Sediment reduction and deposition regulation method for backwater area of cascade reservoir drawdown period

Abstract

The application discloses a kind of cascade reservoir drawdown period variable backwater area silt reduction scheduling methods, it is related to reservoir scheduling operation and water and sediment control technical field, the method first determines the range of silt reduction river section and bed sand starting average flow velocity, combined with backwater end position Quantitative scheduling start flow and reservoir water level;Establish the reservoir water level daily average drop threshold range considering silt scouring intensity and bank stability;Real-time monitoring hydrological data and forecast, according to the self-adaptive switching of hydrodynamic condition Single reservoir or cascade joint scheduling mode, according to the principle of minimum power loss distribution flow increment;Control reservoir water level drawdown rate during scheduling, for self-adaptive adjustment to riverbed coarsening, to determine the effectiveness of scheduling with cumulative scheduling duration.The application constructs a whole-process standardized scheduling system, realizes the efficient transport of silt accumulation during drawdown period, and considers geological safety and reservoir comprehensive benefit, and is suitable for cascade reservoir group with different basins and different bed sand characteristics.

Description

Technical Field

[0001] This invention relates to the field of reservoir scheduling and operation and water and sediment control technology, and in particular to a method for sediment reduction scheduling in the backwater zone during the drawdown period of a cascade reservoir. Background Technology

[0002] Reservoirs offer irreplaceable comprehensive benefits in flood control, power generation, navigation, water resource utilization, and ecological protection. Most large and medium-sized rivers in my country have formed cascade reservoir systems. However, reservoir impoundment significantly alters the water and sediment conditions of natural river channels. Rising water levels in the reservoir area slow water flow, leading to substantial siltation. The variable backwater zone, serving as a transitional area between the natural river channel and the reservoir's perennial backwater zone, exhibits complex and variable water and sediment conditions. Coarse-grained sediment entering the reservoir during the flood season easily accumulates here and is difficult to transport naturally. Long-term accumulation can cause problems such as loss of effective reservoir capacity, navigational obstructions due to shallow shoals, and rising flood levels, severely restricting the realization of the reservoir's comprehensive benefits.

[0003] In my country, river sediment transport is highly concentrated during the flood season, with large amounts of sediment accumulating in fluctuating backwater areas. During the dry season, the combined effects of upstream reservoir impoundment and a sharp decrease in natural inflow significantly reduce the hydrodynamic intensity of these backwater areas, preventing the effective transport of flood-accumulated sediment to the perennial backwater area, thus exacerbating the sedimentation problem year by year. Currently, reservoir sediment management mainly falls into two categories: engineering measures and regulatory measures. Engineering measures, including mechanical dredging and the installation of sediment-trapping structures, suffer from drawbacks such as high costs, long construction periods, and potential damage to the aquatic ecosystem. Reservoir-regulated sediment discharge, with its advantages of low cost and the ability to operate routinely, has become the mainstream technology for sediment management.

[0004] In existing technologies, research on reservoir sediment management mainly focuses on the flood season. For example, Chinese patent CN111723995A discloses an optimized sediment management method for reservoirs during the flood season under the joint operation of cascade reservoirs. This method is designed for high sediment concentration and large flow conditions during the flood season, with density flow sediment discharge and scouring along the course as its core logic. However, there are fundamental differences in sediment movement patterns between the flood season and the drawdown period, and the management method for the flood season cannot be directly applied to the drawdown period. Regarding the issue of sediment reduction during the drawdown period, Xu Quanxi et al. proposed specific control indicators for the Three Gorges Reservoir in "Research on Sediment Reduction Management Control Indicators of the Tail River Section after 175m Impoundment of the Three Gorges Reservoir" (Acta Geographica Sinica, 2021). However, this method is based on empirical values ​​derived from the specific bed sediment composition and channel morphology of the Three Gorges Reservoir, and has not formed a universal method applicable to reservoirs with different bed sediment characteristics in different basins. In recent years, the Yangtze River Water Resources Commission has attempted coordinated operation of cascade reservoirs in the lower reaches of the Jinsha River during the Three Gorges Reservoir's silt reduction scheduling. However, this practice is temporary and based on experience, and no clear scheduling start-up and switching conditions, flow allocation optimization mechanisms, or scheduling effectiveness assessment standards have been established.

