A method for reverse transformation of Elodea habitat in reservoir area

Abstract

The present invention relates to a method for reverse transformation of the habitat of Elodea in a reservoir area. Remote sensing images of the reservoir area are formed through drone aerial survey. UAV remote sensing has the characteristics of flexible data acquisition and high image resolution, and is very suitable for dynamic monitoring of different vegetation cover types and coverage of lakes, reservoirs and rivers at a landscape scale. The water depth threshold and flow rate threshold for reverse transformation of Elodea in each reservoir area are collected in real time, so that targeted reverse transformation can be carried out for Elodea in different growth environments in each reservoir area, thereby maximizing the transformation efficiency and reducing the transformation cost. After the threshold is collected in real time, hydrological conditions that are not conducive to the growth of Elodea can be created by increasing the water output Q of the upstream reservoir or opening the gates of the downstream reservoir to release water or carrying out local terrain transformation. The Elodea reproduction and growth are effectively suppressed in the early stages, thereby effectively inhibiting the reproduction and growth of the Elodea.

Description

Technical Field

[0001] The present invention relates to the technical field of river ecological management, and in particular to a method for reversely transforming the habitat of Elodea in a reservoir area. Background Art

[0002] Elodean uttallii is a sun-loving, fast-growing submerged plant native to South America. It was introduced into my country to improve the water quality of lakes and reservoirs and assist aquaculture. However, due to the lack of natural enemies, it is easy to be poorly controlled, overgrow, and expand in large areas of water, bringing new ecological hazards and even engineering hazards. Taking the Wangfuzhou and Cuijiaying reservoirs below the Danjiangkou Reservoir of the Han River as an example, due to the siltation of the reservoirs, the weakening of water dynamics, and the reduction of sediment content, the Elodean nuttallii has grown wildly, resulting in the following adverse effects: (1) Impact on flood control safety. The growth and accumulation of a large number of aquatic plants hinders the flow of water, affecting the discharge of flood water during floods and is not conducive to flood control; (2) Impact on navigation safety. The growth of a large number of aquatic plants will block the waterway, causing the propellers of ships to be entangled and difficult to navigate; (3) Hinder the normal operation of hydropower equipment. Aquatic plants gather in front of the dam of the hydropower station, affecting the normal operation of hydropower equipment. In serious cases, it will cause the generator set to malfunction, stop operating or be damaged; (4) Impact on the health of the water ecology. Aquatic plants cover the water surface, resulting in insufficient sunlight reaching the water body, indirectly affecting the distribution of aquatic ecosystem communities. After the aquatic plants die, their remnants, which are difficult to decompose, accumulate at the bottom of the water, accelerating the swamping of lakes and reservoirs. (5) They cause the water environment to deteriorate, seriously affecting water safety. Aquatic plants hinder the atmosphere's reoxygenation of the water body, resulting in insufficient dissolved oxygen in the water. A large number of dead aquatic plants sink in the water, rot, and decompose. The nutrients and other substances absorbed during the growth period are released back into the water body, becoming a source of endogenous pollution, causing water quality deterioration and reducing the value of water resources.

[0003] Take the Wangfuzhou Hydropower Station on the Han River as an example. The reservoir area is home to a vast biomass of Elodea, forming an "underwater forest." During periods of high water flow, this algae is uprooted and washed into the Wangfuzhou Hydropower Station area, where it accumulates in large quantities outside the trash racks, severely impacting the station's flood control and power generation capabilities. In 2017 and 2019, the weed disasters resulted in annual power generation losses of 51 million and 24 million kWh, respectively, resulting in direct economic losses of 20.4 million and 9.6 million yuan, respectively. Furthermore, the weed disasters have severely impacted the aquatic ecological safety of the reservoir area.

