A device suitable for the entrance section of a fishway in the case of low downstream water level

Abstract

The application discloses a device suitable for a fishway inlet section with low downstream water level, which comprises a fishway section, a water supplement section and a natural imitation section. The natural imitation section is arranged along the slope of the river channel and along the flow direction of the river channel. The upstream end of the natural imitation section is open and connected with the inlet end of the fishway section and the water outlet end of the water supplement section. The downstream end of the natural imitation section is open and connected with the river channel. The natural imitation section comprises water retaining walls on both sides. A plurality of water permeable weirs for high water level are arranged side by side between the water retaining walls along the flow direction of the river channel. The water permeable weirs are provided with water passing openings and used as the upstream migration openings for fish. The upstream end of the natural imitation section is provided with an overflow weir at a position between the inlet end of the fishway section and the water outlet end of the water supplement section. The overflow weir is used to separate the inlet end of the fishway section and the water outlet end of the water supplement section and guide fish into the fishway section. The application can improve the flow conditions in the natural imitation section within the range of the inlet end of the fishway section, and facilitate the fish in the river channel to migrate upstream to the fishway section through the natural imitation section.

Description

Technical Field

[0001] The invention belongs to the technical field of river fish passage, and particularly relates to a fishway inlet section device suitable for a downstream water level that is too low. Background Art

[0002] Fishways, as an important ecological compensation measure for barrages, are being widely used at various hydropower stations. In recent years, small hydropower projects in mountainous areas, as a key target for ecological remediation, have seen an increase in fishway construction to restore blocked upstream fish migration pathways and improve fish habitats.

[0003] Rivers where small hydropower stations are located in mountainous areas are often characterized by significant seasonal flow fluctuations, steep slopes, and low water levels. During the design of fishway inlets, a series of problems often arise due to low downstream water levels, specifically in the following two aspects:

[0004] On the one hand, due to the low water level downstream, when the traditional vertical slot fishway structure design is adopted, the water depth at the entrance often does not reach the recommended value of the current specifications and guidelines, and the operation effect cannot be fully exerted. To solve this problem, the riverbed within the fishway entrance range can usually be appropriately deepened to form a deep water area within a certain range, thereby ensuring that the water depth at the fishway entrance is within the recommended value range of the specifications and guidelines. However, mountainous rivers usually have obvious flood and dry season rhythms, large flow and fast flow rate during flood season, and the riverbed is highly developed and evolves rapidly. The deep water areas artificially formed in the fishway entrance range are usually affected by the flood season and will usually shift and fill up. After being washed away by the flood season, most of them are difficult to maintain the water depth and cannot continue to play their corresponding role.

[0005] On the other hand, water replenishment design is a commonly used supporting facility to improve the fish-luring effect of fishways. The effect is more significant when the water depth at the fishway entrance is certain. The high flow rate and large flow rate of the fishway water flow used to lure fish are used to distinguish the mainstream of the river, induce fish to enter the relatively narrow fishway entrance, and then enter the fishway facilities to achieve upstream. When the downstream water depth is shallow, the fishway water flow used to lure fish and the large flow of water replenishment will quickly dissipate energy near the fishway entrance, resulting in complex water flow conditions with large local turbulence. Fish may exhibit avoidance behavior, which is not conducive to fish quickly finding the fishway entrance and entering the fishway. Summary of the Invention

[0006] In view of the above-mentioned defects of the prior art, the present invention provides a fishway inlet section device suitable for use when the downstream water level is too low, which can improve the water flow conditions within the simulated natural section within the inlet end of the fishway section, making it easier for fish in the river to swim upstream to the fishway section through the simulated natural section.

[0007] The technical solution adopted by the present invention to solve its technical problem is:

[0008] A fishway inlet section device suitable for use with a downstream water level that is too low, comprising a fishway section, a water replenishment section and an artificial natural section, wherein the artificial natural section is arranged along the slope of the river channel and along the flow direction of the river channel, the upstream end of the artificial natural section is open and connected to the inlet end of the fishway section and the outlet end of the water replenishment section, and the downstream end of the artificial natural section is open and connected to the river channel; the artificial natural section comprises retaining walls on both sides, and multiple levels of permeable weirs for raising the water level are arranged side by side between the retaining walls on both sides along the flow direction of the river channel, the permeable weirs are provided with water outlets and serve as upstream ports for fish, and the upstream end of the artificial natural section is provided with an overflow weir at a position between the inlet end of the fishway section and the outlet end of the water replenishment section, which is used to separate the inlet end of the fishway section from the outlet end of the water replenishment section and to guide fish into the fishway section.

