River submerged plant recovery method based on flow velocity zoning

Abstract

The invention belongs to the technical field of riverway vegetation restoration of water conservancy projects, and particularly relates to a riverway submerged plant restoration method based on flow velocity zoning, which comprises the following steps of: measuring adaptive threshold values of fishes to flow velocity in a target riverway, including an unsuitable flow velocity lower limit Vu and a suitable flow velocity upper limit Vs; according to Vu and Vs, a rapid flow area, a transition area and a slow flow area are constructed in the river channel, the flow speed of the rapid flow area is larger than or equal to Vu, the flow speed of the slow flow area is smaller than or equal to Vs, and the flow speed ratio of the rapid flow area to the slow flow area is 1.5 times or above; fish with the body length larger than or equal to 10 cm in the river channel is removed, and the density is smaller than or equal to 0.3 fish / m < 2 >; submerged plants capable of adapting to the range that the flow speed is larger than or equal to Vs are planted in the torrent area and / or the transition area. The method has the advantages that the adaptive capacity difference of the submerged plants and the fishes to different flow speeds is utilized, and the rapid flow area-transition area-slow flow area is built, so that conditions are created for the recovery of the submerged plants, the habitat diversity is increased, and the ecological biodiversity recovery of the whole riverway is facilitated.

Description

Technical Field

[0001] The present invention belongs to the technical field of water conservancy projects, and specifically relates to the technical field of river vegetation restoration, in particular to a method for restoring submerged plants in a river based on flow velocity zoning. Background Art

[0002] Submerged plants are an essential component of aquatic ecosystems, and their restoration is a key component of water ecological restoration projects. Currently, submerged plant growth is affected by a variety of factors, including water quality, depth, flow rate, transparency, and animal activity. Fish grazing can directly lead to a decrease in submerged plant biomass or even its extinction. Fish activity also disturbs bottom sediments and increases suspended matter, thereby reducing transparency and negatively impacting submerged plant growth.

[0003] Therefore, fish control is often a crucial measure for submerged plant restoration. To achieve this, many aquatic ecological restoration projects employ enclosures to isolate the restoration area, remove fish from the enclosures, and prevent entry of fish from the surrounding areas, creating a relatively closed and stable environment for submerged plant growth. However, enclosures are primarily suitable for submerged plant restoration in shallow lakes. For mountain rivers and other waterways that carry floodwaters, enclosures can compromise flood safety, limiting their application.

[0004] At present, there are many cases where the restoration of submerged plants in rivers has failed due to fish activity. Although some researchers and environmental protection companies have developed some fish-proof planting devices, such as a device for planting submerged plants with water disclosed in authorization announcement number CN 220274376U and a suspended submerged and emergent plant planting device disclosed in publication number CN 116686583A, although the above devices all have the function of preventing fish from gnawing, these devices, whether they are sunk to the bottom of the water or floating on the water, pose certain safety hazards to the flow of water in the river, and there is a possibility of being washed away during floods. Summary of the Invention

[0005] The purpose of the present invention is to solve the above-mentioned problems existing in the prior art and to provide a method for restoring submerged plants in a river channel based on flow velocity zoning.

[0006] To achieve the above object, the technical solution adopted by the present invention is:

[0007] A method for restoring submerged macrophytes in a river channel based on flow velocity zoning comprises the following steps:

[0008] S1. Determine the adaptability threshold of fish to flow velocity in the target river, including the unsuitable flow velocity lower limit Vu and the suitable flow velocity upper limit Vs;

[0009] S2. Based on Vu and Vs, construct a rapids zone, a transition zone, and a slow-flow zone in the river channel, so that the flow velocity in the rapids zone is ≥ Vu, the flow velocity in the slow-flow zone is ≤ Vs, and the flow velocity ratio between the rapids zone and the slow-flow zone is 1.5 times or more;

[0010] S3. Remove fish with a body length of ≥10 cm from the river channel and reduce the density to ≤0.3 fish / m 2 ;

[0011] S4. Planting submerged plants that can adapt to a flow velocity range of ≥ Vs in the rapids zone and / or transition zone;

[0012] S5. Maintain and manage submerged plants.

