A system for attracting, gathering and raising fish in canyon river sections

Abstract

The invention discloses a system for attracting, gathering and lifting fish in a canyon river section, and belongs to the technical field of ecological environmental protection of water conservancy and hydropower engineering. The system comprises a tailwater channel / hole and a fish attracting, gathering and lifting structure, wherein a reverse slope is arranged on the downstream side of the tailwater channel / hole, and the fish attracting, gathering and lifting structure comprises a force dissipation rectifying mechanism, a fish collecting mechanism and a fish lifting mechanism, wherein one end of the force dissipation rectifying mechanism is connected to the reverse slope surface through a drainage mechanism, and the other end is connected to one end of the fish collecting mechanism, and the fish lifting mechanism is arranged on the fish collecting mechanism and connected to the top of the tailwater channel / hole. Part of the power generation tailwater enters the tailwater diversion dark channel through a plurality of tailwater diversion holes, and flows into the regulating channel from the water inlet A, and part of the power generation tailwater directly enters the regulating channel through the water inlet B, and the water diversion flow is large, which greatly improves the effect of attracting and gathering fish. The power generation tailwater entering the regulating channel is blocked and dissipated by the force dissipation sill, and flows into the fish collecting mechanism after being rectified by the rectifying wall, so as to form a water flow condition suitable for fish colonies.

Description

Technical Field

[0001] The invention relates to a system for luring, gathering and lifting fish in a canyon river section, belonging to the technical field of ecological and environmental protection of water conservancy and hydropower engineering. Background Art

[0002] Fish-passing facilities are an effective means to alleviate the barrier of dams to the free exchange of fish. Common fish-passing facilities include fishways, fish collection and transportation systems, and fish elevators. Fishways are channels for fish to swim upstream autonomously. Limited by the fish's ability to overcome currents, the bottom slope of fishways is relatively gentle, and they are often used in low-head water conservancy and hydropower projects. Common fish collection and transportation systems are mainly fish-collecting vessels. The draft of fish-collecting vessels is limited, and the effect of attracting fish in the middle and lower layers, especially the bottom layer, is not obvious. In addition, the wide application of fish-collecting vessels is limited by river terrain, navigation conditions, and operation and management requirements. The working principle of fish elevators is similar to that of elevators. Fish are transported from downstream waters to upstream waters by lifting and transporting, reducing the energy consumption of fish swimming over long distances. It has the advantages of saving fish energy and low investment, and is suitable for fish passage in high-head hydropower projects. The key to the operation effect of the fish lift lies in the fish gathering effect. Water flow is regarded as the best means to attract and gather fish. The inlet of the fish lift is often arranged at a certain position on the river bank or in the dam. Fish are attracted by water replenishment. The replenishment water flow is smaller than the power generation tail water flow. The fish swimming upstream from the dam often find it difficult to sense the fish-attracting water flow of the fish lift, and are attracted by the power generation tail water instead, resulting in poor fish gathering effect of the fish lift.

[0003] A Chinese patent document with publication number CN209873695U discloses a fish lifting device for gathering fish using tail water of a hydropower station. The device uses the tail water of a power plant to attract fish, has a large flow rate and a high fish gathering efficiency. It utilizes the flow-seeking characteristics of fish to gather fish in the most densely populated area of ​​fish, which can greatly improve the fish gathering efficiency. The device overcomes the disadvantage that the fish-attracting water flow at the fish inlet is small and cannot compete with the tail water of the power station, so most of the fish gather at the tail water of the power station, resulting in low fish gathering efficiency of the fish passing facilities.

[0004] In the fish lift device, the fish collecting pool is set in the downstream side of the tailwater hole / pipe or in the energy dissipation pool. However, the water flow velocity in the downstream side of the tailwater hole / pipe and the energy dissipation pool is high, and the flow pattern is extremely turbulent, which may exceed the flow resistance of fish. In addition, there are vertical circulations and lateral backflows, which have an adverse effect on the lured fish, making it difficult for them to maintain a stable swimming state, and even causing damage to the fish. Therefore, how to effectively use the power generation tailwater to form water flow conditions suitable for fish clusters to improve the fish luring and gathering effect of the fish lift has become a technical problem that needs to be solved urgently. Summary of the invention

[0005] In order to solve the above technical problems, the present invention provides a system for luring, gathering and lifting fish in a canyon river section.