[0004] Currently, there are three main types of aquatic weed control technologies, both domestically and internationally: physical, chemical, and biological. Chemical methods primarily employ herbicides and other chemical agents. These methods are easy to use and quick to produce results, but they can easily cause secondary pollution to the aquatic environment, and lakes and reservoirs are often water sources, so chemical methods are generally not suitable. Biological methods primarily involve the use of grazing organisms such as fish and waterfowl. These methods are low-cost, long-lasting, and relatively safe. However, they require extensive experimental research and demonstration, are difficult to manage, and can introduce new dominant species or negatively impact the aquatic ecosystem. Therefore, their use is generally approached with caution. Physical methods primarily include harvesting and physical barriers. These techniques are relatively simple, have minimal environmental impact, and are quick to produce results. However, they are difficult to eradicate, are only temporary solutions, require regular maintenance, and are costly. Therefore, they are currently only effective on a small scale and are difficult to completely eliminate. Physical methods generally do not cause secondary environmental or ecological problems, but there are no effective treatments for Elodea, so developing more effective methods to address the root cause of the problem is imperative. Summary of the Invention

[0005] In view of the above situation, in order to overcome the defects of the existing technology, the purpose of the present invention is to provide a method for reverse transformation of the habitat of Elodea in the reservoir area, which can effectively solve the problem of aquatic weed disasters represented by Elodea while ensuring the health of the lake water ecological environment.

[0006] The technical solution provided by the present invention is:

[0007] A method for reversely transforming the habitat of Elodea in a reservoir area comprises the following steps:

[0008] Step S1, using drone aerial survey to form a remote sensing image of the reservoir area, extracting the vegetation-covered area of ​​the reservoir area from the remote sensing image, and obtaining a remote sensing image of the reservoir area containing the Elodea / water body boundary;

[0009] Step S2, obtaining a depth contour map of the reservoir area based on the measured underwater topography of the reservoir area and the water level during the survey period;

[0010] Step S3: Establish a two-dimensional mathematical model of water flow in the reservoir area. Use the measured underwater topography as the bottom boundary, the reservoir inlet flow and the water level in front of the dam as upstream and downstream calculation conditions to calculate the flow velocity field. The velocity contour map of the reservoir area is obtained by plotting the flow velocity field.

[0011] Step S4, superimposing the remote sensing image of the reservoir area containing the Elodea / water body boundary with the water depth contour map at the same coordinates to obtain the water depth where the Elodea / water body boundary is located, and taking the maximum water depth as the water depth threshold h for Elodea reverse transformation;

[0012] Step S5, superimposing the remote sensing image of the reservoir area containing the Elodea / water body boundary with the velocity contour map on the same coordinates to obtain the flow velocity at the Elodea / water body boundary, and taking the maximum flow velocity as the flow velocity threshold v for Elodea reverse transformation;

[0013] Step S6: Adjust the water depth and flow rate of the reservoir area based on the water depth threshold h and the flow rate threshold v. By adjusting the changes in the water level and flow rate in the reservoir area, hydrodynamic conditions that are unfavorable for the growth of Elodea are created, thereby controlling the growth of Elodea and forming a technical system for reverse transformation of the Elodea habitat in the reservoir area. The specific adjustment method is as follows:

[0014] A. The upstream reservoir increases its water output Q, thereby raising the water level in the reservoir area where the Elodea is located, making the water level in the area covered by the Elodea greater than the water depth threshold h;

[0015] B. When increasing the water discharge Q of the upstream reservoir is no longer able to meet the water level in the Elodea-covered area of ​​the reservoir greater than the water depth threshold h, the downstream gate is opened to release water so that the flow rate in the Elodea-covered area exceeds the flow rate threshold v.

[0016] Preferably, when there is no water to be discharged from the upstream reservoir and the water level of the reservoir where the Elodea is located has also dropped to the lowest, and its flow rate and water depth are still less than the corresponding threshold, the underwater topography of the reservoir where the Elodea is located is transformed, that is, the gentle slope near the beach is changed into a steep slope, and the shallow water area is deepened to reduce the area where the water depth is less than the water depth threshold h.

[0017] Compared with the prior art, the present invention has the following advantages:

[0018] 1. Using drones to survey reservoirs, we generate remote sensing images of the reservoir area. Drone remote sensing offers flexible data acquisition and high-resolution images, making it ideal for analyzing the dynamic coverage and coverage of different vegetation types in lakes, reservoirs, and rivers at a landscape scale. Compared to digital cameras, hyperspectral instruments are expensive, pose greater risks when operating on water, and require complex data processing. This paper uses consumer-grade drones equipped with digital cameras to monitor aquatic plant coverage in reservoirs. This method utilizes the distinctive color of Elodea to quickly extract vegetation coverage areas within the reservoir area from remote sensing images.