[0013] Preferably, in step S1, the method for determining Vu and Vs includes:

[0014] S1a, select fish density ≥ 2 fish / m 2 The slow-flow or still-water test section is divided into 10m×50m grids;

[0015] S1b, monitoring the fish density in the grid for ≥ 3 days and calculating the initial density C0;

[0016] S1c, increase the flow velocity of the test river section to ≥0.5 m / s by water replenishment or pump circulation for ≥5 days, divide the flow velocity into intervals and monitor the fish density in each interval C1;

[0017] S1d. Calculate the density drop in each velocity interval X = (C0-C1) / C0×100%. When X≥70% and C1≤2 tail / m 2 When X≥90% and C1≤0.2 tail / m 2 When , the lower limit of the interval is defined as Vu.

[0018] Preferably, in step S2, the flow velocity in the transition zone is between the flow velocities in the rapid flow zone and the slow flow zone.

[0019] Preferably, in step S2, the length of the rapids zone is ≥50m, the length of the slow flow zone is 50-300m, and the length of the transition zone is 100-500m; and the flow velocity of the rapids zone is increased through ecological dams, shallow ridges or terrain transformation.

[0020] Preferably, in step S3, the fish removed include omnivorous fish that feed on plants, specifically tilapia.

[0021] Preferably, in step S4, the submerged plants are Vallisneria, Hydrilla or a mixed planting of the two.

[0022] Preferably, in step S5, the maintenance management includes adopting an intelligent monitoring and dynamic control system; specifically:

[0023] Intelligent monitoring includes deploying multi-parameter smart sensors in rapid, transition, and slow-flowing areas of the river to monitor flow velocity, submerged plant coverage, and fish density in real time.

[0024] The dynamic control system mainly includes:

[0025] If monitoring shows that the coverage of submerged macrophytes in the rapids-transition zone is ≥60% or the coverage of the entire river section is ≥30% for more than 15 months, fish removal will be stopped;

[0026] When the coverage rate of submerged plants in the rapids-transition zone is less than 60% or the coverage rate of the entire river section is less than 30%, and the flow velocity in the rapids zone differs from the designed flow velocity by less than 30%, an early warning is triggered and the first-level fish control is initiated, so that the fish density is ≤ 0.3 fish / m 2 ;

[0027] Among them, fish control methods include building safe zones and trap zones, gradually reducing fish density by separating feeding in safe zones from fishing in trap zones and creating a sense of environmental safety;

[0028] When the coverage rate of submerged plants in the rapids-transition zone is less than 60% or the coverage rate of the entire river section is less than 30%, and the flow rate in the rapids zone is less than 50% of the designed flow rate, an early warning is triggered and secondary fish control is initiated to reduce the fish density to ≤ 0.05 fish / m 2 .

[0029] Preferably, the method is applicable to mountain rivers or flood-carrying rivers with a width of 6-20 m, a water depth of 0.1-0.5 m in the dry season, and a water depth of 0.5-2 m in the flood season.

[0030] Due to the adoption of the above technical solution, the beneficial effects obtained by the present invention include:

[0031] 1. The submerged plant restoration method provided by the present invention does not require complete fish control, nor does it require the arrangement of water-blocking structures such as enclosures in the river channel, thus not affecting flood flow; it will not interfere with flood flow and drainage in the river channel;

[0032] 2. The rapid-flow zone and slow-flow zone constructed by the present invention not only creates conditions for the recovery of submerged plants, but also increases habitat diversity, which is conducive to the restoration of biodiversity in the entire river ecosystem. It solves the problems of traditional enclosure methods that hinder flood flow and fish prevention devices are easily damaged;

[0033] 3. The overall operation and maintenance of the present invention is simple, because the river channel does not fully control the fish and maintains a certain grazing pressure, so the excessive growth of submerged plants can be avoided and the operation and maintenance pressure can be reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a flow chart of an embodiment of a method for restoring submerged macrophytes in a river channel based on flow velocity zoning according to the present invention.

[0035] Figure 2 It is a flow chart of a specific embodiment of the method for restoring submerged plants in a river channel based on flow velocity zoning according to the present invention.

[0036] Figure 3 It is a schematic diagram of the rapid flow zone-transition zone-slow flow zone in the present invention.

