Method for evaluating influence of different flow under siltation promoting dam on scouring and deposition of lower reaches of Yellow River
By dividing the river channel cross-section into multiple scour and sedimentation sections and assigning hydraulic parameters, the problem of the failure of the one-dimensional water and sediment model in the complex shoal and channel morphology of the lower Yellow River was solved, achieving a higher accuracy assessment of scour and sedimentation impacts and supporting flood control safety in the lower Yellow River channel.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- 山东菏泽黄河工程有限公司
- Filing Date
- 2026-04-15
- Publication Date
- 2026-07-10
AI Technical Summary
Existing one-dimensional water and sediment models fail to assess the impact of scouring and deposition on the lower reaches of the Yellow River due to the complex morphology of the riverbed and the resulting significant differences in lateral velocity distribution, thus affecting flood control safety.
By acquiring the lateral elevation data of the river channel cross-section, it is divided into multiple scour and deposition cross-sections. The hydraulic parameters of each scour and deposition cross-section are obtained, and the flow rate is allocated according to the hydraulic parameters. The one-dimensional water and sediment model is driven to independently calculate the time series curve of scour and deposition. Finally, the results of each scour and deposition cross-section are merged to obtain the time series curve of scour and deposition of the target river channel cross-section.
It improves the assessment accuracy under complex shoal and channel morphology, ensures the effectiveness of the one-dimensional model within its applicable boundaries, significantly enhances the assessment accuracy of the impact of silt-promoting dams on downstream river channel scouring and deposition under different flow rates, and provides reliable data for flood control scheduling.
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Figure CN122367010A_ABST
Abstract
Description
Technical Field
[0001] This application pertains to the field of river management, specifically to an assessment method for the impact of different flow rates on the scouring and silting effects of silt-promoting dam flow on the lower reaches of the Yellow River. Background Technology
[0002] Accurately assessing the impact of silt-promoting dams on the scouring and sedimentation of the lower Yellow River channel is a core prerequisite for the planning, design, and operation management of the Yellow River channel management project.
[0003] Traditional methods for assessing the impact of siltation and sedimentation on silt-promoting dams mainly rely on one-dimensional hydro-sediment models for simulation calculations. Specifically, the one-dimensional hydro-sediment model generalizes the river channel into a one-dimensional straight river segment. Then, for any point in the riverbed where scour and sedimentation occur, that point in the river channel is considered a cross-section. By calculating the difference between the total amount of sediment entering the cross-section and the total amount of sediment flowing out of the cross-section during a given time period, the change in sediment scour and sedimentation at that cross-section can be obtained. Finally, by integrating the changes in sediment scour and sedimentation at all cross-sections of the river channel, the overall total amount of scour and sedimentation and the long-term evolution trend of the river channel can be quickly calculated.
[0004] However, in actual long-term scouring and sedimentation impact assessments of silt-promoting dams, the drastic changes in the flow rate of the lower Yellow River mean that sediment-laden river water at different flow rates, after passing through the obstruction and control effects of the silt-promoting dams, will cause irregular scouring of the channel morphology downstream of the dams, resulting in the channel morphology gradually becoming more complex and variable. At this time, under the influence of the channel morphology, there are significant differences in the lateral velocity distribution across the cross-section of the downstream river channel, which leads to the failure of the one-dimensional water and sediment model scouring and sedimentation impact assessment, ultimately posing a major threat to the flood control safety of the lower Yellow River channel. Summary of the Invention
[0005] To address the problem that the complex morphology of the channel in the lower Yellow River leads to significant differences in lateral flow velocity distribution, which causes the one-dimensional water-sediment model to fail in assessing the impact of scouring and deposition, this application provides a method for assessing the impact of silt-promoting dam flow on the scouring and deposition of the lower Yellow River channel under different flow rates.
[0006] Firstly, this application provides a method for assessing the impact of silt-promoting dams on the scouring and deposition of the lower Yellow River channel under different flow rates, applicable to a river channel scouring and deposition monitoring system. The method includes:
[0007] The discharge flow of the siltation dam and the lateral elevation data of the downstream target river section are obtained, and the target river section is divided into multiple scour and siltation sections based on the lateral elevation data.
[0008] The hydraulic parameters of multiple scour and siltation sections are obtained, and the discharge flow of the siltation dam is allocated according to the hydraulic parameters of the multiple scour and siltation sections to obtain the cross-sectional flow corresponding to each of the multiple scour and siltation sections.
[0009] The cross-sectional flow rate of each of the aforementioned scour and sedimentation sections is used as a boundary condition to drive a preset one-dimensional water and sediment model to calculate the time series curve of the scour and sedimentation volume of each of the aforementioned scour and sedimentation sections.
[0010] The time-series curves of scour and sedimentation volume of each of the aforementioned scour and sedimentation sections are merged to obtain and output the time-series curve of scour and sedimentation volume of the target river section.
[0011] Optionally, the lateral elevation data consists of elevation values from multiple riverbed measuring points arranged along the width of the river channel. The elevation values are the straight-line distances from the riverbed measuring points to the water surface. The step of dividing the target river channel cross-section into multiple scour and deposition sections based on the lateral elevation data specifically includes:
[0012] The elevation values of the multiple riverbed measuring points are differentially calculated along the width of the river channel to obtain a transverse difference curve;
[0013] Identify multiple abrupt change points in the lateral difference curve;
[0014] Based on the multiple mutation points, the lateral difference curve is divided into multiple difference segments;
[0015] The multiple differential segments are restored into multiple lateral elevation segments, and the target river channel section is divided into multiple scour and deposition sections according to the multiple lateral elevation segments, wherein one lateral elevation segment corresponds to one scour and deposition section.
