A cofferdam structure suitable for gentle slope water intake river channel construction

Abstract

The application discloses a cofferdam structure suitable for gentle slope water-taking river channel construction, which is used for being installed on any side of a river bank and comprises a water intake pipe, an upstream cofferdam, a downstream cofferdam and a longitudinal cofferdam. One end of the water intake pipe is connected with a water intake arranged close to the river bank, and the other end is located on one side of the river bank. The upstream cofferdam is arranged on the upstream side of the water intake. The downstream cofferdam is arranged on the downstream side of the water intake. The longitudinal cofferdam is connected between the upstream cofferdam and the downstream cofferdam. The river bank, the upstream cofferdam, the downstream cofferdam and the longitudinal cofferdam jointly form a sedimentation water area, which is used for carrying out secondary sedimentation and purification on the low-speed water flow filtered through the downstream cofferdam. The cofferdam structure has the advantages of good purification effect and strong practicability, can realize effective purification of the construction turbid water through the interception, filtration, diversion, speed reduction and sedimentation of the cofferdam, and can minimize the influence of the construction on the water taking of the river channel.

Description

Technical Field

[0001] This invention relates to a cofferdam structure, specifically a cofferdam structure suitable for construction of water intake channels on gentle slopes, and belongs to the field of cofferdam technology. Background Technology

[0002] In general, gently sloping rivers are important water sources for agricultural irrigation, drinking water for humans and livestock, and ensuring stable water quality at the intake points is crucial for the lives and livelihoods of nearby residents. However, during the construction of gently sloping rivers, disturbances can easily lead to turbid water flow, which directly affects the water quality at the intake points, causing significant inconvenience to the normal lives and livelihoods of nearby residents. Therefore, effectively protecting the intake points during river construction to avoid or mitigate the impact of turbid water on the water quality has become one of the key requirements in river construction.

[0003] Currently, three main methods are used to prevent turbid water from river construction: first, installing mud curtains downstream of the construction site; second, setting up fences and filtration facilities near the water intake; and third, coordinating construction and water intake periods to reduce the impact of construction. However, these traditional methods have many inherent defects and limitations: on the one hand, mud curtains need to be laid out along the entire cross-section of the river, and must simultaneously consider both filtration and river flow requirements, resulting in them only being able to intercept relatively large soil particles, thus having a limited overall purification effect on the turbid water from construction and failing to fundamentally solve the problem of turbid water quality at the water intake; on the other hand, the practice of setting up fences and filtration facilities at the water intake lacks universality, has low technical maturity, and is difficult to form a large-scale, standardized protective effect, failing to meet the protection needs of water intakes in rivers with different gentle slopes; furthermore, while coordinating construction and water intake periods can temporarily reduce the impact, it is not a fundamental technical measure, and its operational flexibility in actual construction is poor, making it difficult to continuously guarantee the quality of the water intake.

[0004] A search revealed that Chinese invention patent CN108277815B discloses a construction method for a cofferdam structure used in the construction of a water intake structure in a river. The method involves constructing widened cofferdams on the inner side of the end cofferdam and the inner side of the front end of the upper cofferdam. A composite geomembrane is laid between the widened cofferdam and the end and upper cofferdams. An inner cofferdam is constructed between the widened cofferdam and the lower cofferdam. The construction area of ​​the water intake structure is located in the area between the lower and inner cofferdams. Several piles are installed within the front end of the upper cofferdam, the front end of the lower cofferdam, and the end cofferdam using a high-pressure jet grouting method, forming a water-stop curtain between adjacent piles. This cofferdam is impermeable. The problem this invention aims to solve is strengthening the structural strength of the outer cofferdam. Simultaneously, the inner cofferdam makes construction operations in the water intake structure construction area safer and more reliable, effectively enabling construction operations on the water intake structure. However, it cannot simultaneously solve the problems of water intake and water purification.

[0005] Therefore, developing a practical and reliable cofferdam structure suitable for construction in gently sloping water intake channels is the key to solving the above-mentioned technical problems. Summary of the Invention

[0006] In view of the many defects and shortcomings of the above-mentioned background technology, the present invention has made improvements and innovations, aiming to provide a cofferdam structure with good purification effect and strong practicality suitable for construction of water intake channels on gentle slopes. Through the interception, filtration, diversion, deceleration and sedimentation of the cofferdam, the turbid water of construction can be effectively purified, thereby minimizing the impact of construction on water intake of the river.

