Underwater protection system and method for submerged plant communities in flood-carrying rivers

Abstract

The present invention discloses an underwater protection system and method for submerged plants in flood-carrying rivers. The system includes a riprap gabion structure, a pebble gabion structure, a horizontal row of pinewood piles, and a vertical row of pinewood piles, all arranged below the normal water level. The riprap gabion structure is arranged at an angle of 20° to 60° to the riverbank. The pebble gabion structure is arranged along the riverbank and near the center of the riverchannel, and the lower end of the pebble gabion structure is connected to the downstream riprap gabion structure. The riprap gabion structure, the pebble gabion structure, and the riverbank enclose a submerged plant protection zone and a suspended sediment deposition zone, wherein no submerged plants are planted in the suspended sediment deposition zone. The present invention can effectively protect submerged plant communities during floods and improve the survival rate of submerged plants. It also has a highly targeted regulation of water flow, ensuring the normal flood-carrying capacity of the riverchannel. It can also improve the water flow structure and aquatic habitat during the dry season, thereby improving the purification capacity of the riverchannel during the dry season.

Description

Technical Field

[0001] The present invention relates to the technical field of water ecological restoration, and in particular to an underwater protection system and method for submerged plant communities in flood-carrying rivers. Background Art

[0002] The Chinese invention patent application number CN201710656783.2 discloses a river channel deep ditch underwater forest system and its construction method, including a river channel, in which a water flow isolation device is arranged along the direction of water flow in the river channel, and the water flow isolation device is approximately higher than the designed water surface of the river channel to divide the river channel into an underwater forest shallow water area and a deep ditch diversion area; the bottom of the underwater forest shallow water area is higher than the bottom of the deep ditch diversion area; the bottom of the water flow isolation device is arranged in the deep ditch diversion area; a water flow deceleration section is provided at the water flow inlet of the underwater forest shallow water area, the water flow deceleration section is connected to the front end of the water flow isolation device and extends to the river bank on one side of the underwater forest shallow water area, and its height corresponds to the water flow isolation device; submerged plants are planted in the underwater forest shallow water area.

[0003] After long-term testing, the defects of the existing technology are summarized as follows:

[0004] 1. The protection range of the water flow isolation device is limited. During floods, it cannot cover the entire shallow water area of the underwater forest. During floods, submerged plants are likely to be destroyed on a large scale.

[0005] 2. The water flow isolation device is higher than the designed maximum water level. During floods, significant water congestion will occur in local areas, causing water levels to rise and seriously affecting the flow of water in the river;

[0006] 3. Submerged plant communities grow only 0 to 1.5 meters from the base, and the space that needs to be protected is mainly the root system of the submerged plant community and the base soil. The water flow isolation device is higher than the designed maximum water surface, which results in serious cost waste and lack of targeting.

[0007] 4. The water flow isolation device is higher than the water surface all year round, affecting the water surface landscape effect;

[0008] 5. There is backflow around the water flow isolation device, and silt may accumulate. It is meaningless to plant submerged plants in this area. After long-term silt accumulation, the plants will be submerged.

[0009] 6. The ecological structure is blocked and separated to a certain extent, which is not conducive to the habitat and stay of animals and plants. Summary of the Invention

[0010] In order to solve the above technical problems, the purpose of the present invention is to provide an underwater protection system and method for submerged plant communities in flood-carrying rivers.

[0011] To achieve the above object, the present invention provides the following technical solutions:

[0012] An underwater protection system for submerged plants in a flood-carrying river channel comprises a riprap gabion structure, a pebble gabion structure, a horizontal row of pinewood piles, and a vertical row of pinewood piles, all of which are arranged below the normal water level. The riprap gabion structure comprises an upstream riprap gabion structure and a downstream riprap gabion structure, both of which extend from the river bank to the center of the river channel in an "I" shape and are arranged at an angle of 20° to 60° to the river bank. The pebble gabion structure is arranged along the river bank and near the center of the river channel, and the lower end of the pebble gabion structure is connected to the downstream riprap gabion structure.