[0006] The present invention is achieved through the following technical solutions:

[0007] A system for luring, gathering and lifting fish in a canyon river section comprises a tailwater channel / hole and a fish luring, gathering and lifting structure, wherein a reverse slope is arranged on the downstream side of the tailwater channel / hole, and the fish luring, gathering and lifting structure comprises a force dissipating and rectifying mechanism, a fish gathering mechanism and a fish lifting mechanism, wherein one end of the force dissipating and rectifying mechanism is connected to the reverse slope surface through a drainage mechanism, and the other end is connected to one end of the fish gathering mechanism, and the fish lifting mechanism is arranged on the fish gathering mechanism and connected to the top of the tailwater channel / hole.

[0008] The drainage mechanism comprises a tailwater diversion culvert, which is buried in the reverse slope and connected to the reverse slope surface through a plurality of tailwater diversion holes. A water inlet A is provided at one end of the tailwater diversion culvert to connect to the force dissipation and rectification mechanism.

[0009] The downstream end of the reverse slope surface is inclined upward relative to the upstream end, and a tailwater sill is arranged at the edge of the downstream end of the reverse slope surface.

[0010] The plurality of tailwater diversion holes are perpendicular to the tailwater diversion culvert, a water inlet B is provided on one side of the reverse slope to communicate with the energy dissipation and rectification mechanism, and the water inlet B is located on the upper side of the reverse slope surface.

[0011] The energy dissipation and rectification mechanism comprises a regulating channel and an energy dissipation sill, wherein the energy dissipation sill is arranged at one end of the regulating channel away from the drainage mechanism.

[0012] A rectifying wall is arranged on the energy dissipation sill. The rectifying wall is a concrete wall and a plurality of water-permeable holes are arranged on the rectifying wall.

[0013] The fish collecting mechanism comprises a fish collecting channel, in which a fish blocking fence and a plurality of fish inlet escape prevention cages are arranged, and the fish blocking fence is located between the fish inlet escape prevention cages and the force dissipation and rectification mechanism, and a fish collecting pool is arranged at the bottom of the fish collecting channel between the fish blocking fence and the fish inlet escape prevention cages.

[0014] The fish collecting channel is provided with a plurality of fish inlet escape prevention cages, and the plurality of fish inlet escape prevention cages are arranged in a row along the water depth direction, the fish inlet escape prevention cages are figure eight cages with a shape and size gradually decreasing from the inlet to the outlet, and the plurality of fish inlet escape prevention cages and fish barriers are arranged close to the fish collecting pond.

[0015] The fish lifting mechanism comprises a load-bearing frame, a transfer layer, a sorting temporary holding layer and a fish collecting bucket. A road is provided on the top of the tailwater channel / hole. The load-bearing frame comprises four columns A arranged side by side, and the tops of the four columns A are connected through a roof panel. A crane is provided at the bottom of the roof panel. The fish collecting bucket is connected to a hook on the crane through a rope and a lifting ring. The transfer layer and the sorting temporary holding layer are arranged side by side, and the transfer layer is located below the sorting temporary holding layer. The transfer layer and the sorting temporary holding layer are both connected to the four columns A, and avoidance openings are provided on the transfer layer and the sorting temporary holding layer at positions corresponding to the fish collecting buckets. One end of the transfer layer is connected to the road, and one end of the sorting temporary holding layer close to the road is connected to the transfer layer through a column B.

[0016] The fish collecting bucket is provided with a plurality of water holes, the sorting temporary rearing layer is provided with a sorting temporary rearing pool, the bottom of the sorting temporary rearing pool is provided with a fish draining pipe, the lower end of the fish draining pipe extends to the bottom of the sorting temporary rearing layer, and a valve is installed on the fish draining pipe.

[0017] A transporter is arranged between the sorting and temporary holding pool and the escape port on the sorting and temporary holding layer. The system also comprises a live fish transport vehicle, which can be driven to the transport layer along the road.

[0018] The beneficial effects of the present invention are:

[0019] 1. The tailwater flowing out of the tailwater channel / hole is initially dissipated through the reverse slope, and then part of the tailwater flows into the tailwater diversion dark channel through multiple tailwater diversion holes for further energy dissipation, and flows into the regulating channel from the water inlet A, and part of the tailwater flows directly into the regulating channel through the water inlet B. The water diversion flow is large, which greatly improves the effect of attracting and gathering fish.