[0007] To solve the above problems and achieve the above-mentioned objectives, the present invention provides a cofferdam structure suitable for construction of gently sloping water intake channels, achieved by adopting the following design structure and the following technical solution:

[0008] A cofferdam structure suitable for construction of water intake channels on gentle slopes, for installation on any side of the riverbank, the cofferdam structure includes: a water intake pipe (1), one end of the water intake pipe (1) is connected to a water intake (6) arranged near the riverbank (5), and the other end is located on one side of the riverbank (5);

[0009] Upstream cofferdam (2) is set on the upstream side of the water intake (6);

[0010] Downstream cofferdam (3) is set on the downstream side of the water intake (6);

[0011] A longitudinal cofferdam (4) is connected between the upstream cofferdam (2) and the downstream cofferdam (3);

[0012] Among them, the riverbank (5), the upstream cofferdam (2), the downstream cofferdam (3) and the longitudinal cofferdam (4) together enclose the sedimentation area, which is used for secondary sedimentation and purification of the low-speed water flow after being filtered by the downstream cofferdam (3).

[0013] Preferably, the angle between the upstream cofferdam (2) and the riverbank (5) is 30° to 40°.

[0014] Preferably, the distance from the water intake axis to the side of the connection surface between the upstream cofferdam (2) and the longitudinal cofferdam (4) near the water intake (6) is 15 to 20 times the diameter of the water intake pipe (1).

[0015] Preferably, the downstream cofferdam (3) is closely connected to the longitudinal cofferdam (4), and the angle between the downstream cofferdam (3) and the riverbank (5) is 30° to 40°.

[0016] Preferably, the distance from the water intake axis to the side of the connection surface between the downstream cofferdam (3) and the longitudinal cofferdam (4) near the water intake (6) is 30 to 50 times the diameter of the water intake pipe (1).

[0017] Preferably, the longitudinal cofferdam (4) is arranged parallel to the direction of water flow, and the distance between the top of the cofferdam and the water intake (6) is 20 to 30 times the diameter of the water intake pipe (1).

[0018] Preferably, the upstream cofferdam (2) is a relatively impermeable cofferdam, which is constructed by filling woven sandbags. The width of the cofferdam crest is 1.0 to 1.5 m, the cofferdam crest is 0.5 to 0.7 m above the design water level during construction, the cofferdam toe is buried 0.3 to 0.5 m below the riverbed surface, the cofferdam slope on the main stream side is 1:0.5 to 1:1.0, and the cofferdam slope on the intake side is 1:0.3 to 1:0.5.

[0019] Preferably, the longitudinal cofferdam (4) is a relatively impermeable cofferdam, which is constructed by filling woven sandbags, with a crest width of 1.0 to 1.5 m and a crest height of 0.5 to 0.7 m above the design water level during construction.

[0020] Preferably, the downstream cofferdam (3) is a permeable cofferdam, and its body is arranged in the following order relative to the direction of incoming water: riprap surface layer (31), upstream gravel layer (32), permeable geotextile (33), downstream gravel layer (34), and a cofferdam skeleton (35) filled with riprap.

[0021] The top width of the weir frame (35) is 0.6 to 1.0 m, the weir height is consistent with that of the longitudinal cofferdam (4), the weir toe is buried 0.3 to 0.5 m below the riverbed surface, the weir slope on the main stream side is 1:0.5 to 1:1.0, and the weir slope on the intake side is 1:0.3 to 1:0.5.

[0022] Preferably, the riprap surface layer (31) is used for erosion resistance and fixing of geotextile (33), with a layer thickness of 30-40cm and a block diameter of 10-20cm;

[0023] The upstream gravel layer (32) and the downstream gravel layer (34) are both used for leveling and protecting the geotextile (33) from being punctured by boulders. The upstream gravel layer (32) has a thickness of 20-30cm and a particle size of 1-5cm, while the downstream gravel layer (34) has a thickness of 20-30cm and a particle size of 2-10cm.