[0016] Optionally, identifying multiple abrupt change points in the lateral difference curve further includes:
[0017] Using the target river section as the center, obtain the lateral difference curves of multiple adjacent river sections within a preset river length range;
[0018] Multiple abrupt change points of the transverse difference curve of each adjacent river section are identified to obtain the set of abrupt change point locations for each adjacent river section.
[0019] The positions of multiple abrupt change points in the target river section are compared with the sets of multiple abrupt change point positions in the longitudinal direction of the river to obtain a set of continuous points of multiple abrupt change points in the target river section along the longitudinal direction of the river.
[0020] If the number of points in the continuous set of the first mutation point of the target river section is greater than or equal to a preset threshold, then the first mutation point is determined to be a valid mutation point, and the first mutation point is any one of the multiple mutation points.
[0021] Optionally, the hydraulic parameters include a roughness coefficient, and the process of allocating the discharge flow of the siltation-promoting dam according to the hydraulic parameters of the multiple scour and siltation sections to obtain the cross-sectional flow corresponding to each of the multiple scour and siltation sections specifically includes:
[0022] Based on the lateral elevation data, the hydraulic radii corresponding to each of the multiple scour and deposition sections are calculated;
[0023] Based on the roughness coefficient and hydraulic radius of each of the aforementioned scour and deposition cross sections, the average flow velocity of each of the aforementioned scour and deposition cross sections is calculated using the Manning formula.
[0024] Based on the ratio of the average flow velocities of each of the aforementioned scour and siltation sections, the discharge flow of the siltation-promoting dam is proportionally allocated to obtain the cross-sectional flow of each of the aforementioned scour and siltation sections.
[0025] Optionally, the step of proportionally distributing the discharge flow of the siltation-promoting dam according to the ratio of the average flow velocities of each of the scour-siltation sections to obtain the cross-sectional flow of each of the scour-siltation sections further includes:
[0026] Calculate the velocity difference between the average flow velocity of the first scour and sedimentation section and the average flow velocity of the second scour and sedimentation section, wherein the first scour and sedimentation section and the second scour and sedimentation section are any two adjacent scour and sedimentation sections among the plurality of scour and sedimentation sections.
[0027] Obtain the elevation values at the intersection point of the first scour and siltation section and the second scour and siltation section;
[0028] Based on the velocity difference between the first and second scour sections and the elevation at the junction, the momentum transfer ratio between the first and second scour sections is calculated.
[0029] Based on the momentum transfer ratio, the cross-sectional flow rates of the first scour and siltation section and the second scour and siltation section are corrected respectively.
[0030] Optionally, the step of correcting the cross-sectional flow rates of the first scour and siltation section and the second scour and siltation section according to the momentum transfer ratio further includes:
[0031] Obtain the proportion of sand particles of different sizes in a unit volume of water in the sediment-laden water flow discharged from the siltation dam;
[0032] From the preset damping coefficient table, various damping coefficients for different particle sizes can be obtained;
[0033] Based on the damping coefficients of various particle sizes, the momentum transfer correction coefficient of the current sediment-laden water flow is calculated.
[0034] The momentum transfer ratio is corrected based on the momentum transfer correction coefficient.
[0035] Optionally, the step of fusing the time-series curves of scour and sedimentation at each of the aforementioned cross-sections to obtain and output the time-series curve of scour and sedimentation at the target river cross-section specifically includes:
[0036] Based on the lateral elevation data, calculate the average lateral elevation of multiple scour and siltation sections;
[0037] The scour and siltation section with the smallest mean lateral elevation among the multiple scour and siltation sections is selected as the benchmark scour and siltation section.
[0038] Starting from the current moment, the cross-correlation coefficient between the time series curve of the scour and siltation volume of the third scour and siltation section and the time series curve of the scour and siltation volume of the reference scour and siltation section is calculated by shifting the curves one by one through historical time points. The third scour and siltation section is any one of the multiple scour and siltation sections.
[0039] If, when the third scour and siltation section is shifted to the first moment, the cross-correlation coefficient between the scour and siltation volume time series curve of the third scour and siltation section and the scour and siltation volume time series curve of the reference scour and siltation section is greater than a preset cross-correlation coefficient threshold, then the time difference between the first moment and the current moment is calculated.
[0040] The time series curve of scour and siltation volume of the third scour and siltation section is shifted forward by the time difference between the first moment and the current moment to obtain the time series shift curve of scour and siltation volume of the third scour and siltation section.
[0041] The time-series translation curves of scour and sedimentation volume of multiple scour and sedimentation sections are summed to obtain the time-series curve of scour and sedimentation volume of the target river section.
[0042] Secondly, this application provides a system for assessing the impact of silt-promoting dams on the scouring and deposition of the lower Yellow River channel under different flow rates. The system is a river channel scouring and deposition monitoring system, comprising an acquisition module, a processing module, and an output module, wherein:
[0043] The acquisition module is used to acquire the discharge flow of the siltation dam and the lateral elevation data of the downstream target river section, and to divide the target river section into multiple scour and siltation sections based on the lateral elevation data.
