Water level amplitude adaptive composite partition type fishway

Abstract

The technical solution adopted in this invention is: a composite baffle-type fishway with adaptive water level variation, comprising: a flow channel with a consistent width and slope along its length; sidewalls respectively disposed on both sides of the flow channel; and several composite baffles installed within the flow channel, the composite baffles including a first baffle and a second baffle; the first baffle is located in front of the second baffle in the direction of water flow; wherein, the first baffle is composed of two trapezoidal symmetrical baffles fixedly connected to the sidewalls and the flow channel, forming a trapezoidal vertical slit flow structure that is narrow at the top and wide at the bottom; the second baffle is a composite structure that is U-shaped in plan and trapezoidal in elevation, narrow at the top and wide at the bottom, fixed at the centerline of the flow channel; there are gaps between the two sides of the second baffle and the sidewalls, forming an inverted trapezoidal vertical slit flow structure that is wide at the top and narrow at the bottom; this invention improves the fishway's ability to adapt to water level variation, forms a stable flow field conducive to fish swimming upstream, better protects fish, and reduces the obstructive impact of dams on watershed connectivity.

Description

Technical Field

[0001] This invention belongs to the technical field of water conservancy and environmental protection engineering, and specifically relates to a composite baffle-type fishway that adapts to water level fluctuations. Background Technology

[0002] For a long time, the construction of water conservancy projects has ensured the realization of various economic and social functions such as flood control, power generation, navigation, and water supply. However, engineering facilities such as dams have also had a profound impact on river ecosystems. The construction of large-scale dams has led to significant changes in the environmental characteristics of upstream and downstream areas, obstructing nutrient transport, fragmenting river habitats, reducing aquatic biodiversity, and seriously affecting the migration and ecological exchange of aquatic organisms such as fish. As an important ecological compensation measure to alleviate the obstruction effect of dams, fishways have been used internationally for more than 300 years. Their basic principle is to decompose the total water level difference between upstream and downstream areas into several smaller water level differences, thereby reducing the water flow velocity and providing a suitable passage for fish to migrate upstream and downstream.

[0003] Traditional fishway designs mainly include vertical slot, submersible, and Daniell structures, among which the vertical slot fishway is widely used due to its simple construction and uniform structure. However, due to the complex topography and climate conditions of my country's major rivers, the water level fluctuations upstream and downstream of the fishway are significant, and the existing vertical slot structure is clearly insufficient to adapt to these water level variations.

[0004] Specifically, this manifests in the following aspects:

[0005] 1. Mismatch in flow cross-sectional changes

[0006] When the water level drops, the cross-sectional area of ​​a traditional vertical slotted fishway decreases due to its fixed or uniform distribution, resulting in a sharp increase in flow velocity. This causes fish to encounter excessively high water velocities within the tank, hindering their ability to swim upstream.

[0007] 2. Limited flow pattern control capability

[0008] In existing technologies, the flow cross-sections are uniformly distributed longitudinally, making it difficult to effectively control local flow velocities. This uniform flow field structure interferes with fish's perception of the mainstream direction, affecting their normal migratory behavior.

[0009] 3. Insufficient local energy dissipation

[0010] The fixed width of the slits in the vertical slit structure makes it impossible to provide effective energy dissipation measures for different water depths and local flow patterns. This results in a mismatch in the spatial distribution of energy dissipation rate per unit water volume, which further exacerbates the occurrence of local high-velocity areas within the fishway. Summary of the Invention

[0011] The purpose of this invention is to address the shortcomings of the aforementioned background technology by providing a composite baffle-type fishway with adaptive water level variation, thereby improving the fishway's ability to adapt to water level variations, forming a stable flow field that is conducive to fish swimming upstream, better protecting fish, and reducing the obstructive impact of dams on watershed connectivity.

