Riverway submerged plant restoration method based on flow velocity zoning

Abstract

The present application belongs to the technical field of river vegetation restoration in water conservancy projects, and particularly relates to a river submerged plant restoration method based on flow velocity zoning, comprising the following steps: determining a fish adaptability threshold to flow velocity in a target river, including a lower limit of unsuitable flow velocity Vu and an upper limit of suitable flow velocity Vs; constructing a rapid flow zone, a transition zone and a slow flow zone in the river according to Vu and Vs, so that the flow velocity of the rapid flow zone is greater than or equal to Vu, the flow velocity of the slow flow zone is less than or equal to Vs, and the flow velocity ratio of the rapid flow zone to the slow flow zone is greater than or equal to 1.5 times; removing fish with a body length greater than or equal to 10 cm in the river so that the density is less than or equal to 0.3 tail / m 2 ; and planting submerged plants that can adapt to a flow velocity greater than or equal to Vs in the rapid flow zone and / or the transition zone. The present application has the advantages that the present application utilizes the adaptability difference of submerged plants and fish to different flow velocities, and creates a rapid flow zone-transition zone-slow flow zone, which not only creates conditions for submerged plant restoration, but also increases habitat diversity, which is conducive to the restoration of ecological and biological diversity of the entire river.

Description

Technical Field

[0001] This invention belongs to the field of water conservancy engineering technology, specifically relating to the field of river vegetation restoration technology, and in particular to a method for restoring submerged plants in rivers based on flow velocity zoning. Background Technology

[0002] Submerged plants are an important component of aquatic ecosystems, and their restoration is a crucial step in aquatic ecological restoration projects. Currently, the growth of submerged plants is affected by various factors, including water quality, water depth, flow velocity, transparency, and animal activity. Among these, fish feeding can directly lead to a decrease in the biomass of submerged plants or even their death. Fish activity can also disturb the bottom sediment, increasing suspended matter and thus reducing transparency, which negatively impacts the growth of submerged plants.

[0003] Therefore, fish control is often a crucial measure for the restoration of submerged plants. To control fish, many aquatic ecological restoration projects use enclosures to isolate the restoration area, remove fish from within the enclosure, and prevent fish from entering from the outside, creating a relatively closed and stable environment for the growth of submerged plants. However, enclosure methods are mainly suitable for the restoration of submerged plants in shallow lakes. For mountainous rivers and other waterways that serve flood control functions, enclosures can affect flood safety, thus limiting their application.

[0004] Currently, there are numerous cases where the restoration of submerged plants in river channels 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 in water disclosed in authorization announcement number CN 220274376 U and a suspended submerged and emergent plant planting device disclosed in publication number CN 116686583 A, although the above devices all have the function of preventing fish from eating them, these devices, whether submerged at the bottom of the water or floating on the surface, still pose certain safety hazards to the flood discharge of the river channel and may be destroyed during the flood season. Summary of the Invention

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

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

[0007] A method for restoring submerged vegetation in river channels based on flow velocity zoning includes the following steps:

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

[0009] S2. Based on Vu and Vs, construct a rapid flow zone, a transition zone, and a slow flow zone in the river channel, such that the flow velocity in the rapid flow zone is ≥ Vu, the flow velocity in the slow flow zone is ≤ Vs, and the flow velocity ratio between the rapid flow zone and the slow flow zone is ≥ 1.5 times.

[0010] S3. Remove fish with a body length of ≥10cm from the river channel to reduce their density to ≤0.3 fish / m³. 2 ;

[0011] S4. Plant submerged plants that can adapt to flow velocities ≥ Vs in the rapid flow 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 a slow-flowing or still water test section with a fish density ≥ 2 fish / m² and divide it into a grid of 10m × 50m.

[0015] S1b. Monitor the fish density within the grid for ≥3 days and calculate the initial density C0;

[0016] S1c, Increase the flow velocity of the test river section to ≥0.5m / s by replenishing water or circulating water with pumps, and continue for ≥5 days. Divide the flow velocity range and monitor the fish density in each range C1.

[0017] S1d, calculate the density decrease rate X for each velocity range: X = (C0 - C1) / C0 × 100%. When X ≥ 70% and C1 ≤ 2 tails / m 2 When X ≥ 90% and C1 ≤ 0.2 tails / m, the upper limit of the interval is defined as Vs; 2 When Vu is defined as the lower limit of the interval, 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 rapid flow 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 rapid flow zone is increased through ecological dams, shallow embankments, or terrain modification.