[0013] A submerged plant protection zone and a suspended sediment siltation zone are formed by enclosing riprap gabion structures, pebble gabion structures and river banks. In the submerged plant protection zone, several horizontal pine pile structures are arranged from the river bank to the center of the river channel, and no less than one vertical pine pile structure is arranged along the river bank from the horizontal pine pile structure closest to the upstream riprap gabion structure to the downstream riprap gabion structure, so that the vertical pine pile structure and the horizontal pine pile structure are interpenetrated, so that the submerged plant protection zone is divided into several submerged plant protection units by the vertical pine pile structure and the horizontal pine pile structure; a suspended sediment siltation zone is formed by the upstream riprap gabion structure, the river bank and the horizontal pine pile structure closest to the upstream riprap gabion structure. No submerged plants are arranged in the suspended sediment siltation zone to avoid the submerged plants from being submerged after long-term sedimentation, resulting in waste of resources.

[0014] A further technical solution is that submerged plants are arranged in a plurality of submerged plant protection units, and each submerged plant protection unit has an area of 20 to 25 m 2 By setting up the protection unit in this way, the horizontal and vertical water flows are adjusted through horizontal and vertical rows of pine piles, so that the flow of bottom water is relatively stable and the flow velocity is further reduced, which can greatly reduce the dragging effect on submerged plants and the erosion of the base soil by the water flow.

[0015] A further technical solution is that the riprap gabion structure is not lower than the pebble gabion structure, the horizontal pine pile structure and the vertical pine pile structure, and can effectively protect the pebble gabion structure, the horizontal pine pile structure and the vertical pine pile structure, as well as the submerged plants arranged therein.

[0016] A further technical solution is: the riprap gabion structure has a height of 0.5 to 1 m and a length of 5 to 10 m; the riprap gabion structure is composed of stones with a length, width and height of not less than 45 cm and not more than 50 cm, and can resist erosion at a flow rate of not less than 5 to 7 m / s.

[0017] A further technical solution is: the height of the pebble gabion structure is 0.5m; the pebble gabion structure is arranged with pebbles with a particle size of 20 to 40cm, and can resist erosion at a flow rate of 3 to 6m / s.

[0018] A further technical solution is that the horizontal row of pine wood pile structures and the vertical row of pine wood pile structures are formed by arranging pine wood piles in rows, and the diameter of the pine wood piles used is 20 to 30 cm and the spacing is 2 to 4 cm.

[0019] A further technical solution is that the pine piles are exposed from the riverbed at a height of not less than 0.5m and are inserted into the riverbed at a depth of not less than 0.5m, so as to increase the stability and anti-scouring ability of the pine piles.

[0020] At the same time, the present invention also provides the following technical solutions:

[0021] A method for underwater protection of submerged plants in a flood-carrying river channel, comprising the steps of:

[0022] Step A: Measure the river section topography in the river ecological restoration area and establish a flow velocity simulation model through 3D modeling.

[0023] Step B. Conducting a flow velocity simulation within a flow velocity simulation model based on the flood control standards for river sections in the river ecological restoration zone, and determining a water area with a certain flow velocity as a submerged plant community restoration zone based on the flow velocity results of the flow velocity simulation;

[0024] Step C. Build temporary cofferdams upstream and downstream of the submerged plant community restoration area, and divert river water to the downstream along the gaps reserved in the cofferdams;

[0025] Step D. installing the above-described submerged plant underwater protection system for a flood channel in the submerged plant community restoration area;

[0026] Step E. Plant submerged plants in the submerged plant protection unit. After the submerged plants have grown for more than one month, remove the temporary cofferdam and perform regular maintenance on the submerged plants.

[0027] A further technical solution is: said step A comprises:

[0028] A1. During the dry season, an electromagnetic rangefinder was used to measure the underwater topography of the river ecological restoration area with an accuracy of 0.5m.

[0029] A2. Import the underwater terrain measured in A1 into CAD software, export it to a DXF file, use dxf2xyz software to convert the terrain data into an XYZ file, and import the XYZ file into fluid dynamics simulation software for STL file conversion, ultimately generating a 3D river terrain file.

