A method for reversing reservoir area Elodea habitat.

Abstract

To provide a method for constructing a habitat unsuitable for growth of Elodea nuttallii in a reservoir area.SOLUTION: A reverse remodeling method for Elodea nuttallii habitat in a reservoir area includes the steps of: acquiring an Elodea nuttallii / water body boundary; acquiring a water depth isoline map and a flow velocity isoline map; superimposing the Elodea nuttallii / water body boundary on the water depth isoline map and the flow velocity isoline map respectively to acquire critical water depth and flow velocity, and the thresholds of Elodea nuttallii habitat suitability factors; collecting statistics on hydrodynamic conditions of the Elodea nuttallii distribution water area to acquire a habitat factor control index system; and remodeling an environment disadvantageous to growth of Elodea nuttallii based on the thresholds of the Elodea nuttallii habitat suitability factors and the habitat factor control index system which are acquired to form a technical system for reversely remodeling the Elodea nuttallii habitat in the reservoir area.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to the technical field of river ecological management, in particular to a method for reversing the habitat of Elodea canadensis in a reservoir area. [Background technology]

[0002] Elodea canadensis is a fast-growing submerged plant native to South America that grows well in sunny conditions. It was introduced to China to improve the water quality of lakes and reservoirs and to assist in aquaculture. However, due to a lack of natural predators, it is difficult to control in large water areas, and overgrowth and expansion of scale can cause new ecological and even construction risks. Taking reservoirs such as Wang Fuzhou and Cui Jiaying, which belong to the Hanjiang Danjiangkou Reservoir, as examples, Elodea canadensis grows wildly due to sand deposition in the reservoirs, reduced water fluidity, and reduced sand content, and the main adverse effects are as follows: (1) Affects the safety of flood control. The excessive growth and accumulation of aquatic plants obstructs the flow of water, affects flood discharge during flood periods, and is detrimental to flood control. (2) Affects the safety of navigation. The excessive growth of aquatic plants blocks waterways and entangles the screw propellers of ships, making navigation difficult. (3) Affects the normal operation of hydroelectric power generation equipment. Aquatic plants gather in front of hydroelectric dams, affecting the normal operation of hydroelectric power generation equipment, and in severe cases causing breakdowns, shutdowns or damage to power generation units. (4) Affecting the health of the aquatic ecosystem. Aquatic plants cover the water surface, reducing the amount of sunlight irradiated to the water body, indirectly affecting the distribution of the aquatic ecosystem population, and when the aquatic plants die, their remains that are difficult to decompose accumulate on the water bottom, accelerating the formation of marshes in lakes and reservoirs. (5) Causes the deterioration of the aquatic environment, seriously affecting the safety of water use. Aquatic plants inhibit the re-oxygenation effect of the atmosphere on water bodies, and a large number of aquatic plants die and rot due to the lack of dissolved oxygen, and nutrients and other substances absorbed during the growth period are released back into the water body, becoming an endogenous source of pollution for the water body, leading to the deterioration of water quality and reducing the value of water resources.

[0003] Taking the Hanjiang Wangfuzhou Hydropower Station as an example, the biomass of Elodea canadensis in the reservoir area is very large, forming an "underwater forest." During heavy floods, they are uprooted and washed into the Wangfuzhou Hydropower Station area, where they are deposited in large quantities outside the sewage barrier, seriously affecting the flood control and power generation functions of the station. In 2017 and 2019, the annual power generation losses due to aquatic weed disasters amounted to 51 million cc and 24 million cc, respectively, and the direct economic losses were 20.4 million yuan and 9.6 million yuan, respectively. The aquatic weed disasters have had a serious impact on the safety of the aquatic ecological environment in the reservoir area.