[0019] 2. The water depth threshold and flow rate threshold for the reverse transformation of Elodea in each reservoir area are collected in real time, so that targeted reverse transformation can be carried out for the Elodea in different growth environments in each reservoir area, thereby maximizing the transformation efficiency and reducing the transformation cost.

[0020] 3. The method of the present invention is simple. After the threshold is collected in real time, hydrological conditions unfavorable for the growth of Elodea can be created by increasing the water output Q of the upstream reservoir or opening the gates of the downstream reservoir to release water, or performing local terrain modification. This effectively inhibits the reproduction and growth of Elodea in the early stages, thereby effectively suppressing the reproduction and growth of Elodea.

[0021] 4. Since no other biological species or chemicals are added to the water body, no secondary environmental or ecological disasters will be caused;

[0022] 5. Increasing the discharge of upstream reservoirs can increase the power generation and water supply benefits of the reservoirs at this level. Local terrain transformation, such as changing gentle slopes to steep slopes, will produce certain sand dredging benefits. In addition to controlling Elodea, it can also generate certain economic benefits to offset the investment in the control project. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a flowchart of the method of the present invention.

[0024] Figure 2 This is a remote sensing image of the key distribution area of ​​Elodea, an application example of the present invention.

[0025] Figure 3 This is a water depth contour map of area A, an application example of the present invention.

[0026] Figure 4 This is a velocity contour map of area A in the application example of the present invention.

[0027] Figure 5 This is a statistical chart of the inflow and water level process of Wangfuzhou Reservoir during the second ecological scheduling experiment in the spring of 2021, an application example of the present invention.

[0028] Figure 6 This is a comparison diagram of water depth and flow velocity before and after the terrain transformation of a typical section in area A of the application example of the present invention. DETAILED DESCRIPTION

[0029] The specific embodiments of the present invention are further described in detail below with reference to the examples.

[0030] A method for reversely transforming the habitat of Elodea in a reservoir area comprises the following steps:

[0031] Step S1 uses drone aerial surveying to generate a remote sensing image of the reservoir area. Vegetation-covered areas within the reservoir area are extracted from the remote sensing image to obtain a remote sensing image of the reservoir area, including the Elodea / water boundary. Before conducting the aerial survey, image control points are deployed based on the actual conditions of the survey area, and a route is then planned based on these control points. After the image control points are deployed and the route is planned, the drone is launched and imagery of the survey area is captured along the planned route. The imagery is then imported into a computer, and plant patches and water bodies are identified. The plant patch boundaries are delineated to form the Elodea / water boundary.

[0032] Step S2, based on the measured underwater topography of the reservoir area (reservoirs are generally monitored annually) and the water level during the survey period, obtain the depth contour map of the reservoir area; export the three-dimensional elevation point data of the measured underwater topography of the reservoir area in absolute coordinates in dwg format (if it is in MapInfo format, it can be used directly), and then convert the elevation into water depth value with reference to the water level value, and then use GIS software such as MapInfo or Surfer to import the above data to draw the depth contour map.

[0033] Step S3, establish a two-dimensional water flow mathematical model of the reservoir area, import the measured underwater topography as the bottom boundary, and use the reservoir inlet flow and the water level in front of the dam as the upstream and downstream calculation conditions to calculate the flow velocity field. The flow velocity contour map of the reservoir area is obtained by drawing the flow velocity field of the reservoir area; export the three-dimensional elevation point data in dwg format of the measured underwater topography of the reservoir area with absolute coordinates (if it is in MapInfo format, it can be used directly), and then convert the elevation into water depth value with reference to the water level value. Then use GIS software such as MapInfo or Surfer to import the above data to draw the water depth contour map.

