DEBRIS FLOW DRAINAGE CANAL BASED ON CASCADE ANTISCOUR NOTCHED SILL GROUP AND APPLICATION THEREOF

Abstract

A system of debris-flow drainage canal with cascaded sills is provided, which allows a high-efficient and low-cost realization of debris flow drainage and scour prevention. The canal contains two converging walls and a series of scour prevention sills, which are laid between the two converging walls. The sills are embedded to a certain depth and are evenly spaced and symmetrical to the centre line of the canal to form a cascaded structure for scour prevention. The drainage canal's width is 2 times wider than the sill's horizontal length along the cross-section. Compared with the prior art, this system can drain off a wide variety of flows from debris flow to flood and prevent debris-flow siltation even on a gentle slope. This system has a much higher stability and longer life of service. Moreover, this system can maintain the aquatic habitat in gullies and contribute to ecological restoration.

Description

FIELD

This disclosure relates to the field of debris flow drainage technology. In particular, the disclosure relates to a system of drainage canal with scour-prevention cascaded sills, for the purpose of draining off low viscosity debris flow, water-rock flow and flood through dissipating flow energy by soft streambed.

BACKGROUND

Debris flow is characterized by high inertia, strong transporting ability and great impact force because of its composition of elastic soil. Strong erosion caused by debris flow can bring dramatic changes to gully bed, making gully bed revealed and bank collapse, which in turn supplies solid materials to the debris flow and magnifies the damage. Thus, debris flow brings severe harms to towns, villages, roads, canals, electric and communication lines, farmlands and forests. Therefore, it would have great significance on society, economy and ecological environment to invent new structure type that can effectively control the scour caused by debris flow, reduce damage and enhance safety of downstream protecting objects.

In recent years, the utilization of debris flow fans has increased with the growing of construction of many large capital construction projects. It is becoming more important to control scour and siltation of debris flow. Among numerous debris flow basins, the occurrence probability of diluted debris flow, transitional debris flow and floods is high. Thus, it is urgent to develop new drainage canal that can meet the drainage requirement of these kinds of debris flows.

The traditional entirely lined canal is usually of high cost but has a short life due to the extremely strong erosion by debris flow. The currently used canal with transverse throughout sills is generally applied in steep slope gully. When the slope gradient is smaller than 5%, the canal will be silted notably and the drainage effect is very poor. In perennial streams, the entirely lined canal and transverse throughout sills would break the connection between upstream and downstream aquatic organisms, thereby going against ecological restoration of the gully.

The Patent Application No. 200910058217.7, directed to Applicants' previous research achievement, discloses a drainage canal with crisscross-spurs structures to drain spreading gradation fluid and keep hydraulic connection in gullies for the benefit of ecological restoration. However, the crisscross-spurs structures may cause back flow and threaten the safety of canal walls. Moreover, strong back flow may lead to energy dissipation and sediment deposition. Reducing the length of sill is effective in decreasing back flow in gullies with gentle slope, but this decreases the stability of the walls. It will be of high cost to reinforce the walls' foundation.

SUMMARY

The purpose of this invention is to provide a low cost drainage system of canal with cascaded sills. This approach can implement safe and smooth drainage of a variety of flows, keep dynamic balance between erosion and siltation, maintain the habitat of water living in gullies, and help ecological restoration. Furthermore, this approach can fully ensure the stability of the side walls in view of the centripetal converging flow effect and avoid siltation even when the slope is small, making the drainage canal work for a longer time.

To achieve the above purpose, among others, the following exemplary solution is provided by the invention.

An embodiment of the invention relates to a debris-flow drainage canal based on scour prevention cascaded sills, which includes two flow converging walls and a series of scour prevention cascaded sills. The series of scour prevention cascaded sills are placed between the two walls, connected to the walls and utilized together with the walls. The cascaded sills are made of a number of scour prevention sills, which are placed with a certain embedded depth and each two steps are distributed with a certain space. Each two sills are laid between the two walls symmetrically with respect to the centre line of the drainage canal, and make up a step of the scour prevention cascaded sills. The drainage canal's width D (i.e., the distance between the two side walls) is 2 times wider than the sill's horizontal length B along the vertical direction of the wall (i.e., the sill's projected length in the vertical direction of the wall), meeting the requirement of D>2 B. Stated differently, only one end of each sill is connected to the side wall, without crossing the canal, and the sills are laid between the two walls symmetrically with respect to the centre line of the canal and make up a symmetric-form step of the scour prevention cascaded sills, This symmetrical structure can maintain full aquatic organism connection in gullies and is beneficial to the ecological restoration; this symmetrical structure can also ensure the stability of the side walls and avoid siltation even on a gentle slope, and work for a long time.

