Shallow lake endogenous pollution long-acting control method based on hydrodynamic control

Abstract

The invention relates to the technical field of lake ecological restoration and water pollution control, in particular to a shallow lake endogenous pollution long-acting control method based on hydrodynamic control. Collecting historical hydrological, meteorological and sediment data of the target lake; arranging a multi-parameter sensor monitor in a target lake to synchronously monitor the wind speed, wind wave, suspended matter concentration, dissolved oxygen and water nitrogen and phosphorus content of the target lake at high frequency; the method comprises the following steps: adopting an SWAN wind wave model to simulate the effective wave height of a lake, combining sediment survey data, and screening an area in which the sediment thickness is greater than or equal to 0.3 m, the TN is greater than or equal to 1500mg / kg and the TP is greater than or equal to 600mg / kg as a sediment resuspension hot spot area; an underwater shoal is designed on the periphery of the hot spot area; a water flow transportation path is simulated based on a three-dimensional lake flow model, lake bottom traps are arranged among hydraulic channels among underwater shoals, and the control method can remarkably reduce the resuspension strength of sediments and intercept high-pollution particles in transportation by integrating wave reduction, flow guide and mud catching functions, so that the collaborative target of water quality improvement and ecological restoration is achieved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lake ecological restoration and water pollution control, and particularly relates to a long-term control method for internal source pollution in a shallow lake based on water power manipulation. BACKGROUND

[0002] Internal source pollution in a shallow lake is a core problem restricting water quality improvement. After external source pollutants enter the lake, about 70% to 90% of nitrogen and phosphorus are accumulated in the sediment, which is repeatedly resuspended under the action of wind and wave disturbance and lake flow, forming a vicious cycle of "pollution-release-repollution". In view of the situation of internal source pollution, the following treatment methods are generally used, but the existing treatment methods also have the following shortcomings.

[0003] Sediment dredging: although it can remove the surface polluted sediment in the short term, the disposal cost of silt is high, and the benthic ecosystem is destroyed. Under the influence of water power, the sediment in other areas not dredged will quickly cover the dredged area, reducing the dredging effect.

[0004] In-situ passivation: fixed phosphorus by adding aluminum salt, lanthanum modified clay and the like, but the passivation agent is easily affected by water power disturbance, and the long-term effect is unstable. In addition, the safety of raw materials is unknown, and the secondary pollution caused thereby is unknown.

[0005] Ecological restoration: planting aquatic plants can absorb nutrient salts, but the survival rate is low in high turbidity water, and they are easily damaged by wind and wave;

[0006] Water power manipulation: in recent years, water power manipulation technology has gradually attracted attention. For example, Zhang et al. (2021) proposed to lay artificial grooves on the lake bottom to capture particles, but based on static parameters, it cannot adapt to the dynamic changes of lake flow, resulting in fluctuation of capture efficiency and lack of systematic consideration of directional control of lake flow to improve collection efficiency. Zhang et al. (2024) used underwater dike to reduce wind and wave, but lacked constraint on sediment transport path.

[0007] Therefore, it is necessary to improve the existing technology to solve the above technical problems. SUMMARY

[0008] This section aims to summarize some aspects of the embodiments of the present application and briefly introduce some preferred embodiments. Some simplifications or omissions may be made in this section and the abstract and title of the specification to avoid obscuring the purpose of this section, abstract and title, and such simplifications or omissions cannot be used to limit the scope of the present application.

[0009] In view of the problem of unsatisfactory treatment effect of the existing sewage treatment method in dealing with internal source pollution in a shallow lake, a long-term control method for internal source pollution in a shallow lake based on water power manipulation is proposed.

[0010] To solve the above technical problems, the present application provides the following technical solutions: a long-term control method for internal source pollution in shallow lakes based on water power operation, which is suitable for shallow lakes with a water depth of less than or equal to 2 m, a bottom mud thickness of more than or equal to 0.3 m, TN of more than or equal to 1500 mg / kg, and TP of more than or equal to 600 mg / kg, and comprises the following steps: S1: collecting historical hydrological, meteorological and bottom data of the target lake; S2: arranging a multi-parameter sensor monitor in the target lake to synchronously and high-frequency monitor the wind speed, wind wave, suspended matter concentration, dissolved oxygen and water body nitrogen and phosphorus content of the target lake, and combining Sentinel-2 or Landsat-8 satellite images to inversely calculate the large-range chlorophyll a concentration and water body turbidity; S3: unifying and calibrating the sensor monitor data and satellite images by a Kalman filtering algorithm to construct a lake environment parameter space-time database, and training a wind wave, suspended matter concentration and nitrogen and phosphorus nutrient content prediction model by an XGBoost algorithm; S4: simulating the effective wave height of the lake by a SWAN wind wave model, and combining the bottom survey data to screen the areas with a bottom mud thickness of more than or equal to 0.3 m, TN of more than or equal to 1500 mg / kg and TP of more than or equal to 600 mg / kg as sediment resuspension hotspots; S5: designing underwater shoals in the periphery of the hotspots, with a top elevation of 10-20 cm below the normal water level of the lake, a top width of 20-50 m, a bottom width of 100-160 m and a slope ratio of 1:50; S6: simulating the water flow transport path based on a three-dimensional lake flow model, and arranging lake bottom traps in the hydraulic passages between the underwater shoals; S7: combining GPS positioning technology, and constructing by a long-arm excavator, with the hard earthwork excavated from the traps used for the heaping of the underwater shoals; and S8: regularly monitoring the sediment deposition amount in the traps, and removing the sediments in the areas with TN of more than or equal to 1800 mg / kg and TP of more than or equal to 900 mg / kg by a cutter suction dredger once or twice a year.