[0004] At present, there are three main methods for controlling the growth of aquatic plants at home and abroad: physical, chemical and biological. Chemical methods mainly use herbicides and other chemicals, which are easy to operate and have a fast effect, but chemicals are prone to secondary pollution of the water environment, and lakes and reservoirs are usually water sources, so the use of chemical methods is generally prohibited. Biological methods mainly use the feeding of fish, waterfowl and other organisms to suppress the growth of aquatic plants, which is low-cost and has high safety over a long period of time. However, biological methods require long-term testing and demonstration, are difficult to manage, and are prone to introducing new dominant species and causing adverse effects on the aquatic ecosystem, so these methods are usually used with caution. Physical methods mainly include harvesting, physical obstruction, etc., which are relatively simple, have little impact on the environment and are fast-acting, but are difficult to cure, and belong to "palliative treatment", require regular maintenance and are expensive, so they are often used in a small area at present, making it difficult to fundamentally eliminate the harm. Although the physical methods as a whole do not have any secondary impacts on the natural environment or ecosystem, there is an urgent need to develop a "curative treatment" for Elodea canadensis, as there is no effective management method for it. Summary of the Invention [Means for solving the problem]

[0005] The object of the present invention is to provide a method for reconstructing Elodea habitat in a reservoir area to solve the problems proposed in the background art.

[0006] In order to achieve the above objectives, the present invention provides the following technical solutions: 1. A method for reconstructing Elodea habitat in a reservoir area, comprising: Step S100: forming a remote sensing image by aerial survey using a drone and extracting a vegetation-covered area of ​​the reservoir area from the remote sensing image to obtain a water body boundary line; A step S200 of acquiring a water depth contour map and a current velocity contour map; Step S300 of acquiring the critical water depth and flow velocity, i.e., the threshold value of the habitat suitability factor of Elodea canadensis by overlaying the Elodea canadensis / water body boundary line on the water depth contour map and the flow velocity contour map, respectively; Step S400: statistically calculating the hydrodynamic conditions of the water area where Elodea canadensis is distributed and obtaining a habitat factor control index system represented by the following formula 1;

[0007]

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[0008] Based on the obtained threshold values ​​of suitable habitat factors for Elodea canadensis and the habitat factor control index system, the environment unfavorable to Elodea canadensis growth is modified in terms of increasing water depth, increasing flow velocity, decreasing underwater light intensity, etc., to form a reservoir area Elodea canadensis habitat reverse modification technical system. Here, the reservoir area Elodea canadensis habitat reverse modification technical system includes step S500, which includes modifying hydrodynamic conditions and modifying light irradiation conditions.

[0009] In addition to the above technical solutions, the present invention further provides the following optional technical solutions: In an optional technical solution, the bathymetry map is generated using GIS-based software based on the measured underwater topography and water levels during the survey period.

[0010] In the optional technical proposal, the specific method of obtaining the flow velocity contour map includes constructing a planar two-dimensional water flow mathematical model in the reservoir area, introducing the measured underwater topography as the bottom boundary, taking the reservoir inlet flow rate and the water level in front of the dam as the upstream and downstream calculation conditions, calculating the fluid velocity field, that is, obtaining the flow velocity contour map.

[0011] In the optional technical proposal, the modification of the hydrodynamic conditions includes reservoir ecological scheduling and local topographic modification, where the reservoir ecological scheduling is to increase the water discharge of the upstream reservoir to raise the reservoir water level and increase the flow rate in the reservoir area where Elodea nigricans is located, and the local topographic modification is to modify the topography by local dredging or local filling, i.e., changing the gentle slope underwater to a steep slope, and in the shallow water area underwater, further raising the high area to expose the water surface and further digging the low area.

[0012] In an optional technical solution, the modification of the light conditions includes shading and sediment injection, where the shading is carried out by constructing a floating solar power station in the key area where Elodea canadensis grows. Effect of the Invention

[0013] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention proposes a habitat reversal technique for blocking and influencing the photosynthesis of Elodea canadensis from the perspective of determining the threshold value of habitat factors and reversal modification. Specifically, it includes investigating suitable habitat factors and identifying indicators, modifying the underwater topography, replenishing and restoring sand content, raising the water level during spring and summer operation, and shading the solar panels. The advantages are: (1) it will not cause secondary nature or impact on the ecosystem; (2) it can create a habitat that is not suitable for the growth of Elodea canadensis, achieving the purpose of "radical treatment"; and (3) it can generate a certain economic effect and compensate for the input into the management project. [Brief description of the drawings]