[0005] In addition, the existing technology has the following obvious defects: First, it does not specifically distinguish between the difference between the variable backwater area and the ordinary reservoir tail section, and does not accurately delineate the dispatching section in combination with the dynamic coverage of backwater; Second, the reservoir water level drawdown rate only considers the scouring effect and does not take into account the stability of the reservoir bank slope, which can easily cause geological disasters such as landslides and collapses; Third, single reservoir dispatching is completely ineffective when natural water inflow is insufficient, and conventional cascade joint dispatching lacks standardized procedures, resulting in strong subjectivity and significant loss of benefits; Fourth, there is a lack of unified quantitative judgment standards for dispatching effectiveness, making it impossible to standardize dispatching acceptance work.

[0006] Therefore, there is an urgent need to propose a standardized method for sediment reduction and scheduling in the variable backwater area during the drawdown period of cascade reservoirs. This method would guide each reservoir to carry out sediment reduction and scheduling in the variable backwater area during the drawdown period, flushing and transporting the sediment accumulated in the river section to the reservoir's perennial backwater area as much as possible, restoring the reservoir's effective storage capacity, and thus ensuring the full realization of the reservoir's comprehensive benefits. Summary of the Invention

[0007] The purpose of this invention is to overcome the above-mentioned shortcomings in the existing technology and provide a method for sediment reduction scheduling in the variable backwater area of ​​cascade reservoirs during the drawdown period. This method combines the water and sediment movement law of the variable backwater area, the stability constraints of the reservoir bank slope, and the joint regulation and storage capacity of cascade reservoirs to establish a full-process quantitative and standardized scheduling system. This achieves efficient transport of sediment during the drawdown period, effectively improves the sediment distribution of the terminal reservoirs, and takes into account flood control, power generation, navigation, and geological safety of the reservoir area. It is applicable to cascade reservoir groups with different watersheds and different bed characteristics.

[0008] To achieve the above-mentioned technical features, the objective of this invention is as follows: a method for sediment reduction and scheduling in the fluctuating backwater zone during the drawdown period of a cascade reservoir, comprising the following steps: Step 1: Based on the operational characteristics and sediment deposition patterns of the terminal reservoirs in the cascade reservoir system, determine the range of the variable backwater section in which sediment reduction operations will be carried out. Step 2: Based on the characteristics of the bed sediment composition in the fluctuating backwater section, determine the average initiation velocity of the bed sediment in that section. ; Step 3: Combine the location of the backwater end corresponding to different reservoir water levels, the delineated range of the variable backwater zone, and the average velocity of bed sediment initiation. Determine the starting flow rate corresponding to the sediment reduction scheduling. With the start-up reservoir water level This serves as the initiation condition for scheduling; Step 4: Based on the correlation between the reservoir water level drawdown rate and the intensity of sediment scouring in the fluctuating backwater area, and the impact of the reservoir water level drawdown rate on the stability of the reservoir bank slopes, determine the daily average water level drop threshold range during the sediment reduction and mitigation period. ; Step 5: During the drawdown period of the terminal reservoir, monitor the hydrological data of each reservoir area in the cascade reservoir group in real time, and forecast the flow and water level changes of the terminal reservoir in the next few days; Step 6: Based on monitoring and forecast data, determine whether the hydrodynamic conditions of the change backwater area meet the activation conditions; if they do, activate the single-reservoir sediment reduction scheduling of the terminal reservoir; if they do not, activate the joint sediment reduction scheduling of the cascade reservoirs, and increase the hydrodynamics of the terminal reservoir by increasing the outflow of the upstream cascade reservoirs. Step 7: After initiating the scheduling, control the outflow from the terminal reservoir to be greater than the inflow, so that the average daily drop in reservoir water level remains within the threshold range. The sediment accumulated in the early stage of the change backwater area will be transported to the perennial backwater area of ​​the reservoir; Step 8: When the average daily drop in reservoir water level cannot be maintained within the threshold range or the reservoir water level drops to the preset target water level. Scheduling will terminate when the cumulative scheduling time is reached; T Greater than or equal to the preset minimum scheduling duration If the silt reduction and dispatching is completed, then the current silt reduction and dispatching operation is deemed to be finished.

[0009] Preferably, step 3 includes: Step 31: Based on the location of the backwater endpoint corresponding to different reservoir water levels, determine the lowest reservoir water level at which the backwater can cover the river section of the designated variable backwater zone. ; Step 32, Combine the average flow velocity of the bed sand at startup Determine the start traffic for scheduling. With the start-up reservoir water level And satisfy .