[0024] The permeable geotextile (33) has a unit area mass of not less than 400g / ㎡ and a thickness of not less than 2mm;

[0025] The stone boulders of the weir skeleton (35) have a diameter of 20-50cm and are used to support the stability of the cofferdam structure.

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0027] 1. This invention forms a targeted protection system by coordinating upstream, longitudinal, and downstream cofferdams around the existing river intake. This system can effectively intercept construction wastewater from directly impacting the intake. At the same time, the downstream permeable cofferdams can filter, divert, and slow down the incoming water, significantly reducing the mud content of the river water before it enters the intake. The slowed water flow is also more conducive to sediment sedimentation. Combined with the secondary sedimentation effect of the cofferdams and the enclosed water area, multi-stage purification of construction wastewater can be achieved, significantly improving the quality of the water intake. This fundamentally reduces the impact of construction on river water intake and ensures the safety of drinking water for the surrounding residents.

[0028] 2. This invention uses woven sandbags, gravel and boulders as the main cofferdam filling materials. These materials can be sourced locally without long-distance transportation, which not only reduces material procurement and transportation costs, but also simplifies the construction process, greatly improves construction efficiency, and can quickly complete the construction of the protection system, ensuring the orderly progress of river construction and water intake operations.

[0029] 3. The invention is reasonably designed and adapted to the terrain characteristics of gentle slope river channels. It is easy to construct and operate, and does not require complicated construction equipment or professional technical teams, which can effectively reduce the construction threshold and project cost. At the same time, its standardized structural layout can be adapted to the water intake protection needs of gentle slope water intake channels of different sizes, and has a wide range of applications and strong practicality.

[0030] 4. This invention can achieve coordinated construction and water intake while ensuring the smooth progress of construction, avoiding water intake interruption or water quality deterioration caused by construction, reducing conflicts between the construction party and surrounding residents, helping to create a harmonious and friendly construction environment, and enhancing the social acceptance of the project construction.

[0031] 5. This invention has good purification effect and strong practicality. It can fill the gap in existing technology, effectively solve the problem of water intake protection in the construction of gentle slope water intake channels, and achieve efficient purification of construction turbid water and stable guarantee of water quality. Attached Figure Description

[0032] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings, wherein:

[0033] Figure 1 This is a top view of the present invention;

[0034] Figure 2 This is a cross-sectional view of the upstream cofferdam and the longitudinal cofferdam structure of the present invention;

[0035] Figure 3 This is a cross-sectional view of the downstream cofferdam structure of the present invention;

[0036] Figure 4 This is one of the overall structural schematic diagrams of the present invention;

[0037] Figure 5 This is the second schematic diagram of the overall structure of the present invention;

[0038] Figure 6 This is one of the usage state diagrams of the present invention;

[0039] Figure 7 This is the second usage state diagram of the present invention;

[0040] Figure 8 This is a partial structural schematic diagram of the present invention;

[0041] In the diagram, number 1 represents the water pipe.

[0042] 2—Upstream cofferdam;

[0043] 3—Downstream cofferdam, 31—Rock surface layer, 32—Upstream gravel layer, 33—Permeable geotextile, 34—Downstream gravel layer, 35—Cofferdam skeleton;

[0044] 4—Longitudinal cofferdam;

[0045] 5—Riverbank;

[0046] 6—Water intake. Detailed Implementation

[0047] To make the technical means, inventive features, objectives, and effects of this invention readily understandable, the technical solution of this invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that, unless otherwise specified, the embodiments and features described in these embodiments can be combined with each other. The invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0048] As per the instruction manual Figures 1 to 8 As shown, a cofferdam structure suitable for construction of water intake channels on gentle slopes is used for installation on either side of the riverbank. The cofferdam structure includes:

[0049] Water pipe 1, one end of which is connected to water intake 6 located near the riverbank 5, and the other end is located on one side of the riverbank 5;

[0050] Upstream cofferdam 2 is located on the upstream side of water intake 6;

[0051] Downstream cofferdam 3 is located on the downstream side of water intake 6;

[0052] Longitudinal cofferdam 4 connects the upstream cofferdam 2 and the downstream cofferdam 3;

[0053] Among them, the riverbank 5, the upstream cofferdam 2, the downstream cofferdam 3 and the longitudinal cofferdam 4 together enclose a sedimentation area, which is used for secondary sedimentation and purification of the low-speed water flow after being filtered by the downstream cofferdam 3.