[0012] The technical solution adopted in this invention is: a composite baffle-type fishway with adaptive water level variation, comprising:

[0013] The flow channel has a consistent width and a slope along the entire flow path;

[0014] They are respectively installed on the side walls on both sides of the flow channel;

[0015] Several composite baffles are installed in the flow channel, the composite baffles include a first baffle and a second baffle; the first baffle is located in front of the second baffle in the direction of water flow;

[0016] The first baffle consists of two trapezoidal plates that gradually widen from top to bottom and are fixed to the bottom and side wall of the flow channel. The two trapezoidal plates have a vertical flow gap in the middle, which is narrow at the top and wide at the bottom, forming a flow structure that is narrow at the top and wide at the bottom.

[0017] The second baffle is a U-shaped structure in plan and a trapezoidal structure that is narrower at the top and wider at the bottom in elevation. It is fixed at the center line of the flow channel. Vertical flow gaps are left between the left and right sides of the baffle and the side wall, which correspond to the central gap of the first baffle, forming a side channel that is wider at the top and narrower at the bottom.

[0018] The composite baffle causes the flow velocity in the flow channel to be unevenly distributed along the height direction, with a larger velocity at the top and a smaller velocity at the bottom, forming a slow-flow zone with a certain depth at the bottom. This reduces the increase in flow velocity in the pool chamber when the downstream water level drops and adapts to water level changes.

[0019] In the above technical solution, the width of the top of the flow structure formed by the first baffle is greater than 1.5 times the tail swing amplitude of the fish with the longest body length passing through the fish passage.

[0020] In the above technical solution, the width of the bottom end of the flow structure formed by the second baffle is greater than 1.5 times the tail swing amplitude of the fish with the longest body length passing through the fish passage.

[0021] In the above technical solution, the width of the top of the flow structure formed by the first baffle is greater than 0.2 meters.

[0022] In the above technical solution, the width of the bottom end of the flow structure formed by the second baffle is greater than 0.2 meters.

[0023] In the above technical solution, the cross-sectional area S1 formed by the flow structure formed by any water level in the first baffle and the cross-sectional area S2 formed by the flow structure formed by the corresponding water level in the second baffle satisfy the following condition: (1-a)S2≦S1≦(1+a)S2; where a is the coordination coefficient.

[0024] In the above technical solution, the design process of the planar dimensions of the first and second baffles is as follows: In the water tank experiment, a water tank is constructed according to the scale reduction, and the baffles are installed and water is circulated according to the initial design dimensions; the water flow velocity at different measuring points is measured, or tracers are placed to observe whether the water flow is continuous through video monitoring, and the baffle size is adjusted according to the test results until the set flow field conditions are met.

[0025] In the above technical solution, the set flow field conditions include: the flow velocity in the water tank chamber is between 0.15 and 1.8 m / s, the water depth variation in the chamber is less than 0.3 m; there are no water drops or jumps, the streamlines are continuous, and there are no local areas of strong water flow turbulence.

[0026] In the above technical solution, the slope of the flow channel is a fixed angle, and the fixed angle within the design range ensures that the water flows smoothly along the channel.

[0027] In the above technical solution, the composite baffle is arranged at preset intervals along the longitudinal direction of the flow channel to form multiple local slow flow zones to meet the water flow environment requirements for different fish species.

[0028] The beneficial effects of this invention are as follows: By employing a composite structure of a first baffle and a second baffle, the water flow within the fishway is unevenly distributed along the height direction, forming a "larger at the top and smaller at the bottom," thus creating a slow-flow zone of a certain depth at the bottom of the fishway. This structural design reduces the reduction in cross-sectional area and the increase in flow velocity when the downstream water level drops, improving the local flow pattern and maintaining a relatively gentle change in the internal flow field, which is beneficial for the safe passage of different species of fish with varying flow capacities. The composite energy-dissipating baffle inside the invention ensures that the energy dissipation effect at the bottom is greater than at the top, enhancing the overall energy dissipation capacity and slowing the flow velocity when the water level drops. The invention also features two main migratory channels, making it less likely for fish to lose their way within the fishway. The width of the openings increases linearly from bottom to top, facilitating the passage of fish of different lengths and sizes. By regulating the flow field within the fishway through the composite baffle, this invention enables the fishway to maintain suitable hydraulic conditions even under large water level fluctuations, overcoming the weakness of existing vertical slotted fishways in adapting to water level changes. In fishway engineering, the use of this composite partition-type fishway can enhance the adaptability of fishways with high head differences and long distances to water level fluctuations, improve the fish passage effect, and better protect fish.