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

[0021] Preferably, in step S4, the submerged plant is Vallisneria natans, Hydrilla verticillata, or a mixture of both.

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

[0023] Among them, intelligent monitoring includes deploying multi-parameter intelligent sensors in the rapid flow zone, transition zone and slow flow zone of the river to monitor the flow velocity, submerged plant coverage and fish density in each area in real time;

[0024] The dynamic control system mainly includes:

[0025] Fish removal will cease if the submerged plant coverage in the rapid flow-transition zone is ≥60% or the coverage in the entire river section is ≥30% for more than 15 months.

[0026] When the submerged plant coverage rate in the rapid flow-transition zone is less than 60% or the coverage rate in the entire river section is less than 30%, and the flow velocity in the rapid flow zone differs from the design flow velocity by less than 30%, an early warning is triggered and a first-level fish control is initiated to keep the fish density ≤0.3 fish / m².

[0027] Fish control methods include constructing safe zones and trap zones, gradually reducing fish density by separating the space for feeding in safe zones from the space for catching in trap zones, and by creating a sense of environmental safety.

[0028] When the submerged plant coverage rate in the rapid flow-transition zone is less than 60% or the coverage rate in the entire river section is less than 30%, and the flow velocity in the rapid flow zone is less than 50% of the design flow velocity, an early warning is triggered and a secondary fish control measure is initiated to ensure that the fish density is ≤0.05 fish / m².

[0029] Preferably, the method is applicable to mountainous rivers or flood-prone rivers with a width of 6-20 m, a water depth of 0.1-0.5 m during the dry season, and a water depth of 0.5-2 m during 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 this invention does not require complete fish control, nor does it require the installation of water-blocking structures such as enclosures in the river channel, thus it does not affect flood discharge and will not interfere with the flood discharge and drainage of the river channel;

[0032] 2. The rapid flow zone-slow flow zone constructed by this invention not only creates conditions for the restoration of submerged plants, but also increases habitat diversity, which is conducive to the restoration of the entire river's ecological biodiversity and solves the problems of traditional enclosure methods hindering flood discharge and fish prevention devices being easily damaged.

[0033] 3. The overall operation and maintenance of this invention is simple. Because fish are not completely controlled in the river, a certain amount of grazing pressure is maintained, which can prevent the excessive growth of submerged plants and reduce the pressure of operation and maintenance. Attached Figure Description

[0034] Figure 1 This is a flowchart illustrating an embodiment of the riverbed submerged plant restoration method based on flow velocity zoning according to the present invention.

[0035] Figure 2 This is a flowchart illustrating a specific embodiment of the river channel submerged plant restoration method based on flow velocity zoning according to the present invention.

[0036] Figure 3 This is a schematic diagram of the rapid flow zone, transition zone, and slow flow zone in this invention.

[0037] Figure 4 This is a comparison diagram of the repair effects of the present invention and the traditional enclosure method. Detailed Implementation

[0038] Please see Figure 1-4 As shown, this invention mainly provides a method for restoring submerged plants in river channels based on flow velocity zoning, to address the difficulty in restoring submerged plants in rivers due to fish grazing. In this embodiment, taking the restoration of submerged plants in a specific river channel as an example, the specific implementation process of this invention is described in detail:

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

[0040] Specifically, this involves: firstly investigating or measuring the flow velocity and water depth of the river during the high-water season, normal-water season, and low-water season; and secondly investigating the distribution of submerged plants in the river and the types and sizes of fish.

[0041] Then, according to step S1a, select a slow-flowing or still water test section with a fish density ≥ 2 fish / m², and divide the test section into multiple grids (e.g., 10m × 50m). Among them, the test section can be a slow-flowing or still water section with a high fish density, and the corresponding test section length is 200-2000 m.

[0042] The rules for dividing the flow velocity range include:

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

[0044] Each flow velocity range must include 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 within a fixed time period, with a continuous monitoring time of no less than 3 days, and calculate the initial density C0, which can be taken as the average value of each monitoring session; the density monitoring methods include:

[0046] Fish density was determined using the tag-and-recapture method or sonar detection technology.