[0011] As a preferred scheme of the present application, the long-term control method for internal source pollution in shallow lakes based on water power operation, wherein: the data collected in step S1 include wind speed, wind direction, water level, bottom mud thickness, total nitrogen, total phosphorus and organic matter content.

[0012] As a preferred scheme of the present application, the long-term control method for internal source pollution in shallow lakes based on water power operation, wherein: the input parameters of the wind wave model in step S4 include the prevailing wind field, the wind speed and the model spatial resolution.

[0013] As a preferred scheme of the present application, the long-term control method for internal source pollution in shallow lakes based on water power operation, wherein: the determination method of the prevailing wind field is to determine the wind direction with the top three proportion frequencies as the prevailing wind direction according to the wind field data of the lake periodic weather station for more than or equal to 5 years; the determination method of the wind speed is to determine the wind speed values corresponding to the 10%, 25% and 50% guarantee rates by PIII analysis of the wind speed values; and the determination method of the model spatial resolution is to determine the spatial resolution to be more than 100 m x 100 m.

[0014] As a preferred scheme of the long-term control method for internal source pollution in shallow lakes based on water power manipulation of the application, in step S5, the layout of the underwater shoal should meet the following conditions: the shoal trend is perpendicular to the prevailing wind direction or / and the water wave direction, the interval between adjacent shoals is less than 200m, and the water depth on the top of the shoal is less than or equal to 0.2m.

[0015] As a preferred scheme of the long-term control method for internal source pollution in shallow lakes based on water power manipulation of the application, in step S6, the three-dimensional lake flow model is simulated according to the following method: taking the lake flow field, water depth and trap layout as input values, predicting the particle sedimentation path and outputting a high-pollution sediment accumulation probability graph, and then designing a reward function including the capture efficiency and construction cost based on the probability graph, and iteratively optimizing the trap width L and depth H through the Q-learning algorithm.

[0016] As a preferred scheme of the long-term control method for internal source pollution in shallow lakes based on water power manipulation of the application, when iteratively optimizing the trap width L and depth H through the Q-learning algorithm, the following formula should be met: L >= 1.25 * V * H / D; wherein L is the trap width, V is the horizontal flow velocity of the lake bottom, H is the trap depth, and D is the particle settling velocity.

[0017] As a preferred scheme of the long-term control method for internal source pollution in shallow lakes based on water power manipulation of the application, in step S7, the trap excavation depth error is less than or equal to ±10cm, the depth is greater than or equal to 3m, the shoal filling slope error is less than or equal to ±5%, and the suspended solids diffusion range during the construction period is less than or equal to 500m.

[0018] As a preferred scheme of the long-term control method for internal source pollution in shallow lakes based on water power manipulation of the application, in step S8, the dredging frequency is dynamically adjusted according to the trap accumulation rate.

[0019] As a preferred scheme of the long-term control method for internal source pollution in shallow lakes based on water power manipulation of the application, in step S8, the dredging frequency is dynamically adjusted according to the trap accumulation rate. 2 .

[0020] The beneficial effects of the application are as follows:

[0021] 1. The method can determine the prevailing wind field and the wind power by collecting historical hydrological, meteorological and bottom data of the target lake and monitoring the lake data in real time through a multi-parameter sensor monitoring instrument, so that the shoal can be constructed in the lake in a targeted manner, the shoal construction can block the wind wave, reduce the disturbance intensity of the wind wave to the lake bottom, reduce the sediment resuspension and the nutrient salt content of the water body, and achieve the long-term weakening effect on the internal source pollution.

[0022] 2. The design of the shoal can form a guide flow between the shoals. Under the disturbance of wind wave, the high-pollution surface sediment of the lake bottom is easy to transport in the lake body. According to the spatial distribution characteristics of the sediment, the guide flow measure is arranged to guide the orderly flow of the water flow carrying the high-pollution sediment, constrain the disorder diffusion of the suspended particles, reduce the influence range of the resuspended sediment, and realize the long-term constraint effect on the sediment of the shallow lake.

[0023] 3. The lake bottom trap is arranged on the flow transport channel of the shallow lake, and a still water environment can be formed locally. When the water flow carrying the high-pollution particles flows from the trap, a large amount of particles rich in nutrients can be captured in the trap due to the gravity effect of the particles. When the high-pollution sediment stored in the trap reaches a certain amount, the mechanical excavation method is used for removal, and the long-term removal of the high-pollution sediment on the surface of the lake bottom is realized. BRIEF DESCRIPTION OF DRAWINGS

[0024] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed in the embodiment description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor. Among them:

[0025] Figure 1 The figure is a monitoring point diagram for data collection of the Gi Lake.