[0020] 2. The tail water of power generation entering the regulating channel is blocked and dissipated by the stilling sill. Under the blocking effect of the stilling sill, the water level in the regulating channel gradually rises. When the water level is higher than the stilling sill, the tail water of power generation is rectified by the rectifying wall and then flows into the fish gathering mechanism to form water flow conditions suitable for fish aggregation.

[0021] 3. The fish lifted to the sorting and temporary holding layer can be classified and temporarily held in the sorting and temporary holding pond. Classification and temporary holding can not only help to improve the survival rate of various fish, but also improve the flexibility of transporting fish to the upper reaches of the river. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a structural schematic diagram of the present invention;

[0023] Figure 2 It is a schematic diagram of the assembly structure of the tailrace channel / hole and the drainage mechanism of the present invention;

[0024] Figure 3 It is a schematic diagram of the assembly structure of the tailwater channel / hole, the drainage mechanism, the force dissipation and rectification mechanism and the fish gathering mechanism of the present invention;

[0025] Figure 4 It is a schematic diagram of the assembly structure of the fish attracting, gathering and lifting structure and the tailwater channel / hole of the present invention;

[0026] Figure 5 It is a schematic diagram of the assembly structure of the force dissipation and rectification mechanism and the fish gathering mechanism of the present invention;

[0027] Figure 6 It is a structural schematic diagram of the fish gathering mechanism of the present invention;

[0028] Figure 7 It is a structural schematic diagram of the fish lifting mechanism of the present invention.

[0029] In the figure: 1-tailwater channel / hole, 11-tailwater bank, 12-tailwater diversion hole, 13-tailwater diversion underground channel, 14-water inlet A, 15-water inlet B, 2-river channel, 3-fish attracting, gathering and lifting structure, 31-energy dissipation and rectification mechanism, 311-regulating channel, 312-energy dissipation bank, 313-rectification wall, 32-fish gathering mechanism, 321-fish inlet escape prevention cage, 322-fish gathering pond, 323-fish barrier, 33-fish lifting mechanism, 331-transfer layer, 332-sorting temporary holding layer, 333-transporter, 334-sorting temporary holding pond, 335-live fish transport vehicle, 336-fish gathering bucket, 4-road. DETAILED DESCRIPTION

[0030] The technical solution of the present invention is further described below, but the scope of protection claimed is not limited to the description.

[0031] like Figures 1 to 7 As shown, a canyon river section fish luring, gathering and lifting system described in the present invention comprises a tailwater channel / hole 1 and a fish luring, gathering and lifting structure 3, wherein a reverse slope is constructed on the downstream side of the tailwater channel / hole 1, and the fish luring, gathering and lifting structure 3 comprises a force dissipating and rectifying mechanism 31, a fish gathering mechanism 32 and a fish lifting mechanism 33, wherein one end of the force dissipating and rectifying mechanism 31 is connected to the reverse slope surface through a drainage mechanism, and the other end is connected to one end of the fish gathering mechanism 32, and the fish lifting mechanism 33 is constructed on the fish gathering mechanism 32 and connected to the top of the tailwater channel / hole 1.

[0032] The drainage mechanism includes a tailwater diversion culvert 13, which is buried in the reverse slope and communicated with the reverse slope surface through a plurality of tailwater diversion holes 12. A water inlet A14 is provided at one end of the tailwater diversion culvert 13 to communicate with the energy dissipation and rectification mechanism 31. When in use, the opening of the tailwater diversion hole 12 on the reverse slope surface faces the power generation tailwater outlet, and the power generation tailwater enters the tailwater diversion culvert 13 through the plurality of tailwater diversion holes 12, and then flows into the energy dissipation and rectification mechanism 31 through the water inlet A14, forming a larger water diversion flow, which helps to improve the effect of attracting and gathering fish.

[0033] The downstream end of the reverse slope slope is inclined upward relative to the upstream end, and a tailwater bank 11 is built at the edge of the downstream end of the reverse slope slope. When in use, high-head hydropower projects are often arranged in canyon areas. Affected by topographic conditions, the outlet of the tailwater channel / tunnel 1 often has a certain angle with the river channel 2, so a reverse slope and tailwater bank 11 are set on the downstream side of the tailwater channel / tunnel 1 for energy dissipation to reduce the scouring of the slopes on both sides of the river channel 2 by the tailwater of power generation.

