JP7022630B2 - Driftwood capture facility - Google Patents

Description

Application of Article 30, Paragraph 2 of the Patent Act (1) JSCE Proceedings B1 (Hydraulic Engineering) Vol. 74, No. 4, 2018 Hydraulic Engineering Papers Vol. 62 (2) The 62nd Hydraulic Engineering Lecture held on March 6, 2018

The present invention relates to a facility for capturing driftwood that flows down together with a debris flow, a debris flow, etc. (hereinafter referred to as "debris flow, etc."). Regarding the driftwood capture facility.

In the heavy rains in northern Kyushu in 2017, which caused enormous damage to houses, roads, railroads, bridges, etc., a large amount of driftwood occurred, leading to the spread of damage.
Generally, a sabo dam (sabo dam) is used as a debris flow countermeasure.
As sabo dams, opaque sabo dams with a water passage at the top of the dam and sabo dams with a highly rigid screen provided at the water passage to improve the ability to capture drifting trees and large gravel are also known. (Patent Documents 1 to 3). The mainstream of the screen is a steel pipe frame structure assembled in the shape of a girder, and it is firmly fixed to the dam frame.
Further, it is disclosed in Patent Document 4 that a separate screen is retrofitted to the upstream side of the water passage portion for the existing sabo dam, and two sabo dams (main bank and sub-bank) are further provided along the flow direction. Patent Document 5 discloses that the arrangement is arranged in columns.

Jikkai Sho 51-558536 Japanese Unexamined Patent Publication No. 2004-60388 Japanese Unexamined Patent Publication No. 2007-277792 JP-A-2017-101507 Japanese Unexamined Patent Publication No. 2009-243196

Conventional sabo dams have the following problems.
<1> Driftwood that flows down with debris flow shows complicated behavior due to various external factors, so the behavior of driftwood has hardly been elucidated so far.
When the actual disaster site was verified, the driftwood to be captured in the conventional sabo dam was found to have a low probability of being captured by the driftwood that flowed over the water passage part along with the debris flow and the like. The sabo dam equipped with a screen exerted some effect of capturing driftwood, but allowed some driftwood to pass through.
As described above, the conventional sabo dam did not fully exhibit the original driftwood trapping action.
<2> In order to improve the efficiency of capturing driftwood in a sabo dam equipped with a screen, it is conceivable to reduce the transmission space by narrowing the arrangement interval of steel pipes and the like constituting the screen.
While this countermeasure can improve the efficiency of catching driftwood, it has the problem of increasing the construction cost of the screen and the difficulty of applying it to the existing sabo dam.
<3> A method of adding a new sabo dam near the existing sabo dam is conceivable, but the problem that the construction period is long and the burden of construction cost remains large when the new sabo dam is constructed.
<4> As described above, the conventional sabo dams, regardless of whether they are permeable or opaque, have a common problem of how to improve the efficiency of catching driftwood.
<5> In recent years, the damage caused by heavy rain has tended to increase year by year, so there is a demand for proposals for driftwood countermeasures that can be constructed at low cost in a short period of time.

The present invention has been made in view of the above points, and an object thereof is to provide a facility for capturing the following driftwood.
<1> To improve the efficiency of catching driftwood by correcting the direction of driftwood flowing down by utilizing the power of running water.
<2> Construction can be done at low cost in a short period of time.
<3> Effectively control the damage caused by driftwood in the downstream area while making effective use of the existing sabo dam.