[0047] The monitoring period is from 8:00 to 10:00 every day (peak fish activity period), and the monitoring is carried out continuously for ≥5 days.

[0048] S1c, Increase the flow velocity of the test river section to ≥0.5 m / s through water replenishment or pump circulation, and maintain this for ≥5 days. Divide the flow velocity into intervals and monitor the fish density in each interval. C1, Specifically, increase the river flow velocity through measures such as water replenishment and pump circulation, ensuring the maximum flow velocity is not less than 0.5 m / s. The pump type can be an axial flow pump or a centrifugal pump. The flow rate range is calculated based on the cross-sectional area of ​​the river channel (e.g., 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 velocity). 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 velocity. Divide the test river section into several flow velocity intervals, each interval being 0.05-0.2 m / s. Each interval includes one to several grids, and the number of fish in each interval is counted to calculate the fish density. The flow rate increase must last for at least 5 days, and monitoring must be carried out continuously within a fixed time period, with a continuous monitoring time of at least 5 days. The density is taken as the average value of each monitoring.

[0049] Based on the monitoring data, a flow velocity-density table was plotted, and the decrease in fish density before and after the flow velocity increase was calculated for each flow velocity range. The density decrease was calculated as follows: (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]

[0051] S1d. Calculate the density decrease range X = (C0 - C1) / C0 for each flow velocity interval. When X ≥ 70% and C1 ≤ 2 fish / m² in a certain flow velocity interval, the upper limit of that flow velocity interval is the upper limit of the suitable flow velocity Vs for fish; when X ≥ 90% and C1 ≤ 0.2 fish / m², the lower limit is the upper limit of the suitable flow velocity Vs for fish. 2 At that time, the lower limit of this flow velocity range is the unsuitable flow velocity Vu for fish.

[0052] S2. Based on Vu and Vs, construct a rapid flow zone, a transition zone, and a slow flow zone within the river channel; ensure that the flow velocity in the rapid flow zone is ≥ Vu, the flow velocity in the slow flow zone is ≤ Vs, and the flow velocity ratio between the rapid flow zone and the slow flow zone is ≥ 1.5 times.

[0053] Specifically, this involves creating rapid flow zones, transition zones, and slow flow zones, or multiple rapid flow-transition-slow flow zones, in different river channels through topographic shaping, overflow weirs, shallow dikes, or a combination of these measures. The distribution spaces of submerged plants and fish are separated by their varying adaptability to flow velocity. During the corresponding normal and low water periods, the flow velocity in the rapid flow zone is ensured to be no less than Vu, the flow velocity in the slow flow zone no more than Vs, and the flow velocity in the rapid flow zone at any given time is at least 1.5 times that of the slow flow zone. The flow velocity in the transition zone falls between the velocities of the rapid flow zone and the slow flow zone.

[0054] In addition, when creating a rapid-flow zone-slow-flow zone using measures such as topography, overflow weirs, and ecological water replenishment, or a combination of these measures, each rapid-flow zone should be at least 50 m long (to prevent fish from migrating upstream), with a transition zone length of 100-500 m and a slow-flow zone length of 50-300 m (to balance fish activity and water quality, retain small fish to maintain a food balance, and prevent excessive proliferation of submerged plants). If the rapid-flow zone is too short, fish can easily migrate upstream, moving back and forth between the two slow-flow zones, disturbing the rapid-flow zone and hindering the recovery of submerged plants. If the slow-flow zone is too short, fish will lack sufficient space to move, increasing the probability of migrating upstream, which is also detrimental to the recovery of submerged plants in the rapid-flow zone. If the slow-flow zone is too long, it will lead to insufficient hydrodynamic conditions in the river channel, potentially causing oxygen depletion and water quality deterioration. Fish will then migrate upstream to escape the harsh environment, which is detrimental to the overall ecological restoration of the river channel.

[0055] S3. Remove fish with a body length ≥10cm from the river channel (including omnivorous fish that feed on plants; fishing nets or other removal tools can be used), reducing their density to ≤0.3 fish / m² (to reduce their feeding and activity levels). Fish feeding and swimming abilities are positively correlated with their body length. Removing fish longer than 10cm reduces the number of fish that can enter the fast-flowing area and also reduces their food intake; details are shown in the table below.