[0034] The plurality of tailwater diversion holes 12 are perpendicular to the tailwater diversion culvert 13, and a water inlet B15 is provided on one side of the reverse slope to communicate with the energy dissipation and rectification mechanism 31, and the water inlet B15 is located on the upper side of the reverse slope surface. When in use, the tailwater diversion hole 12 is perpendicular to the tailwater diversion culvert 13, so that the power generation tailwater flowing from the tailwater diversion hole 12 into the tailwater diversion culvert 13 is forced to be diverted to reduce the flow rate of the power generation tailwater, which has a certain energy dissipation effect. A water inlet B15 is provided on one side of the reverse slope to communicate with the energy dissipation and rectification mechanism 31, and the water inlet B15 increases the water diversion flow of the power generation tailwater, which helps to improve the effect of attracting and gathering fish.

[0035] The energy dissipation and rectification mechanism 31 comprises a regulating channel 311 and an energy dissipation sill 312. The energy dissipation sill 312 is built at one end of the regulating channel 311 away from the drainage mechanism. When in use, the power generation tail water entering the regulating channel 311 is blocked and energy dissipated by the energy dissipation sill 312.

[0036] A rectifying wall 313 is built on the energy dissipation sill 312. The rectifying wall 313 is a concrete wall and has a plurality of water permeable holes. Under the blocking effect of the energy dissipation sill 312, the water level in the regulating channel 311 gradually rises. When the water level is higher than the energy dissipation sill 312, the tail water of power generation flows into the fish gathering mechanism 32 after being rectified by the rectifying wall 313, so as to form a water flow condition suitable for fish aggregation.

[0037] The fish collecting mechanism 32 comprises a fish collecting channel, in which a fish fence 323 and a plurality of fish inlet escape prevention cages 321 are installed, and the fish fence 323 is located between the fish inlet escape prevention cages 321 and the force dissipation rectifying mechanism 31, and a fish collecting pool 322 is built at the bottom of the fish collecting channel between the fish fence 323 and the fish inlet escape prevention cages 321. When in use, the fish fence 323 is a permeable grille, which is used to prevent the fish between the fish fence 323 and the fish inlet escape prevention cages 321 from continuing to go upstream along the water flow.

[0038] A plurality of fish inlet escape prevention cages 321 are installed in the fish collecting channel, and the plurality of fish inlet escape prevention cages 321 are arranged in a row along the water depth direction, and the fish inlet escape prevention cages 321 are shaped like an eight-shaped cage with a gradually decreasing shape and size from the inlet to the outlet, and the plurality of fish inlet escape prevention cages 321 and the fish fence 323 are arranged close to the fish collecting pond 322. When in use, the plurality of fish inlet escape prevention cages 321 are installed in the fish collecting channel to induce fishes of different water layers to enter the waters above the fish collecting pond 322.

[0039] The fish lifting mechanism 33 includes a load-bearing frame, a transfer layer 331, a sorting and temporary holding layer 332 and a fish collecting bucket 336. A road 4 is built on the top of the tailwater channel / hole 1. The load-bearing frame includes four columns A arranged side by side, and the tops of the four columns A are connected through a roof panel. A crane is installed at the bottom of the roof panel. The fish collecting bucket 336 is connected to the hook on the crane through ropes and rings. The transfer layer 331 and the sorting and temporary holding layer 332 are arranged side by side, and the transfer layer 331 is located below the sorting and temporary holding layer 332. The transfer layer 331 and the sorting and temporary holding layer 332 are both connected to the four columns A, and avoidance openings are provided on the transfer layer 331 and the sorting and temporary holding layer 332 at positions corresponding to the fish collecting bucket 336. One end of the transfer layer 331 is connected to the road 4, and the end of the sorting and temporary holding layer 332 close to the road 4 is connected to the transfer layer 331 through a column B. When in use, the size of the fish collecting bucket 336 is slightly smaller than the size of the fish collecting pond 322 and can be placed in the fish collecting pond 322.