[0026] Figure 2 The figure is a sediment thickness distribution diagram of the Gi Lake before treatment.

[0027] Figure 3 The figure is a total nitrogen and total phosphorus distribution diagram of the Gi Lake before treatment.

[0028] Figure 4 The figure is the wind field statistical data of the Gi Lake before treatment.

[0029] Figure 5 The figure is a relationship diagram of wind wave and suspended matter of the Gi Lake.

[0030] Figure 6 The figure is a relationship diagram of wind wave and nutrients of the Gi Lake.

[0031] Figure 7 The figure is a distribution of effective wave height of the Gi Lake and a lake flow movement diagram of the Gi Lake.

[0032] Figure 8 The figure is a spatial layout diagram of the shoal in the Gi Lake.

[0033] Figure 9 The figure is a three-dimensional lake flow simulation result diagram of the Gi Lake under the prevailing wind.

[0034] Figure 10 The figure is an engineering layout diagram of the lake bottom trap of the Gi Lake.

[0035] Figure 11 The monthly average effective wave height chart of different areas of the shallow lake before and after the implementation of the shallow lake.

[0036] Figure 12 The wave height reduction rate chart of different areas of the shallow lake before and after the implementation of the shallow lake.

[0037] Figure 13 The water environment improvement chart of part of the shallow lake. DETAILED DESCRIPTION

[0038] In order to make the above objectives, characteristics and advantages of the present application more apparent, specific embodiments of the present application will be described in detail below with reference to the accompanying drawings.

[0039] In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present application. However, it will be apparent to one skilled in the art that the present application can be practiced without the specific details given herein, that the present application can be practiced with other than the described implementations, and that variations of the described implementations can be made. Thus, the present application is not intended to be limited to the particular implementations described.

[0040] Secondly, the "one embodiment" or "embodiment" referred to herein means that the specific features, structures or characteristics can be included in at least one implementation of the present application. "In one embodiment" appearing in different places in the specification does not mean the same embodiment, nor is it an embodiment that is independent or alternative to other embodiments.

[0041] Thirdly, the present application is described in detail in conjunction with the schematic diagram. In the detailed description of the embodiments of the present application, the cross-sectional view of the device structure is locally enlarged without the general proportion for the convenience of description, and the schematic diagram is only an example, which should not limit the scope of protection of the present application. In addition, the three-dimensional spatial dimensions of length, width and depth should be included in actual manufacture.

[0042] Embodiment 1

[0043] This embodiment is the first embodiment of the present application, which provides a long-term control method for in-situ pollution in shallow lakes based on hydrodynamic control. The control method is suitable for shallow lakes with a water depth of ≤2m, a bottom mud thickness of ≥0.3m, TN of ≥1500mg / kg and TP of ≥600mg / kg.

[0044] Specifically, the following steps are included;

[0045] 1. Collect historical hydrological, meteorological and bottom data of the target lake, including wind speed, wind direction, water level, bottom mud thickness, total nitrogen (TN), total phosphorus (TP) and organic matter (OM) content;

[0046] 2. Deploy multi-parameter sensor monitoring instruments in key areas of the target lake. The key areas are determined based on sufficient data collection of the target lake. The wind speed, wind wave, suspended matter concentration, dissolved oxygen, and water body nitrogen and phosphorus content are monitored simultaneously at high frequency. At the same time, the Sentinel-2 or Landsat-8 satellite image is combined to retrieve large-scale chlorophyll-a concentration and water turbidity, which makes up for the spatial limitations of fixed-point monitoring;

[0047] 3. The sensor monitoring instrument data and satellite image are calibrated by the Kalman filter algorithm to construct a lake environmental parameter spatio-temporal database. The XGBoost algorithm is used to train the wind wave, suspended matter concentration, and nitrogen and phosphorus nutrient content prediction model to determine the water environmental effect of wind wave;

[0048] 4. The SWAN wind wave model is used to simulate the effective wave height (Hs) of the lake. The wind wave parameters are monitored by the bottom-mounted wave instrument combined with the bottom sediment survey data. The TN and TP distribution are analyzed by the bottom sediment column sampling. The areas with a sediment thickness of ≥0.3 m, TN of ≥1500 mg / kg, and TP of ≥600 mg / kg are selected as the sediment resuspension hotspots. The input parameters of the wind wave model include the prevailing wind field, wind speed, and model spatial resolution;

[0049] The method for determining the prevailing wind field is as follows: according to the wind field data of the lake periodic meteorological station for more than or equal to 5 years, the frequency distribution of each wind direction is counted, and the wind direction with the top three proportion frequencies is determined as the prevailing wind direction. The method for determining the wind speed is as follows: PIII analysis is performed on the wind speed values to determine the wind speed values corresponding to the 10%, 25%, and 50% guarantee rates. The method for determining the model spatial resolution is as follows: the spatial resolution is more than 100 m x 100 m;

[0050] 5. An underwater shoal is designed outside the hotspot area. The shoal top elevation is 10-20 cm below the lake normal water level, the top width is 20-50 m, the bottom width is 100-160 m, the slope ratio is 1:50, the terrain is reshaped to form a gentle slope structure, and the wind wave propagation energy is actively weakened. The layout of the underwater shoal should meet the following conditions: the shoal strike is perpendicular to the prevailing wind direction or / and water wave direction, the distance between adjacent shoals is less than 200 m, and the water depth at the top of the shoal is less than or equal to 0.2 m, so as to enhance the wind wave attenuation effect, reduce the shear force of the wave on the sediment, and reduce the sediment resuspension rate;