[0037] Figure 4 This is a comparison chart of the repair effects of the present invention and the traditional enclosure method. DETAILED DESCRIPTION

[0038] See Figure 1-4 As shown, the present invention mainly provides a method for restoring submerged plants in a river channel based on flow velocity zoning to solve the problem that submerged plants in a river channel are difficult to restore due to fish grazing. In this embodiment, the specific implementation process of the present invention is described in detail by taking the restoration of submerged plants in a river channel as an example:

[0039] S1. Determine the adaptability threshold of fish to flow velocity in the target river, including the unsuitable flow velocity lower limit Vu and the suitable flow velocity upper limit Vs;

[0040] Specifically: first investigate or measure the flow rate and water depth of the river during the flood season, normal water season and dry season; and investigate the distribution of submerged plants in the river and the species and size of fish.

[0041] Then according to step S1a, select fish density ≥ 2 tails / m 2 A slow-flow or still-water test river section is selected, and the test river section is divided into multiple grids (such as 10m×50m); among them, a slow-flow or still-water river section with a higher fish density can be selected as the test river section, and correspondingly, the length of the test river section is 200-2000m.

[0042] The flow rate interval division rules include:

[0043] The test river section is divided into flow velocity intervals of 0.1 m / s (e.g. 0.1-0.2 m / s, 0.2-0.3 m / s), and the interval width shall not exceed 0.15 m / s;

[0044] Each flow rate interval must contain at least three 10m×50m monitoring grids to ensure data representativeness.

[0045] S1b. Monitor the number of fish in each grid and calculate the fish density. This monitoring must be carried out continuously over a fixed period of time, with a continuous monitoring period of at least 3 days. Calculate the initial density C0, which can be the average of each monitoring period. Density monitoring methods include:

[0046] Fish density was counted using the mark-recapture method or sonar detection technology;

[0047] The monitoring period is 8:00-10:00 every day (peak period of fish activity), and continuous monitoring is ≥5 days.

[0048] S1c. Increase the flow velocity of the test river section to ≥0.5 m / s by water replenishment or pump circulation for ≥5 days, divide the flow velocity into intervals, and monitor the fish density within each interval. C1. Specifically, increase the flow velocity of the river channel through water replenishment, pump circulation, and other measures to ensure that the maximum flow velocity is no less than 0.5 m / s. The pump type can be an axial flow pump or a centrifugal pump, and the flow rate range is calculated based on the cross-sectional area of ​​the river channel (for example, when the flow velocity is increased to ≥0.5 m / s, the pump flow rate formula is Q==A×v, where A is the cross-sectional area of ​​the test river section and v is the target flow rate). The water replenishment flow rate can be monitored in real time using a flow meter, and the pump speed can be adjusted using a frequency converter to maintain the target flow rate. The test river section is divided into several flow velocity intervals based on the flow velocity, with each flow velocity interval consisting of 0.05-0.2 m / s, and each flow velocity interval includes one to several grids. The number of fish in each flow velocity interval is counted to calculate the fish density. Among them, the flow rate increase lasts for no less than 5 days, and its monitoring needs to be carried out continuously within a fixed time period. The continuous monitoring time is no less than 5 days, and the density is the average value of each monitoring.

[0049] Based on the monitoring data, a flow velocity-density table was drawn to calculate the decrease in fish density before and after the flow velocity was increased in each flow velocity interval. Density decrease = (fish density before flow velocity increase - fish density after flow velocity increase) / fish density before flow velocity increase (as shown in the table below):

[0050] Flow rate (m / s) <![CDATA[Density (tail / m 2 )]]> Density reduction 0.05～0.1 <![CDATA[C 0.1 ]]> <![CDATA[X 0.1 ]]> 0.1～0.2 <![CDATA[C 0.2 ]]> <![CDATA[X 0.2 ]]> 0.2～0.3 <![CDATA[C 0.3 ]]> <![CDATA[X 0.3 ]]> 0.3～0.4 <![CDATA[C 0.4 ]]> <![CDATA[X 0.4 ]]> 0.4～0.5 <![CDATA[C 0.5 ]]> <![CDATA[X 0.5 ]]> 0.5～0.6 <![CDATA[C 0.6 ]]> <![CDATA[X 0.6 <!-- 3 -->]]> ＞0.6 <![CDATA[C 0.6+ ]]> <![CDATA[X 0.6+ ]]>

[0051] S1d, calculate the density drop range of each flow rate interval X = (C0-C1) / C0, when X ≥ 70% and C1 ≤ 2 tails / m 2 When X≥90% and C1≤0.2 fish / m 2 When , the lower limit of the flow velocity range is the unsuitable flow velocity Vu for fish.

