A method for restoring submerged macrophytes in rivers based on flow rate regulation

Abstract

The present invention belongs to the technical field of river vegetation restoration in water conservancy projects, and specifically relates to a method for restoring submerged plants in river channels based on flow rate regulation. By measuring the adaptability thresholds Vu and Vs of tilapia to flow rate, the method dynamically regulates the amount of water replenished in combination with the hydrodynamic model MIKE, constructing a flow velocity gradient between the rapid flow area Vu and the slow flow area Vs, and utilizing the difference in flow velocity adaptability between fish and plants to achieve spatial isolation. At the same time, snakehead fish and benthic organisms are introduced to form ecological synergistic control. The advantages of the present invention are as follows: the present invention solves the problems of traditional enclosure methods hindering flood flow and the easy damage of fish prevention devices. It also constructs rapid flow areas and slow flow areas through water replenishment regulation, replacing traditional physical barrier devices, resolving the contradiction between flood flow safety and fish control, enhancing flood flow safety, and reducing maintenance costs.

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 rate regulation. Background Art

[0002] Submerged macrophytes are a vital component of aquatic ecosystems, and their restoration is a key component of aquatic ecological restoration projects. Currently, submerged macrophyte growth is influenced by a variety of factors, including water quality, depth, flow velocity, transparency, and animal activity. Tilapias possess significant adaptability and reproductive capacity. Furthermore, tilapia grazing can directly lead to a decrease in submerged macrophyte biomass, or even its extinction. Fish activity also disturbs bottom sediments and increases suspended matter, reducing transparency and negatively impacting submerged macrophyte 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 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 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 rate regulation.

[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 rate regulation 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. Divide the river flow velocity into zones according to Vu and Vs, and construct a rapid flow zone, a transition zone, and a slow flow zone in the river, so 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 in the transition zone is Vs~Vu;

[0010] S3. Remove fish with a body length of 10 cm or more from the river channel to a density of 0.3 fish / m² or less;

[0011] S4. Plant submerged plants in the river channel that are adapted to the flow velocity range of the rapids and transition zones;

[0012] S5. Dynamically regulate the amount of water replenishment to maintain the stability of the flow rate zones, and introduce carnivorous fish and benthic organisms after the submerged plant coverage reaches the standard. Dynamically regulate water replenishment includes intermittent water replenishment, and the duration of intermittent water replenishment is determined by the submerged plant coverage. The intermittent water replenishment formula is:

[0013] in:

[0014] R = F / F max;

[0015] F is the current cover of submerged macrophytes in the transition zone;

[0016] F max is the maximum cover of submerged macrophytes in the transition zone;

[0017] T is the daily water replenishment time, in hours;

[0018] When the coverage of submerged plants in the transition zone is ≥60%, start the intermittent water replenishment mode and introduce snakehead fish and snails.

[0019] Preferably, in step S1, the method for determining Vu and Vs includes:

[0020] S1a. Select a slow-flow or still-water test section with a fish density of ≥ 2 fish / m² and divide it into 10m × 50m grids.

[0021] S1b, continuously monitor the fish density in the grid for ≥ 3 days and calculate the initial density C0;

[0022] 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;

[0023] S1d. Calculate the density drop in each velocity interval as X = (C0 - C1) / C0 × 100%. When X ≥ 70% and C1 ≤ 2 m², define the upper limit of this interval as Vs. When X ≥ 90% and C1 ≤ 0.2 m², define the lower limit of this interval as Vu.

[0024] Preferably, in step S2, the flow velocity in the rapid flow area is ≥0.5 m / s;

[0025] The flow velocity of the slow flow zone is ≤0.3 m / s; the rapid flow zone and the slow flow zone are connected through the transition zone, and the flow velocity of the transition zone is between Vu and Vs, wherein the threshold values ​​of Vu and Vs are determined based on the adaptability of tilapia.

[0026] Preferably, in step S2, the flow rate zoning is achieved by regulating the water replenishment amount, and the water replenishment amount is calculated using the MIKE hydrodynamic model, and the model parameters include:

[0027] The grid type is a square or rectangular grid with a side length of 5-50m;

[0028] The Manning roughness coefficient is set in sections: 0.025 for the silt section and 0.035 for the gravel section;

[0029] The time step is set to 10 seconds, and the calibration error is controlled within ±8%;

[0030] The above parameters are used to calculate that the rapids area accounts for 10-35% of the total length of the river, and the slow-flow area accounts for 20-45%.