[0051] 6. The lake flow model is simulated based on the three-dimensional lake flow model. The lake bottom traps are placed in the appropriate positions of the hydraulic passage between the underwater shoals. The appropriate positions are used for sufficient sediment deposition under the premise of meeting the trap structure. The three-dimensional lake flow model simulates the data of the lake bottom traps according to the following method;

[0052] With the lake flow field, water depth and trap layout as input values, the particle settling path is predicted and the high pollution sediment accumulation probability map is output, then a reward function including capture efficiency and construction cost is designed based on the probability map, and the trap width L and depth H are iteratively optimized through Q-learning algorithm, while satisfying the formula: L≥1.25×V×H / D; wherein,

[0053] L is the trap width (m);

[0054] V is the horizontal flow velocity of the lake bottom (m / s, determined according to the measured conditions of different lakes);

[0055] H is the trap depth (m, determined according to the water depth and measured suspended matter concentration of different lakes);

[0056] D is the settling velocity of particles (m / s, determined according to the measured conditions of different lakes);

[0057] 7. Combined with GPS positioning technology, the trap is excavated by a long-arm excavator, and the hard earthwork excavated from the trap is used for filling on the underwater shoal to realize self-balancing of earthwork, the error of the excavation depth of the trap is ≤±10 cm, the depth is ≥3 m, the error of the slope of the shoal filling is ≤±5%, the diffusion range of suspended matter during construction period is ≤500 m, and secondary pollution is controlled through enclosing measures;

[0058] 8. The sediment deposition amount in the trap is regularly monitored, and the sediment in the area with TN≥1800 mg / kg and TP≥900 mg / kg is removed by a cutter suction dredger 1-2 times a year; in actual use, the dredging frequency is dynamically adjusted according to the trap deposition rate, and preferably, in the initial stage (1-2 years), the sediment is dredged 2 times a year, and in the stable stage (after 3 years), the sediment is dredged 1 time a year;

[0059] 9. Emergent plants are planted on the top of the shoal, the planting density is 30-40 plants / m 2 , the emergent plants are preferably reed and cattail, the density ratio of the two is 5:1, the water depth of the normal water level is ≤0.2 m, the shoal structure is reinforced by the root system, and the nitrogen and phosphorus concentrations in the water body are reduced through plant absorption; of course, the slope can also be planted with submerged plants such as Vallisneria and Ceratophyllum, to form an ecological barrier.

[0060] Example 2

[0061] This example is the second embodiment of the present application, the difference is that the method in example 1 is used in the treatment of specific lakes, combined with the data collected and embodied in the treatment process of the treated lake, to further prove the feasibility and effectiveness of the method, at the same time, the specific example is more convenient and clear for the use of the method in reality, this example takes Gehu Lake as the object;

[0062] As shown in the accompanying Figure 1As shown, the lake is located between the southwest of Wujin District of Changzhou City and the northeast of Yixing City of Wuxi City, Jiangsu Province, at 119°44'~119°53' east longitude and 31°29'~31°42' north latitude, belonging to the west region of Taihu Lake Basin, and is the sixth largest lake in Jiangsu Province and an important part of the lake group in Taihu Lake Basin. The average water level is 3.37 m (Wusong Datum), the corresponding average water depth is 1.32 m, the area is 164.0 km2, and it has multiple functions such as aquaculture, flood storage and irrigation, water transportation, and modern tourism, playing a very important role in the local economic construction. The main inflow channels include Tangmen Port, Beigan River, Huangli River, Zhonggan River, and Wunan River, and the main outflow channels include Taige Canal, Caoqiao River, Shaohonggang, Yincun Port, and Shaohonggang, and there are no hydraulic structures on the inflow and outflow channels. As an important part of the Taohe River system, the water source mainly comes from surface runoff and lake surface precipitation, and the main inflow channels include Tangmen Port, Beigan River, Huangli River, Zhonggan River, and Wunan River, and the main outflow channels include Taige Canal, Caoqiao River, Shaohonggang, Yincun Port, and Shaohonggang, and there are no hydraulic structures on the inflow and outflow channels.

[0063] Specifically, the thickness distribution of the lake sediment is shown in the attached Figure 2 As shown, the lake sediment distribution presents obvious unevenness, and the average thickness of the lake sediment is about 0.27 m. The heavy sedimentation area with a thickness of more than 0.5 m is in a snake shape, starting from the northwestern position to the southeast in the form of a nearly semicircular ring, with a length of about 6-7 km, and the thickness of the sediment is about 0.5-1.0 m, locally exceeding 1.2 m. Then it extends to the west and reaches the west bank, with a length of about 7 km, and the thickness of the sediment is relatively shallow, about 0.6 m, with a maximum thickness of more than 0.9 m. In addition, the depth of the sediment around the lake, especially near the lake entrance, also exceeds 0.6 m.