[0052] S2. Based on Vu and Vs, construct a rapids zone, a transition zone, and a slow-flow zone in the river channel; make the flow velocity of the rapids zone ≥ Vu, the flow velocity of the slow-flow zone ≤ Vs, and the flow velocity ratio of the rapids zone to the slow-flow zone be 1.5 times or more;

[0053] Specifically, through measures such as topography, overflow weirs, and shallow embankments, or a combination of these measures, rapids, transition zones, and slow-flow zones, or multiple rapids-transition zones-slow-flow zones, are created in different river channels. The distribution of submerged plants and fish is spatially separated by their varying adaptability to flow rates. During normal and dry seasons, the flow velocity in the rapids is no less than Vu, while the flow velocity in the slow-flow zone does not exceed Vs. Furthermore, the flow velocity in the rapids is at least 1.5 times that of the slow-flow zone at any given time, and the flow velocity in the transition zone is between the rapids and slow-flow zones.

[0054] In addition, when creating rapid-flow and slow-flow zones through measures such as topography, overflow weirs, and ecological water replenishment, or a combination of these measures, each rapid-flow zone should be no less than 50 meters long (to prevent fish from migrating upstream), with transition zones ranging from 100 to 500 meters and slow-flow zones from 50 to 300 meters (to balance fish activity and water quality, retain small fish for grazing, and prevent overproduction of submerged plants). If the rapid-flow zone is too short, fish will easily migrate upstream and move back and forth between the two slow-flow zones, causing disturbances in the rapid-flow zone and hindering the recovery of submerged plants. If the slow-flow zone is too short, fish will lack space for movement, increasing the probability of migrating upstream to the rapid-flow zone and hindering the recovery of submerged plants in the rapid-flow zone. If the slow-flow zone is too long, the hydrodynamic conditions in the river channel may be insufficient, leading to hypoxia and deterioration of water quality. Fish will migrate upstream to escape the harsh environment, hindering the overall ecological restoration of the river channel.

[0055] S3. Remove fish with a body length of 10 cm or more from the river (including omnivorous fish that feed on plants, which can be removed using tools such as fishing nets or electric fishing equipment) to a density of 0.3 fish / m 2 (Reduced feeding and activity); Fish feeding and swimming abilities are positively correlated with body length. Removing fish larger than 10 cm reduces the number of fish that can enter the rapids and reduces their feeding capacity; as shown in the following table:

[0056]

[0057] Through comparative experiments, it was found that tilapia with a body length of ≥10 cm are more than three times more efficient at grazing on submerged plants than those with a body length of <10 cm (see the table above for specific data), and their range of activity can cover the slow-flow zone to the transition zone. The fish density should be controlled at ≤0.3 fish / m 2 Based on the above test results: when the density is > 0.5 tails / m 2 When the coverage rate of submerged plants decreases by more than 50% per month; when the density is ≤ 0.3 tails / m 2 When the coverage rate is stable, it can be increased to more than 60%.

[0058] S4. Plant submerged plants that can adapt to flow velocities ≥ Vs in rapids and / or transition zones. Select submerged plants that can adapt to flow velocities ≥ Vs, such as Vallisneria serrata and Myriophyllum paniculate. You can choose to plant a single species or a mixture of two or more species.

[0059] In this embodiment, the method also includes maintenance management: within the first 15 months after the submerged plants are planted, when the submerged plant coverage rate of the entire river section is greater than 30%, or the submerged plant coverage rate in the rapids area and the transition area is more than 60%, fish control is no longer required. Otherwise, fish control is still required to ensure that the density of fish with a body length of more than 10 cm does not exceed 0.3 fish / ㎡; among which, the fish control method includes constructing safe areas and trap areas, and gradually reducing the fish density through spatial separation of feeding in the safe areas and fishing in the trap areas and creating a sense of environmental safety.