[0029] Furthermore, the top width of the flow structure formed by the first baffle of the present invention is greater than 1.5 times the swaying amplitude of the fish's tail, ensuring that the width of the flow area is sufficient to meet the requirements of the fish's swaying and passage, avoiding mechanical obstruction of the fish or causing local water flow turbulence due to the narrow channel, and improving the throughput.

[0030] Furthermore, the bottom width of the flow structure formed by the second baffle of the present invention is greater than 1.5 times the swaying amplitude of the fish's tail, which also ensures that the bottom flow area has sufficient width, ensuring that the fish can pass smoothly in the low flow velocity area, while taking into account hydraulic stability and reducing the adverse effects of local high flow velocity.

[0031] Furthermore, the flow width at the top of the first baffle of the present invention is greater than 0.2 meters, providing a clear minimum size standard to ensure that sufficient flow channel width can be formed under various operating conditions, effectively dispersing water flow energy, reducing peak flow velocity, and improving the environment for fish to pass through.

[0032] Furthermore, the flow width at the bottom of the second baffle of the present invention is greater than 0.2 meters, which also ensures that the lower part of the fishway has at least a basic passage width, guarantees the formation and stability of the low flow velocity zone, and provides safe passage conditions for fish.

[0033] Furthermore, by controlling the proportional relationship between the cross-sectional areas S1 and S2 formed by the first and second baffles (S2≦S1≦(1+a)S2), the present invention achieves the balance and coordination of water flow energy in different parts of the fishway, prevents rapid changes in water flow due to uneven local flow distribution, thereby improving the overall hydraulic regulation effect and the adaptability of fish passage.

[0034] Furthermore, this invention employs a water tank test to dynamically adjust and optimize the planar dimensions of the first and second baffles, ensuring that the final design achieves the preset flow field conditions. This method provides a practical and repeatable optimization process that can continuously correct design parameters based on experimental data, thereby ensuring that the fishway exhibits ideal hydraulic performance under actual operating conditions.

[0035] Furthermore, the flow field conditions set in this invention (pool velocity of 0.15–1.8 m / s, water depth variation of less than 0.3 m, no water drops or jumps, continuous streamlines, and no localized areas of strong turbulence) ensure that the fishway maintains a stable and continuous water flow environment during operation. This not only facilitates fish perception and successful upstream movement but also avoids energy concentration and turbulence problems caused by sudden changes in local flow patterns.

[0036] Furthermore, by setting up a flow channel with a fixed slope, the present invention allows water to flow smoothly along the channel, thereby providing a continuous and stable water flow channel. This design helps to control the overall flow velocity distribution within the fishway, reduces the impact on fish caused by sudden changes in water flow, and ensures the overall operational stability of the fishway.

[0037] Furthermore, the composite baffles of the present invention are arranged at predetermined intervals along the longitudinal direction of the flow channel to form multiple local slow-flow zones. This layout design can provide multiple low-flow-velocity areas for rest and adaptation according to the differences in fish species and swimming abilities, improve the passage conditions for fish, and enhance the adaptability of the fishway to different water level changes, ensuring the efficient operation of the ecological channel. Attached Figure Description

[0038] Figure 1 This is a three-dimensional structural rendering of the present invention.

[0039] Figure 2 This is a schematic longitudinal section of the structure of the present invention.

[0040] Figure 3 This is a schematic diagram of the planar dimensions of an embodiment.

[0041] Figure 4 This is a schematic diagram showing the structural dimensions of the first and second partitions in the embodiment.

[0042] Figure 5 This is a flow field distribution diagram of the pool chamber surface in an embodiment.

[0043] Figure 6 This is a flow field distribution diagram of the bottom layer of the pool chamber in an embodiment.

[0044] Figure 7 This is a flow field distribution diagram of the first baffle section in the embodiment.