[0044] The processing module is used to acquire the hydraulic parameters of multiple scour and siltation sections, and allocate the discharge flow of the siltation dam according to the hydraulic parameters of multiple scour and siltation sections to obtain the cross-sectional flow corresponding to each of the multiple scour and siltation sections.
[0045] The cross-sectional flow rate of each of the aforementioned scour and sedimentation sections is used as a boundary condition to drive a preset one-dimensional water and sediment model to calculate the time series curve of the scour and sedimentation volume of each of the aforementioned scour and sedimentation sections.
[0046] The output module is used to fuse the time-series curves of scour and sedimentation of each of the scour and sedimentation sections to obtain and output the time-series curve of scour and sedimentation of the target river section.
[0047] Thirdly, this application provides an electronic device including a processor, a memory, a user interface, and a network interface. The memory is used to store instructions, the user interface and the network interface are used to communicate with other devices, and the processor is used to execute the instructions stored in the memory to cause the electronic device to perform the method as described in any one of the first aspects.
[0048] Fourthly, this application provides a computer-readable storage medium storing instructions that, when executed, perform the method described in any one of the first aspects.
[0049] In summary, one or more technical solutions provided in the embodiments of this application have at least the following technical effects or advantages:
[0050] This application first obtains the transverse elevation data of the target river section and divides the section into multiple scour-deposition sections based on the transverse elevation data. The transverse elevation data can be understood as an elevation curve formed by multiple riverbed measuring points arranged along the river width direction. The elevation value is the straight-line distance from the riverbed measuring point to the water surface. These scour-deposition sections correspond to regions in the actual river channel with varying flow velocities, water depths, and roughness, such as the main channel, transition zone, and shoal area. Then, the hydraulic parameters of each scour-deposition section are obtained, and based on these hydraulic parameters, the Manning formula is used to calculate the total discharge of the siltation dam. The flow rate is allocated so that each scour and sedimentation cross-section receives a flow rate that matches its actual flow capacity. Then, using the allocated flow rate of each scour and sedimentation cross-section as boundary conditions, the one-dimensional hydro-sediment model is driven to independently calculate the scour and sedimentation time series curve of each cross-section. Since the velocity distribution within each scour and sedimentation cross-section is relatively uniform, the one-dimensional model recovers its effectiveness within its respective applicable boundaries, thus accurately capturing the scour and sedimentation response of each region under different flow rates. Finally, the scour and sedimentation time series curves of each scour and sedimentation cross-section are merged to obtain the overall scour and sedimentation time series curve of the target river cross-section. In summary, this application decomposes a complex transversely non-uniform cross section into multiple transversely uniform sub-sections and performs flow distribution and independent simulation based on the differences in hydraulic parameters of each sub-section. This transforms the two-dimensional transverse distribution problem into the superposition of multiple one-dimensional problems, enabling the one-dimensional water and sediment model, which was originally ineffective under complex channel morphology, to regain its evaluation capability. Thus, while retaining the computational efficiency of the one-dimensional model, it significantly improves the evaluation accuracy of the impact of silt-promoting dams on downstream channel scouring and deposition under different flow rates, providing reliable data support for flood control scheduling in the lower reaches of the Yellow River. Attached Figure Description
[0051] Figure 1This is a flowchart illustrating a method for assessing the impact of silt-promoting dams on the downstream channel of the Yellow River under different flow rates, as provided in an embodiment of this application.
[0052] Figure 2 This is a schematic diagram of the structure of an assessment system for the impact of silt-promoting dams on the downstream channel of the Yellow River under different flow rates, provided in an embodiment of this application.
[0053] Figure 3 This is a schematic diagram of the structure of an electronic device provided in an embodiment of this application.
[0054] Explanation of reference numerals in the attached drawings: 1. Acquisition module; 2. Processing module; 3. Output module; 300. Electronic device; 301. Processor; 302. Communication bus; 303. User interface; 304. Network interface; 305. Memory. Detailed Implementation
[0055] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.
[0056] The current one-dimensional sediment model, when assessing scouring and deposition in river channels, first generalizes the river channel as a one-dimensional straight channel, then divides the channel into multiple continuous cross-sections along the flow direction. For any given cross-section, the one-dimensional sediment model calculates the difference between the total sediment entering and leaving the cross-section over a given period to obtain the sediment scouring and deposition variation. Finally, integrating all cross-sections yields the overall total scouring and deposition volume and long-term trend. However, in actual long-term scouring and deposition assessments of silt-promoting dams, the downstream Yellow River channel, due to the long-term water obstruction and control effects of these dams, experiences irregular scouring under varying flow rates. This leads to a gradual evolution of the channel morphology from regular to complex and variable, resulting in significant differences in lateral velocity distribution at different locations on the same cross-section. The one-dimensional sediment model, by simplifying the entire cross-section as a single uniform flow channel, cannot characterize this lateral non-uniformity, and its scouring and deposition assessment results gradually become ineffective, posing a significant threat to flood control safety.
[0057] To address the aforementioned issues, this application provides a method for assessing the impact of silt-promoting dams on the scouring and deposition of the lower Yellow River channel under different flow rates. This method is applied to a river scouring and deposition monitoring system, such as... Figure 1 As shown, the method includes steps S101 to S104, which are as follows:
[0058] S101. Obtain the discharge flow of the siltation dam and the lateral elevation data of the downstream target river section, and divide the target river section into multiple scour and siltation sections based on the lateral elevation data.