[0064] As shown in Figure 3 a, the average total nitrogen content of the lake is 459.3-3925.8 mg / kg, with an average of 1804.6 mg / kg. The content is low in the northeast and southwest, and relatively high in the central-eastern-southeastern part. The highest total nitrogen concentration appears in the nearshore water area in the southeastern part. As shown in Figure 3 b, the average total phosphorus content is 480.1-2411.7 mg / kg, with an average of 915.9 mg / kg. The content is low in the northeast and north-southwest, and high in the central-eastern-southeastern part. The highest total phosphorus concentration appears near the heavy sedimentation area in the north-central part. Compared with the thickness of the sediment, the total nitrogen and total phosphorus in the heavy sedimentation area in the lake are also relatively high, which is the high-value area of the nutrient salt content in the study area.

[0065] As shown in Figure 4As shown, based on the hourly average wind field data from the Yixing National Meteorological Station, which is near Gehu Lake, from 2016 to 2022, the prevailing wind direction in the Gehu Lake basin throughout the year is southeast. The average wind speeds at 10%, 25%, and 50% guarantee rates are 3.61 m / s, 2.75 m / s, and 1.90 m / s, respectively. According to the model inversion coefficients, the wind speeds at 10%, 25%, and 50% guarantee rates on the surface of Gehu Lake are 4.69 m / s, 3.57 m / s, and 2.47 m / s, respectively.

[0066] The floods occurred on December 30, 2021 (dry season) and June 17, 2022 (high water season). Figure 1 At the monitoring point shown, a 500ml water sample was collected using a portable water sampler for nutrient analysis. The water sample was immediately filtered through a 0.45μm glass fiber membrane on-site. The filter membrane, filtered water, and part of the original water were stored in the dark at low temperature and brought back to the laboratory for further analysis. After digestion with alkaline potassium persulfate, the total nitrogen (TN) and total phosphorus (TP) of the original water sample were determined by ultraviolet spectrophotometry and ammonium molybdate spectrophotometry. The dissolved total nitrogen (DTN) and dissolved total phosphorus (DTP) of the filtered water sample were determined by subtracting the two values ​​to obtain particulate total nitrogen (PTN) and particulate total phosphorus (PTP). The suspended solids concentration (SS) was obtained by weighing.

[0067] A simulated area of ​​Gehu Lake, measuring 14.4 km east-west and 22.4 km north-south, was established. The SWAN wave model was used to simulate the wind and wave distribution in Gehu Lake. The spatial resolution of the model was 100m×100m, the calculation time step was 2min, and the frequency range was set to 0.2~2.5Hz, divided into 50 frequency bands. The direction was divided into 36 equal parts along the entire circumference, i.e., the directional resolution was 10°. In the physical process of the model, the wind input was considered to have both linear and exponential growth. The loss caused by bottom friction was modeled using the JONSWAP model with a coefficient of 0.067. The shallow water wind and wave breaking coefficient was taken as its average value of 0.73. The interaction of three waves in shallow water was considered in the model, and other default values ​​were used.

[0068] The Ecolake model was used to simulate the flow of Gehu Lake with a time step of 10 seconds. The model employs a free surface and topographically tracked vertical coordinate system, which is scaled according to the water column depth and has five vertical sigma layers. The hydrodynamic model is mainly driven by the inflow and outflow of rivers and the wind field on the lake surface. Based on hydrological monitoring, the rivers around Gehu Lake were generalized into 13 rivers, including the North Main River, Tangmen Port, Yangzhuang Port, Huangli River, Zhonggan River, Wunan River, Taige Canal, Caoqiao River, Shaogang Port, Taige South Canal, Zhandu Port, Pengdu Port, and Yincun Port. The flow rate of the rivers was set at a 10% guarantee rate under normal water conditions as the model input condition, thus reflecting the flow field structure of Gehu Lake under the overall inflow and outflow conditions.

[0069] Based on the dry season of Gehu Lake ( Figure 1(China 20211230 monitoring point) and high water season ( Figure 1 The suspended particulate matter concentration and wind and wave simulation results during the sampling period of the monitoring point (20220617) were used to conduct correlation and fitting analysis, and the calculation results are attached. Figure 5 As shown, the concentration of suspended matter in Gehu Lake is highly correlated with the intensity of wind and waves (significant wave height / water depth). This indicates that the significant wave height and water depth at different spatial locations in Gehu Lake are key factors affecting the concentration of suspended matter at those locations. When the water depth is low, even small wind and waves can cause the suspension effect of sediments. However, when the water depth is high, a certain intensity of wind and waves is required to reach the lake bottom and cause the sediments to be suspended. Therefore, the suspension effect of sediments can be reduced by constructing weak wind and wave zones and deep-water environments, thereby reducing the concentration of suspended matter in the water and improving the transparency of the water.