[0045] Figure 8 This is a flow field distribution diagram of the second baffle section in the embodiment.

[0046] Figure 9 This is a water depth distribution map along the route of the embodiment.

[0047] Figure 10 This is a diagram showing the average flow velocity distribution along the orifice in the embodiment.

[0048] Wherein, 1-flow channel, 2-side wall, 3-first baffle, 4-second baffle. Detailed Implementation

[0049] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments to facilitate a clear understanding of the present invention, but these descriptions do not constitute a limitation on the present invention.

[0050] like Figure 1-4As shown, the present invention provides a composite baffle-type fishway with adaptive water level variation, comprising:

[0051] The flow channel 1 has a consistent width along the flow path and a slope;

[0052] They are respectively installed on the side walls 2 on both sides of the flow channel 1;

[0053] Several composite baffles are installed in the flow channel 1. The composite baffles include a first baffle 3 and a second baffle 4. The first baffle 3 is located in front of the second baffle 4 in the water flow direction.

[0054] The first baffle 3 is composed of two vertical trapezoidal symmetrical baffles that are fixedly connected to the side wall 2 and the flow channel 1, which together form a trapezoidal vertical slit flow structure that is narrow at the top and wide at the bottom.

[0055] The second baffle 4 is a composite structure that is U-shaped in plan and trapezoidal in height with narrow top and wide bottom, and is fixed at the center line of the flow channel 1; there are gaps between the two sides of the second baffle 4 and the side wall 2, forming an inverted trapezoidal vertical slit flow structure with wide top and narrow bottom;

[0056] The composite baffle causes the flow velocity in the flow channel 1 to be unevenly distributed along the height direction, with a larger velocity at the top and a smaller velocity at the bottom, forming a slow-flow zone with a certain depth at the bottom. This reduces the increase in inlet flow velocity when the downstream water level drops and adapts to water level changes.

[0057] Specifically, the width a2 at the top of the flow structure formed by the first baffle 3 is greater than 1.5 times the tail swing amplitude of the longest fish passing through the fish passage, and the width a1 at the bottom of the flow structure formed by the first baffle 3 is greater than a2. These values ​​are set according to specific fish passage requirements. For example... Figure 4 As shown,

[0058] Specifically, the width of the bottom b1 of the flow passage structure formed by the second baffle 4 is greater than 1.5 times the tail swing amplitude of the fish with the longest body length passing through the fish passage. The width b1 of the top of the flow passage structure formed by the second baffle 4 is greater than b2, and its value is set according to the specific fish passage requirements. The top cross-section of the second baffle 4 is a trapezoid with one side open, and its bottom cross-section is a rectangle with the same side open.

[0059] Specifically, the width at the top of the flow structure formed by the first baffle 3 is greater than 0.2 meters. The width at the bottom of the flow structure formed by the second baffle 4 is greater than 0.2 meters.

[0060] Preferably, the first baffle is composed of two trapezoidal plates that gradually widen from top to bottom, and is fixed to the bottom and side wall of the flow channel. The two trapezoidal plates have a vertical flow gap in the middle, which is narrow at the top and wide at the bottom, forming a "narrow at the top and wide at the bottom" flow structure.

[0061] The example dimensions of the first partition are as follows:

[0062] Top gap width: approximately 0.20m;

[0063] Bottom gap width: approximately 0.80m;

[0064] Distance between the partition and the side wall: approximately 0.60m (the exact distance can be adjusted according to the total width of the fishway and the size of the target fish).

[0065] Baffle height: Matches the depth of the flow channel (approximately 3.0m in this embodiment).

[0066] The functional characteristics of the first partition are as follows:

[0067] The design of the slit, which is narrower at the top and wider at the bottom, creates a more obvious stratification of flow velocity when water flows through the baffle: the flow velocity is higher at the top and relatively lower at the bottom.

[0068] When the downstream water level drops, causing the inlet flow velocity to increase, the slow-flow zone at the bottom can still maintain a certain depth, helping fish to pass through the low-velocity zone.