[0059] In the above steps, the discharge flow of the silt-promoting dam can be obtained in real time by acquiring data such as the dam's gate opening, gate width, and upstream and downstream water level difference, and calculated using the gate outflow formula. Then, when assessing the scouring and silting situation of a certain channel of the Yellow River downstream of the silt-promoting dam, this application first divides the channel into multiple equal-spaced cross-sections along the river direction. The distance between two cross-sections can be determined based on the distance between the assessed channel and the silt-promoting dam; the closer to the silt-promoting dam, the smaller the distance between the cross-sections. This application preferably uses 50 to 100 meters. Then, for each cross-section, this application uses a mobile multibeam echo sounder. Using a high-precision GPS system, riverbed measuring points are set up at equal intervals (preferably 2 meters) along the river cross-section. The riverbed elevation value (the straight-line distance from the measuring point to the water surface) and the starting distance from the starting point of the measuring point are recorded for each measuring point. Finally, the starting distance of multiple measuring points is used as the abscissa and the riverbed elevation value of multiple measuring points is used as the ordinate to obtain the transverse elevation curve (i.e., transverse elevation data) of each river cross-section. This digitally describes the undulation of the riverbed from the left bank to the right bank at each river cross-section, providing an analytical basis for subsequent analysis of the scouring and deposition changes of each river cross-section.
[0060] When assessing the scour and deposition situation of any one of the aforementioned multiple river cross-sections, the river scour and deposition monitoring system first acquires the lateral elevation data of the target river cross-section, and then divides the target river cross-section into multiple scour and deposition sections based on the lateral elevation data. Specifically:
[0061] First, the transverse elevation curve of the target river channel cross-section is differentially analyzed to obtain the transverse difference curve. This curve represents the rate of change of the riverbed elevation along the transverse direction. Therefore, when the difference value at a point in the transverse difference curve jumps compared to the difference value at the previous adjacent point and the numerical direction reverses, this difference point can be regarded as the abrupt change point of the riverbed undulation. It should be noted that if the riverbed elevation changes significantly from a certain point, this indicates that the point is the boundary between the channel and the floodplain. Thus, this application identifies the transverse difference curve. The system identifies all abrupt changes in the data and then cuts the transverse difference curve at these abrupt changes, splitting it into multiple difference segments. These multiple difference segments are then reconstructed into multiple transverse elevation segments. Based on the starting point of each transverse elevation segment, the corresponding section on the target river channel cross-section is found, thereby dividing the target river channel cross-section into multiple scour and deposition cross-sections. Since the elevation values of multiple riverbed measuring points in the same scour and deposition cross-section are relatively small, they can be well adapted to the calculation accuracy of the subsequent one-dimensional water and sediment model, thus improving the accuracy of the assessment of scour and deposition changes in the target river channel cross-section.
[0062] In one possible implementation, when identifying abrupt change points on the transverse difference curve of the target river channel, due to the large width of the lower Yellow River channel, the multibeam echo sounder system is affected by factors such as waves, water turbulence, ship course deviation, and local underwater obstacles (such as rocks, driftwood, and accumulated debris) during transverse scanning. The elevation values of individual riverbed measuring points on the cross-section may contain random measurement errors. If these riverbed measuring points themselves have slight local undulations, under the influence of the superposition of random measurement errors, they will produce numerical jumps on the difference curve, thus forming pseudo-abrupt change points similar to the actual channel-shoal boundary. If these pseudo-abrupt change points are directly used for cross-section partitioning, a originally hydraulically homogeneous continuous area will be incorrectly cut into multiple fragmented scour and deposition sections, causing subsequent partitioned flow allocation and independent simulation of the one-dimensional sediment model to lose physical meaning. Therefore, to improve the robustness of abrupt change point identification, this application considers that the true channel-shoal boundary is often a geomorphic boundary formed by long-term hydrodynamic forces in the river channel. It does not undergo drastic jumps between adjacent river sections, but rather presents a gradual, continuous transition. Conversely, pseudo-abrupt changes caused by random measurement errors lack this longitudinal continuity; their corresponding positions on upstream and downstream adjacent sections usually cannot be matched. Based on this characteristic, this application further verifies the spatial consistency of each abrupt change point initially identified on the target river section, thereby filtering out false abrupt changes caused by random measurement errors. This ensures that the abrupt changes ultimately used to delineate scour and sedimentation sections more reliably reflect the true channel-shoal boundary, thus improving the accuracy and stability of section zoning. Specifically:
[0063] First, taking the target river section as the center, the lateral elevation data of multiple adjacent river sections located upstream and downstream of the target river section within a preset river length range are obtained. Then, using the same differential operation and abrupt change point identification method as the target river section, the lateral differential curve corresponding to each adjacent river section and its multiple abrupt change points are obtained, thereby constructing a set of abrupt change point locations for each adjacent river section. The preset river length range can be adapted according to the intensity of the river's wandering and swaying. If the intensity of the river's wandering and swaying is large, the preset river length range is reduced to ensure a strong correlation between the morphologies of the sections.