[0014] [Figure 1]1 is a flowchart of a method for investigating hydrodynamic factors of suitable habitats for Elodea canadensis according to the present invention. [Diagram 2] 1 is a flow chart of the implementation of the reservoir area Elodea habitat remodeling technology system according to the present invention. [Diagram 3] 1 is a remote sensing image of an important distribution area of ​​Elodea canadensis in an embodiment according to the present invention. [Figure 4] FIG. 1 is a schematic diagram showing an important distribution area of ​​Elodea canadensis according to an embodiment of the present invention. [Diagram 5] The scope of modification of the embodiment of the present invention. [Figure 6] FIG. 2 is a comparison diagram of the topography before and after modification of the example area A according to the present invention. [Figure 7] FIG. 1 is a comparison diagram of the terrain before and after modification of the embodiment area B according to the present invention. [Figure 8] FIG. 11 is a comparison diagram of the topography before and after modification of the example area C according to the present invention. [Figure 9] FIG. 2 is a comparison diagram of water depth and flow velocity before and after modification of a representative cross section A1 of an embodiment of the present invention. [Figure 10] FIG. 2 is a comparison diagram of water depth and flow velocity before and after modification of the representative cross section A2 of an embodiment of the present invention. [Figure 11] FIG. 1 is a comparison diagram of water depth and flow velocity before and after modification of a representative cross section B1 of an embodiment of the present invention. [Figure 12] FIG. 11 is a comparison diagram of water depth and flow velocity before and after modification of a representative cross section B2 of an embodiment of the present invention. [Figure 13] FIG. 1 is a comparison diagram of water depth and flow velocity before and after modification of a representative cross section C1 of an embodiment of the present invention. [Figure 14] FIG. 1 is a comparison diagram of water depth and flow velocity before and after modification of a representative cross-section C2 of an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] In order to clarify the object, claims and advantages of the present invention, the present invention will be described in more detail in conjunction with the accompanying drawings and examples. Each embodiment given in the present invention is only for the purpose of illustrating the present invention, and is not intended to limit the scope of the present invention. Any modifications or changes made to the present invention will not depart from the subject and scope of the present invention.

[0016] An embodiment of the present invention proposes a method for reconstructing Elodea habitat in a reservoir area, as shown in Figures 1 and 2, the method includes the following steps: (1) A step of forming a remote sensing image by aerial survey using a drone, extracting the vegetation coverage area of ​​the reservoir area from the remote sensing image, and obtaining the Elodea canadensis / water body boundary line. Before aerial photography, it is necessary to place ground control points based on the actual situation of the measurement area, and plan a route based on the ground control points. After the placement of ground control points and route planning are completed, the drone takes off and collects UAV images of the measurement area according to the planned route. Then, the images are imported into a computer, and after identifying the plant patches and water bodies, the boundaries of the plant patches are drawn, and the Elodea canadensis / water body boundary line is created. The use of low-cost drones makes it possible to quickly and cheaply obtain aerial images of aquatic plants in reservoirs and lakes. UAV remote sensing has the characteristics of flexible data collection, high image resolution, etc., and is very suitable for the analysis of different vegetation coverage types and coverage dynamic monitoring of lake reservoir rivers at the plandoscape scale. Compared with digital cameras, hyperspectral cameras are expensive, have high water work risks, and are complicated to process data, but have relatively good prospects for implementation. At present, consumer drones equipped with digital cameras are suitable for daily monitoring of aquatic plants in lakes, reservoirs, and rivers. The present invention uses consumer drones equipped with digital cameras to monitor the coverage of aquatic plants in reservoirs. There are mainly two types of feature classification methods in drone remote sensing images: one is a visual interpretation method based on classification of the size, shape, color, texture, etc. of patches in the image, and the other is an automatic classification method based on image spectral characteristics. The latter is suitable for multiple types of vegetation identification, and requires monitoring and classification of patches of images with divided thickness by a method of constructing a neural network, random forest, combined with aquatic plant samples constructed by field surveys.

[0017] (2) A step of obtaining water depth contour maps and current velocity contour maps. Based on the measured underwater topography of the reservoir area (reservoirs are generally monitored annually) and the water level during the survey period, a water depth contour map of the reservoir area can be obtained. Using a 3D digital elevation model, the measured underwater topography of the reservoir area absolute coordinates (if it is in mapinfo format, it can be used as is) is derived in DWG format, and then the elevation is converted to water depth value while referring to the water level value, and the water depth contour map can be drawn by introducing the above data using GIS software such as mapinfo or surfer.