The present invention focuses on the fact that the direction of driftwood changes under the influence of running water such as debris flow, and creates a water area with a difference in flow velocity in the process of flowing down the driftwood so that the direction of the driftwood is aligned in a specific direction. Is.
The present invention is a driftwood capture facility installed along a flow path such as a debris flow, and is directed toward a capture screen having a driftwood capture function and a crossing direction of the flow path such as a debris flow on the upstream side of the capture screen. The backwater transition section where the water level rises when a debris flow occurs and the direction of the driftwood flowing down due to the difference in flow velocity is corrected to a specific direction that is easily captured by the capture screen is the capture screen. It is formed on the upstream side of.
In the present invention, before the driftwood arrives at the capture screen, the direction of the driftwood is corrected to a specific direction in which it is easy to be captured by the capture screen. It can be suppressed.
In another embodiment of the present invention, the cross-sectional shape of the overflow weir is rectangular or triangular, and an upright surface is formed on the upstream side of the overflow weir.
In another embodiment of the present invention, a pile screen having a simple structure is applicable to the capture screen.
In another embodiment of the present invention, an existing or new dam may be located upstream of the overflow dam, and the overflow dam may be located between the dam and the capture screen.

The present invention has at least one of the following effects.
<1> Before the driftwood arrives at the capture screen, the direction of the driftwood can be corrected to a specific direction in which the driftwood is easily captured by the capture screen by utilizing the force of the running water, so that the capture efficiency of the driftwood is significantly improved.
<2> Since the overflow weir and the capture screen that make up the driftwood capture facility have a simple structure, the material cost and installation cost are low, and the construction can be done in a short period of time.
Therefore, it is effective as a driftwood countermeasure work required as a countermeasure work for heavy rain damage in recent years.
<3> By simply installing an additional driftwood capture facility on the downstream side of the existing or new dam, while effectively utilizing the existing or new dam, the lack of driftwood capture performance of the dam is compensated for and the driftwood damage in the downstream area is effective. Can be suppressed.

An overall perspective view of the capture facility in which a part is omitted in the explanatory view of the driftwood capture facility according to the present invention. Longitudinal section of upstream sabo dam and capture facility An explanatory diagram of the capture action of driftwood, a model diagram of the upstream sabo dam and capture facility as seen from a plane. In the cross-sectional view of the overflow weir, (a) is a cross-sectional view of the overflow weir having a rectangular cross-sectional shape, and (b) is a cross-sectional view of the overflow weir having a triangular cross-sectional shape.

The present invention will be described in detail below with reference to the drawings.

<1> Outline of Driftwood Capture Facility Explaining with reference to FIGS. 1 and 2, the driftwood capture facility 10 according to the present invention has a capture screen 20 provided in a flow path such as a debris flow and an upstream of the capture screen 20. It is composed of an overflow weir 30 projecting in the transverse direction with respect to the flow direction of a debris flow or the like.
In this example, the form in which the upstream sabo dam 40 is located upstream of the overflow dam 30 will be described, but the upstream sabo dam 40 may be omitted.

<2> Capture screen The capture screen 20 is a transmissive rigid structure having a function of capturing driftwood.
In this example, a form in which the capture screen 20 is composed of a pile-type screen in which a plurality of capture members 22 are erected vertically at intervals on the upper surface of the support foundation 21 is illustrated, but a plurality of captures other than the illustrated form are illustrated. The material 22 may be assembled in a grid pattern, or may be three-dimensionally assembled in a chevron shape, a gate shape, or the like with a thickness in the flowing water direction.
Further, the capture screen 20 may be a known opaque sabo dam, permeable sabo dam, or partially permeable sabo dam, and may be existing or new.
When the capture screen 20 is newly installed, the capture screen 20 has a simple structure and can be installed at low cost.

<3> Overflow Weir The overflow weir 30 raises the water level of the flowing water 50 when a debris flow or the like occurs (weir backwater), and forms a backwater transition section 51 due to the flowing water 50 on the upstream side of the overflow weir 30. It is a protrusion and is fixed to the flow path 12 or the riverbed 11 which is a flow path such as a debris flow.
As a method of fixing the overflow weir 30, the lower part of the overflow weir 30 is buried or pins are placed and fixed.
The overflow weir 30 arranged in the direction orthogonal to the flow direction of the flowing water 50 such as a debris flow may be installed with continuity as shown in FIG. 1, or may be discontinuously provided at intervals. It may be installed.
Since the overflow weir 30 has a simple structure, the material cost and the installation cost can be reduced.