[0070] Appendix Figure 6 To analyze the correlation and fit between the monitored particulate nitrogen and phosphorus content in the water and the simulated wind and wave results and suspended solids concentration during the sampling period, the correlation between particulate phosphorus and suspended solids was found to be higher than that between particulate nitrogen and suspended solids. This indicates that shallow lakes like Gehu Lake are frequently affected by wind and waves, resulting in a rapid response in the particulate nitrogen and phosphorus content, with phosphorus content showing a more significant change. Therefore, for shallow lakes with high bottom nutrient content, reducing the intensity of wind and waves can, in the long term, reduce the content of particulate nitrogen and phosphorus in the water, thereby reducing the content of total nitrogen and total phosphorus in the water. In particular, for total phosphorus, which is not easily degraded, reducing the intensity of wind and waves to reduce the total phosphorus content in the water is feasible. Therefore, reducing wind and waves is key to reducing the endogenous impact of wind and waves on the nutrient content of water bodies.

[0071] Using the Gehu Lake wind and wave model, a simulation of the wind and wave conditions under the prevailing southeast wind of 4.69 m / s was conducted based on the current topography of Gehu Lake. The effective wave height and wave disturbance intensity were calculated, such as... Figure 7 As shown in a; under the current topography, the distribution of wind and waves in Gehu Lake is generally consistent with the topographical changes. The wind and wave intensity is relatively large in the central area of ​​the lake. Most areas in the central area are in the strong wind and wave zone under the wind field conditions, with a large effective wave height. The wind and wave intensity is relatively small in the near-shore area due to the protection of the shoreline and the influence of the shallower water depth. In particular, the wind and wave intensity is relatively the smallest in the waters near the upwind shoreline (i.e., the waters along the southeast coast of Gehu Lake).

[0072] Shallow lake currents are mainly wind-driven and inflow / outflow. Based on the established Gehu Lake current model, the vertical average current field of Gehu Lake under the influence of prevailing southeast wind of 4.69 m / s and 10% guaranteed river inflow / outflow during a normal year is as follows: Figure 7As shown in FIG. b, the overall flow field of the lake shows a characteristic of flowing from west to east and from north to south, which is mainly determined by the characteristics of the water system of the lake, which is mainly westward and southeastward. The flow velocity of the river mouth is large, and the flow velocity of the lake body is small. Affected by the characteristics of the shallow water, large waves and lake flow transport of the lake, the high nutrient salt particles resuspended in the lake body will frequently transport within the lake body, thereby adversely affecting different water areas and sensitive areas.

[0073] According to the distribution of the thickness of the sediment Figure 2 , the distribution of total nitrogen and total phosphorus in the sediment Figure 3 , the distribution of effective wave height Figure 7 a, and the lake flow movement of the lake Figure 7 b, the key siltation area in the middle of the lake and the inlet area are determined as the hot spot area of sediment resuspension in the lake, which is the key area that needs to be operated by water power.

[0074] An underwater shoal is designed outside the hot spot area, the top elevation of the shoal is 10-20 cm below the normal water level of the lake, the top width is 20-50 m, the bottom width is 100-160 m, and the slope ratio is 1:50. A gentle slope structure is formed by reshaping the terrain to actively weaken the wave propagation energy. The spatial layout is shown in Figure 8 ; wherein the No. 1 and No. 2 shoals are respectively arranged outside the heavy siltation area along the Hualili River and the Zhonggan River inlet, to reduce the wind wave intensity inside the shoal and guide the inflow to flow southward, slow down the direct inflow of the inflow water body carrying a large amount of sediment and external pollutants into the lake body, and reduce the adverse effects of the high-pollution inflow; the No. 3 shoal is arranged perpendicular to the prevailing wind direction outside the heavy siltation area in the northwest corner of the lake to reduce the wind wave intensity in the northwest corner of the lake; the No. 5 shoal group is arranged along the edge of the heavy siltation area of the lake to reduce the wind wave intensity of the heavy siltation area, while blocking the lake flow outside the heavy siltation area from crossing the area, and reducing the exchange intensity of the water body in the heavy siltation area and the external water body; the No. 4 shoal group works together to reduce the wind wave intensity of the Beigan River inlet, limit the flow of the Beigan River inflow carrying a large amount of sediment and external pollutants to the northeast heavy siltation area, guide the Beigan River inflow to flow eastward, and reduce the intensity of its southward diffusion; according to Figure 8 the arrangement scheme, the Ecolake model is used to carry out three-dimensional lake flow simulation of the lake under the southeast prevailing wind, and the vertical average lake flow simulation result is shown in Figure 9 .

[0075] According to the simulation results of lake flow, based on the layout principle of lake bottom trap: the cross section of the water flow channel, the lake bottom trap is set on the water flow channel between the underwater shoal, according to the hydraulic design: L≥1.25×V×H / D to determine the size of the trap; According to the simulation results of lake flow, considering the instantaneous nature of lake flow and extreme working conditions, the flow velocity V=3cm / s is taken; According to the water level and bottom elevation of Dike Lake, H=2.0m is taken; According to the investigation results of Taihu Lake and Dike Lake, two typical shallow lakes, D=0.5cm / s is taken; Comprehensive calculation, the width of single flow mud capture trap is 15m, L=15m is taken; Its engineering layout is shown in Figure 10 .