[0069] The second baffle is a U-shaped structure in plan and a trapezoidal structure that is narrower at the top and wider at the bottom in elevation. It is installed at the center line of the flow channel. Vertical flow gaps are left between the left and right sides of the baffle and the side walls, corresponding to the central gap of the first baffle, forming an inverted trapezoidal (wider at the top and narrower at the bottom) side channel. The second baffle includes a baffle body, with symmetrical wing plates vertically arranged on both sides of the baffle body. The baffle body is a trapezoidal flat plate structure that is narrower at the top and wider at the bottom, and the wing plates are triangular flat plate structures. The wing plates are distributed along both sides of the baffle body.

[0070] The sample dimensions for the second partition are as follows:

[0071] Top width (partition body): Approximately 0.50m;

[0072] Bottom width (partition body): Approximately 1.10m;

[0073] Side gaps: For example, leave a flow channel of about 0.25m at the bottom and about 0.55m at the top (the specific design depends on the total width of the fishway and the needs of the target fish species);

[0074] Baffle height: also matches the depth of the flow channel.

[0075] The functional characteristics of the second partition are as follows:

[0076] Compared to the central flow pattern of the first baffle, the second baffle places the main structure on the centerline, forming flow channels on both sides; its "narrow at the top and wide at the bottom" main body makes the water flow in the middle relatively uniform, while the side gaps provide slow flow zones or rest areas under different water level conditions; the alternating arrangement of the first and second baffles can form different flow patterns along the fishway, enhancing the fishway's adaptability to water level fluctuations.

[0077] The alternating appearance of the central gap of the first baffle and the side gap of the second baffle creates different flow patterns in different sections, ensuring smooth flow at high water levels while suppressing excessive flow velocity at low water levels.

[0078] Both types of partitions are characterized by being narrow at the top and wide at the bottom or being inverted trapezoidal, which can create a relatively stable low-velocity area at the bottom, providing an upstream passage or resting place for fish with different swimming abilities.

[0079] When the downstream water level drops, the flow velocity at the inlet section inevitably increases. However, through the orderly arrangement of the aforementioned composite baffle structure, the increase in the peak flow velocity can be effectively reduced, thereby improving the overall hydraulic stability and passage efficiency of the fishway.

[0080] Specifically, the cross-sectional area S1 formed by the flow structure of the first baffle 3 at any water level and the cross-sectional area S2 formed by the flow structure of the corresponding water level in the second baffle 4 satisfy the following condition: (1-a)S2≦S1≦(1+a)S2; where a is a coordination coefficient, with a value of 0.1-0.3, and its value decreases as the scale of the fishway construction increases. Figure 4 As shown, the dark blue shaded area is S1, and the light yellow shaded area is S2.

[0081] Specifically, the design process for the planar dimensions of the first baffle 3 and the second baffle 4 is as follows: In the water tank experiment, a water tank is constructed by scaling down, and the baffles are installed and water is circulated according to the initial design dimensions; the water flow velocity at different measuring points is measured, or tracers are placed to observe whether the water flow is continuous through video monitoring, and the baffle dimensions are adjusted according to the test results until the set flow field conditions are met.

[0082] The established flow field conditions include: the flow velocity in the tank chamber is between 0.15 and 1.8 m / s; the water depth variation within the chamber is less than 0.3 m; there are no water drops or jumps; the streamlines are continuous; there are no localized areas of strong turbulence, i.e., the Froude number Fr < 1.7; and the energy dissipation rate per unit volume of water E is less than 200 W / m³. 3 The continuous water flow was observed through manual review of video monitoring.

[0083] Specifically, the slope of the flow channel 1 is a fixed angle, which ensures that the water flows smoothly along the channel within the design range, and is set according to the specific application scenario.

[0084] Specifically, the composite baffles are arranged at preset intervals along the longitudinal direction of the flow channel 1 to form multiple local slow-flow zones to meet the water flow environment requirements for different fish species.

[0085] The following operating conditions were proposed for calculation and analysis of the embodiment to simulate the impact of the drop in the inlet water level. The calculation conditions are shown in Table 1.