[0031] Preferably, in step S4, the submerged plant is Vallisneria or Myriophyllum spicatum, and during planting, a gabion mat with a thickness of ≥10 cm is laid on the bottom of the riverbed to fix the plant roots in the gravel.

[0032] Preferably, the gabion mat is made of 304 stainless steel wire mesh with a pore size of 5 cm, filled with basalt gravel with a particle size of 10-20 mm, with a filling density of ≥90%, and 12 mm diameter galvanized steel piles are set every 1.5 m along the water flow direction for anchoring, and the anchoring depth is ≥0.8 m.

[0033] Preferably, the method is applicable to mountain rivers or flood-carrying rivers with a width of 6-20 m and a water depth of 0.1-0.8 m in the dry season.

[0034] Due to the adoption of the above technical solution, the beneficial effects obtained by the present invention include:

[0035] 1. The present invention combines grid monitoring, the density reduction formula X = (C0 - C1) / C0 × 100% and MIKE model calculation to quantitatively determine the Vu / Vs threshold, making the measurement more scientific. In addition, the introduction of snakehead fish to suppress the tilapia population and simultaneously restore benthic organisms (such as snails) to build a self-sustaining ecosystem, increase habitat diversity, and promote the restoration of biodiversity in the entire river ecosystem.

[0036] 2. This invention creates rapid flow zones (Vu ≥ 0.5 m / s) and slow flow zones (Vs ≤ 0.3 m / s) by regulating the amount of water replenished, replacing traditional physical barriers. This resolves the contradiction between flood safety and fish control, enhances flood safety, and reduces maintenance costs.

[0037] 3. The overall operation and maintenance of the present invention is simple. Because the river channel does not fully control fish and maintains a certain grazing pressure, it can avoid excessive growth of submerged plants and reduce operation and maintenance pressure. At the same time, it also solves the problem that traditional enclosure methods hinder flood discharge and fish prevention devices are easily damaged. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 It is a flow chart of the method for restoring submerged plants in a river channel based on flow rate regulation of the present invention.

[0039] Figure 2 It is a schematic diagram of the rapid flow zone-transition zone-slow flow zone of the present invention.

[0040] Figure 3 This is a comparison chart of the repair effects of the present invention and the traditional enclosure method. DETAILED DESCRIPTION

[0041] See Figure 1-3 As shown, the present invention mainly provides a method for restoring submerged plants in a river channel based on flow rate regulation to solve the problem that the restoration of submerged plants is difficult due to the grazing of tilapia in the river channel. In this embodiment, the specific implementation process of the present invention is described in detail using the restoration of submerged plants in a river channel as an example:

[0042] 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;

[0043] Specifically: first, investigate the river hydrology, aquatic life and habitat;

[0044] (1) Investigate or measure the flow velocity and water depth of the river during the flood season, normal water season and dry season;

[0045] (2) Investigate the species, quantity, size and distribution of aquatic plants and fish in the river;

[0046] (3) Investigate the bottom conditions of the river.

[0047] Then, according to step S1a, a slow-flow or still-water test river section with a fish density of ≥ 2 fish / m² is selected, and the test river section is divided into multiple monitoring grids. The test river section can be a slow-flow or still-water river section with a higher fish density as the test river section, and the corresponding test river section length is 200-2000 m. The flow rate interval division rules include:

[0048] 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;

[0049] Each flow rate interval must contain at least one complete monitoring grid to ensure data representativeness.

[0050] Monitoring grid layout method:

[0051] (1) When the river channel width is 5-10 m, the monitoring grid width is the river channel width, and the length of each monitoring grid is 1-3 times the river channel width;

[0052] (2) When the river channel width is 10-15 m, the monitoring grid width is the river channel width, and the length of each monitoring grid is 1-5 times the river channel width;

[0053] (3) When the river channel width is 15-20 m, the monitoring grid width is the river channel width, the width of each monitoring grid is 1 / 2 of the river channel width, and the length is 1-5 times the river channel width;

[0054] 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 5 days. Calculate the initial density C0, which can be the average of each monitoring period. Density monitoring methods include:

[0055] Fish density was counted using the mark-recapture method or sonar detection technology;

[0056] The monitoring period is 8:00-10:00 every day (peak period of fish activity), and continuous monitoring is ≥5 days.