[0030] A3. Use a square grid in fluid dynamics simulation software to simulate the terrain. The roughness is n = 0.04, which is typical for mountain river channels. The simulated operating conditions are the flood standard for the river section in the ecological restoration zone, the water temperature is T = 20°C, the model calculation grid division accuracy is 0.5m * 0.5m, and the total number of grids is 5 million. This is to establish a flow velocity simulation model.

[0031] A4. Use the post-processing software included in the fluid mechanics simulation software to visualize the simulation results. By setting the displayed flow velocity range, a velocity plane zoning map of the river ecological restoration zone is obtained.

[0032] A further technical solution is: in step B, the submerged plant community restoration area is a plane range of water area with a flow rate of less than 2m / s.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] (1) It can effectively protect submerged plant communities during floods and ensure a high survival rate. When facing floods within 2 m / s, the survival rate can reach more than 90%, which can effectively protect submerged plants;

[0035] (2) It occupies a small area of river channel, and has a highly targeted regulation of water flow. It only regulates the bottom flood and does not completely block the flood, thus ensuring the normal flood discharge capacity of the river channel.

[0036] (3) According to the characteristics of water flow, a suspended sediment deposition area was set up to reduce the impact of sediment on the growth of submerged plant communities.

[0037] (4) All structures are located below the designed normal water level and do not affect the water surface landscape during flood and dry seasons;

[0038] (5) During the dry season, it can improve the water flow structure and aquatic habitat, provide a habitat for various aquatic organisms, and enhance the purification capacity of the river during the dry season. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 This is a plan view of an underwater protection system for submerged plant communities in a flood channel according to an embodiment of the present invention;

[0040] Figure 2 This is a cross-sectional schematic diagram of an underwater protection system for submerged plant communities in a flood channel according to an embodiment of the present invention;

[0041] Figure 3 The present invention is a flowchart of an underwater protection method for submerged plant communities in flood-carrying rivers according to an embodiment of the present invention.

[0042] Reference numerals:

[0043] 1-Riprap gabion structure; 2-Suspended sediment deposition area; 3-Horizontal pine pile structure; 4-Vertical pine pile structure; 5-Submerged plants; 6-Submerged plant protection unit; 7-Pebble gabion structure; 8-Flow velocity direction; 9-Flood channel; 10-Base soil; 11-River bank. DETAILED DESCRIPTION

[0044] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0045] Example 1;

[0046] Refer to the attached Figure 1-2 , an underwater protection system for submerged plants in a flood-carrying river channel, comprising a riprap gabion structure 1, a pebble gabion structure 7, a horizontal row of pine wood pile structures 3 and a vertical row of pine wood pile structures 4, etc., which are arranged below the normal water level; the riprap gabion structure 1 is arranged in the area directly impacted by the flood, including an upstream riprap gabion structure and a downstream riprap gabion structure, both of which extend in an "I" shape from the river bank to the center of the river channel, and are arranged at 20° to 60° to the surface of the river bank away from the direct impact of the flood; the pebble gabion structure is arranged along the river bank and close to the center of the river channel, the pebble gabion structure is not connected to the upstream riprap gabion structure, and the lower end of the pebble gabion structure is connected to the downstream riprap gabion structure.

[0047] A slow-flow area is formed by enclosing the upstream riprap gabion structure, the downstream riprap gabion structure, the pebble gabion structure and the river bank. The slow-flow area includes a submerged plant protection area and a suspended sediment sedimentation area. In the submerged plant protection area, several horizontal pine pile structures 3 are arranged from the river bank to the center of the river channel, and no less than one vertical pine pile structure 4 is arranged along the river bank from the horizontal pine pile structure closest to the upstream riprap gabion structure to the downstream riprap gabion structure, so that the vertical pine pile structure and the horizontal pine pile structure are penetrated, so that the submerged plant protection area is divided into several submerged plant protection units by the vertical pine pile structure and the horizontal pine pile structure; in this embodiment, one vertical pine pile structure 4 is provided. The longitudinal pine pile structure is arranged at the connection between the transverse pine pile structure and the submerged plant underwater protection system, which is closest to the upstream riprap gabion structure. It is not connected to the upstream riprap gabion structure, but is connected to the downstream riprap gabion structure. The suspended sediment deposition area 2 is enclosed by the upstream riprap gabion structure, the river bank and the transverse pine pile structure closest to the upstream riprap gabion structure. No submerged plants are set in the suspended sediment deposition area 2.