<3.1> Backwater transition section The backwater transition section 51 is a water level rising area for correcting the direction of a plurality of driftwood 60 flowing down in a specific direction and aligning them, and has a flow velocity difference between upstream and downstream of the backwater transition section 51. is doing.

<3.2> Cross-sectional shape of the overflow weir In this example, a form in which the cross-sectional shape of the overflow weir 30 has a rectangular shape will be described (FIG. 4A), but the cross-sectional shape of the overflow weir 30 has an acute angle on the downstream side. It may be a triangular shape (Fig. 4 (b)).
In short, it suffices if an upright surface 31 is formed on the upstream side of the overflow weir 30.

<3.3> Height of the overflow weir In order to form the backwater transition section 51 having a large flow velocity difference, the height H of the upright surface 31 of the overflow weir 30 is taken into consideration in consideration of the gradient of the flow path 12, the floor width, and the like. Is selected as appropriate.
The longitudinal gradient of the backwater transition section 51 increases in proportion to the height H of the upright surface 31.
Practically, if the height H of the upright surface 31 is in the range of about 0.3 m to 2 m, the backwater transition section 51 having a difference in flow velocity can be formed.

<3.4> Number of Overflow Weirs Installed In this example, one overflow weir 30 is installed for the flow path 12, but a plurality of overflow weirs 30 are arranged in parallel at intervals. May be good.
When a plurality of overflow weirs 30 are arranged, a backwater transition section 51 is formed on the upstream side of each overflow weir 30.

<4> Upstream sabo dam The upstream sabo dam 40 is a sabo dam, a check dam, a valley dam, etc., and may be existing or new.
In this example, the form in which the upstream sabo dam 40 is an impermeable type sabo dam in which a water passage portion 42 is formed between the sleeve portions 41 and 41 is exemplified, but it is a known permeable type sabo dam or a partially permeable type sabo dam. May be.

[Driftwood capture action]
The capture action of the driftwood 60 by the driftwood capture facility 10 will be described with reference to FIGS. 1 to 3.

<1> Overflow of driftwood from upstream sabo dam When debris flow including driftwood 60 occurs, debris and boulders are captured by the upstream sabo dam 40.
When the volume of the debris flow or the like in the upstream sabo dam 40 exceeds a certain value, the flowing water 50 such as the debris flow flows down to the downstream side through the water passage portion 42.
Most of the driftwood 60 is captured by the upstream sabo dam 40, but some of the driftwood 60 that has become vertical due to the influence of the flow of the flowing water 50 flows down to the downstream side through the water passage portion 42.

<2> Correction of the direction of driftwood in the backwater transition section The driftwood 60 flowing down from the upstream sabo dam 40 flows down together with the running water 50 toward the downstream capture screen 20.
When passing through the backwater transition section 51, as will be described in detail below, the turning force F acts on each driftwood 60 so that the direction of the driftwood 60 is easily captured by the capture screen 20 (orthogonal to the flow direction of the driftwood 50). It is corrected to the direction (or the transverse direction of the flow path 12).

<2.1> Flow velocity difference in the backwater transition section Explaining with reference to FIG. 3, the flow velocity changes in the backwater transition section 51 formed on the upstream side of the overflow weir 30, and the flow velocity difference is observed upstream and downstream thereof. It is happening.
That is, in the backwater transition section 51, the water level rises from the upstream side to the downstream side, and as the water level rises, the flow velocity V ₁ on the upstream side of the backwater transition section 51 gradually shifts to the low speed V ₂ toward the downstream side. It is changing.