[0054] Furthermore, the angle between the upstream cofferdam 2 and the riverbank 5 is 30° to 40°.

[0055] Specifically, the distance from the water intake axis to the side of the connection surface between the upstream cofferdam 2 and the longitudinal cofferdam 4 near the water intake 6 is 15 to 20 times the diameter of the water intake pipe 1.

[0056] Furthermore, the downstream cofferdam 3 is closely connected to the longitudinal cofferdam 4, and the angle between the downstream cofferdam 3 and the riverbank 5 is 30° to 40°.

[0057] Specifically, the distance from the water intake axis to the side of the connection surface between the downstream cofferdam 3 and the longitudinal cofferdam 4 near the water intake 6 is 30 to 50 times the diameter of the water intake pipe 1.

[0058] Furthermore, the longitudinal cofferdam 4 is arranged parallel to the direction of water flow, and the distance between the top of the cofferdam and the water intake 6 is 20 to 30 times the diameter of the water intake pipe 1.

[0059] Furthermore, the upstream cofferdam 2 is a relatively impermeable cofferdam, which is constructed by filling woven sandbags. The width of the cofferdam crest is 1.0 to 1.5 m, the cofferdam crest is 0.5 to 0.7 m above the design water level during construction, the cofferdam toe is buried 0.3 to 0.5 m below the riverbed surface, the cofferdam slope on the main stream side is 1:0.5 to 1:1.0, and the cofferdam slope on the intake side is 1:0.3 to 1:0.5.

[0060] Furthermore, the longitudinal cofferdam 4 is a relatively impermeable cofferdam, which is constructed by filling woven sandbags, with a crest width of 1.0 to 1.5 m and a crest height of 0.5 to 0.7 m above the design water level during construction.

[0061] Furthermore, the downstream cofferdam 3 is a permeable cofferdam, and its body is arranged from upstream to downstream as follows: 31 riprap surface layer, 32 upstream gravel layer, 33 permeable geotextile, 34 downstream gravel layer, and 35 cofferdam body skeleton filled with riprap.

[0062] The top width of the weir frame 35 is 0.6 to 1.0 m, the weir height is consistent with that of the longitudinal cofferdam 4, the weir toe is buried 0.3 to 0.5 m below the riverbed surface, the slope of the main stream side is 1:0.5 to 1:1.0, and the slope of the intake side is 1:0.3 to 1:0.5.

[0063] Specifically, the riprap surface layer 31 is used for erosion resistance and to fix the geotextile 33, with a layer thickness of 30-40cm and a block diameter of 10-20cm;

[0064] Both the upstream gravel layer 32 and the downstream gravel layer 34 are used for leveling and protecting the geotextile 33 from being punctured by boulders. The upstream gravel layer 32 has a thickness of 20-30cm and a particle size of 1-5cm, while the downstream gravel layer 34 has a thickness of 20-30cm and a particle size of 2-10cm.

[0065] The permeable geotextile 33 has a unit area mass of not less than 400g / ㎡ and a thickness of not less than 2mm;

[0066] The stone blocks of the weir frame 35 have a diameter of 20-50cm and are used to support the stability of the cofferdam structure.

[0067] In this invention, the downstream cofferdam 3 adopts a layered reverse filtration design. The riprap surface layer 31 is located on the water-facing side to reduce the impact of water flow and block large-diameter debris. The upstream gravel layer 32 serves as a coarse filtration transition layer to intercept medium-diameter suspended solids and protect the internal structure. The permeable geotextile 33 serves as the core filter medium to intercept fine silt particles, allowing only water flow to pass through, thus achieving mud-water separation. The downstream gravel layer 34 protects the permeable geotextile and quickly guides the filtered water flow to prevent the accumulation of seepage pressure. The cofferdam skeleton 35 is constructed of large riprap, forming the main load-bearing structure of the cofferdam, and its large pore size ensures that the filtered water flow can smoothly flow into the water intake area.