[0056]

[0057] Comparative experiments revealed that tilapia with a body length ≥10cm were more than three times more efficient at grazing on submerged plants than individuals with a body length <10cm (see table above for specific data), and their activity range covered the slow-flowing zone to the transition zone. Maintaining a fish density of ≤0.3 fish / m² was based on the above experimental results: when the density >0.5 fish / m², the submerged plant coverage decreased by more than 50% per month; when the density ≤0.3 fish / m², the coverage could be stably increased to over 60%.

[0058] S4. Plant submerged plants that can adapt to flow velocities ≥ Vs in the fast-flowing and / or transitional zones. Select submerged plants that can adapt to flow velocities ≥ Vs, such as Vallisneria natans and Myriophyllum spicatum. 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 and management: within the first 15 months after the submerged plants are planted, when the coverage rate of submerged plants in the entire river section is greater than 30%, or the coverage rate of submerged plants in the rapid flow area and transition area is greater than 60%, fish control can be discontinued; 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 / m². The fish control methods include constructing safe zones and trap zones, and gradually reducing the fish density by separating the space for feeding in safe zones from the space for catching in trap zones and by creating a sense of environmental safety.

[0060] Reference Case: Restoration of Submerged Plants in Rivers of a Mountainous Town in Southeast China (e.g.) Figure 2 (As shown)

[0061] 1. River hydrology and habitat survey

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

[0063] Through on-site measurements and the collection of historical hydrological data, it was found that the river depth fluctuates greatly, with water levels rising and falling rapidly. When it is not raining, the water depth is 0.1 to 0.3 m, while when it rains, the water depth can reach 2 m.

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

[0065] 2. River aquatic life survey

[0066] Due to severe pollution from river overflows, the aquatic ecosystem is severely imbalanced. No submerged plants survive in the river, tilapia are rampant, with their body length mainly concentrated in the range of 5-20 cm, and golden apple snails are visible. No other higher aquatic animals are present.

[0067] Tilapia are omnivorous fish that primarily feed on plant matter. They enjoy nibbling on the roots and stems of submerged plants, which can cause devastating damage to young submerged plants.

[0068] Because the river is an open water system, connected to other water systems both upstream and downstream, the tilapia cannot be completely removed, resulting in the failure of the previous two submerged plant restoration projects due to the tilapia's nibbling.

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

[0070] Tilapia with a body length not exceeding 10 cm have a preferred upper limit for current velocity of approximately 0.5 m / s. Based on the current river conditions, the river channel was divided into 10 zones—Rapid Current Zone I, Transition Zone I, Slow Current Zone I, Rapid Current Zone II, Transition Zone II, Slow Current Zone II, Transition Zone III, Rapid Current Zone IV, Transition Zone IV, and Slow Current Zone IV—through ecological dams, shallow banks, and micro-topography shaping. The flow velocity and water depth in each zone during non-rainfall periods are shown in the table below.

[0071]

[0072] 4. Fish control

[0073] Tilapia longer than 10 cm are removed by fishing nets, so that the density of tilapia longer than 10 cm does not exceed 0.2 fish / m².

[0074] 5. Selection and cultivation of submerged plants

[0075] In this restored river section, the flow velocity in the rapids is mainly 0.4~0.8 m / s when there is no rainfall. Two submerged plants, dwarf Vallisneria natans and Hydrilla verticillata, were selected and planted in a 1:1 ratio throughout the entire restored river section.

[0076] Vallisneria natans, with its robust root system and soft, ribbon-like leaves, thrives in flowing water, even in environments with flow velocities exceeding 0.5 m / s. Hydrilla verticillata, adaptable to a wider range of flow velocities, also survives in environments with flow velocities above 0.5 m / s. Therefore, Vallisneria natans and Hydrilla verticillata were chosen as the species for the restoration of submerged plants in this section of the river.

[0077] 6. Maintenance and Management

[0078] Three months after the submerged plant planting was completed (the comparison of the restoration effects of this method and the traditional enclosure method is shown in the table below), the plant coverage rate in the rapid flow area reached about 25-40%, the plant coverage rate in the transition area reached 60-100%, and the tilapia in the slow flow area were active and dense, with almost no submerged plants. The submerged plant coverage rate of the entire river section was about 45%. Therefore, fish control was no longer required in the restored river section.