[0009] Furthermore, the distance between the retaining walls on both sides gradually decreases along the flow direction of the river channel, and the opening width of the downstream end of the simulated natural section is greater than the width of the inlet end of the fishway section.

[0010] Furthermore, the retaining wall is a gabion retaining wall, which includes one or more rows of gabion retaining wall units stacked and fixedly connected from top to bottom, and the gabion retaining wall units include multiple gabion retaining wall segments spliced ​​and fixedly connected end to end along the length direction, and the gabion retaining wall segments include gabion nets, and the gabion nets are provided with anti-seepage parts vertically arranged along the length direction of the gabion retaining wall segments, and the gabion nets on both sides of the anti-seepage parts are filled with graded blocks of stone.

[0011] Furthermore, the gabion net includes a gabion net outer periphery which is located around the outside of the gabion retaining wall segment and has an open top. A plurality of gabion net partitions are vertically arranged along the width direction of the gabion retaining wall segment. A gabion net top cover is provided at the top opening of the gabion net outer periphery, and the anti-seepage member intersects with each gabion net partition.

[0012] Furthermore, the anti-seepage member is an anti-seepage plate or an anti-seepage membrane.

[0013] Furthermore, one end of the permeable weir is connected to the side of one retaining wall away from the river channel, and the other end is connected to the side of the other retaining wall away from the river channel. The permeable weir is formed by splicing multiple blocks of stone, and there are one or more water outlets.

[0014] Furthermore, the blocks are flat blocks with a length greater than or equal to 1 m, the spacing between adjacent permeable weirs is controlled at 5-10 m, and the width of the water outlet is greater than or equal to 0.5 m.

[0015] Furthermore, a group of wild rocks for slowing down the flow rate of water is provided in the simulated natural section area between the adjacent levels of the permeable weirs.

[0016] Furthermore, the barbarian stone community includes a plurality of barbarian stones, and the plurality of barbarian stones are arranged in a plum blossom shape, and the distance between adjacent barbarian stones is controlled to be 1-3m.

[0017] Furthermore, the opening width of the downstream end of the simulated natural section is greater than or equal to twice the width of the inlet end of the fishway section, and the water depth at the downstream end of the simulated natural section is greater than or equal to 0.3 m.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] The present invention is suitable for a fishway inlet section device with a downstream water level that is too low, and comprises a fishway section, a water replenishment section and a simulated natural section. The simulated natural section is arranged along the slope of the river channel and along the flow direction of the river channel. The upstream end of the simulated natural section is open and connected to the inlet end of the fishway section and the outlet end of the water replenishment section. The downstream end of the simulated natural section is open and connected to the river channel. The simulated natural section comprises retaining walls on both sides. Between the retaining walls on both sides, multiple levels of permeable weirs for raising the water level are arranged side by side along the flow direction of the river channel. The permeable weirs are provided with water outlets and serve as upstream ports for fish. The upstream end of the simulated natural section is located between the inlet end of the fishway section and the outlet end of the water replenishment section. An overflow weir is provided to separate the inlet of the fishway section from the outlet of the water replenishment section and to guide fish into the fishway section. In this way, by setting up multi-stage permeable weirs in the simulated natural section, the water level is raised, and combined with the water flow supplemented by the water replenishment section, the water flow conditions in the simulated natural section within the inlet of the fishway section are improved, so that fish in the river channel can flow upstream to the fishway section through the water outlet, i.e., the upstream outlet, of the permeable weir in the simulated natural section. The water flow in the water replenishment section enters the simulated natural section through the overflow weir to raise the water level in the simulated natural section. The overflow weir can prevent fish that flow upstream to the simulated natural section from entering the water replenishment section through the overflow weir, thereby facilitating the guidance of fish into the fishway section.