[0068] Specifically, the riprap surface layer 31 has extremely high permeability and extremely large pores. As the first line of defense on the water-facing side, the large riprap can effectively resist the direct impact of river flow, especially the muddy water after construction disturbance, consume the kinetic energy of the water flow, and prevent the water flow from destroying the internal structure. It can also block large debris or large-diameter block pollutants floating in the water from entering the cofferdam and prevent them from clogging the subsequent fine stone layer.

[0069] The upstream gravel layer 32 has good permeability, but its porosity is lower than that of the boulders surface layer. It is located between the boulders surface layer 31 and the permeable geotextile 33, preventing large external boulders from directly squeezing or puncturing the fragile geotextile. It uses the secondary pores formed by the accumulation of gravel to intercept medium-sized mud and sand particles and suspended solids in the turbid water, reduce the turbidity of the turbid water, reduce the load on the core filter layer geotextile, and prevent the geotextile from being blocked too quickly.

[0070] Permeable geotextile 33 has microporous permeability and is the slowest and most precise part of the entire structure. It is the key to achieving "clear water". By utilizing the microporous structure of the geotextile, it effectively intercepts small suspended soil particles and silt in turbid water, allowing only relatively clear water to pass through. It prevents upstream sediment from penetrating the cofferdam and entering the water intake area, thus achieving the core barrier function of mud-water separation.

[0071] The downstream gravel layer 34 has good permeability and a stable pore structure; it receives water flowing through the permeable geotextile 33 and quickly discharges it, preventing water from accumulating behind the permeable geotextile 33 and generating excessive seepage pressure back pressure, which could cause the geotextile to bulge or break; it also serves as a backing for the permeable geotextile 33, preventing the permeable geotextile 33 from deforming under water pressure or being squeezed into the large pores of the rear weir skeleton and failing.

[0072] The weir frame 35 is constructed of riprap, possessing extremely high porosity and permeability. It serves as the structural stability of the entire cofferdam, bearing water pressure and its own weight. After passing through the previous layers of filtration, the clear water reaches this point and flows rapidly and unimpeded through the huge gaps between the frames into the still water area or water intake area inside the cofferdam. This ensures that the water levels inside and outside the cofferdam remain dynamically connected, preventing the cofferdam from collapsing due to poor drainage.

[0073] In summary, to facilitate understanding of the present invention, the cofferdam structure of the above-described design, suitable for construction of water intake channels with gentle slopes, will be further described below with reference to the accompanying drawings:

[0074] More specifically, such as Figure 1 As shown, a cofferdam structure suitable for construction of water intake channels on gentle slopes includes: a water intake pipe 1, an upstream cofferdam 2, a downstream cofferdam 3, a longitudinal cofferdam 4, a riverbank 5, and a water intake 6.

[0075] The water intake pipe 1 has a diameter of 150mm and is located on one side of the riverbank. The water intake 6 is located at the beginning of the water intake pipe 1. The upstream cofferdam 2 forms an angle α1 of 30° with the riverbank 5. The distance L1 from the water intake axis to the intersection point b of the upstream cofferdam 2 and the longitudinal cofferdam 4 near the water intake is 2.25m. The longitudinal cofferdam 4 is immediately connected to the upstream cofferdam 2 and is arranged parallel to the direction of water flow. The distance B from the water intake to the water intake is 4m. The downstream cofferdam 3 is immediately connected to the longitudinal cofferdam 4 and forms an angle α2 of 30° with the riverbank. The distance L2 from the water intake axis to the intersection point c of the downstream cofferdam 3 and the longitudinal cofferdam 4 near the water intake is 7m.

[0076] like Figure 2 As shown, the upstream cofferdam 2 and the longitudinal cofferdam 4 are relatively impermeable cofferdams, and the cofferdam bodies are all filled with woven sandbags; the width b1 of the top of the upstream cofferdam 2 is 1.0m, the top of the cofferdam is 0.6m above the design water level h1 during the construction period, the toe of the cofferdam is 0.3m below the riverbed surface h2, the slope ratio of the cofferdam on the side with the main flow is 1:0.5, and the slope ratio of the cofferdam on the side with the water intake is 1:0.3.