[0034] Step S4: Overlaying the remote sensing image of the reservoir area containing the Elodea / water body boundary with the water depth contour map at the same coordinates to obtain the water depth at the Elodea / water body boundary, and taking the maximum water depth as the water depth threshold h for reverse transformation of Elodea; overlaying the Elodea / water body boundary with the water depth contour map in absolute coordinates to obtain the water depth at the boundary. The boundary and the water depth contour may differ, and taking the maximum water depth at the boundary as the water depth threshold h for reverse transformation of Elodea;

[0035] Step S5: Overlaying the remote sensing image of the reservoir area containing the Elodea / water body boundary with the velocity contour map at the same coordinates to obtain the flow velocity at the Elodea / water body boundary, and taking the maximum flow velocity as the flow velocity threshold v for Elodea reverse transformation; overlaying the Elodea / water body boundary of absolute coordinates with the velocity contour map to obtain the flow velocity at the boundary. The boundary and the velocity contour map may differ, and taking the maximum flow velocity at the boundary as the water depth threshold v for Elodea reverse transformation;

[0036] Step S6: Adjust the water depth and flow rate of the reservoir area based on the water depth threshold h and the flow rate threshold v. By adjusting the changes in the water level and flow rate in the reservoir area, hydrodynamic conditions that are unfavorable for the growth of Elodea are created, thereby controlling the growth of Elodea and forming a technical system for reverse transformation of the Elodea habitat in the reservoir area. The specific adjustment method is as follows:

[0037] A. The upstream reservoir increases its water output Q, thereby raising the water level in the reservoir area where the Elodea is located, making the water level in the area covered by the Elodea greater than the water depth threshold h;

[0038] B. When increasing the water discharge Q of the upstream reservoir is no longer able to meet the water level in the Elodea-covered area of ​​the reservoir greater than the water depth threshold h, the downstream gate is opened to release water so that the flow rate in the Elodea-covered area exceeds the flow rate threshold v.

[0039] C. When there is no water to be discharged from the upstream reservoir and the water level of the reservoir where the Elodea is located has also dropped to the lowest level, and its flow rate and water depth are still less than the corresponding threshold, the underwater topography of the reservoir where the Elodea is located will be modified. That is, the gentle slope near the beach will be changed to a steep slope. At the same time, the shallow water area will be deepened to reduce the area where the water depth is less than the water depth threshold h.

[0040] The present invention has achieved good technical effects through practical application, and the application examples are as follows:

[0041] (1) Basic Information

[0042] The Wangfuzhou Water Conservancy Project is the first cascade hub project connecting the middle and lower reaches of the Han River to the Danjiangkou Water Conservancy Project. It is a large-scale (2) water conservancy project with power generation as its main function, combined with shipping, and with comprehensive benefits such as irrigation, aquaculture, and tourism. It controls a basin area of ​​95,900 km2. The reservoir is located on the main stream of the Han River in Laohekou City, Hubei Province, about 30 km upstream from the Danjiangkou Hub and about 3 km downstream from the urban area of ​​Laohekou City. It is the 10th of the 16-level development projects on the main stream of the Han River. The normal water level of the Wangfuzhou Reservoir is 86.23m, with a corresponding storage capacity of 149.5 million m3. The verified flood level is 89.3m, with a total storage capacity of 309.5 million m3.

[0043] The first unit of the Wangfuzhou Power Station officially began operation in May 2000. Aquatic weeds began to accumulate in front of the wastewater discharge system in 2011. During the autumn flood season of September to November 2017 and 2019, aquatic weeds from the river flowed into the Wangfuzhou Power Station reservoir, causing a sudden increase in the amount of weeds and debris ahead of the wastewater discharge system, resulting in a large accumulation of weeds and debris outside the discharge system. The floating weeds in the reservoir are primarily Elodea. These accumulated weeds and debris squeezed against the wastewater discharge system and, as the water continued to flow, were squeezed out from under the discharge system and accumulated on the inclined trash racks of the four generator units. The weed disasters in 2017 and 2019 resulted in annual power generation losses of 51 million kWh and 24 million kWh, respectively, resulting in significant direct economic losses. Furthermore, large amounts of dead Elodea sank into the water, rotting and decomposing. The nutrients absorbed during their growth period were released back into the water, potentially exceeding nutrient levels and causing endogenous water pollution.

[0044] (2) Transformation

[0045] Step S1:

[0046] In 2020, an on-site survey was conducted in the Wangfuzhou Reservoir area. UAV aerial surveys were used to generate remote sensing photos of the reservoir area. By identifying plant patches and water bodies in the photos and outlining the boundaries of plant patches, the key distribution areas of Elodea and the boundaries with water bodies were formed, such as Figure 2 shown.