[0086] Table 1. Simulation Calculation Conditions for Composite Partition Fishway

[0087]

[0088] like Figure 5 and Figure 6 As shown, where Figure 5 The flow field distribution on the surface of the fishway in the embodiment shows that the flow width at the first baffle 3 on the surface is small, and the second baffle 4 plays a role in flow obstruction and energy dissipation, but the water backflow is not significant.

[0089] Figure 6 The flow field distribution at the bottom of the fishway shows that the flow width at the first baffle 3 is relatively large, and the second baffle 4 plays a stronger role in flow obstruction and energy dissipation. The water flow back is significant, and the flow velocity at the bottom is effectively reduced.

[0090] like Figure 7 The figures show the simulated flow field distribution of the first baffle 3 cross section under three different operating conditions in the embodiment. It can be seen that the flow velocity at the first baffle 3 is generally distributed as "higher at the top and lower at the bottom". The surface velocity in operating condition 3 is about 1.5 m / s, the bottom velocity is about 0.6 m / s, and the highest velocity is distributed in the middle of the baffle, with a maximum velocity of about 1.9 m / s. The average flow velocity of the baffle cross section is 1.08 m / s.

[0091] The velocity distribution pattern at section 2 is consistent with that at section 3, but as the downstream water level drops, the maximum velocity increases to about 2.4 m / s, and the average velocity at the first baffle 3 is 1.35 m / s.

[0092] In condition 1, the downstream water level drops significantly, leading to a substantial increase in the inlet velocity. The average velocity at section 3 of the first baffle is approximately 1.71 m / s. This non-uniform velocity distribution facilitates the passage of different species of fish with varying flow capacities. Furthermore, while the average velocity at the cross-section increases, the velocity at the bottom remains relatively low, which also helps fish pass through.

[0093] like Figure 8 The figures show the simulated flow field distribution of the second baffle 4 section under three different operating conditions in the embodiment. It can be seen that the flow velocity at the second baffle 4 is slightly lower than that at the first baffle 3, and the flow velocity distribution is relatively more uniform.

[0094] There are low-velocity zones inside the pool chamber in front of and behind the second partition 4, which can provide resting water for fish and are conducive to fish swimming upstream.

[0095] like Figure 9As shown, the water depth distribution along the composite baffle under three calculation conditions in the embodiment is as follows. It can be seen that the water depth at the outlet section fluctuates around 2.98m under the three conditions and is relatively stable. The water depth gradually decreases along the baffle. Under the condition that the inlet water level drops by 1m, the overall water surface line can still remain relatively stable. Under the condition that the inlet water level drops by 2m, the drop in the water surface line at the inlet section is more significant.

[0096] like Figure 10 As shown, the distribution of the average flow velocity along the vertical joint of the composite baffle is shown in the three calculation conditions in the embodiment. It can be seen that the flow velocity along the fishway outlet section and the middle section is basically stable, and the flow velocity change mainly occurs in the inlet section.

[0097] In both operating conditions 1 and 2, the average flow velocity at the inlet section continuously increases as the water level decreases, reaching 1.41 m / s and 2.26 m / s respectively. Although this is an increase compared to operating condition 3, the magnitude is smaller than that of a conventional fishway.

[0098] Analysis of the average flow velocity at the inlet vertical slot cross-section under different operating conditions in the embodiments shows that the inlet flow velocity of the composite baffle scheme increases when the downstream water level drops. Under the condition that the downstream water level drops by 1.0m, the inlet flow velocity of the fishway under normal operating condition 3 increases to 1.41m / s, an increase of 29%, while the flow velocity increase of the conventional vertical slot fishway should be 50%. The flow velocity reduction of the composite baffle is 21%.

[0099] When the downstream water level drops by 2m, the inlet velocity of the fishway increases to 2.26m / s compared to the normal operating condition, an increase of 107.2%, while the velocity increase of a conventional vertical slotted fishway should be 200%. The velocity reduction achieved by using composite baffles is 92.8%.