[0018] A planar 2D water flow mathematical model is constructed in the reservoir area, and the measured underwater topography is introduced as the bottom boundary. The reservoir inlet flow rate and the water level in front of the dam are then used as the upstream and downstream calculation conditions to calculate the flow velocity field, and a flow velocity contour map can be drawn based on the flow velocity field in the reservoir area. Using a 3D digital elevation model, the measured underwater topography in the absolute coordinates of the reservoir area (mapinfo format can be used as is) is derived as DWG format data, and the elevation is converted to water depth value while referring to the water level value. The above data can be introduced using GIS software such as mapinfo and surfer to draw the flow velocity contour map.

[0019] (3) The critical depth and flow velocity, i.e., the threshold value of the habitat suitability factor of Elodea can be obtained by superimposing the Elodea / water body boundary line on the water depth contour map and the flow velocity contour map, respectively. The reservoir area remote sensing image including the Elodea / water body boundary line and the water depth contour map are superimposed on the same coordinate to obtain the water depth where the Elodea / water body boundary line is located, and the maximum water depth is the water depth threshold h of the Elodea reverse reconstruction. The Elodea / water body boundary line in absolute coordinates is superimposed on the water depth contour map to obtain the water depth where the boundary line is located. The boundary line and the water depth contour line may be different, and the maximum water depth where the boundary line is located is the water depth threshold h of the Elodea reverse reconstruction.

[0020] (4) Statistical analysis of the hydrodynamic conditions in the waters where Elodea canadensis is distributed will be carried out to obtain an index system of habitat factors controlling the conditions.

[0021]

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[0022] First, we studied the habitat factors of Elodea canadensis. Through the whole life cycle and large water area survey, we statistically obtained the hydrodynamic conditions of the main distribution areas of Elodea canadensis. The light illumination and transparency conditions were obtained. The range was 3500-5600 lx (the maximum illumination at the water surface under all illumination conditions in summer is about 100,000 lx). The photosynthesis of the water area was strong, the growth was vigorous, and the light illumination at a certain water depth was I h =Ie -kh , where I h is the light illuminance at water depth h, I is the light illuminance on the water surface, k is the vertical attenuation coefficient of light in the water body, which is related to turbidity, and the coefficient has a negative correlation with transparency. Second, the flow velocity conditions are obtained. Most of the measured flow velocities in densely grown areas are less than 0.14 m / s. If the flow velocity is too high, the roots of plants are likely to be washed away, which is detrimental to growth. Third, the water depth conditions are obtained. In areas with a water depth of less than 2.5 m, the colony advantage is great, and in areas with a water depth of more than 3.5 m, there is almost no growth of Elodea canadensis. Through the above-mentioned investigation into suitable habitats for Elodea canadensis, a habitat factor control index system was obtained, which is expressed by the following equation 3:

[0023]

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[0024] (5) Based on the obtained threshold values ​​of suitable habitat factors for Elodea canadensis and the habitat factor control index system, the environment unfavorable to Elodea canadensis growth is modified from the perspectives of increasing water depth, increasing flow velocity, decreasing underwater light intensity, etc., to form a reservoir area Elodea canadensis habitat reverse modification technology system, where the reservoir area Elodea canadensis habitat reverse modification technology system includes modification of hydrodynamic conditions and modification of light irradiation conditions.

[0025] Based on the survey data for the above-mentioned indicators, we propose a technological system for reconstructing the habitat of Elodea canadensis in reservoir areas by modifying the environment that is unfavorable to the growth of Elodea canadensis from the perspectives of increasing water depth, increasing flow velocity, and decreasing underwater light intensity.

