused land subsidence, or where sediment has accumulated on the riverbed, causing the levees to have a relatively lower height than when they were first built, there is a risk of the river water level reaching the levees' height and spilling over into the land inside the levees, a phenomenon known as overtopping. When overtopping occurs, parts of the river levees may locally breach, causing river water containing large amounts of sediment to flow into the land inside the levees, causing severe damage to settlements and houses, and potentially having a major impact on the lives and livelihoods of residents.

In this context, various technologies for raising river levees to prevent overflowing are being developed. For example, Patent Document 1 discloses a raising structure to be installed on an existing levee. Specifically, a foundation is installed on the top of the existing levee, and a height-adjusting spacer and rubber packing are placed at a specified position on this foundation. Next, a raising concrete block is placed on top of the height-adjusting spacer and rubber packing, and the gap between the raising concrete and the foundation is filled with a binder such as mortar.

The embankment raising structure of Patent Document 1, constructed on the top of an existing embankment using the above procedure, seals the gaps between the raising concrete blocks and the foundations installed on the top of the river embankment, preventing river water from leaking through these gaps into the land inside the embankment even if the river water level rises.

JP 2018-178644 A

Generally, raising works are not carried out over the entire length of a river levee, but are often carried out only partially in areas where the levee height has decreased or near flood-prone areas where levee breaches have occurred in the past. As a result, while overflows can be prevented in the areas near where the raising works have been carried out, the raising works cause the river water level to rise during precipitation. For this reason, if there are parts of the downstream area that do not have a levee height sufficient to handle the raised river water levels, overflows will occur in this downstream area, which could ultimately lead to a levee breach.

The present invention was developed in consideration of these problems, and its main objective is to control the amount of river water flowing into the riverbank when the river water level rises, in order to prevent overflowing that could cause the river bank to break.

In order to achieve this object, the overflow control structure for a river levee of the present invention is an overflow control structure provided on a river levee, comprising a water-passing section extending from the front slope side to the back slope side of the river levee, the water-passing section being continuously arranged in the longitudinal direction of the river levee, and a blocking section for blocking the water-passing section being provided within a predetermined range in the longitudinal direction of the river levee . Also, the overflow control structure for a river levee of the present invention is an overflow control structure provided on a river levee, comprising a water-passing section extending from the front slope side to the back slope side of the river levee, the water-passing section being made of a water-permeable material, and an impermeable layer being provided below the water-permeable material.

The overflow control structure for a river levee of the present invention is characterized in that the river levee is an existing levee, and the water passage section is provided above the top of the existing levee.

The overflow control structure for a river levee of the present invention is characterized in that the river levee is a newly constructed levee, and the water passage section is provided above a height obtained by adding up the planned high water level of the newly constructed levee and the margin specified for the planned high water level.

The overflow control structure for a river levee of the present invention is characterized in that the water passage section is partially arranged in the longitudinal direction of the river levee.

The overflow control structure for a river embankment of the present invention is characterized in that the water passage section is formed from a non-perforated pipe.

The overflow control structure for a river levee of the present invention is characterized in that the water passage section is provided so that the amount of water passing through can be changed.

According to the river levee overflow control structure of the present invention, when the river water level rises, the water flow section controls the amount of river water to flow into the inside of the levee. This makes it possible to lower the river water level by the amount of water that is controlled to flow into the inside of the levee.

As a result, it is possible to reduce overflows that could cause levee breaches, and to prevent levee breaches caused by overflows, or to delay the time it takes for a levee to breach. Furthermore, by lowering the river water level, it is possible to increase the amount of rainfall that leads to a levee breach during rainfall, making it possible to strengthen river levees.

Even if river water flows into the area inside the levee, the amount of water is controlled by the water passage, so even if the river water flows down the back slope of the river levee, it is possible to prevent the phenomenon of the back slope being eroded. It is also possible to prevent river water containing a large amount of sediment from flowing into the area inside the levee all at once, making it possible to minimize damage to settlements, houses, etc.

Furthermore, by appropriately adjusting the water passage section, not only can the amount of river water flowing into the land inside the embankment be controlled, but by providing a blocking section in the desired range in the water passage section, it is also possible to control the gradual expansion of the flooded area inside the embankment, starting from an area that has little impact on the lives of residents, such as unused land.

This will help buy time even if flooding extends into urban areas, helping to give residents in urban areas time to make preparations for flooding, such as evacuating.

According to the present invention, by controlling the amount of river water flowing into the levee area due to a rise in the river water level in the water passage section, it is possible to strengthen the river levee by preventing the river levee from breaching or by delaying the time it takes for the levee to breach.