[0057] S1c. Increase the flow velocity of the test river section to ≥0.5 m / s through water replenishment or pump circulation for ≥5 days, divide the flow velocity into intervals, and monitor the fish density in each interval. C1. Specifically, increase the flow velocity of the river section through water replenishment, pump circulation, etc., so that the maximum flow velocity is not less than 0.5 m / s. Divide the test river section into several flow velocity intervals based on the flow velocity, with each flow velocity interval of 0.05-0.2 m / s, and each flow velocity interval includes one to several grids. Count the number of fish in each flow velocity interval and calculate the fish density. The flow velocity increase must last for at least 5 days, and monitoring must be carried out continuously within a fixed time period for at least 5 consecutive days. The density is the average of each monitoring period.

[0058] 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. The decrease in density = (fish density before the flow velocity was increased - fish density after the flow velocity was increased) / fish density before the flow velocity was increased (as shown in the table below):

[0059]

[0060] S1d. Calculate the density decrease for each flow velocity interval (X = (C0 - C1) / C0 × 100%). When X ≥ 70% and C1 ≤ 2 fish / m² within a flow velocity interval, the upper limit of this flow velocity interval is the upper limit of the suitable flow velocity for fish (Vs). When X ≥ 90% and C1 ≤ 0.2 fish / m², the lower limit of this flow velocity interval is the unsuitable flow velocity for fish (Vu).

[0061] S2. Divide the river flow velocity zones according to Vu and Vs, and construct rapid flow zones, transition zones, and slow flow zones in the river, so 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 in the transition zone is Vs~Vu;

[0062] Specifically, by replenishing water in the river, rapids, transition zones, and slow-flow zones are created in different river sections, or multiple rapids, transition zones, and slow-flow zones are created. The distribution of submerged plants and fish is separated by their varying adaptability to flow rates. During normal and dry seasons, the flow velocity in the rapids is maintained at no less than Vu, the flow velocity in the slow-flow zone is maintained at no more than Vs, and the flow velocity in the transition zone is between the rapids and slow-flow zones. In addition, the length of the rapids area accounts for 10-35% of the total river length (which can prevent fish from migrating upstream); the length of the slow-flow area accounts for 20-45% of the total river length (providing habitat conditions for fish activities, maintaining grazing balance through a certain number of fish, and avoiding excessive reproduction of submerged plants); among them, the rapids area and the slow-flow area are connected by a transition zone, and the flow rate in the transition zone is between Vu and Vs. Among them, the thresholds of Vu and Vs are based on the adaptability measurement of tilapia, and this method is suitable for mountain rivers or flood-carrying rivers with a width of 6-20 m and a water depth of 0.1-0.8 m in the dry season.

[0063] S3. Remove fish ≥10 cm in length from the river channel to a density of ≤0.3 fish / m². This will reduce the number of fish that can enter the rapids and their food intake. The details are shown in the following table:

[0064]

[0065] Comparative experiments have shown that tilapia 10 cm or longer are more than three times more efficient at grazing on submerged plants than those <10 cm (see the table above for specific data), and their range extends from slow-flow zones to transition zones. Controlling fish density to 0.3 fish / m² is based on these experimental results: when the density is greater than 0.5 fish / m², submerged plant cover decreases at a rate exceeding 50% per month; when the density is 0.3 fish / m² or less, cover steadily increases to over 60%.

[0066] S4. Plant submerged plants that can adapt to the flow velocity range of the rapids and transition zones in the river channel (in previous actual projects, there were no clear boundaries between the rapids, transition zones and slow-flow zones. In order to facilitate construction management, planting was generally done throughout the entire river channel. Although the flow velocity in the rapids is not conducive to the growth of submerged plants, observations of natural river channels in mountainous areas show that submerged plants have a certain probability of survival under rapid flow conditions). Specifically, select submerged plants that can adapt to the flow velocity range of the rapids and transition zones, such as Vallisneria and Myriophyllum paniculate. During the process, you can choose to plant a single species, or you can choose to plant two or more species in a mixed manner.