[0060] Reference case: Restoration of submerged macrophytes in a river channel in a mountainous town in the southeast region (e.g. Figure 2 shown)

[0061] 1. River hydrology and habitat survey

[0062] The river channel is 6-10m wide, about 2.45km long, and has a gravel riverbed.

[0063] Through on-site measurements and the collection of historical hydrological data, it was found that the water depth of the river fluctuated greatly, with the water level rising and falling suddenly. When it was not raining, the water depth was 0.1 to 0.3 meters, and when it rained, the water depth could reach 2 meters.

[0064] When it is not raining, the flow velocity is about 0.03 to 0.2 m / s. When it is raining, the surface flow velocity can be as high as 1.5 to 2.0 m / s.

[0065] 2. Survey of aquatic organisms in rivers

[0066] Due to serious river overflow pollution, the water ecology is seriously unbalanced. There are no submerged plants in the river. Tilapia is rampant, and their body length is mainly concentrated in the range of 5-20cm. The only snail that can be seen is the golden apple snail, but there are no other higher aquatic animals.

[0067] Tilapia is an omnivorous fish that mainly feeds on plant-based bait. It likes to gnaw on the roots and stems of submerged plants, which can cause devastating damage to submerged plants in their seedling stage.

[0068] Since the river is an open water system and is connected to other water systems upstream and downstream, tilapia cannot be completely eliminated. As a result, the previous two submerged plant restoration projects ended in failure due to the gnawing of tilapia.

[0069] 3. Construct rapid flow zone, transition zone and slow flow zone

[0070] The upper limit of the preferred flow velocity for tilapia (less than 10 cm in length) is approximately 0.5 m / s. Based on the current state of the river, through ecological dams, shallow embankments, and micro-topography, the river has been divided into 10 zones: Rapids Zone I - Transition Zone I - Slow Flow Zone I - Rapids Zone II - Transition Zone II - Slow Flow Zone II - Transition Zone III - Rapids Zone IV - Transition Zone IV - Slow Flow Zone IV. During non-rainfall periods, the flow velocity and water depth of each zone are shown in the following table:

[0071]

[0072]

[0073] 4. Fish control

[0074] Tilapias longer than 10 cm are removed through fishing nets, so that the density of tilapia longer than 10 cm does not exceed 0.2 per m2.

[0075] 5. Screening and planting of submerged plants

[0076] In this restored river section, the flow velocity in the rapids is primarily 0.4-0.8 m / s during non-rainfall periods. Two submerged plants, Vallisneria dwarfi and Hydrilla verticillata, were selected and planted in a 1:1 ratio throughout the entire restored river section.

[0077] Vallisneria, with its robust root system and flexible, ribbon-like leaves, thrives in flowing water, even in habitats with currents exceeding 0.5 m / s. Hydrilla verticillata is adaptable to a wide range of flow rates and can also survive in habitats with currents exceeding 0.5 m / s. Therefore, Vallisneria and Hydrilla verticillata were selected as the species for submerged plant restoration in this river reach.

[0078] 6. Maintenance and management

[0079] Three months after the submerged plant planting was completed (the comparison of this restoration scheme and traditional enclosures is shown in the table below), plant coverage reached approximately 25-40% in the rapids, 60-100% in the transition zone, and approximately 45% in the slow-flowing zone, where tilapia were active and densely populated and submerged plants were largely absent. Therefore, fish control measures were no longer implemented in the restored section.

[0080]

[0081]

[0082] Among them, the intelligent monitoring and dynamic control system is mainly used during the maintenance and management period, as follows:

[0083] Intelligent monitoring involves deploying multi-parameter smart sensors (current meters, underwater cameras, sonar detection, etc.) at key locations in the river (rapids, transition zones, slow-flow zones) to monitor flow velocity, submerged plant coverage (through image recognition), and fish density in each area in real time.

[0084] The dynamic control system mainly includes:

[0085] When monitoring shows that the submerged plant coverage rate in the rapids-transition zone is ≥60% or the coverage rate in the entire river section is ≥30% for more than 15 months, fish removal will be stopped.