[0020] In the present invention, since the spacing between the water retaining walls on both sides gradually decreases along the flow direction of the river channel, it can ensure that the water level at the downstream end of the simulated natural section is at a relatively high water level and smoothly transitions to the water level of the downstream river channel, so that fish can enter the simulated natural section through the downstream end opening of the simulated natural section; since the width of the downstream end opening of the simulated natural section is greater than the width of the inlet end of the fishway section, and the width of the simulated natural section gradually increases from downstream to upstream, the cross-sectional width of the simulated natural section can be significantly expanded, so as to provide a more spacious fish upstream channel. In addition, the setting of the simulated natural section can combine the traditional fishway fish-attracting water flow and the water-replenishing fish-attracting water flow into one, and form an overall fish-attracting water flow, and the overall fish-attracting water flow is more stable and concentrated, and while maintaining a large flow rate and high flow rate, a wider inlet section is used, which can more effectively improve the fish-attracting effect of the fishway section. At the same time, the simulated natural section can also reduce the "lost" rate after failing to enter the fishway section for the first time, and continue to provide directional guidance for fish, so as to ensure the continuity of fish upstream.

[0021] In the present invention, a rock community is provided in the simulated natural section area between adjacent permeable weirs; the provision of such a rock community can slow down the water flow velocity and create a diverse habitat; in addition, it can make the fish-attracting water flow in the simulated natural section flow more stable while ensuring the required water level, and can make it easier for fish to enter the simulated natural section through the downstream end opening of the simulated natural section. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Schematic diagram of the top view of the structure of the fishway inlet section device suitable for use in a case where the downstream water level is too low;

[0023] Figure 2 for Figure 1 Schematic diagram of the main structure of the middle permeable weir;

[0024] Figure 3 This is a schematic diagram of the stacking of gabion retaining walls;

[0025] Figure 4 This is a schematic diagram of the three-dimensional structure of the gabion retaining wall segment when the gabion mesh is not filled with graded blocks of stone.

[0026] Explanation of the reference numerals in the figure: 1. Imitation natural section, 11. Gabion retaining wall, 1101. Gabion retaining wall segment, 11011. Gabion mesh periphery, 11012. Gabion mesh partition, 11013. Gabion mesh top cover, 11014. Anti-seepage component, 12. Permeable weir, 13. Water outlet, 14. Overflow weir, 15. Stone, 2. Fishway section, 3. Water replenishment section. DETAILED DESCRIPTION

[0027] The following is a further detailed description of the specific embodiments of the present invention in conjunction with the accompanying drawings. These embodiments are only used to illustrate the present invention and are not intended to limit the present invention.

[0028] In the description of the present invention, it should be noted that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "back," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer" and the like, indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings and are intended solely to facilitate and simplify the description of the present invention. They are not intended to indicate or imply that the devices or components referred to must have, be constructed, or operate in a specific orientation, and therefore should not be construed as limiting the present invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0029] In the description of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "mounted," "connected," and "connected" should be understood in a broad sense. For example, they may refer to fixed, detachable, or integral connections; mechanical or electrical connections; direct or indirect connections through an intermediate medium; and internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0030] Furthermore, in the description of the present invention, unless otherwise specified, “plurality” means two or more.

[0031] like Figure 1-2 As shown, a fishway inlet section device suitable for use in situations where the downstream water level is too low comprises a fishway section 2, a water replenishment section 3 and an artificial natural section 1, wherein the fishway section 2 is a vertical slit fishway section, the artificial natural section 1 is arranged along the slope of the river channel and along the flow direction of the river channel, preferably, the slope of the artificial natural section 1 is not greater than 5%, the upstream end of the artificial natural section 1 is open and connected to both the inlet end of the fishway section 2 and the outlet end of the water replenishment section 3, and the downstream end of the artificial natural section 1 is open and connected to the river channel; the artificial natural section 1 comprises retaining walls on both sides, and a plurality of permeable weirs 12 for raising the water level are arranged side by side between the retaining walls on both sides along the flow direction of the river channel, the permeable weir 12 is provided with a water outlet 13 and serves as an upstream port for fish, and an overflow weir 14 is provided at the upstream end of the artificial natural section 1 between the inlet end of the fishway section 2 and the outlet end of the water replenishment section 3, for separating the inlet end of the fishway section 2 from the outlet end of the water replenishment section 3 and guiding fish into the fishway section 2.