The sill's horizontal length B along the vertical direction of the wall is 1/10˜½ of the drainage canal's width D, meeting the requirement of 1/10 D≦B<½ D; the greater the gully's longitudinal slope is, the longer the sill's horizontal length B should be. This helps keep said sills' quantities as few as possible.

The sill inclines at an angle a at its connection to the wall and inclines to the downstream direction; i.e., the sill's connection end is upstream with respect to the other end. The angle α is between 45°˜75°. The greater the gully's longitudinal slope is, the larger the angle α should be. This inclined structure contributes to converging flow.

Along the vertical direction of the side wall, the central portion of the sill is lower and the sides adjacent the wall is higher, The transverse slope 1:n, which is the sill's height difference h divides the sill's horizontal length B along the vertical direction of the wall, is 1:4˜1:20, in other words, 1:n=h: B. This structure of lower in the centre than at the sides is used to improve converging flow and bottom turbulence, which is helpful to energy dissipation.

Along the vertical direction of the wall, the sill's top width b₁<the bottom width b₂, and the downstream side is vertical, while the upstream side inclined. The sill's top width b₁ is 0.6˜1.5 m and bottom width h₂ is 1.0˜2.0 m, and the upstream side's slope 1:m (which is upstream slope's height H₁ divides (b₂−b₁)) is 1:0.4˜1:1, in other words, 1:m=H₁: (b₂−b₁). This structure of narrow top and wide bottom stabilizes the sill under the impact force of debris flow.

To build the drainage canal, the structure of grouted stone masonry, concrete, reinforced concrete, protection lead gabion can be used. The space L between each two steps of the scour prevention cascaded sills is 8.0˜25.0 m, and the sill's embedded depth H is 1.5˜2.5 m. A reasonable embedded depth and space can keep the sill and side wall safe.

The drainage canal, which provides both energy dissipation effect in view of the longitudinal soft foundation and centripetal converging flow effect in view of the symmetrical sills, is particularly appropriate for preventing and controlling diluted debris flow, water-rock flow and floods with longitudinal slope 3%˜12%. Due to the sill's centripetal converging flow effect, the side walls' stability can be ensured and stronger scour can be achieved to avoid siltation when the longitudinal slope is gentle, thereby ensuring long operation period.

An embodiment of the invention, based on the energy dissipation effect of soft foundation and centripetal converging flow effect of symmetrical sills and side walls, deals with the alternate effects of downward erosion and siltation by fluid to prevent and control diluted debris flow, water-rock flow and floods. When the flow rate is big, the embodiment dissipates internal kinetic energy in fluid by mean of material interchange between the lower turbulence and the upper descending current in debris flow (or flood), thereby avoiding downward erosion. When the flow rate is small, the embodiment prevents siltation in view of the scour effect by the centripetal converging flow, implements the dynamic balance of downward erosion and siltation, and drains debris flow safely and smoothly. The symmetric structure is capable of regulating the balance of downward erosion and siltation in gully, reducing debris-flow erosion, preventing siltation in gully, decreasing the costs and maintenance of operation, and ensuring the safety of downstream protected objects. The drainage canal can be built mainly on debris flow fans, leading debris flow into the designed regions according to the designed flow velocity and direction.

The advantages of the invention include, but are not limited to, the following. More than 15% cost can be saved compared with the entirely lined canal, which in turn favors operation management. When the gradient of gully bed is gentle, better effect for preventing siltation and lower cost can be achieved compared with the transverse throughout sills, and the drainage demand can still be satisfied when several kinds of fluid varying from diluted debris flow to flood occur in the same basin. Considering the disclosure of Application Number 200910058217.7 (A debris-flow drainage canal with indented-sill), this invention can not only effectively carry on the advantages of ecological protection, but also avoid scouring the foundation of the side walls because of the centripetal converging flow effect of the symmetrical sills, which would fully ensure the stability of the walls. In addition, there can be stronger scour to avoid siltation when the longitudinal slope is gentle, ensuring that the canal safely run for a long time.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a longitudinal profile of scour prevention cascaded sills;

FIG. 2 illustrates a top plan view of an embodiment of the invention; and

FIG. 3 illustrates a lateral profile of the embodiment.

The labels in the figures are shown as follows: 1 the scour prevention cascaded sill 2 the flow converging side wall; B horizontal length of the sill along the vertical direction of the wall; D width of the drainage canal; α inclined angle of the sill; b₁ top width of the sill b₂ bottom width of the sill; H embedded depth of the sill; L distance between each two steps of the scour prevention cascaded sills; H height difference between the two ends of the sill; H₁ height of upstream incline; 1:n the transverse slope; and 1:m the upstream side's slope.