[0064] Then, each abrupt change point on the target river section is extracted one by one. For any first abrupt change point, its position (distance from the starting point to the coordinates) is compared with the set of abrupt change point positions of multiple adjacent river sections in the longitudinal direction of the river. Specifically, for each adjacent river section, it is checked whether there is a abrupt change point in its set of abrupt change point positions whose position deviates from the position of the first abrupt change point within a preset lateral tolerance range. If there is an abrupt change point in the set of abrupt change point positions of an adjacent river section that satisfies the position deviation condition, then it is considered that the adjacent river section and the target river section have formed a continuous longitudinal correspondence at the first abrupt change point. After traversing all the adjacent river sections participating in the verification, the multiple abrupt change points that form a continuous correspondence with the first abrupt change point constitute a continuous point set of the first abrupt change point.
[0065] Finally, it is determined whether the number of points in the continuous set of the first mutation point is greater than or equal to a preset threshold. If the number of points in the continuous set of the first mutation point is greater than or equal to the preset threshold, it indicates that the first mutation point has good consistency along the longitudinal direction of the river channel and is not an isolated local noise or measurement error. Therefore, the first mutation point is determined as a valid mutation point and retained for subsequent cross-section partitioning operations. Conversely, if the number of points in the continuous set of points is less than the preset threshold, the first mutation point is determined to be an invalid pseudo-mutation point and is removed, and is not used as the basis for cross-section partitioning.
[0066] S102. Obtain the hydraulic parameters of multiple scour and siltation sections, and allocate the discharge flow of the siltation dam according to the hydraulic parameters of multiple scour and siltation sections to obtain the cross-sectional flow corresponding to each of the multiple scour and siltation sections.
[0067] In the above steps, after dividing the target river section into sections, the hydraulic parameters differ within each scour and sedimentation section. Since these hydraulic parameters determine the flow capacity of the section, if the traditional one-dimensional hydro-sediment model is still used to simplify the entire section into a single uniform flow channel, the accuracy of the one-dimensional hydro-sediment model in assessing scour and sedimentation changes will significantly decrease. Therefore, this application uses the Manning formula to first allocate the total discharge flow of the siltation-promoting dam based on the hydraulic parameters of each of the multiple scour and sedimentation sections, so that each scour and sedimentation section obtains a cross-sectional flow rate that matches its actual flow capacity. Specifically:
[0068] The hydraulic parameters of the scour and sedimentation section include the hydraulic radius and the roughness coefficient. The hydraulic radius can be obtained by calculating the water-passing area and wetted perimeter of the scour and sedimentation section from the lateral elevation data of the section. The roughness coefficient is obtained by looking up the Manning roughness coefficient in a preset table based on the bed sand composition and vegetation of the scour and sedimentation section.
[0069] After obtaining the hydraulic parameters of each scour and deposition cross-section, since the water level is the same at all locations on the same scour and deposition cross-section, the hydraulic gradient is also the same at all locations. At this time, for any one of the multiple scour and deposition cross-sections, the Manning formula can be used to calculate the average flow velocity of the cross-section, as follows:
[0070]
[0071] in, Let be the average flow velocity at the i-th scour and sedimentation cross section. Let be the roughness coefficient of the i-th scour and siltation section. Let be the hydraulic radius of the i-th scour and deposition cross section. The hydraulic gradient of the target river section.
[0072] Then, for the cross-sectional flow rate of the i-th scour and siltation section:
[0073]
[0074] in, The cross-sectional flow rate allocated to the i-th scour and sedimentation cross-section. To increase the total discharge flow of the silt-retaining dam, Let m be the average flow velocity at the i-th scour and deposition cross section, and m be the total number of scour and deposition cross sections divided into the target river channel.
[0075] In the above formula, the greater the average flow velocity of the scour and sedimentation section, the greater its cross-sectional flow, thus truly reflecting the lateral flow distribution law of the target cross-section, thereby improving the adaptability of the one-dimensional water and sediment model to the uneven lateral flow distribution of the target cross-section.
[0076] In one possible implementation, under long-term scouring and silting, the river channel downstream of the silt-promoting dam gradually forms significant complex cross-sectional morphologies. For example, the scouring and silting cross-section representing the main channel is narrow and deep, while the scouring and silting cross-section representing the beach is wide and shallow. There are significant differences between the two in terms of water depth and lateral extension area, resulting in significant differences in cross-sectional flow velocity. At this time, a violent momentum exchange occurs between the high-speed and low-speed scouring and silting cross-section flows at the interface. Some of the momentum in the high-speed flow zone is dissipated to form lateral circulation and turbulence, resulting in flow loss in the high-speed flow zone and exchange to the low-speed flow zone. This makes the actual flow in the low-speed flow zone slightly higher than the allocation result of the Manning formula, while the actual flow in the high-speed flow zone is lower than the allocation result of the Manning formula. This leads to a decrease in the accuracy of scouring and silting volume assessment in the high-speed and low-speed flow zones. Therefore, when allocating the scouring and sedimentation flow rates for each scouring and sedimentation section, this application calculates the velocity difference between any two adjacent first and second scouring and sedimentation sections, and then obtains the elevation (i.e., water depth) at the interface between the first and second scouring and sedimentation sections. Finally, based on the momentum transfer formula for open channel flow in a compound section, the momentum transfer ratio between the first and second scouring and sedimentation sections is calculated. The specific momentum transfer formula is as follows:
[0077]
[0078] Where I is the momentum transfer ratio between the first and second scour-siltation sections, and L is the elevation value at the junction of the first and second scour-siltation sections. The velocity difference between the first and second scour-deposition sections. For the water-passing area of a high-velocity scour and sedimentation cross-section, The average flow velocity of the high-velocity scouring and sedimentation section.