[0067] S5. Dynamically control the water supply to maintain the stability of the flow rate zones and introduce carnivorous fish and benthic organisms after the submerged plant coverage reaches the standard. Specifically:

[0068] Flow velocity zoning is achieved through water replenishment regulation (single-point water replenishment or multi-point water replenishment can be used in the process to form multiple flow velocity intervals in the river channel). The water replenishment amount is calculated using the MIKE hydrodynamic model, engineering experiments or physical models to make the proportion of river sections with a flow velocity ≥ Vu account for 10-35% of the total river length, and the proportion of river sections with a flow velocity ≤ Vs account for 20-45% of the total river length.

[0069] Specifically:

[0070] When the coverage of submerged plants in the transition zone reaches 60% through sampling, the intermittent watering mode is started:

[0071]

[0072] in:

[0073] R = F / Fmax;

[0074] F is the current cover of submerged macrophytes in the transition zone;

[0075] F max is the maximum cover of submerged macrophytes in the transition zone;

[0076] T The daily water replenishment time, in hours.

[0077] When the coverage of submerged macrophytes in the slow-flowing area (river sections with a flow rate of Vs to Vu) is greater than 60%, the water replenishment plan can be optimized and an intermittent water replenishment mode can be started. The water replenishment time can be calculated based on the coverage of submerged macrophytes, and the replenishment time and cost can be gradually reduced. At the same time, other types of submerged macrophytes, carnivorous fish, and benthic organisms such as snails and clams can be introduced to increase the diversity of submerged macrophytes in the river and build a healthy water ecosystem.

[0078] Reference case: Restoration of submerged macrophytes in a river in the southeast region (e.g. Figure 2 shown)

[0079] The submerged plant restoration project is part of the comprehensive water system improvement project in the Xiuyu area of ​​the Mulan River Basin in Putian City, Fujian Province. The specific implementation site is one of the rivers. The water supply source is water from the upstream reservoir, which is purified by magnetic separation integrated water treatment equipment and then supplied to the river.

[0080] 1. River hydrology and aquatic life survey

[0081] The river channel is 10-50 m wide and 1.5 km long, with poor hydrodynamic conditions, a flow rate of 0-0.05 m / s, a water depth of 0.3-0.8 m, and a muddy bottom.

[0082] There are no aquatic plants in the river, and the fish are tilapia, most of which are less than 10 cm in length, and those over 10 cm account for no more than 5%.

[0083] 2. Determination of fish's ability to adapt to flow rate

[0084] (1) Selection of the test river section: The river section with a high fish density in the middle reaches of the river was selected as the test river section. The length of the test river section was 300 m and the water depth was 0.3-0.4 m.

[0085] (2) Monitoring fish density: Divide the test river section into 5 grids, each grid size is river width × 2 times the river width, monitor the number of fish in each grid, and calculate the fish density. Monitoring is carried out during consecutive sunny days, between 8:00 and 10:00 every day, for 7 consecutive days. The density is the average of each monitoring. The fish density in each grid is shown in the following table:

[0086]

[0087] (3) Increase the flow rate: Use a water pump to draw water from another river upstream of the river to replenish the water, so that the maximum flow rate downstream of the replenishment point reaches 0.8 m / s. Divide the test river section into several flow rate intervals according to the flow rate, with each 0.2 m / s as a flow rate interval. Count the number of fish in each flow rate interval and calculate the fish density.

[0088] (4) The flow rate increase lasts for 7 days; the monitoring is completed within two hours from 8:00 to 10:00, and the monitoring is continuous for 7 days. The density is taken as the average value of each monitoring.

[0089] (5) Draw a flow velocity-density table and calculate the decrease in fish density before and after the flow velocity is increased in each flow velocity interval. The decrease in density = (fish density before the flow velocity is increased - fish density after the flow velocity is increased) / fish density before the flow velocity is increased, as shown in the following table:

[0090]

[0091] (6) Determine the range of flow velocity that fish can adapt to: when the fish density is 0.3-2 fish / m2 within a certain flow velocity range and X is not less than 70%, the upper limit of the flow velocity range is the upper limit of the flow velocity that is suitable for fish (Vs); when the fish density does not exceed 0.2 fish / m2 within a certain flow velocity range and X is greater than 90%, the lower limit of the flow velocity range is the unsuitable flow velocity for fish (Vu).