[0048] Furthermore, submerged plants are arranged in several submerged plant protection units, and each submerged plant protection unit has an area of 20 to 25 m 2 .

[0049] The riprap gabion structure should be no less than the pebble gabion structure, the horizontal pinewood pile structure, and the vertical pinewood pile structure. Specifically, the riprap gabion structure is set below the designed normal water level, at a height of approximately 0.5 to 1 m. The length of the riprap gabion is set according to the width of the river channel, and its length is 5 to 10 m. The riprap gabion structure is composed of stones with a length, width, and height of no less than 45 cm and no more than 50 cm. Preferably, the riprap gabion structure uses stones with a length * width * height of approximately 50 * 45 * 55 cm. This arrangement can withstand scouring at a flow rate of 5 to 7 m / s and has strong impact resistance. The pebble gabion structure is located below the designed normal water level, at a height of approximately 0.5 m. Because the pebble gabion structure is not directly exposed to flood impact, pebbles with a particle size of approximately 20 to 40 cm can be used, which can withstand scouring at a flow rate of 3 to 6 m / s.

[0050] Several submerged plant underwater protection systems can be set up along the river bank. The downstream riprap gabion structure in the upstream submerged plant underwater protection system can be used as the upstream riprap gabion structure of the downstream submerged plant underwater protection system, so as to set up several submerged plant underwater protection systems in the flood channel.

[0051] The submerged plant underwater protection system has the following functions:

[0052] 1) The riprap gabion structure 1 can divert most of the bottom floodwater to the center of the river channel, ensuring that the bottom floodwater will not cause serious scouring of the submerged plant protection area; the pebble gabion structure 7 can further reduce the impact of the bottom water flow in the flood channel 9 on the submerged plant protection area;

[0053] 2) The riprap gabion structure 1 and the pebble gabion structure 7 form a diversion system located below the water surface. They only regulate the bottom floodwaters, without changing the velocity and direction of the mid-surface floodwaters. Furthermore, they do not completely block the bottom floodwaters. A small amount of bottom floodwater can still enter the submerged plant protection area through the gaps in the diversion system, thus having little impact on the flow of the river channel.

[0054] 3) The diversion system can block the bedload brought by floods outside the submerged plant protection area, preventing the bedload from damaging the submerged plants;

[0055] 4) A certain area behind the riprap gabion structure is the return flow area. There will be some sediment accumulation in the return flow area. No submerged plant communities are planted in this area. It is set as a suspended sediment sedimentation area. After long-term sedimentation, a natural shallow habitat can be formed, which is conducive to improving the biological habitat environment.

[0056] 5) During the dry season, riprap gabion structures and pebble gabion structures can serve as habitats for aquatic organisms. The riprap surface has a large area for microbial attachment, which allows for large-scale reproduction of microorganisms, thereby improving the water purification capacity.

[0057] After passing through the diversion system, the impact of floods on the submerged plant community area has been reduced. However, based on the principle of minimizing the impact on river flow, the diversion system does not completely block the bottom floods. A small amount of bottom floods can still enter the submerged plant protection area through the gaps in the diversion system. Moreover, since the overall flow velocity of the flood is relatively large and the flow pattern is relatively complex and chaotic, there is still a great risk for submerged plants. Therefore, it needs to be further processed and protected by the slow flow system to further reduce the bottom flow velocity and make the flow pattern more stable.

[0058] A further improvement is the use of pine piles arranged in rows, with diameters of 20 to 30 cm and spacing of 2 to 4 cm. These piles are arranged in a cross-shaped pattern to create a slow-flow system. The piles are located below the design water level, protruding at least 0.5 m above the riverbed and inserted at least 0.5 m below it, to enhance their stability and scour resistance.