[0032] In this way, by setting up the multi-stage permeable weir 12 in the simulated natural section 1 to raise the water level, and combining with the water flow supplemented by the water replenishment section 3, the water flow conditions in the simulated natural section 1 within the inlet end of the fishway section 2 are improved, so that the fish in the river channel can go upstream to the fishway section 2 through the water outlet 13, i.e., the upstream outlet, of the permeable weir 12 in the simulated natural section 1. The water flow in the water replenishment section 3 enters the simulated natural section 1 through the overflow weir 14 to raise the water level in the simulated natural section 1. The overflow weir 14 can prevent the fish that go upstream to the simulated natural section 1 from entering the water replenishment section 3 through the overflow weir 14, thereby facilitating the guidance of the fish into the fishway section 2.

[0033] In one embodiment,

[0034] The spacing between the retaining walls on both sides gradually decreases along the flow direction of the river channel, which can ensure that the water level at the downstream end of the simulated natural section 1 is at a relatively high water level and smoothly transitions to the water level of the downstream river channel, so that fish can enter the simulated natural section 1 through the downstream end opening of the simulated natural section 1; the width of the downstream end opening of the simulated natural section 1 is greater than the width of the inlet end of the fishway section 2, and the width of the simulated natural section gradually increases from downstream to upstream, which can significantly expand the cross-sectional width of the simulated natural section 1, so as to provide a more spacious fish upstream channel. In addition, the setting of the simulated natural section 1 can combine the traditional fishway fish-attracting water flow and the water-replenishing fish-attracting water flow into one, and form an overall fish-attracting water flow, and the overall fish-attracting water flow is more stable and concentrated, and while maintaining a large flow rate and high flow rate, using a wider inlet section, it can more effectively improve the fish-attracting effect of the fishway section 2. At the same time, the simulated natural section 1 can also reduce the "lost" rate after failing to enter the fishway section 2 for the first time, and continue to provide directional guidance for fish to ensure the continuity of fish upstream.

[0035] Preferably, the opening width of the downstream end of the simulated natural section 1 is greater than or equal to twice the width of the inlet end of the fishway section 2, and the water depth at the downstream end of the simulated natural section 1 is greater than or equal to 0.3 m.

[0036] In one embodiment,

[0037] The retaining wall is a gabion retaining wall 11, which includes one or more rows of gabion retaining wall units stacked and fixedly connected from top to bottom. Figure 3 The gabion retaining wall unit includes multiple gabion retaining wall segments 1101 that are spliced ​​and fixedly connected end to end along the length direction. The gabion retaining wall segments 1101 include gabion meshes. The gabion meshes are provided with anti-seepage members 11014 vertically arranged along the length direction of the gabion retaining wall segments 1101. The anti-seepage members 11014 are anti-seepage plates or anti-seepage membranes. The gabion meshes on both sides of the anti-seepage members 11014 are filled with graded stones. The provision of the anti-seepage members 11014 can reduce water seepage in the gabion retaining wall 11.

[0038] like Figure 4 As shown, the gabion net includes a gabion net periphery 11011 which is located around the outside of the gabion retaining wall segment 1101 and has an open top. A plurality of gabion net partitions 11012 are vertically arranged along the width direction of the gabion retaining wall segment 1101 are provided in the gabion net periphery 11011. A gabion net top cover 11013 is provided at the top opening of the gabion net periphery 11011, and an anti-seepage member 11014 intersects with each gabion net partition 11012.

[0039] Preferably, the gabion retaining wall segment 1101 is in the shape of a cuboid, 3 m long, 1 m wide and 1 m high. When the height of the gabion retaining wall 11 is greater than 1 m, multiple rows of gabion retaining wall units are stacked and fixedly connected from top to bottom to form the gabion retaining wall 11.