[0026] Measure 1, reservoir ecological scheduling By adjusting the flow rate and the water level change process, hydrodynamic conditions unfavorable to the growth of aquatic plants are created, and the growth of aquatic plants is controlled. However, this measure requires increasing the water volume Q of the upstream reservoir or raising the water level of the main reservoir, thereby increasing the water depth h and increasing the flow velocity v. If the width B of the river section of the reservoir is constant and the cross section can be roughly modeled as a rectangle,

[0027]

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[0028] Measure 2: Localized terrain modification Local topography modification involves modifying the topography by local dredging or local land filling in the shallow parts of the reservoir area, where Elodea canadensis is suitable for growth, by changing gentle underwater slopes into steep slopes, and in the shallow parts of the reservoir area, raising higher areas to expose the water surface and digging lower areas further, thereby increasing the proportion of underwater areas with a water depth h of greater than 3.5 m as much as possible, and in shallow areas where the flow velocity v is small, improving the water flow and increasing the flow velocity, creating a topographical environment unsuitable for the growth of Elodea canadensis.

[0029] Measure 3: Shade covering Select key areas where Elodea canadensis grows (locations where vegetation coverage reaches 30% or more) and employ methods such as shading or constructing floating solar power plants. By providing shade and reducing the water surface illuminance I, the growth of aquatic plants will be suppressed.

[0030] Measure 4: Sand dumping By adding a certain amount of sediment, the sand content and turbidity k of the water body are increased, reducing the transparency of the water body and thus inhibiting the growth of aquatic plants. It is desirable for the sand content to be close to that of the natural riverbed before the reservoir was constructed.

[0031] Table 1 below is a comparison table of the technical measures for reversing the habitat of Elodea canadensis in the reservoir area.

[0032] [Table 1]

[0033] The above four measures are proposed to be implemented in sequence based on the feasibility of existing technologies and policies. From the perspective of low investment and increased power generation revenue, ecological scheduling measures are the top priority, but the review process for reservoir scheduling regulations changes is complicated and difficult to implement in practice. Topographical modification measures require a large amount of construction and prior testing for sediment pollution, but they can restore the capacity of the reservoir and bring about a certain effect of sediment resource utilization. Solar shading requires a certain investment, but can also generate power generation revenue. However, the current review and approval process for large-area water surface solar power generation projects is strict, and it is necessary to change the natural water body light irradiation conditions and conduct a more detailed environmental impact assessment. Sediment injection requires the purchase of fine sand and regular injection, and cannot be a "radical treatment", but can be carried out as a supplementary measure to topographical modification and reservoir sediment dredging.

[0034] The present invention has been applied in practice and has good technical effects. As shown in Figures 3-15, the embodiments are as follows: (1) Basic situation The Wangfuzhou Water Conservancy Center is the first stage-level hub project linking the middle and lower reaches of the Han River with the Danjiangkou Water Conservancy Center. It is a large-scale water conservancy project that combines power generation with shipping, irrigation, aquaculture, tourism and other comprehensive benefits, with a drainage area of ​​95,900 km2. 2 The reservoir is located on the mainstream of the Han River in Laohekou, Hubei Province, 30 km away from the Danjiangkou hub of the upper river and about 3 km from the lower river of Laohekou city. It is a 10th-class reservoir on the mainstream of the Han River, which is under development and is a 16th-class reservoir. The normal water level of the Wangfuzhou Reservoir is 86.23 m, and the corresponding capacity is 149.5 million m 3 , calibrated flood level is 89.3m, total capacity is 309.5 million m 3 .

[0035] Wang Fuzhou Power Plant Unit 1 was officially put into operation in May 2000. In 2011, the accumulation of aquatic plants in front of the sewage grid began to be observed. During the autumn floods in 2017 and September-November 2019, the aquatic plants in the river channel were swept into the reservoir area of ​​Wang Fuzhou Power Plant, causing a rapid increase in aquatic plants in front of the sewage grid, and a large amount of aquatic plants and debris was deposited outside the sewage grid. The aquatic plants floating in the reservoir area were mainly Elodea canadensis, and the accumulated aquatic plants and debris pushed out the sewage grid, and with the accumulation of water flow, they were pushed out from under the sewage grid and deposited on the sloped sewage grid of the four power generation units. The annual power generation loss due to aquatic plants disasters in 2017 and 2019 was 51 million and 24 million tonnes, respectively, resulting in a large direct annual economic loss. At the same time, a large number of aquatic plants die and settle in the water, rotting and decomposing, and nutrients and other substances absorbed during their growth are released back into the water, making it easy for nutrients in the water to exceed standards, becoming a source of pollution within the water.