[0100] Table 2 shows the comparison results of the energy dissipation effect calculation under various working conditions of the composite baffle fishway in the embodiments, indicating that the present invention can significantly improve the fishway's ability to adapt to water level changes.

[0101] Table 2 compares the energy dissipation effects of the composite baffle fishway under various operating conditions in the embodiments.

[0102]

[0103] The contents not described in detail in this specification are existing technologies known to those skilled in the art.

Claims

1. A composite baffle-type fishway with adaptive water level variation, characterized in that: include: The flow channel has a consistent width and a slope along the entire flow path; They are respectively installed on the side walls on both sides of the flow channel; Several composite baffles are installed in the flow channel, the composite baffles include a first baffle and a second baffle; the first baffle is located in front of the second baffle in the direction of water flow; The first baffle consists of two trapezoidal plates that gradually widen from top to bottom and are fixed to the bottom and side wall of the flow channel. The two trapezoidal plates have a vertical flow gap in the middle, which is narrow at the top and wide at the bottom, forming a flow structure that is narrow at the top and wide at the bottom. The second baffle is a U-shaped structure in plan and a trapezoidal structure that is narrower at the top and wider at the bottom in elevation. It is fixed at the center line of the flow channel. Vertical flow gaps are left between the left and right sides of the baffle and the side wall, which correspond to the central gap of the first baffle, forming a side channel that is wider at the top and narrower at the bottom. The composite baffle causes the flow velocity in the flow channel to be unevenly distributed along the height direction, with a larger velocity at the top and a smaller velocity at the bottom, forming a slow-flow zone with a certain depth at the bottom. This reduces the increase in inlet flow velocity when the downstream water level drops and adapts to water level changes.

2. The composite baffle-type fishway with adaptive water level variation according to claim 1, characterized in that: The width of the top of the flow structure formed by the first baffle is more than 1.5 times the tail swing amplitude of the longest fish passing through the fish passage.

3. The composite baffle-type fishway with adaptive water level variation according to claim 1, characterized in that: The width of the bottom of the flow structure formed by the second baffle is greater than 1.5 times the tail swing amplitude of the fish with the longest body length passing through the fish passage.

4. The composite baffle-type fishway with adaptive water level variation according to claim 1, characterized in that: The width of the top of the flow structure formed by the first baffle is greater than 0.2 meters.

5. The composite baffle-type fishway with adaptive water level variation according to claim 1, characterized in that: The width of the bottom of the flow structure formed by the second baffle is greater than 0.2 meters.

6. The composite baffle-type fishway with adaptive water level variation according to claim 1, characterized in that: The cross-sectional area S1 formed by the flow structure formed by any water level in the first baffle and the cross-sectional area S2 formed by the flow structure formed by the corresponding water level in the second baffle satisfy the following condition: (1-a)S2≦S1≦(1+a)S2; where a is the coordination coefficient.

7. The composite baffle-type fishway with adaptive water level variation according to claim 1, characterized in that: The design process for the planar dimensions of the first and second baffles is as follows: In the water tank experiment, a water tank is constructed according to the scale reduction, and the baffles are installed and water is circulated according to the initial design dimensions; the water flow velocity at different measuring points is measured, or tracers are placed to observe whether the water flow is continuous through video monitoring, and the baffle dimensions are adjusted according to the test results until the set flow field conditions are met.

8. The composite baffle-type fishway with adaptive water level variation according to claim 7, characterized in that: The set flow field conditions include: the flow velocity in the water tank chamber is between 0.15 and 1.8 m / s, the water depth variation in the chamber is less than 0.3 m; there are no water drops or jumps, the streamlines are continuous, and there are no local areas of strong water flow turbulence.

9. The composite baffle-type fishway with adaptive water level variation according to claim 1, characterized in that, The slope of the flow channel is a fixed angle, which, within the design range, ensures that the water flows smoothly along the channel.

10. The composite baffle-type fishway with adaptive water level variation according to claim 1, characterized in that, The composite baffles are arranged at preset intervals along the longitudinal direction of the flow channel to form multiple local slow-flow zones, in order to meet the water flow environment requirements for different fish species.

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