[0079] Finally, based on the momentum transfer ratio between the first and second scour sections, the cross-sectional flow rates of the first and second scour sections are corrected respectively, as follows:
[0080] First, compare the flow velocities at the first and second scouring / deposition sections. If the flow velocity at the first section is greater than that at the second section, then calculate the flow correction.
[0081]
[0082] in, For flow correction amount, For momentum transfer ratio, This represents the cross-sectional flow rate at the first scour and sedimentation section.
[0083] The aforementioned flow correction can be understood as the flow loss caused by momentum exchange in the high-velocity scouring and sedimentation section. This lost flow will then be transferred to the low-velocity scouring and sedimentation section. Therefore, the corrected flow rates for the first and second scouring and sedimentation sections are:
[0084]
[0085]
[0086] in, This is the corrected cross-sectional flow rate for the first scour and siltation section. This is the corrected cross-sectional flow rate for the second scour and siltation section. The cross-sectional flow rate before correction of the first scour and siltation section. The cross-sectional flow rate before correction of the second scour and siltation cross-section. This is the flow correction amount.
[0087] In summary, through the aforementioned momentum exchange correction, the water-sediment exchange process between various scour and sediment cross sections is more accurately characterized, thus providing a more realistic zonal flow boundary for subsequent independent simulation of one-dimensional water-sediment models.
[0088] In one possible implementation, due to the complex sediment conditions in the middle and upper reaches of the Yellow River, the sediment-laden water discharged from the silt-promoting dam often contains sand particles of various sizes. The composition ratio of sand particles of different sizes will have different effects on the rheological properties of the water. For example, when the content of small-sized clay particles is high, the water exhibits higher yield stress and plastic viscosity, which will have a stronger damping effect on transverse momentum exchange. When the content of large-sized coarse sand is high, the silt particles mainly contribute to the inertial effect and contribute less to viscous damping. At this point, considering that the proportion of different particle sizes in the sediment-laden river water will affect momentum exchange, this application, in order to further improve the accuracy of momentum exchange correction, also obtains the proportion of sand particles of various sizes in the current unit volume of water in the discharge flow of the siltation dam, and then retrieves the damping coefficients of various different particle sizes from a preset damping coefficient table. This preset damping coefficient table stores the damping coefficients for different proportions of sand particles of a single size in the unit volume of water. Then, based on the damping coefficients of various different particle sizes, the momentum transfer correction coefficient of the current sediment-laden water flow is calculated. The calculation process is as follows:
[0089]
[0090] in, This is the momentum transfer correction factor. Let be the damping coefficient of the i-th type of sand grain in the current water body, and n be the number of different types of sand grains in the current water body. This is the coefficient of influence of the damping coefficient on momentum transfer.
[0091] Finally, the momentum transfer correction coefficient is multiplied by the momentum transfer ratio of each scour and deposition cross section to further accurately characterize the influence of sand particles of different sizes on the flow of different scour and deposition cross sections, thereby providing more realistic and reliable water and sediment boundary conditions for subsequent zonal scour and deposition simulation.
[0092] S103. Using the cross-sectional flow rate of each scour and sedimentation section as boundary conditions, drive the preset one-dimensional water and sediment model to calculate the time series curve of scour and sedimentation volume of each scour and sedimentation section.
[0093] In the above steps, after the discharge flow of the siltation dam is divided into zones, each scour and sedimentation section has obtained a sectional flow rate that matches its hydraulic characteristics. Since the hydraulic parameters such as water depth, flow velocity, and roughness are relatively uniform within each scour and sedimentation section, and the difference in lateral flow velocity distribution is small, the basic assumptions of the one-dimensional water and sediment model are met within each scour and sedimentation section, namely, the flow velocity within the section is uniform and the sediment transport capacity can be reasonably characterized by the average parameters of the section. Therefore, this application uses the sectional flow rate of each scour and sedimentation section as boundary conditions to drive the preset one-dimensional water and sediment model to independently calculate the current scour and sedimentation volume of each scour and sedimentation section. Then, based on the change of the discharge flow of the siltation dam over time, the scour and sedimentation volume of each scour and sedimentation section at different time points is continuously calculated, and finally the time series curve of the scour and sedimentation volume of each scour and sedimentation section is obtained.
[0094] It should be noted that the one-dimensional water-sediment model used in this application is a commonly used non-equilibrium sediment transport model in this field. Its core governing equations include the flow continuity equation, the Saint-Venant equations, the non-equilibrium sediment transport equation, and the riverbed deformation equation. For any scour-deposition cross section, the model uses the geometric data of the cross section and the cross section discharge as boundary conditions. Combined with hydraulic parameters such as the roughness coefficient and sediment carrying capacity coefficient of the cross section, it calculates the difference between the total sediment entering the cross section and the total sediment leaving the cross section. Then, based on the difference in total sediment, the net scour-deposition thickness (i.e., scour-deposition volume) of the scour-deposition cross section can be calculated using the riverbed deformation equation.
[0095] S104. Merge the time series curves of scour and sedimentation at each scour and sedimentation section to obtain and output the time series curve of scour and sedimentation at the target river section.