[0040] In one embodiment, one end of the permeable weir 12 is connected to the side of one side of the retaining wall away from the river channel, and the other end is connected to the side of the other side of the retaining wall away from the river channel. The permeable weir 12 is formed by splicing multiple blocks of stone, and there are one or more water outlets 13; the blocks are flat blocks with a length greater than or equal to 1m, the spacing between adjacent permeable weirs 12 is controlled at 5-10m, and the width of the water outlet 13 is greater than or equal to 0.5m.

[0041] In one embodiment, a rock cluster is provided within the simulated natural section 1 between adjacent permeable weirs 12 to slow the flow of water. Preferably, the rock cluster includes a plurality of rocks 15 arranged in a plum blossom pattern, with spacing between adjacent rocks 15 controlled to be 1-3 meters. This rock cluster can slow the flow of water and create a diverse habitat. Furthermore, it can stabilize the flow of fish-attracting water within the simulated natural section 1 while maintaining the required water level, allowing fish to more easily enter the simulated natural section 1 through the downstream opening.

[0042] The fishway inlet section device of the present invention is suitable for fish with too low downstream water level. Before the first operation, it should be ensured that the gabion retaining wall 11, permeable weir 12, overflow weir 14 and barbaric stone 15 in the simulated natural section 1 have been arranged according to the design requirements. If necessary, stone throwing protection can be carried out on the river side of the gabion retaining wall 11 to reduce the impact of water scouring. During normal operation, regular inspections should be carried out to clean up the debris inside the simulated natural section 1 in time, and reset the barbaric stone 15 with a large position offset. At the same time, the flow pattern of the water inside the simulated natural section 1 should be observed. When the water flow pattern is not good and is not conducive to fish upstream, the arrangement of the water outlet 13 and barbaric stone 15 can be fine-tuned to achieve the best flow pattern. During maintenance, the discharge gates of the fishway section 2 and the water replenishment section 3 should be closed, and the gabion retaining wall 11, permeable weir 12, overflow weir 14 and barbaric stone 15 in the simulated natural section 1 should be positioned and checked, the structure with a large position offset should be reset, and the internal siltation should be dredged in time.

[0043] In summary, the simulated natural section 1 in the present invention is suitable for the design of river channel projects with lower water levels, and has the advantage of a wide range of water level adaptability. The simulated natural section 1 simulates a natural river channel, and the opening widths of the upstream and downstream ends of the simulated natural section 1 are both large, which can not only ensure the design requirements of the vertical slit fishway section for the water level, but also cleverly transition to the low water level of the river channel, and smoothly build a bridge between the traditional vertical slit fishway section and the existing river channel. At the same time, the super strong adaptability of the simulated natural section 1 to water level can significantly improve the adaptability of the fishway project to changes in river water level.

[0044] Moreover, the opening width of the downstream end of the simulated natural section 1 is greater than the width of the inlet end of the fishway section 2, and the spacing between the water retaining walls on both sides gradually decreases along the flow direction of the river channel. In this way, the opening widths of the upstream and downstream ends of the simulated natural section 1 are both greater than the width of the inlet end of the fishway section 2, thereby significantly expanding the cross-sectional width of the simulated natural section 1 at the inlet end of the fishway section 2, so as to provide a more spacious fish upstream channel. In addition, the simulated natural section 1 combines the traditional fishway fish-attracting water flow and the water-replenishing fish-attracting water flow into one, and forms an overall fish-attracting water flow, and the overall fish-attracting water flow is more stable and concentrated, and while maintaining a large flow rate and high flow rate, using a larger width inlet section can more effectively improve the fish-attracting effect of the fishway section 2. At the same time, the simulated natural section 1 can also reduce the "lost" rate after the first failure to enter the fishway section 2, and continue to provide directional guidance for fish to ensure the continuity of fish upstream.

[0045] In addition, the simulated natural section 1 serves as a transition to the vertical seam fishway section of the traditional reinforced concrete structure, forming a transition buffer section from rigid to flexible. When connected to the river channel, the simulated natural section 1 creates an identical natural environment, which can further reduce the stress response of fish to sudden changes in the natural environment, allowing fish to pass through the simulated natural section 1 from the river channel to the fishway section 2 more naturally.

[0046] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and substitutions can be made without departing from the technical principles of the present invention. These improvements and substitutions should also be regarded as the scope of protection of the present invention.