[0010] Preferably, step 4 includes: Step 41: Based on the correlation between the reservoir water level drawdown rate and the sediment scouring intensity in the fluctuating backwater zone, determine the lower limit of the average daily reservoir water level drop that can improve the sediment scouring effect. ; Step 42: Determine the upper limit of the average daily drop in reservoir water level, using the stability of the reservoir bank slope as a constraint. ; Step 43, combine with the lower limit and upper limit The final daily average drop threshold range of the reservoir water level was determined. .

[0011] Preferably, step 6 includes: Step 61: When the water level in the terminal reservoir drops to... If the real-time flow rate of the control hydrological station in the backwater area changes... Initiate the sediment reduction scheduling for single reservoirs at the end of the water supply chain; Step 62: When the water level in the terminal reservoir drops to... At that time, if Furthermore, the combined downstream release of water from the upstream cascade reservoirs can make Then, the joint silt reduction scheduling of cascade reservoirs will be initiated; Step 63: When the water level in the terminal reservoir drops to... At that time, if Furthermore, even after the upstream cascade reservoirs jointly released water, it was still unable to [make the situation more manageable]. If not, this silt reduction scheduling will not be initiated.

[0012] Preferably, step 8 includes: Step 81: When the reservoir water level has not yet dropped to the preset target water level However, the daily average drop in reservoir water level could not be maintained at that level. If the interval is within the specified range, terminate this scheduling. Step 82: When the average daily drop in reservoir water level can still be maintained at The water level is within the designated range, but it has already dropped to the preset target level. When the time comes, terminate this scheduling; Step 83: If the cumulative scheduling time The sediment reduction and mitigation operation was deemed to have been effectively completed; if It was determined that the current sediment reduction and mitigation operation had not been completed.

[0013] Preferably, the parameters monitored in real time in step 5 include the flow rate of the main hydrological stations in each reservoir area, the water level of each reservoir, the sediment content of the fluctuating backwater area, and the displacement data of the reservoir bank slope.

[0014] Preferably, during the joint silt reduction scheduling of cascade reservoirs, the incremental discharge flow is allocated in order of increasing power generation benefit loss corresponding to the unit water replenishment volume of each upstream reservoir.

[0015] The present invention has the following beneficial effects: 1. Based on the operational characteristics and sediment deposition patterns of the terminal reservoirs in a cascade reservoir system, this invention identifies the range of fluctuating backwater sections in the river that require sediment reduction scheduling. Furthermore, considering factors such as the bed sediment composition characteristics of these sections, the influence range of the reservoir backwater, the relationship between the reservoir water level drawdown rate and the sediment scouring intensity of the fluctuating backwater sections, and the impact of the reservoir water level drawdown rate on the stability of the reservoir bank slopes, this invention determines key indicators such as the initiation conditions for sediment reduction scheduling in the fluctuating backwater areas of different terminal reservoirs and the daily average drop threshold range of the reservoir water level, making sediment reduction scheduling more targeted.

[0016] 2. This invention proposes a standardized method for sediment reduction scheduling in the backwater zone during the drawdown period of cascade reservoirs. By objectively and quantitatively defining indicators such as the scheduling start flow and reservoir water level, the average daily drop in reservoir water level during the scheduling period, and the minimum duration of scheduling, the sediment reduction scheduling process is not only more objective and consistent, but the quantified indicators also make the operation simpler and more convenient.

[0017] 3. Starting from the laws of sediment movement in reservoirs and the optimization of reservoir scheduling technology, this invention, based on the joint scheduling of cascade reservoirs from the upper to the lower reaches of a river, enhances the sediment transport capacity of the fluctuating backwater area of ​​the terminal reservoir during the drawdown period, and washes and transports the sediment accumulated in the river section to the perennial backwater area as much as possible. This provides technical support for improving the sediment distribution of terminal reservoirs and promotes the development of reservoir sediment scheduling theory and technology.