1 is a diagram showing an overflow control structure of an existing levee in an embodiment of the present invention. FIG. 1 is a diagram showing a state in which river water flows into the embankment through a water passage portion of an overflow control structure in an embodiment of the present invention. FIG. FIG. 1 is a diagram showing a case in which an overflow control structure according to an embodiment of the present invention is installed over the entire area of an existing levee. FIG. 1 is a diagram showing a case where an overflow control structure according to an embodiment of the present invention is provided in a part of an existing levee. 11 is a diagram showing a state in which a blocking portion is provided in a water passing portion in an embodiment of the present invention. FIG. FIG. 1 is a diagram showing how flooded areas occurring inside embankments are controlled in an embodiment of the present invention (part 1). FIG. 2 is a diagram showing how flooded areas occurring inside embankments are controlled in an embodiment of the present invention (part 2). 11A and 11B are diagrams showing another example of a water passage portion in an embodiment of the present invention (part 1). 13 is a diagram showing another example of the water passage portion in the embodiment of the present invention (part 2). FIG. FIG. 2 is a diagram showing an overflow control structure of a newly constructed levee in an embodiment of the present invention. FIG. 2 is a diagram showing the state in which slope protection works are installed on the back slope of a river levee in an embodiment of the present invention.

The overflow control structure for a river levee in this invention uses a water passage provided in the structure to control the amount of river water that flows into the land inside the levee when the river water level rises. The details of the overflow control structure for a river levee are described below with reference to Figures 1 to 11.

<<Overflow control structure for existing embankments>>
As shown in Figure 1 (a), the overflow control structure 10 for a river levee is provided on the top end of an existing levee 30, and comprises an embankment section 12, a top end protection section 13 provided on the top end of the embankment section 12, and a permeable layer 14 on which the embankment section 12 is layered.

The embankment 12 is an earth structure constructed by compacting suitable materials selected from those commonly used as embankment materials for river levees. The top protection section 13 is provided to prevent the top of the embankment 12 from collapsing, resulting in a width loss. Its structure can be any structure used as a top protection work for river levees, such as protection work using soil, crushed stone, or other ground materials, environmentally friendly vegetation covering work, or asphalt pavement.

The permeable layer 14 is made by spreading highly permeable ground material such as gravel or gravel-mixed soil and compacting it in layers, and functions as a water-permeable section extending from the front slope 31 to the back slope 32 above the top of the existing embankment 30. The permeable layer 14 can be, for example, a permeable mat, a drain structure such as a paper drain or a perforated pipe, a permeable layer made of ground materials such as a sand mat or gravel mat, or a permeable layer made of artificial ground materials such as waste glass or fly ash granulated material.

In Figure 1(a), such a permeable layer 14 is provided directly above the top of the existing levee 30, but its location is not limited to this. It may be formed between the top protection section 13 and the embankment section 12, or the embankment section 12 may be formed in two layers and sandwiched between them. Furthermore, as shown in Figure 1(b), the overflow control structure 10 may be composed of the permeable layer 14 and the top protection section 13 without providing the embankment section 12.

When the river water level WL rises, the overflow control structure 10 constructed as described above causes the river water W to pass through the permeable layer 14 and flow down the surface of the back slope 32, as shown in FIG. 2(a), and the flowing river water W is drained into the bank foot channel 22 via the drainage works 21. The river water W that cannot be drained by the bank foot channel 22 will continue to flow into the inside of the bank.

If an existing drainage work 21 is installed at the end of the back slope 32 of the existing levee 30, this can be used. If no existing drainage work is installed, the drainage work 21 can be installed with the appropriate filter material and cross-sectional shape, etc., designed taking into account the soil conditions of the existing levee 30 and the amount of river water W flowing down from the permeable layer 14.

As shown in FIG. 2(a), if a layer that functions as an impermeable layer, such as asphalt pavement, is not formed on the top of the existing levee 30, some of the river water W passing through the permeable layer 14 will seep into the existing levee 30. Then, this seeped river water W, together with the river water W flowing down the back slope 32, is drained into the levee foot channel 22 via the drainage works 21.

In this way, the river water W that has infiltrated into the existing levee 30 can be drained into the levee foot channel 22 via the drainage works 21. However, as shown in FIG. 2(b), if an impermeable layer 15 is provided on the underside of the permeable layer 14, the phenomenon of the river water W infiltrating into the existing levee 30 via the permeable layer 14 can be suppressed. As the impermeable layer 15, an asphalt layer, which is a material with high conformability and good workability, is preferably used, but is not limited to this. For example, a waterproof sheet may be laid, or a layer of ground material containing a large amount of fine particles such as clay or silt may be spread out.