<2.2> Principle of correcting the direction of driftwood When the driftwood 60 enters the backwater transition section 51 in a vertical direction along the flow of the driftwood 50, the front end portion 61 of the driftwood 60 enters a slow-flowing water area. At this time, the rear end 62 of the driftwood 60 is located in a fast-flowing water area.
Since a flow velocity difference occurs between the front end portion 61 and the rear end portion 62 of the driftwood 60, a horizontal turning force F due to the running water 50 acts on the driftwood 60 so as to eliminate this flow velocity difference.
The driftwood 60 that has received the turning force F turns while flowing down the backwater transition section 51, and when the flow velocity change point directly above the overflow weir 30 is exceeded, the turning force F disappears and the turning of the driftwood 60 ends. ..
Since the difference in flow velocity between the front end portion 61 and the rear end portion 62 of the driftwood 60 is almost eliminated, the direction of the driftwood 60 is corrected to a specific direction. The direction of the subsequent driftwood 60 is also corrected to a specific direction.

Further, when the backwater transition section 51 is entered from the beginning with the driftwood 60 facing sideways toward the orthogonal direction of the flow path 12 or in a state close to the sideways, a large difference in flow velocity does not occur at both ends of the driftwood 60. , The driftwood 60 will flow down the backwater transition section 51 with almost no change in the direction at the time of approach.

In this way, regardless of which direction the driftwood 60 is facing when entering the backwater transition section 51, the directions of the plurality of driftwood 60 are aligned in a specific direction by passing through the backwater transition section 51.
When a plurality of overflow weirs 30 are arranged at intervals in the flow path 12, the direction of the driftwood 60 is stepped each time the backwater transition section 51 formed on the upstream side of each overflow weir 30 flows down. Therefore, the effect of correcting the orientation of the driftwood 60 is high.

<3> Driftwood capture When the driftwood 60 flows down the backwater transition section 51 upstream of the capture screen 20, the direction of the driftwood 60 is aligned with the specific direction in which the driftwood 60 is easily captured by the capture screen 20, so that the driftwood 60 is efficient in the capture screen 20. It can be captured well and reliably.
Therefore, the passing probability of the driftwood 60 on the capture screen 20 becomes as low as possible, and the driftwood capture action originally possessed by the capture screen 20 can be fully exerted.

When the existing upstream sabo dam 40 exists upstream of the driftwood capture facility 10, the existing upstream sabo dam 40 is effectively utilized, and the insufficient driftwood capture performance of the upstream sabo dam 40 is compensated for the driftwood damage in the downstream area. Can be effectively suppressed.
Since the overflow weir 30 and the capture screen 20 constituting the driftwood capture facility 10 have a simple structure, the material cost and the installation cost can be low, and the construction can be performed in a short period of time.

10 ... Driftwood capture facility 11 ... Riverbed 12 ... Channel 20 ... Capture screen 21 ... Support foundation 22 ... Capture material 30 ... Overflow Weir 31 ... Upright surface 40 ... Upstream sabo dam 41 ... Sleeve 42 ... Water passage 50 ... Driftwood 51 ... Backwater transition section 60 ... Driftwood

Claims (5)

It is a driftwood capture facility installed along the flow path such as debris flow.
A capture screen with a driftwood capture function and
It consists of an overflow weir projecting in the crossing direction of the debris flow flow path on the upstream side of the capture screen.
A sabo dam is located upstream of the overflow dam, and an overflow dam is located between the sabo dam and the capture screen.
The feature is that the backwater transition section is formed on the upstream side of the overflow weir , where the water level rises when a debris flow occurs and the direction of the driftwood flowing down due to the difference in flow velocity is corrected to a specific direction that is easily captured by the capture screen. do,
Driftwood capture facility. The driftwood trapping facility according to claim 1, wherein the cross-sectional shape of the overflow weir is rectangular or triangular. The driftwood trapping facility according to claim 1 or 2, wherein an upright surface is formed on the upstream side of the overflow weir. The driftwood capture facility according to claim 1, wherein the capture screen is a stake screen. The driftwood capture facility according to claim 1 , wherein the sabo dam is an existing or new dam.

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