[0018] In summary, the method described in this invention, considering the supporting role of cascade reservoir joint operation in sediment reduction and mitigation at the end reservoirs, proposes a standardized method for sediment reduction and mitigation in the fluctuating backwater zone during the drawdown period of the end reservoirs. This method first clarifies the range of fluctuating backwater zones in different end reservoirs that require sediment reduction and mitigation operations, and then determines key indicators such as the initiation conditions for sediment reduction and mitigation operations and the daily average drop threshold range of reservoir water levels. This makes the invention more targeted and operable, ensuring that different end reservoirs achieve good sediment reduction and mitigation effects, and facilitating its application to reservoirs in different river basins. Attached Figure Description

[0019] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0020] Figure 1 This is a flowchart of the method described in this invention. Detailed Implementation

[0021] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the scope of the invention.

[0022] Example 1: like Figure 1 As shown, this invention provides a method for sediment reduction and scheduling in the fluctuating backwater zone during the drawdown period of a cascade reservoir. The method includes the following steps: Step 1. Based on the operational characteristics and sediment deposition patterns of the terminal reservoirs in a cascade reservoir system, determine the range of the variable backwater river section where sediment reduction operations will be carried out; Step 2. Based on the characteristics of the bed sediment composition in the backwater zone of the terminal reservoir, this embodiment can use Zhang Ruijin's formula to calculate and determine the average initiation velocity of the bed sediment in this river section. ;in, ; in, Because of the water depth, The median particle size of the bed sand is... It is heavily soiled with silt. The specific gravity of water; For different bed sand compositions, appropriate calculation formulas can be selected based on the actual situation; Step 3. Based on the location of the backwater end corresponding to different reservoir water levels, the defined range of the variable backwater zone, and the average velocity of bed sediment initiation in that river section. Determine the starting flow rate corresponding to the sediment reduction scheduling. With the start-up reservoir water level This serves as the initiation condition for scheduling; Step 4. Based on the correlation between the reservoir water level drawdown rate and the sediment scouring intensity in the fluctuating backwater area, and the impact of the reservoir water level drawdown rate on the stability of the reservoir bank slope, determine the daily average water level drop threshold range during the sediment reduction and siltation control period for this river section. ; Step 5. During the drawdown period of the terminal reservoir, monitor in real time the flow rate of the main hydrological stations in each reservoir area of ​​the cascade reservoir group, the water level of each reservoir, the sediment content of the fluctuating backwater area, and the displacement data of the reservoir bank slope. Step 6. Based on real-time monitored hydrological information and reservoir water level information, this embodiment uses a one-dimensional water-sediment coupling model to predict and obtain data on flow rate and reservoir water level changes in the terminal reservoir over a certain period of time in the future; Step 7. Based on the monitored and forecasted changes in flow and reservoir water level, determine whether the hydrodynamic conditions of the backwater area of ​​the terminal reservoir meet the activation conditions. If they do, initiate the single-reservoir sediment reduction scheduling of the terminal reservoir. If they do not meet the conditions, initiate the joint sediment reduction scheduling of the cascade reservoirs. Allocate the incremental discharge flow according to the order of power generation benefit loss corresponding to the unit water replenishment of each upstream reservoir from low to high. Increase the discharge flow of the upstream cascade reservoirs to enhance the hydrodynamics of the terminal reservoir and make it meet the activation conditions. Step 8. After initiating the sediment reduction and mitigation scheduling of the backwater zone of the terminal reservoir, control the outflow from the terminal reservoir to be greater than the inflow, so that the average daily drop in reservoir water level remains within the threshold range. Within, to enhance the sediment transport capacity of this section of the river at the end of the reservoir, the sediment deposited in the early stage of the fluctuating backwater area is transported to the reservoir's perennial backwater area; when a coarsening layer is detected in the riverbed of the fluctuating backwater area, in Increase the average daily drop in reservoir water level within the interval to disrupt the coarsening layer and enhance the sediment initiation effect; Step 9. Based on the multi-objective requirements of actual scheduling, when the average daily decline in the water level of the terminal reservoir cannot be maintained within the threshold range... Between, or when the reservoir water level drops to the preset target water level. When the time comes, terminate this scheduling; Step 10. Calculate the duration of the terminal reservoir scheduling.T If the cumulative scheduling time T Greater than or equal to the preset minimum scheduling duration If T < If not, then the current sediment reduction and mitigation operation is deemed incomplete.