[0086] When the coverage rate of submerged plants in the rapids-transition zone is less than 60% or the coverage rate of the entire river section is less than 30%, and the flow velocity in the rapids zone differs from the designed flow velocity by less than 30%, an early warning is triggered and the first-level fish control is initiated, so that the fish density is ≤ 0.3 fish / m 2 Among them, the fish control method includes constructing safe areas and trap areas, and gradually reducing the fish density through the spatial separation of feeding in safe areas and fishing in trap areas and the creation of a sense of environmental security.

[0087] Specific methods:

[0088] Set up a safe zone: Set up a fixed feeding point in the slow-flowing area and feed the fish at a fixed time every day (such as in the evening) to attract fish to gather in the slow-flowing area; gather the fish here and then catch them to reduce the fish density.

[0089] Fishing is prohibited in safe areas: This helps fish form a sense of security, preventing them from experiencing stress and fleeing slow-flow areas.

[0090] Set up a trap area: Place passive fishing devices such as ground traps and submerged cages 10-20 meters downstream from the safe zone to allow fish to naturally swim into the trap after eating from the feeding point, avoiding the direct association of "food = danger"

[0091] Reduce the visibility and excitement of fishing

[0092] Reduce fishing disturbance: Choose to fish during the period of least activity for fish (such as high temperatures at noon in summer and low temperatures in early morning in winter) to reduce stimulation to the fish.

[0093] Do not fish too frequently: fish no more than once a week to avoid disturbing the fish's safe zone.

[0094] (2) Mid-stage recovery of submerged plants

[0095] When the submerged plant cover rate exceeds 30% throughout the entire river section, or reaches over 60% in the rapids and transition zones, gradually reduce feeding frequency. Each cycle lasts 1-4 weeks. In the first cycle, reduce feeding frequency to every 2-3 days, in the second cycle to every 3-5 days, and in the third cycle to every 5-7 days, after which feeding should cease.

[0096] When the submerged plant coverage in the river channel remains stable for three consecutive months, the submerged plant coverage in the entire river section is always greater than 30%, or the submerged plant coverage in the rapids and transition zones is always above 60%, fishing will be stopped and the artificial aeration facilities in the slow-flowing areas will be removed.

[0097] 7. Restoration effect of submerged plants

[0098] like Figure 4 As shown in the figure, one year after construction, submerged plant coverage remained stable at around 50%, with no impact on flood flow and no additional measures required during the flood season. However, the adjacent river channel, which used enclosures to restore submerged plants, has seen inconsistent results, with submerged plant coverage below 10%. This is primarily due to the frequent removal of enclosures during the flood season, allowing tilapia to graze large areas of submerged plants in just one week. Furthermore, the frequent removal and installation of enclosures significantly increased river channel operating costs.

[0099] It should be noted that the present invention measures the threshold value (Vu, Vs) of fish adaptability to flow velocity, constructs a flow velocity gradient from a rapids zone to a slow flow zone, utilizes the difference in flow velocity adaptability between fish and submerged plants to achieve spatial isolation, and combines the removal of large fish (≥10 cm) to control feeding pressure, thereby solving the problem of traditional enclosure methods hindering flood flow and fish prevention devices being easily damaged. Moreover, the submerged plant restoration method provided by this method does not require complete fish control, nor does it require the arrangement of water-blocking structures such as enclosures in the river channel, so it does not affect flood flow; at the same time, the constructed rapids zone and slow flow zone not only create conditions for the restoration of submerged plants, but also increase habitat diversity, which is beneficial to the restoration of the ecological biodiversity of the entire river channel; in addition, the overall operation and maintenance are simple, because the river channel does not completely control fish and maintains a certain grazing pressure, so the excessive growth of submerged plants can be avoided, reducing the pressure of operation and maintenance; the present invention can be applied to mountain rivers invaded by tilapia, and has the dual benefits of ecological restoration and flood safety.

[0100] The above descriptions and embodiments are provided to facilitate understanding and application of the present invention by those skilled in the art. It will be apparent that those skilled in the art can readily make various modifications to these contents and apply the general principles described herein to other embodiments without requiring inventive effort. Therefore, the present invention is not limited to the above descriptions and embodiments. Improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the present invention should fall within the scope of protection of the present invention.