Such a river levee overflow control structure 10 can control the amount of river water W flowing into the land inside the levee through the permeable layer 14 by the thickness of the permeable layer 14, the particle size of the ground material used in the permeable layer 14, the height position at which the permeable layer 14 is installed, etc. Therefore, as shown in Figures 2(a) and (b), when the river water level WL rises due to rainfall, for example, and exceeds the top height of the existing levee 30, the amount of river water W controlled by the permeable layer 14 will flow into the land inside the levee.

This allows the river water level WL to be lowered by the amount of water that is allowed to flow into the land inside the levee, reducing overflow that could lead to a breach, and also preventing a breach caused by overflow or delaying the time it takes to breach, thereby strengthening the existing levee 30.

Even if river water W flows into the land inside the bank, the amount of water is controlled by the permeable layer 14, so even if the river water W flows down the back slope 32 of the river bank, it is possible to prevent the phenomenon of erosion of the back slope 32. In addition, it is possible to prevent river water W containing a large amount of sediment from flowing into the land inside the bank all at once, which contributes to reducing damage to settlements and houses.

As shown in Figure 3, this type of overflow control structure 10 is constructed uniformly on the existing levee 30 from the upstream to downstream areas of the river R. In this way, when the river water level WL rises, the river water W can be dispersed and flowed into a wide area within the levee from the upstream to the downstream areas of the river R through the permeable layer 14.

This makes it possible to lower the river water level WL over the entire length of the river R and also to increase the amount of rainfall that can occur before the levee breaks, enabling the existing levee 30 to be designed to be able to handle the increased rainfall that will accompany future climate change.

When allowing river water W to flow into the area inside the bank, the thickness and permeability coefficient of the permeable layer 14 should be appropriately designed, taking into consideration both the amount of water that can be allowed to flow in and the amount of water that should be allowed to flow into the area inside the bank in order to maintain a state in which overflow that would cause a bank breach over the entire length of the river R.

Even if the river water W is allowed to flow into the land inside the levee through the permeable layer 14 in this way, the existing levee 30 may still be breached depending on the amount of precipitation. However, because the amount of river water W flowing into the land inside the levee can be controlled by the permeable layer 14, it is possible to lengthen the time until the levee is breached. This helps to ensure that residents living inside the levee have enough time to evacuate.

In addition, while Figure 3 shows an example in which the overflow control structure 10 is provided over the entire area of the existing levee 30, this is not necessarily limited to this. For example, as shown in Figure 4, the overflow control structure 10 may be provided partially in areas of the existing levee 30 where overflows have occurred in the past, areas where levee breaches have occurred, or areas where the levee height has decreased, similar to so-called height-raising work.

In general, partial embankment work can prevent overflow in the area where the embankment work was implemented, for example, when the river water level WL rises during rainfall. However, raising the river level causes the river water level WL during rainfall to rise compared to before. For this reason, if there is a part of the downstream area that cannot handle the raised river water level WL, overflow due to the embankment work occurs in that downstream area.

However, as mentioned above, the overflow control structure 10 allows the amount of river water W controlled by the permeable layer 14 to flow into the land inside the embankment, thereby lowering the river water level WL by that amount. Therefore, even if the overflow control structure 10 is installed partially in an area where overflow has occurred in the past, it is possible to avoid a situation in which the river water level WL rises due to the overflow control structure 10, causing overflow downstream.

Furthermore, as shown in Figure 3, if an overflow control structure 10 is constructed uniformly on an existing levee 30 from the upstream to downstream areas of a river R, the flooded area Fa caused by the river W inside the levee can be controlled by providing a blocking section 16 as shown in Figures 5(a) and (b) at a predetermined position in the permeable layer 14.

Specifically, as shown in FIG. 5(a), a blocking portion 16 that restricts the inflow of river water W is formed on the side of the permeable layer 14 facing the river R (the side on the front surface 31 side). The blocking portion 16 may be formed by covering the permeable layer 14 with an impermeable material such as a waterproof sheet, a concrete wall, or asphalt material.

As shown in FIG. 5(b), these blocking sections 16 are formed in a predetermined range in the longitudinal direction of the existing levee 30, and the installation range should be set in a range adjacent to the area inside the levee where it is desired to suppress the inflow of river water W. For example, in FIG. 6, the blocking sections 16 are set in a range adjacent to a utilization area E1 such as an urban area where houses, commercial facilities, etc. are densely packed.