[0047] Step S2:

[0048] Based on the measured underwater topography and water level during the survey period, a depth contour map of the reservoir area was obtained. Due to the large scope of the reservoir area, this application example selects the shoal area near the Guanghua Bridge, one of the key distribution areas of Elodea, for specific analysis. The subsequent application examples will also focus on this area and define it as Area A. The water depth distribution map of Area A is shown below. Figure 3 shown.

[0049] Step S3:

[0050] The Wangfuzhou Reservoir is a typical shallow-water reservoir. Without considering the vertical changes in water flow, the MIKE21 model developed by the Danish Institute for Water Resources and the Environment (DHI) was used to construct a two-dimensional hydrodynamic model of this river section. The simulation range is the Hanjiang River mainstream from Danjiangkou Dam to Wangfuzhou Power Station, including the Wangfuzhou Reservoir and the Danjiangkou Dam downstream, with a length of about 35km. The measured 1:2000 underwater topography was used. The reservoir inlet flow and the water level in front of the dam were used as upstream and downstream calculation conditions, and the velocity field of area A was calculated as follows: Figure 4 shown.

[0051] Step S4:

[0052] The absolute coordinate Elodea / water body boundary line is superimposed on the water depth contour map to obtain the water depth where the boundary line is located. The maximum water depth at the boundary line is taken as the water depth threshold h for Elodea reverse transformation, which is approximately 3m.

[0053] Step S5:

[0054] The absolute coordinate Elodea / water body boundary line is superimposed on the velocity contour map to obtain the velocity at the boundary line. The maximum velocity at the boundary line is taken as the water depth threshold v for Elodea reverse transformation, which is approximately 0.03 m / s.

[0055] Step S6:

[0056] In 2021, the Danjiangkou Reservoir and the Wangfuzhou Reservoir carried out ecological regulation in late February and early March respectively, increasing the outflow of the Danjiangkou Reservoir, thereby raising the water level in the reservoir area where the Elodea is located, making the water depth in the area covered by the Elodea greater than the water depth threshold of 3m. From February 22 to 26, 2021, the water flow from the Danjiangkou Reservoir to the middle and lower reaches of the Han River was between 591 and 1280m. 3 / s fluctuation, the ratio of maximum flow to minimum flow exceeds 2 times, and the average water supply flow is 941m 3 / s; the second ecological regulation was implemented from March 8th to 12th, during which the water flow in the middle and lower reaches of the Han River was between 464 and 1240 m 3 / s fluctuation, the ratio of maximum flow to minimum flow is close to 3 times, and the average water supply flow is 873m3 / s, such as Figure 5 As shown in the figure, hydrodynamic changes indicate that the average flow velocity before regulation in the concentrated Elodea distribution area along the shore of Area A was approximately 0.03 m / s, with a maximum flow velocity of 0.05 m / s. During the first ecological regulation period from February 22nd to 26th, the average flow velocity increased to 0.05 m / s, with a maximum flow velocity of 0.09 m / s. During the second ecological regulation period from March 8th to 12th, the average flow velocity increased to 0.04 m / s, with a maximum flow velocity of 0.06 m / s.

[0057] According to 2021 Elodea biomass observations, the revived Elodea in January was primarily concentrated in water depths of 1-2 meters, with sporadic growth at 3 meters. No aquatic plants were present at depths of 5 meters or 7 meters. In January, Elodea in the Shui'an New City area was primarily found in very shallow waters, generally no deeper than 1 meter. In February, it was found in water depths less than 1.5 meters, in May less than 2 meters, and in July less than 3-3.5 meters. Elodea biomass reached its peak in most areas between Danjiangkou and Wangfuzhou in July and August. Compared to 2019 and 2020, the 2021 results showed that typical area A did not develop a dense "underwater forest." Elodea biomass decreased from approximately 770 tons before the renovation to approximately 233 tons, a reduction of approximately 70%, achieving the expected results. Moreover, judging from the changes in the distribution of Elodea, the shallow water areas close to still water, where Elodea was previously mainly distributed, have seen enhanced hydrodynamics and increased water depth due to changes in topography, leading to a significant decrease in the biomass of Elodea. This is the location in Region A where the biomass of Elodea has declined the most.