[0092] From the velocity-density table, we can know that: Vs=0.3 m / s, Vu=0.5 m / s.

[0093] 3. Calculation of water replenishment

[0094] The river channel is replenished at multiple points to form multiple flow velocity intervals in the river channel. The MIKE model is used to calculate the water replenishment amount required to make the river section with a flow velocity ≥ Vu account for about 25% of the total length of the river channel, and the river section with a flow velocity ≤ Vs account for about 30% of the total length of the river channel.

[0095] In this embodiment, the MIKE model parameters include:

[0096] Use square or rectangular grids with a side length of 5-50m;

[0097] The river channel roughness coefficient is set in sections according to the bottom sediment type: the Manning coefficient for the silt section is 0.025 (based on the silt bottom sediment roughness range of 0.02-0.03 in the "River Roughness Manual"); the Manning coefficient for the gravel section is 0.035 (corresponding to the gravel bottom sediment roughness range of 0.03-0.04);

[0098] The recharge point was set at the upstream quarter of the river channel, and the time step was set to 10 seconds (according to the Courant-Friedrichs-Lewy (CFL) stability condition to ensure the convergence of the calculation). The model was calibrated using ADCP measured data, and the calibration error was controlled within ±8%.

[0099] The water replenishment calculation process includes inputting river topography, bottom type, and water replenishment point location;

[0100] The flow rates at the recharge points were adjusted based on the model output so that the rapid flow area occupied 10-35% of the total river length and the slow flow area occupied 20-45%.

[0101] Model validation of velocity partition ratios:

[0102] Simulations using the MIKE hydrodynamic model revealed that when the rapid flow zone accounts for less than 10%, the probability of fish migrating upstream increases to 80%. When the rapid flow zone accounts for more than 35%, flood resistance increases significantly (water level rise ≥ 15%). A slow flow zone accounting for 20-45% can balance the growth requirements of submerged plants (coverage ≥ 60%) and the habitat requirements of fish (density ≤ 0.5 fish / m²). Specific simulation results are shown in the following table:

[0103]

[0104] 4. Screening and planting of submerged plants

[0105] Choose Vallisneria as the submerged plant.

[0106] In order to improve the scour resistance of the river channel, a 10 cm thick gabion mat is laid at the bottom of the riverbed, and the rhizomes of the water hyacinth are buried in the gravel and planted in the entire area to prevent the water hyacinth from being washed away by the water flow. In this embodiment, the gabion mat can be made of a 304 stainless steel wire mesh with a pore size of 5 cm, and is filled with basalt gravel with a particle size of 10-20 mm, with a filling density of ≥90%. Galvanized steel piles with a diameter of 12 mm are set every 1.5 m along the direction of water flow for anchoring, and the anchoring depth is ≥0.8 m.

[0107] Half a year after the submerged plants were planted (before this solution was adopted, the restoration effect of the traditional enclosure method was not good, and the submerged plant coverage was similar to that of the slow-flowing river section in this solution, as shown in the table below).

[0108]

[0109] The coverage of submerged macrophytes in the river channel reached 40%, and the coverage of submerged macrophytes in the river section with a flow rate of Vs~Vu reached 66%. Intermittent water replenishment was adopted, with water replenishment for 3-8 hours a day.

[0110] At this time, naturally growing snails were already in the river channel, and spike-flowered foxtail algae were planted in patches without submerged plants. Snakehead carp, 30-40 cm in length, were introduced at a stocking density of 5% of the existing tilapia population to control the tilapia. One year later, the overall coverage of submerged plants in the river channel remained at around 35-55%.