[0077] The relatively impermeable cofferdam described above refers to a cofferdam with weak or slight permeability, meaning that the permeability coefficient of the relatively impermeable cofferdam is less than 1% of that of a permeable cofferdam.

[0078] like Figure 3As shown, the downstream cofferdam 3 is a permeable cofferdam. The cofferdam body, from upstream to downstream, consists of: a 30cm riprap surface layer 31, a 20cm upstream gravel layer 32, a 400g / m² permeable geotextile 33, a 20cm downstream gravel layer 34, and a cofferdam framework 35 constructed of riprap. The top width b2 of the cofferdam framework 35 is 0.8m, and its height is consistent with the longitudinal cofferdam 4. The toe of the cofferdam is buried 0.3m below the riverbed surface h2. The slope ratio of the cofferdam on the main stream side is 1:0.5, and the slope ratio of the cofferdam on the intake side is 1:0.3.

[0079] In use, the turbid water in the river flows sequentially through the upstream cofferdam 2 and the longitudinal cofferdam 4, and then enters the water intake 6 from the downstream cofferdam 3. Finally, the water in the water intake 6 is diverted to the external water treatment equipment through the water pipe 1 for treatment.

[0080] When the turbid water enters the intake 6 within the downstream cofferdam 3, the water flows through the riprap surface layer 31, the upstream gravel layer 32, the permeable geotextile 33, the downstream gravel layer 34, and the weir frame 35 in sequence before finally entering the intake 6.

[0081] During use, the main functions of the upstream cofferdam 2 and the longitudinal cofferdam 4 are to intercept the construction water from rushing directly into the water intake 6, so that the water flows in from the downstream cofferdam 3, thereby avoiding the impact of the main current and reducing the amount of sediment carried by the incoming water. The river water flowing through the downstream cofferdam 3 has a reduced flow velocity and a significantly reduced sediment content due to its sediment-blocking and filtering effect. After the low-speed water flows through the water area enclosed by the riverbank 5, the upstream cofferdam 2, the downstream cofferdam 3 and the longitudinal cofferdam 4, the water quality is further purified due to sedimentation.

[0082] This invention forms a targeted protection system by coordinating upstream cofferdam 2, downstream cofferdam 3, and longitudinal cofferdam 4 around the existing river water intake. This system can effectively intercept construction water from directly impacting the water intake. At the same time, the downstream permeable cofferdam is used to filter, divert, and slow down the incoming water, significantly reducing the mud content of the river water before it enters the water intake. The slowed water flow is also more conducive to sediment sedimentation. Combined with the secondary sedimentation effect of the cofferdam and the enclosed water area of ​​the riverbank, this invention achieves multi-stage purification of construction water, significantly improves the quality of the water intake, fundamentally reduces the impact of construction on river water intake, and ensures the safety of drinking water for the surrounding residents.

[0083] At the same time, it can also achieve coordinated construction and water intake while ensuring the smooth progress of construction, avoid water intake interruption or water quality deterioration due to construction, reduce conflicts between construction parties and surrounding residents, help create a harmonious and friendly construction environment, and enhance the social acceptance of the project construction.

[0084] Furthermore, in another embodiment of the present invention, a fence device or a mesh filter is provided inside the water intake 6, and the water pipe 1 is located within the space enclosed by the fence device or inside the mesh filter; wherein, the fence device adopts a filter fence structure, and the filter fence can block and filter sand in the water, thereby further preventing sand from entering the water pipe 1 with the water flow and avoiding blockage of the water pipe 1.

[0085] Finally, it should be noted that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any other way. Any person skilled in the art may make changes or modifications to the above-disclosed technical content to create equivalent embodiments. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A cofferdam structure suitable for construction of water intake channels on gentle slopes, for installation on any side of the riverbank (5), characterized in that: The cofferdam structure includes: Water pipe (1), one end of which is connected to the water intake (6) arranged near the riverbank (5), and the other end is located on one side of the riverbank (5); Upstream cofferdam (2) is set on the upstream side of the water intake (6); Downstream cofferdam (3) is set on the downstream side of the water intake (6); A longitudinal cofferdam (4) is connected between the upstream cofferdam (2) and the downstream cofferdam (3); Among them, the riverbank (5), the upstream cofferdam (2), the downstream cofferdam (3) and the longitudinal cofferdam (4) together enclose the sedimentation area, which is used for secondary sedimentation and purification of the low-speed water flow after being filtered by the downstream cofferdam (3).