[0023] Furthermore, step 3 is implemented as follows: Step 31. Based on the location of the backwater endpoint corresponding to different reservoir water levels, determine the lowest reservoir water level at which the backwater can cover the river section of the designated variable backwater zone. ; Step 32. Combine the average velocity of bed sediment initiation in the fluctuating backwater section. Determine the starting flow rate corresponding to the sediment reduction scheduling. With the start-up reservoir water level And satisfy This serves as the initiation condition for scheduling.

[0024] Furthermore, step 4 is implemented as follows: Step 41. Based on the correlation between the reservoir water level drawdown rate and the sediment scouring intensity in the fluctuating backwater zone, determine the lower limit of the average daily water level drop that can improve the sediment scouring effect. ; Step 42. Determine the upper limit of the average daily drop in reservoir water level, using the stability of the reservoir bank slope as a constraint. ; Step 43. Combine with the lower limit and upper limit The final daily average drop threshold range of the reservoir water level was determined. .

[0025] Furthermore, step 7 is implemented as follows: Step 71. When the water level of the terminal reservoir drops to... If the real-time flow rate of the control hydrological station in the backwater area changes... Then, the sediment reduction scheduling of the terminal reservoir will be initiated. Step 72. When the water level in the terminal reservoir drops to... At that time, if Furthermore, the combined downstream release of water from the upstream cascade reservoirs can make Then, the joint silt reduction scheduling of cascade reservoirs will be initiated; Step 73. When the water level in the terminal reservoir drops to... At that time, if Furthermore, even after the upstream cascade reservoirs jointly released water, it was still unable to [make the situation more manageable]. If not, this silt reduction scheduling will not be initiated.

[0026] Furthermore, step 9 is implemented as follows: Step 91. Based on the multi-objective requirements of actual scheduling, the average daily drop in water level of the terminal reservoirs is calculated as follows: The water level continued to drop, but had not yet reached the preset target level. However, the daily average drop in reservoir water level could not be maintained at that level. If this occurs, terminate the current scheduling. Step 92. Based on the multi-objective requirements of actual scheduling, the average daily drop in water level of the terminal reservoirs is calculated as follows: The water level continues to drop, and the average daily decrease in the reservoir level can still be maintained at [a certain level]. The water level remained between [a certain point] and [a certain point], but dropped to the preset target level. When the time comes, the current scheduling will be terminated.

[0027] Furthermore, step 10 is implemented as follows: Step 101. Calculate the duration of the terminal reservoir scheduling. T If the cumulative scheduling time T Greater than or equal to the preset minimum scheduling duration If so, the sediment reduction and mitigation scheduling is deemed to have been effectively completed. Step 102. Calculate the duration of the terminal reservoir scheduling. T If the cumulative scheduling time T Less than the preset minimum scheduling time If not, then the current sediment reduction and mitigation operation is deemed incomplete.

[0028] Example 3: Taking the cascade reservoirs in the Y basin as an example, we carried out sediment reduction scheduling in the backwater area during the drawdown period of the cascade reservoirs.

[0029] Step 1. Based on the operational characteristics and sediment deposition patterns of Reservoir A, the terminal reservoir in the Y-basin cascade reservoirs, the range of the variable backwater section to be carried out for sediment reduction operations in Reservoir A is determined to be the S10 to S40 section.

[0030] Step 2. Based on the bed sediment composition characteristics of the S10-S40 section of the river segment in the fluctuating backwater area of ​​Reservoir A, the average initiation velocity of the bed sediment in this river segment is calculated using Zhang Ruijin's formula. It is approximately 0.3 m / s.

[0031] Step 3. Based on the location of the return water end corresponding to different reservoir water levels in Reservoir A, determine the lowest reservoir water level at which the return water can cover the designated sections S10 to S40. It is 110m; combined with the average flow velocity of the bed sand at startup. =0.3m / s, and satisfies The final reservoir water level for sediment reduction scheduling was determined. =120m, startup flow =3000m 3 / s serves as the initiation condition for sediment reduction scheduling in the fluctuating backwater area of ​​Reservoir A during the drawdown period.

[0032] Step 4. Based on the correlation between the reservoir water level drawdown rate and the intensity of sediment scouring in the fluctuating backwater area, and the impact of the reservoir water level drawdown rate on the stability of the reservoir bank slopes, determine the daily average water level drop threshold range during the sediment reduction and siltation control period for this river section. =0.4m / d~0.7m / d; among which, the lower limit of the average daily decrease that can improve the sediment flushing effect. =0.4m / d, the upper limit of the daily average drop constrained by the stability of the reservoir bank slope. =0.7m / d.