[0076] The lake bottom trap is mainly underwater bottom excavation, and the underwater shoal construction method is mainly earth filling. During the construction, the required trap shape and size are accurately excavated by water excavator and other equipment, and the hard soil is transported to the designated area by mud ship for throwing and filling to form underwater shoal. In order to ensure the construction accuracy, GPS positioning technology is used to accurately measure the construction area to ensure the accuracy and uniformity of throwing and filling. Considering that the two construction methods do not interfere with each other in technology and can cooperate with each other, synchronous construction can be considered. While the water excavator is excavating the flow mud capture trap, the mud ship can transport the excavated hard soil to the underwater shoal engineering area for throwing and filling, fully utilizing resources, improving construction efficiency and shortening construction period. In order to ensure construction accuracy and reduce the adverse effects of excavation and throwing and filling, protective piles and positioning piles are set according to GPS positioning technology before construction. These pile positions can accurately indicate the range and position of the construction area, providing accurate reference for construction.

[0077] After the construction is completed, the underwater shoal and flow mud capture trap elevation are measured every month in the first year to evaluate the stability of the underwater shoal and the siltation progress of the flow mud capture trap, and the corresponding underwater shoal reinforcement measures and lake bottom trap cleaning plan are made according to the evaluation results. In the later period, the wind wave intensity and elevation are measured every half year to adjust the underwater shoal maintenance and lake bottom trap cleaning plan in real time, ensuring that the water power control measures can play a long-term effective role. Due to the small water depth and weak wave intensity on the top of the underwater shoal, reed and cattail and other emergent plants can be planted on the top of the shoal, with a planting density of 30-40 plants / m2, a density ratio of 5:1, using root system to reinforce the shoal structure, and reducing the nitrogen and phosphorus concentration in water body through plant absorption.

[0078] Due to the influence of wind wave shoaling effect caused by Dike Lake topography reshaping, the wind wave intensity of Dike Lake will decrease, which will lead to the weakening of sediment release, thereby improving water quality. Taking the annual meteorological and water level changes of Dike Lake in 2020 as input, the wind wave improvement effect of different areas after the setting of underwater shoal and the improvement of nitrogen and phosphorus content in water body are evaluated. The monthly average effective wave height and the corresponding wave height reduction rate of different areas before and after the implementation of underwater shoal are shown in Table 1 and Figure 1. Figure 11 ​Figure 12 As shown; overall, different regions ( Figure 7 a) The effective wave height reduction rate varies considerably throughout the year. The wave reduction is least significant in July and August because the water level is high during these months, and the underwater shoals are located in deeper waters, resulting in a smaller wave attenuation rate due to the shallow water effect. Although the water level is low from December to January, the prevailing winds are west-northwest and north-northwest, so the wave attenuation rate is also relatively small in all waters except for Area 5. The periods with the largest wave attenuation rates are mainly March and April and November, when the water level is low and the prevailing winds are east-southeast.

[0079] according to Figure 5 and Figure 6 The correlation between wind and waves in Gehu Lake and suspended solids and nutrients can be further assessed to indirectly calculate the improvement of the water environment in different water areas after implementation. The projected improvement of the water environment in areas 3, 5, and 6 in 2020 is as follows: Figure 13 As shown, overall, the levels of suspended solids, particulate nitrogen, and phosphorus in the water all improved to some extent after the wind and wave conditions were improved in different areas. The improvement in suspended solids concentration was particularly significant, especially in the heavily silted No. 5 water area, which is closely related to the layout of the internal pollution control plan. This area provides good protection against wind and waves from different directions. Since particulate phosphorus accounts for a higher proportion of the water in Gehu Lake than particulate nitrogen, the improvement in particulate phosphorus content was more pronounced. With the decrease in suspended solids concentration and wind and wave intensity, water transparency improved, vegetation damage lessened, and the growth environment for aquatic vegetation in shallow water areas (such as underwater shoals and nearshore shallow water areas) was significantly improved, which is conducive to the recovery of aquatic vegetation in local areas. Along with the recovery of aquatic vegetation and the reduction in wind and waves, the content of particulate nutrients in the water decreased, the water purification capacity was improved, and the water quality gradually improved.

[0080] Additionally, it should be noted that components not described in detail in this article are existing technologies.

[0081] It is important to note that the construction and arrangement of the application shown in the various examples presented are illustrative only. Although only a few embodiments have been described in detail in this disclosure, those skilled in the art who review this disclosure will readily appreciate that many modifications are possible (e.g., variations in sizes, dimensions, structures, shapes and proportions of the various elements, values of parameters, mounting arrangements, use of materials, colors, orientations, etc.) without materially departing from the novel teachings and advantages of the subject matter described herein. For example, elements shown as integrally formed can be constructed of multiple parts or elements, the position of elements can be reversed or otherwise varied, and the nature or number of elements can be altered or varied. Other substitutions, modifications, changes and omissions can also be made in the design, operating

[0082] Also, to provide a concise description of the exemplary embodiments, not all features of an actual implementation can be described (that is, not all implementations can include all of the features described or optional implementations can include only a subset of the features described).

[0083] It will be appreciated that in the development of any actual implementation, as in any engineering or design project, numerous implementation-specific decisions can be made. Such development efforts can inevitably lead to modifications, not all of which can be wholly incorporated into this disclosure, but which might be so incorporated into the disclosure after their incorporation, without departing from the scope of the present disclosure. Additionally, skills in the art of the present disclosure will appreciate that such development efforts might reasonably vary from implementation to implementation, depending, without limitation, on such

[0084] It should be noted that the above examples are merely used to illustrate the technical solutions of the present application, rather than limit the present application. Although the present application is described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can be modified or replaced equivalently without departing from the spirit and scope of the present application, and all should be covered in the scope of the claims of the present application.