[0059] The horizontal pine pile structure is mainly used to regulate the longitudinal water flow along the river bank, while the vertical pine pile structure is mainly used to regulate the transverse water flow perpendicular to the river bank. The slow flow system divides the submerged plant protection area into multiple submerged plant protection units of equal size, each protection unit is about 20 to 25m 2 The arrangement of the pine piles in the horizontal and vertical rows of pine pile structures can be adjusted according to the actual river width, area and flood flow rate, thereby adjusting the area of the submerged plant protection unit.

[0060] The main functions of the slow flow system set up in this way are:

[0061] 1) By using horizontal and vertical rows of pine wood piles to regulate the horizontal and vertical water flow, the bottom water flow is made more stable and the flow velocity is further reduced, which can greatly reduce the drag on submerged plants and the erosion of the base soil by the water flow;

[0062] 2) The submerged plant communities within the submerged plant protection unit are not affected by riverbed bedload;

[0063] 3) The pine piles in the submerged plant protection unit are constructed underwater, so the middle and upper layers of floodwater can pass through normally, with little impact on flood flow;

[0064] 4) During the dry season, the slow-flow system has rich habitats, which can provide a diverse habitat for aquatic organisms and microorganisms, thereby improving the overall water environment quality during the dry season.

[0065] The riprap gabion structure, pebble gabion structure, horizontal pine pile structure and vertical pine pile structure of the present invention can be replaced by other similar materials according to local conditions. They can regulate water dynamics and provide biological habitats, and at the same time have strong anti-scouring capabilities, such as concrete, various types of rocks, etc., and have strong engineering convenience and universality, which is conducive to reducing management costs.

[0066] The underwater protection system for submerged plants consists of a diversion system and a slow-flow system. The diversion system can divert the main flow of floodwaters away from the shore and guide them to the middle river channel, thereby reducing the overall flow velocity of the shore zone. The slow-flow system can further improve the hydraulic conditions of the bottom water body of the shore zone, reduce the flow velocity, and smooth the flow state, thereby protecting the roots of the submerged plant community and the base soil. The protection system adopted by the present invention is located below the normal water level, occupies a small area of the river channel, and the technical measures adopted do not completely block the water flow, allowing the water flow to pass through the gaps, so the impact on flood flow is relatively small. At the same time, it also improves the aquatic habitat of the shore zone, provides a diverse habitat for fish, benthic organisms, etc., and is conducive to improving the level of biodiversity.

[0067] Example 2;

[0068] Refer to the attached Figure 3 A method for underwater protection of submerged plants in a flood channel comprises the following steps:

[0069] Step A. Measure the river section topography in the river ecological restoration area and establish a flow velocity simulation model through three-dimensional modeling;

[0070] Specifically:

[0071] A1. During the dry season, an electromagnetic rangefinder was used to measure the underwater topography of the river ecological restoration area with an accuracy of 0.5m.

[0072] During the dry season, the water flow rate is small and the flow rate is low, which makes it convenient to carry out measurement work.

[0073] A2. Import the underwater terrain measured in A1 into CAD software, export it to a DXF file, use dxf2xyz software to convert the terrain data into an XYZ file, and import the XYZ file into flow3d fluid dynamics simulation software for STL file conversion, ultimately generating a 3D river channel terrain file.

[0074] A3. Use the square grid in flow3d fluid dynamics simulation software to simulate the terrain. The roughness is n = 0.04, which is generally the roughness of mountain rivers. The simulated working conditions are the flood standard of the river section in the measured river ecological restoration area, the water temperature is T = 20°C, the model calculation grid division accuracy is 0.5m*0.5m, and the total number of grids is approximately 5 million. This is to establish the flow velocity simulation model.

[0075] A4. Flow velocity simulation was performed using the established flow velocity simulation model. The simulation scenario was the design flood standard (50-year return period) for the river section in the river ecological restoration zone, thereby obtaining the flow velocity simulation results for the river section under a 50-year return period flood. The simulation results were visualized using the post-processing software provided with the fluid mechanics simulation software. By setting the displayed flow velocity range, a flow velocity plane zoning diagram for the river ecological restoration zone was obtained.