[0079]

[0080] During maintenance and management, an intelligent monitoring and dynamic control system is mainly used, as detailed below:

[0081] Intelligent monitoring includes deploying multi-parameter intelligent sensors (current meters, underwater cameras, sonar detectors, etc.) at key locations in the river channel (rapid flow zone, transition zone, slow flow zone) to monitor the flow velocity, submerged plant coverage (through image recognition), and fish density in each area in real time.

[0082] The dynamic control system mainly includes:

[0083] Fish removal will cease if the submerged plant coverage in the rapid flow-transition zone is ≥60% or the coverage in the entire river section is ≥30% for more than 15 months.

[0084] When the submerged plant coverage rate in the rapid flow-transition zone is less than 60% or the coverage rate in the entire river section is less than 30%, and the flow velocity in the rapid flow zone differs from the design flow velocity by less than 30%, an early warning is triggered and a first-level fish control measure is initiated to reduce the fish density to ≤0.3 fish / m². The fish control measures include constructing safe zones and trap zones, and gradually reducing the fish density by separating the space for feeding in the safe zones from the space for catching in the trap zones and by creating a sense of environmental safety.

[0085] Specific methods:

[0086] Set up a safe zone: Set up fixed feeding points in the slow-flowing area and feed the fish at regular times every day (such as in the evening) to attract fish to gather in the slow-flowing area; then catch the fish that gather there to reduce the fish density.

[0087] Fishing is prohibited in safe zones: This helps fish develop the perception that "this place is safe," avoiding disrupting their sense of security, causing stress, and leading them to flee from slow-moving areas.

[0088] Setting up a trap zone: Place passive fishing devices such as fish traps or submerged net cages 10-20 meters downstream of the safe zone. This allows fish to swim naturally into the traps after feeding at the feeding point, avoiding a direct association of "food = danger".

[0089] Reduce the visibility and irritation of fishing

[0090] Reduce disturbance during fishing: Choose to fish during the period when fish activity is at its lowest (such as the high temperature at noon in summer or the low temperature in the early morning in winter) to reduce stimulation to the fish population.

[0091] Fishing should not be too frequent: fishing should not exceed once a week to avoid disturbing the fish's safe zone.

[0092] (2) Mid-stage recovery of submerged plants

[0093] When the submerged plant coverage of the entire river section exceeds 30%, or the submerged plant coverage of the rapid flow area and transition zone reaches 60% or more, gradually reduce the feeding frequency. A cycle is 1-4 weeks. In the first cycle, reduce the feeding frequency to once every 2-3 days; in the second cycle, reduce it to once every 3-5 days; in the third cycle, reduce it to once every 5-7 days, and then stop feeding.

[0094] Fishing shall cease and artificial aeration facilities in slow-flowing areas shall be removed when the coverage of submerged vegetation in the river channel remains stable for three consecutive months, the coverage rate of submerged vegetation in the entire river section is always greater than 30%, or the coverage rate of submerged vegetation in the rapid flow area and the transition area is always greater than 60%.

[0095] 7. Restoration effect of submerged plants

[0096] like Figure 4 As shown, one year after construction, the submerged plant coverage remained relatively stable at around 50%, having no impact on flood control, and requiring no additional measures during the flood season. However, in the adjacent river channel, the submerged plant restoration method using enclosures resulted in inconsistent restoration effects, with submerged plant coverage not exceeding 10%. This was primarily due to the need for frequent enclosure removal during the flood season, allowing tilapia to consume large areas of submerged plants within a week. Furthermore, the frequent removal and installation of enclosures significantly increased the river channel's operating costs.

[0097] It should be noted that this invention constructs a velocity gradient between fast-flowing and slow-flowing zones by measuring the adaptive thresholds of fish to flow velocity (Vu, Vs). It utilizes the velocity adaptation differences between fish and submerged plants to achieve spatial isolation, combined with the removal of large fish (≥10 cm) to control feeding pressure. This solves the problems of traditional enclosure methods hindering flood discharge and the susceptibility of fish-prevention devices to damage. Furthermore, the submerged plant restoration method provided by this approach does not require complete fish control or the placement of water-blocking structures such as enclosures in the river channel, thus not affecting flood discharge. Simultaneously, the constructed fast-flowing-slow-flowing zone not only creates conditions for submerged plant restoration but also increases habitat diversity, which is beneficial to the restoration of biodiversity throughout the river channel. In addition, the overall operation and maintenance are simple because the river channel does not undergo complete fish control, maintaining a certain level of feeding pressure, thus preventing excessive growth of submerged plants and reducing operational burden. This invention is applicable to mountainous rivers where tilapia have invaded, offering both ecological restoration and flood control safety benefits.