[0096] In the above steps, since each scour and sedimentation section is a different sub-region divided from the same target river section, they together form a complete river section. Therefore, the total scour and sedimentation volume of the target river section is equal to the algebraic sum of the scour and sedimentation volumes of each scour and sedimentation section. Thus, this application directly adds the time series curves of the scour and sedimentation volumes of each scour and sedimentation section after time series alignment, and obtains the time series curve of the scour and sedimentation volume of the target river section as a function of scour and sedimentation time. Then, the time series curve of the scour and sedimentation volume of the target river section is output to the display interface of the monitoring system so that engineers can understand the scour and sedimentation impact trend of the siltation dam on the downstream river channel under different flow rates, thereby improving the rationality of the planning of the Yellow River downstream channel management project.
[0097] In one possible implementation, if the elevation difference between various scouring and deposition sections is significant due to long-term scouring and deposition in the downstream channel of the silt-promoting dam, there will be a significant time delay between the sediment settling time of the deeper sections and the shallower sections. If the scouring and deposition time series curves of each section are directly superimposed at the same time, the deposition area of the higher-depth scouring and deposition sections, which should have occurred later, will be brought forward to the current moment, resulting in distorted assessment results. Therefore, when fusing the time-series curves of scour and sedimentation volumes from various scour and sedimentation sections, this application first calculates the average lateral elevation of multiple scour and sedimentation sections. Then, it sorts the average lateral elevations of multiple scour and sedimentation sections in descending order and selects the scour and sedimentation section with the smallest average lateral elevation as the benchmark scour and sedimentation section. Starting from the current time point, it calculates the cross-correlation coefficient between the time-series curve of scour and sedimentation volume of each scour and sedimentation section and the time-series curve of the benchmark scour and sedimentation section by shifting historical time points. If the time-series curve of scour and sedimentation volume of a certain scour and sedimentation section is consistent with the benchmark scour and sedimentation section, the cross-correlation coefficient is calculated. If the cross-correlation coefficient between the time series curves of scour and sedimentation at a certain moment is greater than a preset cross-correlation coefficient threshold, then that moment is determined to be the sediment deposition delay of the scour and sedimentation section. At this time, the time series curve of scour and sedimentation at that scour and sedimentation section is shifted backward to that moment for time alignment. Similarly, after performing the above processing on all scour and sedimentation sections, the time series curves of scour and sedimentation at each scour and sedimentation section are superimposed point by point on the time axis to obtain the time series curve of scour and sedimentation at the target river section. Thus, the time series curve of scour and sedimentation at the target river section is more in line with the actual sediment deposition characteristics.
[0098] For example, the time series curve of scour and sedimentation volume of any third scour and sedimentation section among multiple scour and sedimentation sections contains continuous scour and sedimentation time points a, b, c, and d, where a is the current time point and b, c, and d are historical time points. The time series curve of scour and sedimentation volume of the reference scour and sedimentation section contains continuous scour and sedimentation time points A, B, C, and D, where A is the current time point and B, C, and D are historical time points corresponding one-to-one with b, c, and d. In this case, first calculate the cross-correlation coefficient between the scour and sedimentation volume of the third scour and sedimentation section at a, b, c, and d and the scour and sedimentation volume of the reference scour and sedimentation section at A, B, C, and D. If If the cross-correlation coefficient is less than the preset cross-correlation coefficient threshold, the scouring and silting time point of the third scouring and silting section is shifted forward. At this time, the cross-correlation coefficient between the scouring and silting volume of the third scouring and silting section at a, b, and c and the scouring and silting volume of the reference scouring and silting section at B, C, and D is calculated. If the cross-correlation coefficient is greater than or equal to the preset cross-correlation coefficient threshold, the scouring and silting volume at time point a in the scouring and silting volume time series curve of the third scouring and silting section is aligned with the scouring and silting volume at time point B in the scouring and silting volume time series curve of the reference scouring and silting section. Then, the scouring and silting volume time series curve of the third scouring and silting section is shifted backward by one time point.
[0099] Reference Figure 2This application also provides a system for assessing the impact of silt-promoting dams on the scouring and deposition of the lower Yellow River channel under different flow rates. The system is a river channel scouring and deposition monitoring system, which includes an acquisition module 1, a processing module 2, and an output module 3, wherein:
[0100] Module 1 is used to acquire the discharge flow of the siltation dam and the lateral elevation data of the downstream target river section, and to divide the target river section into multiple scour and siltation sections based on the lateral elevation data.
[0101] Processing module 2 is used to acquire the hydraulic parameters of multiple scour and siltation sections, and to allocate the discharge flow of the siltation dam according to the hydraulic parameters of multiple scour and siltation sections to obtain the cross-sectional flow corresponding to each of the multiple scour and siltation sections.
[0102] The cross-sectional flow rate of each scour and sedimentation section is used as the boundary condition to drive the preset one-dimensional water and sediment model to calculate the time series curve of scour and sedimentation of each scour and sedimentation section.
[0103] Output module 3 is used to fuse the time series curves of scour and sedimentation of each scour and sedimentation section to obtain and output the time series curve of scour and sedimentation of the target river section.
[0104] It should be noted that the above embodiments of the apparatus are only illustrated by the division of the above functional modules. In practical applications, the above functions can be assigned to different functional modules as needed, that is, the internal structure of the device can be divided into different functional modules to complete all or part of the functions described above. In addition, the apparatus and method embodiments provided in the above embodiments belong to the same concept, and the specific implementation process can be found in the method embodiments, which will not be repeated here.
[0105] This application also discloses an electronic device. (See reference...) Figure 3 , Figure 3 This is a schematic diagram of the structure of an electronic device disclosed in an embodiment of this application. The electronic device 300 may include: at least one processor 301, at least one network interface 304, a user interface 303, a memory 305, and at least one communication bus 302.