DETAILED DESCRIPTION OF EMBODIMENTS

The exemplary embodiments the invention are now described with reference to the figures.

Exemplary Embodiment I

As shown in FIGS. 1-3, the valley area is 2.0 km² and the slope of debris fan is 12%, considering diluted debris flow, water-rock flow and flood under designed standard. The debris flow drainage canal can be built on the fan, including side walls 2 and scour prevention cascaded sills which are laid between the two walls, being connected to them and used together with them. Each two steps of the cascaded sills are distributed with a certain space, and are made up of a number of scour prevention sills 1 with a certain embedded depth. The space L is 8.0 m, and the embedded depth is 2.5 m.

The sills are laid between the two walls symmetrically with respect to the centre line of the canal, and make up a symmetric-form step of the scour prevention cascaded sills. The drainage canal's width D is 2 times wider than the sill's horizontal length B along the vertical direction of the wall. Under the P_2% designed standard, the discharge of debris flow in the canal is 28.0 m³/s; D is set as 3.0 m, B as 1.2 m, and α as 75°.

Along the vertical direction of the walls 2, the sill 1 is shown as lower at the center and higher near the wall. The transverse slope 1:n is designed as 1:4. Along the vertical direction of the walls 2, the top width b₁ of the sill 1 is 0.6 m, and bottom width b₂ is 1.0 m. The downstream side is vertical, while the upstream side inclined. The upstream side's slope 1:m, which is upstream slope's height H₁ divides (b₂-b₁), is 1:0.4, and H₁ is 1.0 m.

Exemplary Embodiment II

As shown in FIGS. 1-3, the valley area is 20.0 km² and the slope of debris fan is 3%, considering water-rock flow and flood in designed standard. Beside the same as embodiment I, the differences are in that: the space L is 25.0 m and the embedded depth is 1.5 m.

Under the P_2% designed standard, the discharge of debris flow in the canal is 100.0 m³/s. Set D as 16.0 m, B as 1.6 m, and α as 45°; the transverse slope 1:n is 1:20, the top width b₁ of the sill 1 is 1.5 m, and the bottom width b₂ is 2.0 m; the upstream side's slope 1:m is 1:1, and H₁ is 0.5 m.

Claims

1. A debris flow drainage canal based on scour-prevention cascaded sills comprises:

two flow-converging walls; and

a plurality of sills with a predetermined embedded depth, the plurality of sills being disposed between and connected to the walls,

wherein the sills are evenly spaced and symmetrical with respect to the centre line of the canal, and the width D of canal is at least 2 times wider than the length B of the sills, meeting the requirement of D>2 B.

2. The debris flow drainage canal according to claim 1, wherein the horizontal length B of the sills along the vertical direction of the walls is 1/10˜½ of the drainage canal's width D, meeting the requirement of 1/10 D≦B<½ D.

3. The debris flow drainage canal according to claim 1, wherein an angle is formed between the walls and one end of the sills connected to the walls, and the other end of the sills inclines to a downstream direction.

4. The debris flow drainage canal according to any one of claims 1-3, wherein along the vertical direction of the walls, the sills presents lower at the center and higher near the walls.

5. The debris flow drainage canal according to any one of claims 1-3, wherein along the longitudinal direction of the walls the top width b1 of the sills is smaller than the bottom width b2 of the sills, and the downstream side is vertical, while the upstream side is inclined.

6. The debris flow drainage canal according to claim 3, wherein the angle is within the range of 45° to 75°.

7. The debris flow drainage canal according to claim 4, wherein along the vertical direction of the walls, the horizontal slope 1:n, which is the sills' height difference h divides the sills' sill(1)'s horizontal length B along the vertical direction of the walls, is between 1:4 and 1:20.

8. The debris flow drainage canal according to claim 5, wherein the top width b1 is within the range of 0.6-1.5 m, and the bottom width b2 is within the range of 1.0˜2.0 m, and the upstream side's slope 1:m, which is upstream slope's height H1 divides (b2−b1), is between 1:0.4 and 1:1.

9. The debris flow drainage canal according to any one of claims 1-3, wherein the space L between each two steps of the sills is within the range of 8.0˜25.0 m, and the embedded depth H of the sills is within the range of 1.5˜2.5 m.

10. A method of using the debris flow drainage canal based on scour prevention cascaded sills according to claim 1, comprising using the drainage canal to prevent and control diluted debris flow, water-rock flow and flash floods with longitudinal slope of 3%-12%.