[0040] The fish collecting bucket 336 is processed with a plurality of water holes, and a sorting temporary holding pool 334 is built on the sorting temporary holding layer 332. A fish drain pipe is installed at the bottom of the sorting temporary holding pool 334, and the lower end of the fish drain pipe extends to the bottom of the sorting temporary holding layer 332, and a valve is installed on the fish drain pipe. The fish lifted to the sorting temporary holding layer 332 can be classified and temporarily held in the sorting temporary holding pool 334. Classification and temporary holding are beneficial to improving the survival rate of various fish and can improve the flexibility of fish transportation and delivery to the upper reaches of the river 2. A fish drain pipe is installed at the bottom of the sorting temporary holding pool 334, and a valve is installed on the fish drain pipe. When the live fish transport vehicle 335 moves to the bottom of the fish drain pipe, the valve can be opened to put the fish in the sorting temporary holding pool 334 into the live fish transport vehicle 335.

[0041] A transporter 333 is placed between the sorting and temporary holding pool 334 and the escape port on the sorting and temporary holding layer 332, and the system also includes a live fish transport vehicle 335, which can be driven to the transport layer 331 along the road 4. When in use, the transporter 333 is a mobile trolley with rollers, etc., and the live fish transport vehicle 335 is used to transport the fish to a river section suitable for release. The live fish transport vehicle 335 is equipped with life support systems such as oxygenation, temperature adjustment and monitoring.

[0042] The canyon river section fish attracting, gathering and lifting system of the present invention has the following working principle:

[0043] The lower side of the tailwater channel / hole 1 is provided with a reverse slope and a tailwater bank 11 to dissipate the energy of the power generation tailwater initially. Part of the power generation tailwater enters the tailwater diversion culvert 13 through multiple tailwater diversion holes 12, and then enters the regulating channel 311 from the water intake port A14. The water diversion flow is large, which helps to improve the effect of attracting and gathering fish; the power generation tailwater is forced to turn when it enters the tailwater diversion culvert 13 from the tailwater diversion hole 12, and the flow rate of the power generation tailwater is reduced, so as to achieve the purpose of further dissipating the energy of the power generation tailwater. In addition, part of the power generation tailwater directly enters the regulating channel 311 through the water intake port B15, which further increases the water diversion flow of the power generation tailwater, which helps to improve the effect of attracting and gathering fish.

[0044] The power generation tail water entering the regulating channel 311 is blocked and dissipated by the energy dissipation sill 312. Under the blocking effect of the energy dissipation sill 312, the water level in the regulating channel 311 gradually rises. When the water level is higher than the energy dissipation sill 312, the power generation tail water flows into the fish gathering mechanism 32 after being rectified by the rectifying wall 313 to form a water flow condition suitable for fish aggregation. Then the power generation tail water flows downstream through the fish gathering channel to attract downstream fish to swim upstream along the power generation tail water.

[0045] The fish enter the water area above the fish collecting pond 322 through the fish inlet escape prevention cage 321. When enough fish gather in the water area above the fish collecting pond 322, the fish collecting bucket 336 in the fish collecting pond 322 is lifted upward by a crane, and the fish collecting bucket 336 is lifted onto the sorting temporary holding layer 332, so as to salvage and lift the fish in the water area above the fish collecting pond 322 to the sorting temporary holding layer 332, and then the fish in the fish collecting bucket 336 is transferred to the sorting temporary holding pool 334 by the transporter 333, and sorted to the sorting temporary holding pool 334 for temporary holding. When the live fish transport vehicle 335 moves to the bottom of the fish discharge pipe, the valve can be opened to put the fish in the sorting temporary holding pool 334 into the live fish transport vehicle 335. Then, the live fish transport vehicle 335 transports the fish to a river section suitable for release for release.