[0076] Step B. Conducting a flow velocity simulation within a flow velocity simulation model based on the flood control standards for river sections in the river ecological restoration zone, and determining a water area with a certain flow velocity as a submerged plant community restoration zone based on the flow velocity results of the flow velocity simulation;

[0077] Preferably, the submerged plant community restoration area is a flat area of water with a flow rate of less than 2 m / s.

[0078] Step C. Build temporary cofferdams upstream and downstream of the submerged plant community restoration area, and divert river water to the downstream along the gaps reserved in the cofferdams;

[0079] Temporary cofferdams are set up at the beginning and end of the river section in the submerged plant community restoration area to facilitate the construction of the river section repair. The cofferdam material uses clay from both sides of the river. Since the overall construction period is only 3 months, the cofferdam does not consider the flood control function. The cofferdam height is calculated to meet the flood that occurs once every 5 years during the dry season. Therefore, the temporary cofferdam height is about 2m, and a diversion hole is reserved on one side of the cofferdam, and the water from upstream is discharged to the downstream through the diversion hole.

[0080] Step D. installing a submerged plant underwater protection system for a flood channel as described in Example 1 within the submerged plant community restoration area;

[0081] Determine the uniform height (the height of the submerged plant protection system refers to the layout height of the riprap gabion structure, pebble gabion structure, horizontal pine pile structure and vertical pine pile structure) and uniform spacing (spacing refers to the spacing between individual pebbles, riprap and pine piles) of the underwater protection system for submerged plants: In order to minimize the impact on river flooding, the height of the underwater protection system for submerged plants should be as small as possible and the occupied flood space should be minimized. However, at the same time, the protection effect on submerged plants needs to be taken into account. The lower the height of the underwater protection system for submerged plants, the weaker the protection effect on submerged plants; there should be a certain spacing between individual pebbles, riprap and pine piles, which can allow water to pass through without affecting flooding while reducing the flow rate and protecting the survival of submerged plants.

[0082] Step E. Plant submerged plants in the submerged plant protection unit. After the submerged plants have grown for more than one month, remove the temporary cofferdam and perform regular maintenance on the submerged plants.

[0083] In a specific implementation case, a section of the Houhe River in Chongqing was ecologically restored using the aforementioned submerged plant underwater protection system for flood channels. The river section is approximately 800m long, with an average water depth of approximately 1.5m, an average river width of approximately 20m, and a water area of approximately 16,000m. 2 The average flow rate over many years is about 6.23m 3 / s, the flood control standard is once in 50 years, corresponding to a flood flow of about 750m 3 / s, the planting area of submerged plants is about 10,000m 2 , arranged along both sides of the river channel, and calculated that the average width of the submerged plant underwater protection system is about 6.25m. The submerged plant underwater protection system is constructed in this area.

[0084] Installation of diversion system: Since the overall direction of the studied river section is relatively straight, the direction of water flow is also relatively straight, and the entire river channel is facing water scouring, the riprap gabion structure is set at 20° to the river bank along the direction of water flow, which has little effect on the change of water flow direction. The riprap gabion uses stones with a length * width * height of about 50 * 45 * 30 cm, arranged in a single layer, with a spacing of about 4 cm between ripraps, and a gabion structure length of 6.25 m; the pebble gabion structure is arranged 6.25 m away from the river bank, the pebble particle size is 20 cm, the spacing between pebbles is about 4 cm, the arrangement height is consistent with the riprap gabion, about 65 cm, and the length is about 800 m.

[0085] Installation of slow-flow system: The diameter of the pine piles used in the slow-flow system is 20 cm. The height of the horizontal and vertical pine piles is uniformly 30 cm determined according to the test. The spacing between the pine piles is about 4 cm. After the slow-flow system is completed, a single submerged plant protection unit with an area of about 30 m2 is formed, and a total of 340 protection units are formed.

[0086] Experimental research has shown that when the underwater protection system for submerged plants is greater than 40 cm high and the spacing is between 2 and 4 cm, the survival rate of submerged plants is better. In particular, when the spacing is set to 4 cm, the flow rate can be reduced from 3 m / s to 1.2 m / s, and the survival rate of submerged plants can reach over 90%, with minimal impact on flood flow.