[0058] Due to the critical importance of Danjiangkou Reservoir's water resources, ecological regulation can only be implemented in years with abundant water resources. Under the drought conditions of 2022, ecological regulation measures are impossible. To mitigate the Elodea infestation in the reservoir area, Wangfuzhou Reservoir has explored and implemented underwater topography modification to strengthen Elodea control. Area A, where Elodea is concentrated, was dredged to a controlled elevation of 83.2 meters. This means that at the reservoir's normal water level of 86.2 meters, the water depth is 3 meters, corresponding to the Elodea growth threshold depth of 3 meters obtained in step S4. After underwater topography modification, the water depths in Area A, typically less than 3 meters below normal water levels, were significantly improved. A typical cross-section shows that before the modification, the water depth within a range of 600-1800 meters from the starting point was less than 2 meters, and over 80% of the area had a depth of less than 1 meter. After the modification, the water depth in the same area exceeded 3 meters. From the perspective of flow velocity changes, the flow velocity decreases in the deep channel area, but it decreases significantly in the range where the flow velocity is less than the growth velocity threshold of Elodea 0.03m / s in the terrain modification area (e.g. Figure 6After landform modification, even under low flow conditions, the improved water depth and flow velocity in Area A will be detrimental to the growth of Elodea. Under medium and high flow conditions, the water depth and flow velocity will further increase, thereby creating a habitat unfavorable for Elodea. According to observations, when only landform modification was used without ecological scheduling, the Elodea biomass in Area A during its peak period was approximately 1.16 million tons, a decrease of approximately 85% compared to the average of 7.7 million tons in 2019 and 2020. Compared with the 2021 period when ecological scheduling was used, the Elodea biomass was further reduced, which had a significant effect on inhibiting the growth of Elodea.

Claims

1. A method for reversely transforming the habitat of Elodea in a reservoir area, comprising the following steps: Step S1, using drone aerial survey to form a remote sensing image of the reservoir area, extracting the vegetation-covered area of ​​the reservoir area from the remote sensing image, and obtaining a remote sensing image of the reservoir area containing the Elodea / water body boundary; Step S2, obtaining a depth contour map of the reservoir area based on the measured underwater topography of the reservoir area and the water level during the survey period; Step S3: Establish a two-dimensional mathematical model of water flow in the reservoir area. Use the measured underwater topography as the bottom boundary, the reservoir inlet flow and the water level in front of the dam as upstream and downstream calculation conditions to calculate the flow velocity field. The velocity contour map of the reservoir area is obtained by plotting the flow velocity field. Step S4, superimposing the remote sensing image of the reservoir area containing the Elodea / water body boundary with the water depth contour map at the same coordinates to obtain the water depth where the Elodea / water body boundary is located, and taking the maximum water depth as the water depth threshold h for Elodea reverse transformation; Step S5, superimposing the remote sensing image of the reservoir area containing the Elodea / water body boundary with the velocity contour map on the same coordinates to obtain the flow velocity at the Elodea / water body boundary, and taking the maximum flow velocity as the flow velocity threshold v for Elodea reverse transformation; Step S6: Adjust the water depth and flow rate of the reservoir area based on the water depth threshold h and the flow rate threshold v. By adjusting the changes in the water level and flow rate in the reservoir area, hydrodynamic conditions that are unfavorable for the growth of Elodea are created, thereby controlling the growth of Elodea and forming a technical system for reverse transformation of the Elodea habitat in the reservoir area. The specific adjustment method is as follows: A. The upstream reservoir increases its water output Q, thereby raising the water level in the reservoir area where the Elodea is located, making the water level in the area covered by the Elodea greater than the water depth threshold h; B. When increasing the water output Q of the upstream reservoir is unsustainable and the water level in the Elodea-covered area of ​​the reservoir cannot be kept above the water depth threshold h, the sluice gates of the Elodea-covered reservoir are opened to release water, so that the flow rate in the Elodea-covered area exceeds the flow rate threshold v; In step S6, when there is no water to be discharged from the upstream reservoir and the water level of the reservoir where the Elodea is located has also dropped to the lowest level, and its flow rate and water depth are still less than the corresponding thresholds, the underwater topography of the reservoir area where the Elodea is located is modified, that is, the gentle slope near the beach is changed into a steep slope, and the shallow water area is deepened to reduce the area where the water depth is less than the water depth threshold h.

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