[0033] Step 5. During the drawdown period of Reservoir A from March to May, monitor in real time the flow rate, water level of each reservoir, sediment content of the fluctuating backwater area, and bank slope displacement data of the main hydrological stations in the cascade reservoir group of the Y basin.

[0034] Step 6. Based on real-time monitoring of hydrological information and reservoir water level information, a one-dimensional water-sediment coupling model is used to predict and obtain the flow and reservoir water level change data of each major hydrological station in Reservoir A for the next few days.

[0035] Step 7. Based on real-time monitoring and forecast information, on April 9th, when the water level of Reservoir A drops to 120.3m, the real-time flow rate of the control hydrological station in the backwater area will be adjusted. =2800m 3 / s, less than the startup traffic =3000m 3 / s, but through the joint scheduling of upstream cascade reservoirs, the incremental discharge flow was allocated according to the order of power generation benefit loss corresponding to the unit water replenishment volume of each upstream reservoir from low to high, so that the flow in the backwater area of ​​Reservoir A reached 3200m³ on April 10. 3 / s, the reservoir water level dropped to 120.1m, meeting the start-up conditions; during the scheduling period, the daily flow variation of each reservoir was controlled to not exceed 500m. 3 Therefore, on April 10, the joint silt reduction scheduling of the cascade reservoirs was initiated.

[0036] Step 8. After the scheduling was initiated on April 10, the outflow from Reservoir A was controlled to be greater than the inflow, so that the average daily drop in reservoir water level was maintained within the range of 0.4 m / d to 0.7 m / d, thereby improving the sediment transport capacity of the fluctuating backwater section and transporting the previously accumulated sediment to the reservoir's perennial backwater area. No coarsening layer was detected in the riverbed during this scheduling period, and the reservoir water level drawdown rate was not adjusted.

[0037] Step 9. Based on the multi-objective requirements of actual scheduling during the drawdown period, after Reservoir A has been continuously decreasing its water level by an average daily rate of 0.4 m / d to 0.7 m / d for 6 days, due to the large inflow, continuing to maintain this rate of decrease would require opening the gates to release water, which would significantly affect the overall benefits of the reservoir. The average daily rate of decrease in water level could not be maintained within the threshold range, so this scheduling is terminated.

[0038] Step 10. Cumulative scheduling duration for this scheduling session T =6d, greater than the preset minimum scheduling time T min =5 days, therefore, the sediment reduction and siltation reduction operation is considered to have been effectively completed. The operation lasted from April 10th to April 16th, a total of 6 days. During the operation, the water level of Reservoir A dropped from 120.1m to 117.5m, which is higher than the preset target water level. =108m, the average daily drop in reservoir water level is 0.43m / d, which is within the threshold range of 0.4m / d to 0.7m / d.

[0039] It should be noted that the above examples are merely specific embodiments of the present invention, and the present invention is not limited to these embodiments. All similar variations related to these embodiments are within the protection scope of the present invention. All modifications that can be directly derived or conceived by those skilled in the art from the disclosure of the present invention should fall within the protection scope of the present invention.

Claims

1. A method for sediment reduction and scheduling in the backwater zone during the drawdown period of a cascade reservoir, characterized in that, Includes the following steps: Step 1: Based on the operational characteristics and sediment deposition patterns of the terminal reservoirs in the cascade reservoir system, determine the range of the variable backwater section in which sediment reduction operations will be carried out. Step 2: Based on the characteristics of the bed sediment composition in the fluctuating backwater section, determine the average initiation velocity of the bed sediment in that section. ; Step 3: Combine the location of the backwater end corresponding to different reservoir water levels, the delineated range of the variable backwater zone, and the average velocity of bed sediment initiation. Determine the starting flow rate corresponding to the sediment reduction scheduling. With the start-up reservoir water level This serves as the initiation condition for scheduling; Step 4: Based on the correlation between the reservoir water level drawdown rate and the intensity of sediment scouring in the fluctuating backwater area, and the impact of the reservoir water level drawdown rate on the stability of the reservoir bank slopes, determine the daily average water level drop threshold range during the sediment reduction and mitigation period. ; Step 5: During the drawdown period of the terminal reservoir, monitor the hydrological data of each reservoir area in the cascade reservoir group in real time, and forecast the flow and water level changes of the terminal reservoir in the next few days; Step 6: Based on monitoring and forecast data, determine whether the hydrodynamic conditions of the change backwater area meet the activation conditions; if they do, activate the single-reservoir sediment reduction scheduling of the terminal reservoir; if they do not meet the conditions, activate the joint sediment reduction scheduling of the cascade reservoirs, and increase the hydrodynamics of the terminal reservoir by increasing the outflow of the upstream cascade reservoirs. Step 7: After initiating the scheduling, control the outflow from the terminal reservoir to be greater than the inflow, so that the average daily drop in reservoir water level remains within the threshold range. The sediment accumulated in the early stage of the change backwater area will be transported to the perennial backwater area of ​​the reservoir; Step 8: When the average daily drop in reservoir water level cannot be maintained within the threshold range or the reservoir water level drops to the preset target water level. Scheduling will terminate when the cumulative scheduling time is reached; T Greater than or equal to the preset minimum scheduling duration If the silt reduction and dispatching is completed, then the current silt reduction and dispatching operation is deemed to be finished.