[0036] (2) Modification Step S1, In 2020, a field survey was conducted in the Wang Fuzhou Reservoir area, and (1) remote sensing images were formed through aerial surveying using a drone, plant patches and water bodies in the images were identified, and the boundaries of the plant patches were drawn to form important distribution areas of Elodea canadensis and the boundaries between the water bodies, as shown in Figure 3.

[0037] Step S2, Based on the measured underwater topography of the reservoir area and the water level during the survey period, a water depth contour map of the reservoir area was obtained. Because the reservoir area is large, this example selects the sandbar area near the Gwanghwa Bridge, which is one of the important distribution areas of Elodea canadensis, for specific analysis. The following examples also enclose this area and define it as Area A and the water depth distribution map of Area A.

[0038] Step S3, The Wangfuzhou Reservoir area is a typical shallow-water reservoir, and the vertical change of the water flow is not taken into account. A two-dimensional hydrodynamic model of the river section is constructed using the MIKE21 model developed by the Danish Hydraulic and Environmental Research Institute (DHI). The simulation range is from the lower side of Danjiangkou Reservoir to Wangfuzhou Power Station, including the Wangfuzhou Cang Reservoir area and the river section below Danjiangkou Reservoir, and is about 35 km long. The reservoir inlet flow rate and the water level in front of the dam are used as the calculation conditions upstream and downstream with a 1:2000 measured underwater topography, and the hydrodynamic velocity field of Section A is calculated.

[0039] Step S4, The absolute coordinates of the Elodea canadensis / water body boundary line were overlaid with the depth contour map to obtain the water depth at which the boundary line was located. The maximum water depth at which the boundary line was located was set as the water depth threshold value h for the Elodea canadensis reverse modification, which was approximately 3 m.

[0040] Step S5, The absolute coordinates of the Elodea canadensis / water body boundary line and the flow velocity contour map were overlaid to obtain the flow velocity where the boundary line is located, and the maximum flow velocity where the boundary line is located was set as the flow velocity threshold value v for the Elodea canadensis reverse modification, approximately 0.03 m / s.

[0041] According to the investigation, there is little distribution of Elodea canadensis from the power plant to the discharge gate section, but there is a lot of biomass of Elodea canadensis from above the Gwanghwa Hangang Bridge to the Mokpai Port section, and there is a high risk of grass inundation due to autumn floods, especially in the sandbar section and the area of ​​the crushed stone pile at Mokpai Port. Elodea canadensis is mainly found densely along the riverbanks and in stagnant areas where sand has been artificially excavated and piled up. The maximum water depth of the large, stable-growing colony is about 3-3.5m, and the measured flow speed in the dense growth area is often less than 0.14m / s.

[0042] Based on the measures listed in Table 1, Measure 1 is first considered, but its upstream is the Danjiangkou Reservoir, which is the source of the China South-North Water Diversion, and water resources are precious. It is not possible to increase the discharge flow rate in spring to form an ecological schedule, so Measure 1 cannot be implemented. Measure 2 can be implemented when the cost-effectiveness ratio is feasible. Measure 3 is that surface solar power generation must be approved by the river channel competent authority, but the Han River is a first-class tributary of the Yangtze River, and there are strict restrictions on surface solar power generation, so Measure 3 cannot be implemented at present. Measure 5 requires small input, is convenient, and can be implemented on an emergency basis. Measure 4 does not have an external sand source, and is considered in cooperation with Measure 2, that is, the fine sand generated by the topographical modification is gradually returned to the reservoir area, and the medium and coarse sand can be utilized as resources, generating economic benefits from the sale of gravel. Therefore, the habitat reverse modification technology finally considered by the Wang Fuzhou Reservoir area is Measure 2.

[0043] Based on the results of investigating the distribution characteristics of Elodea canadensis, areas A, B and C, where Elodea canadensis is most concentrated, were selected as the implementation sites, and their locations are shown in Figure 4. Here, areas A and B are within the management area of ​​the Wang Fuzhou Reservoir area, and although area C is not within the management area of ​​the Wang Fuzhou Reservoir area, it is also a high-risk area for Elodea canadensis, so it was considered as a unified area in this management plan.