[0087] When the spacing between individual pebbles, riprap and pine piles is 2 cm, the test results are shown in Table 1:

[0088]

[0089] When the spacing between individual pebbles, riprap, and pinewood piles is 4 cm, the test results are shown in Table 2:

[0090]

[0091]

[0092] When the spacing between individual pebbles, riprap, and pinewood piles is 6 cm, the test results are shown in Table 3 below:

[0093]

[0094] When the spacing between individual pebbles, riprap, and pinewood piles is 8 cm, the test results are shown in Table 4 below:

[0095]

[0096] When the spacing between individual pebbles, riprap and pine piles is 10m, the test results are shown in Table 5:

[0097]

[0098]

[0099] Among them, submerged plants are planted in the submerged plant protection unit:

[0100] 1. Backfill the soil for submerged plant growth: Since this river section has been eroded by floods for a long time, the riverbed is mainly composed of large stones and the soil content is relatively low. Therefore, it is necessary to backfill soil suitable for the growth of submerged plants. The backfill thickness is about 30 cm. The soil should be ecological soil with an organic matter content of less than 10g / kg, free of construction waste, weeds, tree roots, stones and structures, and free of impurities such as gravel. After the protection system is constructed, the soil for submerged plant growth can be prevented from being eroded by water.

[0101] 2. For the planting of submerged plants, the planting varieties are those that are easy to maintain and suitable for flowing water. The main varieties are Vallisneria, Potamogeton edulis, and Potamogeton rubra. The planting ratio is about 3:1:1. The planting method is manual cuttings. The planting depth is about 5 to 7 cm. The plants need to be disinfected, cleaned, and sorted before planting. Water is added through the gap in the cofferdam while planting. After the planting is completed, the water in the repaired river section has also been replenished.

[0102] 3. Remove the temporary cofferdam and enter the maintenance period. The main daily maintenance contents during the maintenance period include cleaning up garbage on the water surface, harvesting and replanting aquatic plants, cleaning up wild fish, etc., cleaning up the attachments on the leaves of aquatic plants after the flood passes, and replanting aquatic plants.

[0103] By using the underwater protection method for submerged plants in flood-carrying rivers of the present invention, an underwater protection system for submerged plants in flood-carrying rivers is provided, and submerged plants can also be repaired. The specific repair effects are as follows:

[0104] After three flood seasons and a five-year flood, it was monitored that the maximum flow rate of the bottom water in the upstream bank of the river section where the submerged plant underwater protection system was set up was about 2.5m / s, and the maximum flow rate of the bottom water in the downstream submerged plant community area was only 0.7m / s. The flow state was stable, and the submerged plant community was not significantly damaged. The survival area was about 9400m 2 , the three-year survival rate reached 94%, and water quality was also improved.

[0105] Changes in water quality

[0106] Water quality parameter indicators Before restoration 1st year after restoration 2nd year after restoration 3 years after restoration Transparency (cm) 60 80～100 90～110 100～120 Total phosphorus (mg / L) 0.30 0.25 0.20 0.15 Total nitrogen (mg / L) 2.3 1.7 1.6 1.45

[0107] Changes in the area of submerged plant communities

[0108]

[0109] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. An underwater protection system for submerged plants in flood-carrying rivers, characterized in that: It includes riprap gabion structures, pebble gabion structures, horizontal pinewood pile structures, and vertical pinewood pile structures set below the normal water level. The riprap gabion structures include upstream and downstream riprap gabion structures, both extending from the river bank to the center of the river channel in a straight line and set at an angle of 20° to 60° to the river bank. The pebble gabion structure is set along the river bank and close to the center of the river channel, with the lower end of the pebble gabion structure connected to the downstream riprap gabion structure. A submerged plant protection zone and a suspended sediment deposition zone are formed by enclosing riprap gabion structures, pebble gabion structures and river banks. In the submerged plant protection zone, several horizontal rows of pine pile structures are arranged from the river bank to the center of the river channel, and no less than one vertical row of pine pile structures are arranged along the river bank from the horizontal row of pine pile structures closest to the upstream riprap gabion structure to the downstream riprap gabion structure, so that the vertical row of pine pile structures and the horizontal row of pine pile structures are interpenetrated, thereby dividing the submerged plant protection zone into several submerged plant protection units by the vertical row of pine pile structures and the horizontal row of pine pile structures; a suspended sediment deposition zone is formed by enclosing the upstream riprap gabion structure, the river bank and the horizontal row of pine pile structures closest to the upstream riprap gabion structure, and no submerged plants are arranged in the suspended sediment deposition zone; The riprap gabion structure has a height of 0.5-1m and a length of 5-10m; the riprap gabion structure is composed of stones with a length, width and height of not less than 45cm and not more than 50cm.