As shown in Figure 6, this allows the river water W to flow into the inside embankment area from the portion of the permeable layer 14 where the blocking portion 16 is not provided when the river water level WL rises. This makes it possible to prevent the utilized land E1 from being included in the flooded area Fa, even if the river water W flows into the inside embankment area.

On the other hand, as shown in Figure 7, if there is unused land E2 on the inside of the bank, such as national forest or unused land, where flooding by river water W will have little impact on the lives of the residents, it is possible to actively allow the river water W to flow into this unused land E2 by using the blocking section 16. In other words, in the permeable layer 14, the blocking section 16 is not formed near the unused land E2, but is formed in other areas.

In this way, as shown in FIG. 7, when the river water level WL rises, the river water W controlled by the permeable layer 14 and the blocking section 16 gradually expands the flooded area Fa from the unused land E2. Therefore, even if the flooded area Fa extends into the utilized land E1 such as an urban area, it is possible to buy time before the river water W reaches the utilized land E1. This can help secure time for residents living in the utilized land E1 to make preparations for flooding, such as evacuation.

<<Other examples of overflow control structures>>
1 to 7, the permeable layer 14 made of a permeable material is shown as an example of the water-passing portion formed in the overflow control structure 10, but the present invention is not limited to this. As long as the structure is capable of passing river water W, the water-passing portion may be formed using, for example, a non-perforated pipe 11.

As shown in FIG. 8(a), the overflow control structure 10 is composed of a non-perforated pipe 11, an embankment 12, and a top protection section 13. The embankment 12 and the top protection section 13 have the same structure as when a permeable layer 14 is used as the water-permeable section.

The non-perforated pipe 11 is a straight pipe with open ends and no holes in the circumferential wall, and is arranged to extend in a direction intersecting the longitudinal direction of the existing embankment 30. As a result, one end is arranged on the front slope 31 side of the existing embankment 30, and the other end is arranged on the back slope 32 side of the existing embankment 30.

By arranging multiple non-perforated pipes 11 of this configuration in parallel with their peripheral walls abutting each other as shown in Figure 8 (b), a water-passing section that is continuous in the longitudinal direction of the existing embankment 30 is formed. These non-perforated pipes 11 may be formed between the top protection section 13 and the embankment section 12, or may be stacked in multiple tiers. They may also be arranged with intervals between them.

Furthermore, the cross-sectional shape of the non-perforated pipe 11 may be any shape, and its extension form may be any shape, such as bent or serpentine, so long as it functions as a water passage section extending from the front slope 31 side to the back slope 32 side of the existing embankment 30. Furthermore, any material may be used for the non-perforated pipe 11, so long as it does not cause cross-sectional deformation due to the load acting from the top protection section 13 through the embankment section 12.

As shown in Figure 8 (c), when the river water level WL rises, the overflow control structure 10 configured as above flows river water W from the non-perforated pipes 11 through the drainage works 21 and the embankment foot channel 22 into the inside of the embankment. Therefore, the amount of river water W flowing into the inside of the embankment can be appropriately adjusted and controlled by the number and diameter of the non-perforated pipes 11.

The overflow control structure 10 that uses non-perforated pipes 11 as the water passage parts can also be constructed uniformly on the existing levee 30 from the upstream to downstream areas of the river R, as shown in Figure 3, just like the case where a permeable layer 14 is used.

When non-perforated pipes 11 are used as the water passage, the number and diameter of the non-perforated pipes 11 should be appropriately designed, taking into consideration both the amount of water that can be allowed to flow into the inside of the bank and the amount of water that should be allowed to flow into the inside of the bank to maintain a state in which overflow that would cause a bank breach over the entire length of the river R.

Even if a non-perforated pipe 11 is used as the water passage section, by providing a blocking section 16 at a predetermined position, it is possible to control the flooded area Fa caused by the river W inside the embankment, as shown in Figures 6 and 7.

For example, in FIG. 9(a), one end of a non-perforated pipe 11 arranged on the front slope 31 side of an existing embankment 30 is covered with a water-impermeable material such as a waterproof sheet, a concrete wall, or asphalt material to form a blocking section 16.

In addition, in FIG. 9(b), the spacing between the non-perforated pipes 11 is changed to form a blocked section 16. Specifically, a bundle of non-perforated pipes 17 is arranged in the area where it is desired to pass the river water W, and the area of only the embankment 12 where no non-perforated pipes 11 are arranged is provided as the blocked section 16.