[0044] The plan area of ​​Area A to be cleared of silt is 3.121 million m 2 The plan area of ​​Area B to remove silt is 5.628 million m 2 The plan area of ​​area C to be desilted is 3.989 million m 2 Since the maximum water depth required for the formation of a large, stable colony of Elodea canadensis is approximately 3-4m, it was proposed that the sandbar reconstruction excavation depth be set at 82.2m, with a water depth of approximately 4m corresponding to the normal water level of the Wang Fuzhou Reservoir of 86.23m. The coverage area for forming the new sandbar should be uniformly filled in at 86.3m or more, above the normal water level. The "section excavation depth - local sandbar heightening and re-formation" creates a topographical environment unfavorable to the survival of Elodea canadensis.

[0045] Area B is an island located under the Han River Bridge, and similar to the sandbar reconstruction plan for Area A, the plan is to excavate this area to a certain depth, tidy up the scattered sandbars left behind by past sand mining, and form a new sandbar.

[0046] Area C is located on the right side of the river near Mokpai Port, about 3km above the Han River Bridge. Sand mining and other activities have resulted in the formation of very scattered blocks. During the field survey, there were nearly 10 sand mining ships in the area over a few kilometers of the river. The area will be excavated to a certain depth to remove small scattered deposits left by past sand mining.

[0047] In 2021, Danjiangkou Reservoir, in conjunction with Wangfuzhou Dam, carried out ecological scheduling at the end of February and early March, respectively, to increase the water outflow of Danjiangkou Reservoir, thereby raising the water level in the reservoir area where Elodea is located and making the water depth of the area covered by Elodea greater than the water depth threshold of 3m. From February 22 to 26, 2021, the water supply flow rate from Danjiangkou Reservoir to the middle and lower reaches of the Han River was 591 to 1,280 m. 3 / s fluctuation, the ratio of maximum flow rate to minimum flow rate is more than twice, and the average water supply flow rate is 941m 3 The second ecological scheduling was carried out from March 8 to 12, during which the water supply flow rate in the middle and lower reaches of the Han River was 464 to 1,240 m3. 3 / s fluctuation, the ratio of maximum flow rate to minimum flow rate is nearly three times, and the average water supply flow rate is 873 m 3 / s, as shown in Figure 5. Looking at the change in hydrodynamic force, the average flow velocity in the concentrated distribution area of ​​Elodea canadensis on the shore of Section A before scheduling was about 0.03 m / s, and the maximum flow velocity was 0.05 m / s. During the first ecological scheduling period from February 22 to 26, the average flow velocity in the section increased to 0.05 m / s, and the maximum value increased to 0.09 m / s. During the second ecological scheduling period from March 8 to 12, the average flow velocity in the section increased to 0.04 m / s, and the maximum value increased to 0.06 m / s.

[0048] According to the observation results of Elodea canadensis biomass in 2021, Elodea canadensis recovered in January was mainly concentrated at a depth of 1-2m, sporadic growth was observed at a depth of 3m, and no aquatic plants were found at depths of 5m and 7m. Elodea canadensis in the Xincheng area of ​​the riverbank in January was mainly distributed in particularly shallow water areas, basically not exceeding 1m, the distribution area's depth in February was less than 1.5m, the distribution depth in May was less than 2m, and the distribution depth in July was less than 3-3.5m. In July-August, most Elodea canadensis in the Danjiangkou-Wangfuzhou section had already reached its biomass peak. Compared with 2019 and 2020, the results in 2021 showed that the representative area A did not form a lush "underwater forest", and the Elodea canadensis biomass decreased from about 770 tons before the modification to about 233 tons, a reduction of about 70% of the biomass, and a good expected effect was achieved. In addition, looking at the changes in the distribution of Elodea canadensis, the shallow water areas where it was previously mainly distributed, which were close to still water, had seen increased hydrodynamic forces due to changes in topographical modification, increasing the water depth and causing a significant decrease in Elodea canadensis biomass, with the largest decrease in Elodea canadensis biomass in Area A.