Claims

1. A fishway inlet device suitable for use in a fishway where the downstream water level is too low, characterized in that: The invention comprises a fishway section (2), a water replenishment section (3) and an artificial natural section (1), wherein the artificial natural section (1) is arranged along the slope of the river and along the flow direction of the river, the upstream end of the artificial natural section (1) is open and connected to the inlet end of the fishway section (2) and the outlet end of the water replenishment section (3), and the downstream end of the artificial natural section (1) is open and connected to the river; the artificial natural section (1) comprises retaining walls on both sides, and multiple levels of permeable weirs (12) for high water levels are arranged side by side between the retaining walls on both sides along the flow direction of the river, and the permeable weirs (12) are provided with water outlets (13) and serve as upstream ports for fish; the upstream end of the artificial natural section (1) is provided with an overflow weir (14) at a position between the inlet end of the fishway section (2) and the outlet end of the water replenishment section (3), which is used to separate the inlet end of the fishway section (2) and the outlet end of the water replenishment section (3) and guide fish into the fishway section (2); The spacing between the retaining walls on both sides gradually decreases along the flow direction of the river channel, and the downstream end opening width of the simulated natural section (1) is greater than the inlet end width of the fishway section (2).

2. The fishway inlet device suitable for use in a fishway with a low downstream water level according to claim 1, characterized in that: The retaining wall is a gabion retaining wall (11), and the gabion retaining wall (11) comprises one or more rows of gabion retaining wall units stacked and fixedly connected from top to bottom, and the gabion retaining wall units comprise a plurality of gabion retaining wall segments (1101) spliced ​​and fixedly connected end to end along the length direction, and the gabion retaining wall segments (1101) comprise gabion nets, and anti-seepage members (11014) vertically arranged along the length direction of the gabion retaining wall segments (1101) are provided in the gabion nets, and the gabion nets on both sides of the anti-seepage members (11014) are filled with graded stone blocks.

3. The fishway inlet device suitable for use in a fishway with a low downstream water level according to claim 2, characterized in that: The gabion mesh comprises a gabion mesh outer periphery (11011) which is located around the outside of the gabion retaining wall segment (1101) and has an open top. A plurality of gabion mesh partitions (11012) are arranged vertically along the width direction of the gabion retaining wall segment (1101) within the gabion mesh outer periphery (11011). A gabion mesh top cover (11013) is provided at the top opening of the gabion mesh outer periphery (11011). The anti-seepage member (11014) intersects with each gabion mesh partition (11012).

4. The fishway inlet device suitable for use in a fishway with a low downstream water level according to claim 2, characterized in that: The anti-seepage member (11014) is an anti-seepage plate or an anti-seepage membrane.

5. The fishway inlet device suitable for use in a fishway with a downstream water level that is too low according to claim 1, characterized in that: One end of the permeable weir (12) is connected to the side of one retaining wall away from the river channel, and the other end is connected to the side of the other retaining wall away from the river channel. The permeable weir (12) is formed by splicing a plurality of stone blocks, and there are one or more water outlets (13).

6. The fishway inlet device suitable for use in a fishway with a low downstream water level according to claim 5, characterized in that: The blocks are flat blocks with a length greater than or equal to 1 m, the spacing between adjacent permeable weirs (12) is controlled to be 5-10 m, and the width of the water outlet (13) is greater than or equal to 0.5 m.

7. The fishway inlet device suitable for use in a fishway with a low downstream water level according to claim 1, characterized in that: A group of wild stones for slowing down the flow of water is provided in the simulated natural section (1) area between the adjacent permeable weirs (12).

8. The fishway inlet device suitable for use in a situation where the downstream water level is too low according to claim 7, characterized in that: The barbarian stone community includes a plurality of barbarian stones (15), wherein the plurality of barbarian stones (15) are arranged in a plum blossom shape, and the spacing between adjacent barbarian stones (15) is controlled to be 1-3m.

9. The fishway inlet device suitable for use in a fishway with a low downstream water level according to claim 1, characterized in that: The opening width of the downstream end of the simulated natural section (1) is greater than or equal to twice the width of the inlet end of the fishway section (2), and the water depth at the downstream end of the simulated natural section (1) is greater than or equal to 0.3 m.

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