<<Overflow control structure for new embankment>>
1 to 9 show an example in which the overflow control structure 10 is provided on an existing levee 30, but a similarly constructed overflow control structure 10 can also be provided on a newly constructed levee 40. An example of this is shown in Figures 10(a) and 10(b).

As shown in Figure 10(a), the new embankment 40 is specified to have a minimum height equal to the sum of the planned high water level L1 and the allowance L2 specified for this planned high water level L1. Therefore, when an overflow control structure 10 is provided, the permeable layer 14 is placed above the height equal to the sum of the planned high water level L1 and the allowance L2.

For example, in FIG. 10(a), the entire area above the combined height of the planned high water level L1 and the allowance L2 is the permeable layer 14. In FIG. 10(b), a portion above the combined height of the planned high water level L1 and the allowance L2 is the permeable layer 14, and the remaining portion is the embankment portion 12. Note that although the permeable layer 14 is shown as an example of the water-permeable portion, it is also possible to use a non-perforated pipe 11.

The river levee overflow control structure 10 of the present invention is not limited to the above embodiment, and various modifications are possible without departing from the spirit of the present invention.

For example, in this embodiment, as shown in Figures 2(a)(b) and 8(c), the river water W, whose volume is controlled by the overflow control structure 10, flows down the surface of the back slope 32 of the existing levee 30. However, this is not necessarily limited to this, and as shown in Figure 11(a), a slope protection work 23 may be provided on the surface of the back slope 32.

This makes it possible to more reliably protect the back slope 32 from the erosion of river water W. The slope protection work 23 may be, for example, block laying, or any of the structures conventionally used for slope protection work, such as laying a basket mat, spraying porous concrete, or forming an impermeable membrane. In the case of a new embankment 40, such slope protection work 23 should also be installed on the back slope 42, as shown in Figure 11 (b).

In addition, in this embodiment, as shown in FIG. 5, the blocking section 16 that blocks the water passage section is provided on the front surface 31 side, but this is not necessarily limited to this, and it may be provided on the back surface 32 side. Similarly, in the case of a new embankment 40, if a blocking section 16 is provided, it may be provided on either the front surface 41 or the back surface 42.

10 Overflow control structure 11 Non-perforated pipe (water passage section)
12 Filling section 13 Top protection section 14 Permeable layer (water passing section)
15 Impermeable layer 16 Blocking portion 17 Bundle of non-perforated pipes 21 Drainage work 22 Levee foot channel 23 Slope protection work 30 Existing levee (river levee)
31 Front slope 32 Back slope 40 New embankment (river embankment)
41 Front slope 42 Back slope R River W Overflow Fa Flooded area E1 Utilized land E2 Unused land

Claims (9)

An overflow control structure provided on a river embankment,
A water passage section is provided extending from the front slope side to the back slope side of the river embankment,
The water passage portion is continuously arranged in the longitudinal direction of the river embankment,
A river levee overflow control structure, characterized in that a blocking portion for blocking the water passage portion is provided in a predetermined range in the longitudinal direction of the river levee . An overflow control structure provided on a river embankment,
A water passage section is provided extending from the front slope side to the back slope side of the river embankment,
1. A river levee overflow control structure, comprising: a water-permeable portion formed of a water-permeable material; and an impermeable layer provided below the water-permeable material . The overflow control structure for a river levee according to claim 1 or 2 ,
The river levee is an existing levee, and
A river levee overflow control structure, characterized in that the water passage portion is provided above the top end of the existing levee. The overflow control structure for a river levee according to claim 1 or 2 ,
The river levee is a new levee, and
An overflow control structure for a river levee, characterized in that the water passage section is located above the height obtained by adding up the planned high water level of the newly constructed levee and the margin specified for the planned high water level. The overflow control structure for a river levee according to claim 1 or 2 ,
13. A river embankment overflow control structure, comprising: a water passage portion configured to change the amount of water passing through the water passage portion; The overflow control structure for a river levee according to claim 1 ,
13. A river embankment overflow control structure, wherein the water passage portion is formed of a non-perforated pipe. The overflow control structure for a river levee according to claim 2 ,
A river levee overflow control structure, characterized in that the water passage sections are arranged continuously in the longitudinal direction of the river levee. The overflow control structure for a river levee according to claim 2 ,
A river levee overflow control structure, characterized in that the water passage portion is partially disposed in the longitudinal direction of the river levee. The overflow control structure for a river levee according to claim 7 ,
A river levee overflow control structure, characterized in that a blocking portion for blocking the water passage portion is provided in a predetermined range in the longitudinal direction of the river levee.

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