Claims

1. A long-term control method for internal pollution in a shallow lake based on water power operation, suitable for shallow lakes with a water depth of ≤2 m, a bottom sediment thickness of ≥0.3 m, TN of ≥1500 mg / kg, and TP of ≥600 mg / kg, characterized in that: The method comprises the following steps: S1: Collecting historical hydrological, meteorological and sediment data of the target lake; S2: Deploying a multi-parameter sensor monitor in the target lake to monitor wind speed, wind wave, suspended matter concentration, dissolved oxygen and water body nitrogen and phosphorus content simultaneously at high frequency, and combining Sentinel-2 or Landsat-8 satellite images to inversely calculate large-scale chlorophyll a concentration and water turbidity; S3: Calibrating the sensor monitor data and satellite images by Kalman filtering algorithm to construct a lake environmental parameter space-time database, and training a wind wave, suspended matter concentration and nitrogen and phosphorus nutrient content prediction model by XGBoost algorithm; S4: Simulating the effective wave height of the lake by the SWAN wind wave model, and combining the sediment survey data to screen the areas with a sediment thickness of ≥0.3 m, TN of ≥1500 mg / kg and TP of ≥600 mg / kg as the sediment resuspension hot spot areas; S5: Designing underwater shoals outside the hot spot areas, with a top elevation of 10-20 cm below the normal water level of the lake, a top width of 20-50 m, a bottom width of 100-160 m and a slope ratio of 1:50; S6: Simulating the water flow transport path based on a three-dimensional lake flow model, and deploying lake bottom traps in the hydraulic passages between the underwater shoals; S7: Combining GPS positioning technology, and constructing by a long-arm excavator, and using the hard earthwork excavated by the trap for the heaping of the underwater shoal; S8: Regularly monitoring the sediment deposition amount in the trap, and removing the sediment in the areas with TN of ≥1800 mg / kg and TP of ≥900 mg / kg by a cutter suction dredger once or twice a year.

2. The long-term control method of water power manipulation-based in-situ pollution in a shallow lake according to claim 1, characterized in that: The data collected in step S1 includes wind speed, wind direction, water level, sediment thickness, total nitrogen, total phosphorus and organic matter content.

3. The long-term control method of water power operation based on shallow lake in-situ pollution according to claim 1 or 2, characterized in that: The input parameters of the wind wave model in step S4 include the prevailing wind field, wind speed and model spatial resolution.

4. The long-term control method of water power manipulation-based in-situ pollution in a shallow lake according to claim 3, characterized in that: The method for determining the prevailing wind field is as follows: according to the wind field data of the lake periodic weather station for more than or equal to 5 years, the frequency distribution of each wind direction is counted, and the wind direction with the top three proportion frequencies is determined as the prevailing wind direction; The method for determining the wind speed is as follows: PIII analysis is performed on the wind speed value to determine the wind speed values corresponding to the 10%, 25% and 50% guarantee rates; The method for determining the model spatial resolution is as follows: the spatial resolution is more than 100 m×100 m.

5. The long-term control method of water power manipulation based on shallow lake in-situ pollution according to claim 3, characterized in that: The layout of the underwater shoal in step S5 should meet the following conditions: the shoal trend is perpendicular to the prevailing wind direction or / and the water wave direction, the interval between adjacent shoals is <200 m, and the water depth of the shoal top is ≤0.2 m.

6. The long-term control method of water power manipulation-based in-situ pollution in a shallow lake according to claim 5, characterized in that: The three-dimensional lake flow model in step S6 is simulated according to the following method: Taking the lake flow field, water depth and trap layout as input values, the particle settling path is predicted and the high-pollution sediment aggregation probability graph is output, then a reward function including the capture efficiency and construction cost is designed based on the probability graph, and the trap width L and depth H are iteratively optimized by the Q-learning algorithm.

7. The long-term control of internal pollution in shallow lakes based on hydrodynamic manipulation according to claim 6, characterized by the fact that: When the trap width L and depth H are iteratively optimized by the Q-learning algorithm, the following formula should be met: L≥1.25×V×H / D; wherein, L is the trap width; V is the lake bottom horizontal flow velocity; H is the trap depth; D is the particle settling velocity.

8. The long-term control method of water power manipulation based on shallow lake in-situ pollution according to claim 6, characterized in that: In step S7, the error of the trap excavation depth is ≤±10 cm, and the depth is ≥3 m; The error of the shallow fill slope is ≤±5%; The suspended matter diffusion range during construction is ≤500 m.

9. The long-term control of internal pollution in shallow lakes based on hydrodynamic manipulation according to claim 8, characterized by the fact that: In step S8, the dredging frequency is dynamically adjusted according to the trap deposition rate.

10. The long-term control of internal pollution in shallow lakes based on hydrodynamic manipulation according to claim 9, characterized by the fact that: Planting emergent plants on the top of the shoal, planting density is 30-40 plants / m 2 .

Images