2. The method for sediment reduction and scheduling in the backwater zone during the drawdown period of a cascade reservoir according to claim 1, characterized in that, Step 3 includes: Step 31: Based on the location of the backwater endpoint corresponding to different reservoir water levels, determine the lowest reservoir water level at which the backwater can cover the river section of the designated variable backwater zone. ; Step 32, Combine the average flow velocity of the bed sand at startup Determine the start traffic for scheduling. With the start-up reservoir water level And satisfy .

3. The method for sediment reduction and scheduling in the backwater zone during the drawdown period of a cascade reservoir according to claim 1, characterized in that, Step 4 includes: Step 41: Based on the correlation between the reservoir water level drawdown rate and the sediment scouring intensity in the fluctuating backwater zone, determine the lower limit of the average daily reservoir water level drop that can improve the sediment scouring effect. ; Step 42: Determine the upper limit of the average daily drop in reservoir water level, using the stability of the reservoir bank slope as a constraint. ; Step 43, combine with the lower limit and upper limit The final daily average drop threshold range of the reservoir water level was determined. .

4. The method for sediment reduction and scheduling in the backwater zone during the drawdown period of a cascade reservoir according to claim 1, characterized in that, Step 6 includes: Step 61: When the water level in the terminal reservoir drops to... If the real-time flow rate of the control hydrological station in the backwater area changes... Initiate the sediment reduction scheduling for single reservoirs at the end of the water supply chain; Step 62: When the water level in the terminal reservoir drops to... At that time, if Furthermore, the combined downstream release of water from the upstream cascade reservoirs can make Then, the joint silt reduction scheduling of cascade reservoirs will be initiated; Step 63: When the water level in the terminal reservoir drops to... At that time, if Furthermore, even after the upstream cascade reservoirs jointly released water, it was still unable to [make the situation more manageable]. If not, this silt reduction scheduling will not be initiated.

5. The method for sediment reduction and scheduling in the backwater zone during the drawdown period of a cascade reservoir according to claim 1, characterized in that, Step 8 includes: Step 81: When the reservoir water level has not yet dropped to the preset target water level However, the daily average drop in reservoir water level could not be maintained at that level. If the interval is within the specified range, terminate this scheduling. Step 82: When the average daily drop in reservoir water level can still be maintained at The water level is within the designated range, but it has already dropped to the preset target level. When the time comes, terminate this scheduling; Step 83: If the cumulative scheduling time The sediment reduction and mitigation operation was deemed to have been effectively completed; if It was determined that the current sediment reduction and mitigation operation had not been completed.

6. The method for sediment reduction and scheduling in the backwater zone during the drawdown period of a cascade reservoir according to claim 1, characterized in that, The parameters monitored in real time in step 5 include the flow rate of the main hydrological stations in each reservoir area, the water level of each reservoir, the sediment content of the fluctuating backwater area, and the displacement data of the reservoir bank slope.

7. The method for sediment reduction and scheduling in the backwater zone during the drawdown period of a cascade reservoir according to claim 1, characterized in that, During the joint silt reduction scheduling of cascade reservoirs, the incremental discharge flow is allocated in order of increasing power generation benefit loss corresponding to the unit water replenishment volume of each upstream reservoir.

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