Claims

1. A method for restoring submerged macrophytes in a river channel based on flow velocity zoning, characterized in that: The following steps are involved: S1. Determine the adaptability threshold of fish to flow velocity in the target river, including the lower limit of unsuitable flow velocity Vu and the upper limit of suitable flow velocity Vs; S2. Based on Vu and Vs, construct a rapids zone, a transition zone, and a slow-flow zone in the river channel, so that the flow velocity in the rapids zone is ≥ Vu, the flow velocity in the slow-flow zone is ≤ Vs, and the flow velocity ratio between the rapids zone and the slow-flow zone is 1.5 times or more; S3. Remove fish with a body length of ≥10 cm from the river channel and reduce the density to ≤0.3 fish / m 2 ; S4. Planting submerged plants that can adapt to a flow velocity range of ≥ Vs in the rapids zone and / or the transition zone; S5. Maintain and manage submerged plants.

2. The method for restoring submerged macrophytes in a river channel based on flow velocity zoning according to claim 1, characterized in that: In step S1, the method for measuring Vu and Vs includes: S1a, select fish density ≥ 2 fish / m 2 The slow-flow or still-water test section is divided into 10m×50m grids; S1b, monitoring the fish density in the grid for ≥ 3 days and calculating the initial density C0; S1c, increase the flow velocity of the test river section to ≥0.5 m / s by water replenishment or pump circulation for ≥5 days, divide the flow velocity into intervals and monitor the fish density in each interval C1; S1d. Calculate the density drop in each velocity interval X = (C0-C1) / C0×100%. When X≥70% and C1≤2 tail / m 2 When X≥90% and C1≤0.2 tail / m 2 When , the lower limit of the interval is defined as Vu.

3. The method for restoring submerged macrophytes in a river channel based on flow velocity zoning according to claim 1, characterized in that: In step S2, the flow velocity in the transition zone is between the flow velocities in the rapid flow zone and the slow flow zone.

4. The method for restoring submerged plants in a river channel based on flow velocity zoning according to claim 1, characterized in that: In step S2, the length of the rapids area is ≥50m, the length of the slow flow area is 50-300m, and the length of the transition area is 100-500m; and the flow velocity of the rapids area is increased through ecological dams, shallow ridges or terrain transformation.

5. The method for restoring submerged macrophytes in a river channel based on flow velocity zoning according to claim 1, characterized in that: In step S3, the fish removed include omnivorous fish that feed on plants.

6. The method for restoring submerged macrophytes in a river channel based on flow velocity zoning according to claim 1, characterized in that: In step S4, the submerged plants are Vallisneria salsa, Hydrilla verticillata or a mixture of the two.

7. The method for restoring submerged macrophytes in a river channel based on flow velocity zoning according to claim 1, characterized in that: In step S5, the maintenance management includes using an intelligent monitoring and dynamic control system; Intelligent monitoring includes deploying multi-parameter smart sensors in rapid, transition, and slow-flowing areas of the river to monitor flow velocity, submerged plant coverage, and fish density in real time. The dynamic control system mainly includes: If monitoring shows that the coverage of submerged macrophytes in the rapids-transition zone is ≥60% or the coverage of the entire river section is ≥30% for more than 15 months, fish removal will be stopped; When the coverage rate of submerged plants in the rapids-transition zone is less than 60% or the coverage rate of the entire river section is less than 30%, and the flow velocity in the rapids zone differs from the designed flow velocity by less than 30%, an early warning is triggered and the first-level fish control is initiated, so that the fish density is ≤ 0.3 fish / m 2 ; Among them, fish control methods include building safe zones and trap zones, gradually reducing fish density by separating feeding in safe zones from fishing in trap zones and creating a sense of environmental safety; When the coverage rate of submerged plants in the rapids-transition zone is less than 60% or the coverage rate of the entire river section is less than 30%, and the flow rate in the rapids zone is less than 50% of the designed flow rate, an early warning is triggered and secondary fish control is initiated to reduce the fish density to ≤ 0.05 fish / m 2 .

8. The method for restoring submerged macrophytes in a river channel based on flow velocity zoning according to claim 1, characterized in that: The method is applicable to mountain river channels or flood-carrying river channels with a river channel width of 6-20 m, a water depth of 0.1-0.5 m in the dry season, and a water depth of 0.5-2 m in the flood season.

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