[0111] It should be noted that: the present invention constructs a rapid flow area (Vu≥0.5 m / s) and a slow flow area (Vs≤0.3 m / s) by regulating the amount of water replenishment, replacing the traditional physical barrier device to solve the contradiction between flood safety and fish control; at the same time, combined with grid monitoring, the density reduction formula X=(C0-C1) / C0×100% and MIKE model calculation, the Vu and Vs thresholds are quantitatively determined to make the measurement more scientific; in addition, the introduction of snakehead fish to suppress the tilapia population, synchronously restore benthic organisms (such as snails), construct a self-sustaining ecosystem, increase habitat diversity, and is beneficial to the restoration of the ecological biodiversity of the entire river; in addition, the overall operation and maintenance are simple, because the river does not completely control the fish and maintains a certain grazing pressure, so the excessive growth of submerged plants can be avoided, reducing the pressure of operation and maintenance.

[0112] 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 plants in a river channel based on flow rate regulation, characterized in that: The following steps are involved: 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; S2. Divide the river flow velocity into zones according to Vu and Vs, and construct a rapid flow zone, a transition zone, and a slow flow zone in the river, so 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 in the transition zone is Vs~Vu; S3. Remove fish with a body length of 10 cm or more from the river channel to a density of 0.3 fish / m² or less; S4. Plant submerged plants in the river channel that are adapted to the flow velocity range of the rapids and transition zones; S5. Dynamically regulate the water replenishment to maintain the stability of the flow velocity zones, and introduce carnivorous fish and benthic organisms after the submerged plant coverage reaches the standard; wherein, the dynamic regulation of water replenishment includes intermittent water replenishment, and the intermittent water replenishment formula is: in: R = F / F max; F is the current cover of submerged macrophytes in the transition zone; F max is the maximum cover of submerged macrophytes in the transition zone; T is the daily water replenishment time, in hours; When the coverage of submerged plants in the transition zone is ≥60%, start the intermittent water replenishment mode and introduce snakehead fish and snails.

2. The method for restoring submerged plants in a river channel based on flow rate regulation according to claim 1, characterized in that: In step S1, the method for measuring Vu and Vs includes: S1a. Select a slow-flow or still-water test section with a fish density of ≥ 2 fish / m² and divide it into 10m × 50m grids. S1b, continuously monitor the fish density in the grid for ≥ 3 days and calculate 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 as X = (C0 - C1) / C0 × 100%. When X ≥ 70% and C1 ≤ 2 m², define the upper limit of this interval as Vs. When X ≥ 90% and C1 ≤ 0.2 m², define the lower limit of this interval as Vu.

3. The method for restoring submerged plants in a river channel based on flow rate regulation according to claim 1, characterized in that: In step S2, the flow velocity of the rapid flow area is ≥0.5 m / s; the flow velocity of the slow flow area is ≤0.3 m / s; the rapid flow area and the slow flow area are connected by the transition area, and the flow velocity of the transition area is between Vu and Vs; wherein the threshold values ​​of Vu and Vs are determined based on the adaptability of tilapia.

4. The method for restoring submerged plants in a river channel based on flow rate regulation according to claim 1, characterized in that: In step S2, the flow rate zoning is achieved by regulating the water replenishment amount. The water replenishment amount is calculated using the MIKE hydrodynamic model. The model parameters include: The grid type is a square or rectangular grid with a grid side length of 5-50 m; The Manning roughness coefficient is set in sections: 0.025 for the silt section and 0.035 for the gravel section; The time step is set to 10 seconds, and the calibration error is controlled within ±8%; The above parameters are used to calculate that the rapids area accounts for 10-35% of the total length of the river, and the slow-flow area accounts for 20-45%.

5. The method for restoring submerged plants in a river channel based on flow rate regulation according to claim 1, characterized in that: In step S4, the submerged plants are Vallisneria or Myriophyllum spicatum. When planting, a gabion mat with a thickness of ≥10 cm is laid on the bottom of the riverbed to fix the plant roots in the gravel.

6. The method for restoring submerged plants in a river channel based on flow rate regulation according to claim 5, characterized in that: The gabion mat is made of 304 stainless steel wire mesh with a pore size of 5 cm, and is filled with basalt gravel with a particle size of 10-20 mm. The filling density is ≥90%, and 12 mm diameter galvanized steel piles are set every 1.5 m along the water flow direction for anchoring, and the anchoring depth is ≥0.8 m.

7. The method for restoring submerged plants in a river channel based on flow rate regulation according to claim 1, characterized in that: The method is applicable to mountainous rivers or flood-carrying rivers with a width of 6-20 m and a water depth of 0.1-0.8 m in the dry season.

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