[0049] Because the water resources of the Danjiangkou Reservoir are very important, ecological scheduling is only carried out in years when the water resources are sufficient, and ecological scheduling cannot be deployed under drought conditions such as in 2022. In order to control the Elodea canadensis disaster in the reservoir area, a method of modifying the underwater topography of the Wang Fuzhou Reservoir area is explored and deployed in local areas as well, and in order to strengthen the control of Elodea canadensis, the local area A where Elodea canadensis is concentrated is dredged, and the dredging control elevation is 83.2 m, that is, when the normal water level of the reservoir is 86.2 m, the water depth is 3 m, which corresponds to the Elodea canadensis growth threshold water depth of 3 m obtained in step S4. After the underwater topography modification, the improvement of the small water depth area of ​​less than 3m in the normal water level area A was obvious: looking at the typical cross section, before modification, within the range of 600-1800m starting distance, the water depth was all less than 2m, and more than 80% of the area had a water depth of less than 1m, but after modification, the water depth in the same area was all more than 3m. Looking at the change in flow velocity, the flow velocity decreased in the area close to the Thalweg, but in the topography modified area, it decreased significantly in the range below the flow velocity threshold of 0.03m / s for Elodea growth (shown in Figure 6). After terrain modification, the improvement of water depth and flow velocity in area A even under relatively low flow conditions was unfavorable to the growth of Elodea. At medium and high flow rates, the water depth and flow velocity further increased, thereby forming an unfavorable habitat for Elodea. Based on the observation results, when only terrain modification was adopted without deploying ecological scheduling, the biomass of Elodea in the biomass peak period was approximately 1.16 million tons, a decrease of approximately 85% compared with the average value of 7.7 million tons in 2019 and 2020, and further decreased than the Elodea biomass in 2021 when ecological scheduling was adopted, which brought about an obvious effect on suppressing the growth of Elodea.

[0050] The above are only specific embodiments of the present disclosure, but the scope of protection of the present disclosure is not limited thereto, and should include any person skilled in the art who can easily think of modifications or replacements that should be included in the scope of protection of the present disclosure within the technical scope of the disclosure of the present disclosure. Therefore, the scope of protection of the present disclosure should be in accordance with the scope of protection of the claims.

Claims

1. Step S100: forming a remote sensing image by aerial survey using a drone, and extracting a vegetation-covered area of ​​the reservoir area from the remote sensing image to obtain a water body boundary line; A step S200 of acquiring a water depth contour map and a current velocity contour map; Step S300 of acquiring the critical water depth and flow velocity, i.e., the threshold value of the habitat suitability factor of Elodea canadensis by superimposing the Elodea canadensis / water body boundary line on the water depth contour map and the flow velocity contour map, respectively; Step S400: statistically calculating the hydrodynamic conditions of the water area where Elodea canadensis is distributed and obtaining a habitat factor control index system represented by the following formula 1; [0050] Based on the obtained threshold value of the habitat suitable for Elodea canadensis and the habitat factor control index system, the environment unfavorable to the growth of Elodea canadensis is modified in terms of increasing water depth, increasing flow velocity, decreasing underwater light illuminance, etc., to form a reservoir area Elodea canadensis habitat reverse modification technology system, where the reservoir area Elodea canadensis habitat reverse modification technology system includes step S500, which includes modifying hydrodynamic conditions and modifying light irradiation conditions; The modification of the hydrodynamic conditions includes reservoir ecological scheduling and local topographical modification, in which the reservoir ecological scheduling increases the water discharge of the upstream reservoir to raise the reservoir water level and increase the flow rate in the reservoir area where the Elodea canadensis is located; the local topographical modification involves modifying the topography by local dredging or local filling, i.e., changing a gentle slope underwater into a steep slope, and in the shallow water area underwater, further raising the high areas to expose the water surface and further digging the low areas. The modification of the light conditions includes shading and adding sediment, and the shading is performed by constructing a floating solar power plant in a key area where the canoderma grows.

2. The method for reconstructing reservoir area Elodea habitat as described in claim 1, characterized in that the water depth contour map is created using GIS-based software based on the measured underwater topography and the water level during the survey period.

3. The specific method for obtaining the flow velocity contour map includes constructing a planar two-dimensional water flow mathematical model in the reservoir area, introducing the measured underwater topography as the bottom boundary, taking the reservoir inlet flow rate and the water level in front of the dam as the upstream and downstream calculation conditions, calculating the fluid velocity field, that is, obtaining the flow velocity contour map. The method for reverse modification of Elodea habitat in a reservoir area as described in claim 1.

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