2. The underwater protection system for submerged plants in flood-carrying rivers according to claim 1, characterized in that: Submerged plants are arranged in a number of submerged plant protection units, and each submerged plant protection unit has an area of 20-25m 2 .

3. The underwater protection system for submerged plants in flood-carrying rivers according to claim 1, characterized in that: The riprap gabion structure is not lower than the pebble gabion structure, the horizontal row of pine wood pile structure and the vertical row of pine wood pile structure.

4. The underwater protection system for submerged plants in flood-carrying rivers according to claim 3, characterized in that: The pebble gabion structure has a height of 0.5m; the pebble gabion structure is made of pebbles with a particle size of 20-40cm.

5. The underwater protection system for submerged plants in flood-carrying rivers according to claim 3, characterized in that: The horizontal row of pine wood pile structures and the vertical row of pine wood pile structures are formed by arranging pine wood piles in rows, and the diameter of the pine wood piles used is 20-30 cm and the spacing is 2-4 cm.

6. The underwater protection system for submerged plants in flood channels according to claim 5, characterized in that: The pine wood piles are exposed from the riverbed at a height of not less than 0.5m and are inserted into the riverbed at not less than 0.5m.

7. A method for underwater protection of submerged plants in flood-carrying rivers, characterized in that: Including steps: Step A. Measure the river section topography in the river ecological restoration area and establish a flow velocity simulation model through three-dimensional modeling; Step B. Conducting a flow velocity simulation within a flow velocity simulation model based on the flood control standards for river sections in the river ecological restoration zone, and determining a water area with a certain flow velocity as a submerged plant community restoration zone based on the flow velocity results of the flow velocity simulation; Step C. Build temporary cofferdams upstream and downstream of the submerged plant community restoration area, and divert river water to the downstream along the gaps reserved in the cofferdams; Step D. installing a submerged plant underwater protection system for a flood channel according to any one of claims 1 to 6 in the submerged plant community restoration area; Step E. Plant submerged plants in the submerged plant protection unit. After the submerged plants have grown for more than one month, remove the temporary cofferdam and perform regular maintenance on the submerged plants.

8. The underwater protection method for submerged plants in flood-carrying rivers according to claim 7, characterized in that: The step A comprises: A1. During the dry season, an electromagnetic rangefinder was used to measure the underwater topography of the river ecological restoration area with an accuracy of 0.5m. A2. Import the underwater terrain measured in A1 into CAD software, export it to a DXF file, use dxf2xyz software to convert the terrain data into an XYZ file, and import the XYZ file into fluid dynamics simulation software for STL file conversion, ultimately generating a 3D river terrain file. A3. Use a square grid in fluid dynamics simulation software to simulate the terrain. The roughness is n = 0.04, which is typical for mountain river channels. The simulated operating conditions are the flood standard for the river section in the ecological restoration zone, the water temperature is T = 20°C, the model calculation grid division accuracy is 0.5m * 0.5m, and the total number of grids is 5 million. This is to establish a flow velocity simulation model. A4. Use the post-processing software included in the fluid mechanics simulation software to visualize the simulation results. By setting the displayed flow velocity range, a velocity plane zoning map of the river ecological restoration zone is obtained.

9. The underwater protection method for submerged plants in flood-carrying rivers according to claim 7, characterized in that: In step B, the submerged plant community restoration area is a water plane range with a flow rate of less than 2 m / s.

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