2. The cofferdam structure suitable for construction of gently sloping water intake channels according to claim 1, characterized in that: The angle between the upstream cofferdam (2) and the riverbank (5) is 30° to 40°.

3. The cofferdam structure suitable for construction of gently sloping water intake channels according to claim 1 or 2, characterized in that: The distance from the water intake axis to the side of the connection surface between the upstream cofferdam (2) and the longitudinal cofferdam (4) near the water intake (6) is 15 to 20 times the diameter of the water intake pipe (1).

4. The cofferdam structure suitable for construction of gently sloping water intake channels according to claim 1, characterized in that: The downstream cofferdam (3) is closely connected to the longitudinal cofferdam (4), and the angle between the downstream cofferdam (3) and the riverbank (5) is 30° to 40°.

5. The cofferdam structure suitable for construction of gently sloping water intake channels according to claim 4, characterized in that: The distance from the water intake axis to the side of the connection surface between the downstream cofferdam (3) and the longitudinal cofferdam (4) near the water intake (6) is 30 to 50 times the diameter of the water intake pipe (1).

6. The cofferdam structure suitable for construction of gently sloping water intake channels according to claim 1 or 5, characterized in that: The longitudinal cofferdam (4) is arranged parallel to the direction of water flow, and the distance between the top of the cofferdam and the water intake (6) is 20 to 30 times the diameter of the water intake pipe (1).

7. The cofferdam structure suitable for construction of gently sloping water intake channels according to claim 1, characterized in that: The upstream cofferdam (2) is a relatively impermeable cofferdam, which is constructed by filling woven sandbags. The width of the cofferdam crest is 1.0 to 1.5 m, the cofferdam crest is 0.5 to 0.7 m above the design water level during construction, the cofferdam toe is buried 0.3 to 0.5 m below the riverbed surface, the cofferdam slope on the main stream side is 1:0.5 to 1:1.0, and the cofferdam slope on the intake side is 1:0.3 to 1:0.

5.

8. The cofferdam structure for construction of gently sloping water intake channels according to claim 1, characterized in that: The longitudinal cofferdam (4) is a relatively impermeable cofferdam, which is constructed by filling woven sandbags. The width of the cofferdam crest is 1.0 to 1.5 m, and the cofferdam crest is 0.5 to 0.7 m above the design water level during the construction period.

9. The cofferdam structure suitable for construction of gently sloping water intake channels according to claim 1, characterized in that: The downstream cofferdam (3) is a permeable cofferdam, and its body is arranged in the following order relative to the direction of incoming water: riprap surface layer (31), upstream gravel layer (32), permeable geotextile (33), downstream gravel layer (34), and cofferdam skeleton (35) filled with riprap. The top width of the weir frame (35) is 0.6 to 1.0 m, the weir height is consistent with that of the longitudinal cofferdam (4), the weir toe is buried 0.3 to 0.5 m below the riverbed surface, the weir slope on the main stream side is 1:0.5 to 1:1.0, and the weir slope on the intake side is 1:0.3 to 1:0.

5.

10. The cofferdam structure for construction of gently sloping water intake channels according to claim 9, characterized in that: The riprap surface layer (31) is used for erosion resistance and to fix the geotextile (33), with a layer thickness of 30-40cm and a block diameter of 10-20cm; The upstream gravel layer (32) and the downstream gravel layer (34) are both used for leveling and protecting the geotextile (33) from being punctured by boulders. The upstream gravel layer (32) has a thickness of 20-30cm and a particle size of 1-5cm, while the downstream gravel layer (34) has a thickness of 20-30cm and a particle size of 2-10cm. The permeable geotextile (33) has a unit area mass of not less than 400g / ㎡ and a thickness of not less than 2mm; The stone boulders of the weir skeleton (35) have a diameter of 20-50cm and are used to support the stability of the cofferdam structure.

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