[0098] The foregoing descriptions and embodiments are provided to enable those skilled in the art to understand and apply the present invention. It will be apparent to those skilled in the art that various modifications can be easily made to these contents, and the general principles described herein can be applied to other embodiments without creative effort. Therefore, the present invention is not limited to the foregoing descriptions and embodiments. Improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from its scope should be within the protection scope of the present invention.

Claims

1. A method for restoring submerged vegetation in river channels based on flow velocity zoning, characterized in that, Includes the following steps: S1. Determine the adaptive threshold of fish in the target river to the flow velocity, 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 rapid flow zone, a transition zone, and a slow flow zone in the river channel, such that the flow velocity in the rapid flow zone is ≥ Vu, the flow velocity in the slow flow zone is ≤ Vs, and the flow velocity ratio between the rapid flow zone and the slow flow zone is ≥ 1.5 times. S3. Remove fish with a body length of ≥10cm from the river channel to reduce their density to ≤0.3 fish / m³. 2 ; S4. Plant submerged plants that can adapt to flow velocities ≥ Vs in the rapid flow zone and / or the transition zone; S5. Maintain and manage submerged plants.

2. The method for restoring submerged vegetation in river channels based on flow velocity zoning according to claim 1, characterized in that, In step S1, the method for determining Vu and Vs includes: S1a, Select fish with a density ≥ 2 fish / m 2 The slow-flowing or still water test sections were divided into a grid of 10m × 50m. S1b. Monitor the fish density within the grid for ≥3 days and calculate the initial density C0; S1c, Increase the flow velocity of the test river section to ≥0.5m / s by replenishing water or circulating water with pumps, and continue for ≥5 days. Divide the flow velocity range and monitor the fish density in each range C1. S1d, calculate the density decrease rate X for each velocity range: X = (C0 - C1) / C0 × 100%. When X ≥ 70% and C1 ≤ 2 tails / m 2 When X ≥ 90% and C1 ≤ 0.2 tails / m, the upper limit of the interval is defined as Vs; 2 When Vu is defined as the lower limit of the interval, the lower limit of the interval is defined as Vu.

3. The method for restoring submerged vegetation in river channels 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 vegetation in river channels based on flow velocity zoning according to claim 1, characterized in that, In step S2, the length of the rapid flow 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 rapid flow zone is increased through ecological dams, shallow embankments, or terrain modification.

5. The method for restoring submerged vegetation in river channels 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 vegetation in river channels based on flow velocity zoning according to claim 1, characterized in that, In step S4, the submerged plant is Vallisneria natans, Hydrilla verticillata, or a mixture of both.

7. The method for restoring submerged vegetation in river channels based on flow velocity zoning according to claim 1, characterized in that, In step S5, the maintenance management includes the use of an intelligent monitoring and dynamic control system; Among them, intelligent monitoring includes deploying multi-parameter intelligent sensors in the rapid flow zone, transition zone and slow flow zone of the river to monitor the flow velocity, submerged plant coverage and fish density in each area in real time; The dynamic control system mainly includes: Fish removal will cease if the submerged plant coverage in the rapid flow-transition zone is ≥60% or the coverage in the entire river section is ≥30% for more than 15 months. When the submerged vegetation coverage in the rapid flow-transition zone is less than 60% or the coverage in the entire river section is less than 30%, and the flow velocity in the rapid flow zone differs from the design flow velocity by less than 30%, an early warning is triggered and a level-one fish control measure is initiated to maintain a fish density of ≤0.3 fish / m³. 2 ; Fish control methods include constructing safe zones and trap zones, gradually reducing fish density by separating the space for feeding in safe zones from the space for catching in trap zones, and by creating a sense of environmental safety. When the submerged vegetation coverage in the rapid flow-transition zone is less than 60% or the coverage in the entire river section is less than 30%, and the flow velocity in the rapid flow zone is less than 50% of the design velocity, an early warning is triggered and a secondary fish control measure is initiated to ensure that the fish density is ≤0.05 fish / m³. 2 .

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

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