Claims

1. A system for attracting, gathering and raising fish in a canyon river section, characterized by: The invention comprises a tailwater channel / hole (1) and a fish attracting, gathering, and lifting structure (3), wherein a reverse slope is provided on the downstream side of the tailwater channel / hole (1), and the fish attracting, gathering, and lifting structure (3) comprises a force dissipating and rectifying mechanism (31), a fish gathering mechanism (32), and a fish lifting mechanism (33), wherein one end of the force dissipating and rectifying mechanism (31) is connected to the reverse slope surface through a drainage mechanism, and the other end is connected to one end of the fish gathering mechanism (32), and the fish lifting mechanism (33) is arranged on the fish gathering mechanism (32) and connected to the top of the tailwater channel / hole (1); The drainage mechanism comprises a tailwater diversion culvert (13), the tailwater diversion culvert (13) being buried in the reverse slope and connected to the reverse slope surface through a plurality of tailwater diversion holes (12), and a water inlet A (14) being provided at one end of the tailwater diversion culvert (13) and connected to the force dissipation and rectification mechanism (31); The plurality of tailwater diversion holes (12) are perpendicular to the tailwater diversion culvert (13); a water inlet B (15) is provided on one side of the reverse slope and is connected to the force dissipation and rectification mechanism (31), and the water inlet B (15) is located on the upper side of the reverse slope surface; The energy dissipation and rectification mechanism (31) comprises a regulating channel (311) and an energy dissipation sill (312), wherein the energy dissipation sill (312) is arranged at one end of the regulating channel (311) away from the drainage mechanism; The energy dissipation sill (312) is provided with a rectifying wall (313), which is a concrete wall and has a plurality of water permeable holes.

2. The system for attracting, gathering and raising fish in a canyon river section as claimed in claim 1, characterized in that: The downstream end of the reverse slope surface is inclined upward relative to the upstream end, and a tailwater sill (11) is provided at the edge of the downstream end of the reverse slope surface.

3. The system for attracting, gathering and raising fish in a canyon river section as claimed in claim 1, characterized in that: The fish collecting mechanism (32) comprises a fish collecting channel, in which a fish blocking fence (323) and a plurality of fish inlet escape prevention cages (321) are arranged, and the fish blocking fence (323) is located between the fish inlet escape prevention cages (321) and the force dissipation and rectification mechanism (31), and a fish collecting pool (322) is arranged at the bottom of the fish collecting channel between the fish blocking fence (323) and the fish inlet escape prevention cages (321).

4. The system for attracting, gathering and raising fish in a canyon river section as claimed in claim 3, characterized in that: A plurality of fish inlet escape prevention cages (321) are provided in the fish collecting channel, and the plurality of fish inlet escape prevention cages (321) are arranged in a row along the water depth direction; the fish inlet escape prevention cages (321) are shaped like an eight-shaped cage whose shape and size gradually decrease from the inlet to the outlet; the plurality of fish inlet escape prevention cages (321) and the fish barrier (323) are all arranged close to the fish collecting pond (322).

5. The system for attracting, gathering and raising fish in a canyon river section as claimed in claim 1, characterized in that: The fish lifting mechanism (33) comprises a load-bearing frame, a transfer layer (331), a sorting and temporary raising layer (332) and a fish collecting bucket (336). A road (4) is provided on the top of the tailwater channel / hole (1). The load-bearing frame comprises four columns A arranged side by side, and the tops of the four columns A are connected by a roof panel. A crane is provided at the bottom of the roof panel. The fish collecting bucket (336) is connected to a hook on the crane by a rope and a lifting ring. The transfer layer (331) and the sorting and temporary raising layer (332) are arranged side by side. The transfer layer (331) is arranged below the sorting temporary holding layer (332), the transfer layer (331) and the sorting temporary holding layer (332) are both connected to four upright posts A, and both the transfer layer (331) and the sorting temporary holding layer (332) are provided with avoidance openings at positions corresponding to the fish collecting bucket (336), one end of the transfer layer (331) is connected to the road (4), and one end of the sorting temporary holding layer (332) close to the road (4) is connected to the transfer layer (331) via an upright post B.

6. The system for attracting, gathering and raising fish in a canyon river section as claimed in claim 5, characterized in that: The fish collecting bucket (336) is provided with a plurality of water holes, the sorting temporary rearing layer (332) is provided with a sorting temporary rearing pool (334), the bottom of the sorting temporary rearing pool (334) is provided with a fish drain pipe, the lower end of the fish drain pipe extends to below the sorting temporary rearing layer (332), and a valve is installed on the fish drain pipe.

7. The system for attracting, gathering and raising fish in a canyon river section as claimed in claim 6, characterized in that: A transporter (333) is provided on the sorting and temporary holding layer (332) between the sorting and temporary holding pool (334) and the escape port; the system also includes a live fish transport vehicle (335), which can be driven along the road (4) to the transport layer (331).

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