[0106] The communication bus 302 is used to enable communication between these components.
[0107] The user interface 303 may include a display screen and a camera. Optionally, the user interface 303 may also include a standard wired interface and a wireless interface.
[0108] The network interface 304 may optionally include a standard wired interface or a wireless interface (such as a Wi-Fi interface).
[0109] The processor 301 may include one or more processing cores. The processor 301 connects to various parts of the server using various interfaces and lines, and performs various server functions and processes data by running or executing instructions, programs, code sets, or instruction sets stored in memory 305, and by calling data stored in memory 305. Optionally, the processor 301 may be implemented using at least one hardware form of Digital Signal Processing (DSP), Field-Programmable Gate Array (FPGA), or Programmable Logic Array (PLA). The processor 301 may integrate one or a combination of several of the following: Central Processing Unit (CPU), Graphics Processing Unit (GPU), and modem. The CPU primarily handles the operating system, user interface, and applications; the GPU is responsible for rendering and drawing the content required for display; and the modem handles wireless communication. It is understood that the modem may also not be integrated into the processor 301 and may be implemented as a separate chip.
[0110] The memory 305 may include random access memory (RAM) or read-only memory. Optionally, the memory 305 may include a non-transitory computer-readable storage medium. The memory 305 may be used to store instructions, programs, code, code sets, or instruction sets. The memory 305 may include a program storage area and a data storage area, wherein the program storage area may store instructions for implementing an operating system, instructions for at least one function (such as touch function, sound playback function, image playback function, etc.), instructions for implementing the above-described method embodiments, etc.; the data storage area may store data involved in the above-described method embodiments, etc. Optionally, the memory 305 may also be at least one storage device located remotely from the aforementioned processor 301. (Refer to...) Figure 3 The memory 305, which serves as a computer storage medium, may include an operating system, a network communication module, a user interface module, and an application program for assessing the impact of silt-promoting dams on the downstream channel of the Yellow River under different flow rates.
[0111] exist Figure 3In the illustrated electronic device 300, the user interface 303 is mainly used to provide an input interface for the user and to acquire user input data; while the processor 301 can be used to call an application stored in the memory 305, which is a method for assessing the impact of silt-promoting dams on the downstream channel of the Yellow River under different flow rates. When executed by one or more processors 301, the electronic device 300 performs one or more of the methods described in the above embodiments. It should be noted that, for the foregoing method embodiments, for the sake of simplicity, they are all described as a series of actions. However, those skilled in the art should understand that this application is not limited to the described order of actions, because according to this application, some steps can be performed in other orders or simultaneously. Secondly, those skilled in the art should also understand that the embodiments described in the specification are all preferred embodiments, and the actions and modules involved are not necessarily essential to this application.
[0112] In the above embodiments, the descriptions of each embodiment have different focuses. For parts not described in detail in a certain embodiment, please refer to the relevant descriptions in other embodiments.
[0113] In the various embodiments provided in this application, it should be understood that the disclosed apparatus can be implemented in other ways. For example, the apparatus embodiments described above are merely illustrative; for instance, the division of units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be through some service interface; the indirect coupling or communication connection between apparatuses or units may be electrical or other forms.
[0114] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.
[0115] Furthermore, the functional units in the various embodiments of this application can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit.
[0116] If the integrated unit is implemented as a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage device (CMD). Based on this understanding, the technical solution of this application, in essence, or the part that contributes to the prior art, or all or part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a memory and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods of the various embodiments of this application. The aforementioned memory includes various media capable of storing program code, such as USB flash drives, portable hard drives, magnetic disks, or optical disks.
[0117] The above description is merely an exemplary embodiment of this disclosure and should not be construed as limiting the scope of this disclosure. Any equivalent changes and modifications made in accordance with the teachings of this disclosure shall still fall within the scope of this disclosure. Other embodiments of this disclosure will be readily apparent to those skilled in the art upon consideration of the specification and the disclosure of practical truths.
[0118] This application is intended to cover any variations, uses, or adaptations of this disclosure that follow the general principles of this disclosure and include common knowledge or customary techniques in the art not described in this disclosure. The specification and embodiments are to be considered exemplary only, and the scope and spirit of this disclosure are defined by the claims.
Claims
1. A method for assessing the impact of silt-promoting dams on the scouring and deposition of the lower Yellow River channel under different flow rates, characterized in that, The method, applied to a river scour and sedimentation monitoring system, includes: The discharge flow of the siltation dam and the lateral elevation data of the downstream target river section are obtained, and the target river section is divided into multiple scour and siltation sections based on the lateral elevation data. The hydraulic parameters of multiple scour and siltation sections are obtained, and the discharge flow of the siltation dam is allocated according to the hydraulic parameters of the multiple scour and siltation sections to obtain the cross-sectional flow corresponding to each of the multiple scour and siltation sections. The cross-sectional flow rate of each of the aforementioned scour and sedimentation sections is used as a boundary condition to drive a preset one-dimensional water and sediment model to calculate the time series curve of the scour and sedimentation volume of each of the aforementioned scour and sedimentation sections. The time-series curves of scour and sedimentation volume of each of the aforementioned scour and sedimentation sections are merged to obtain and output the time-series curve of scour and sedimentation volume of the target river section.
2. The method according to claim 1, characterized in that, The lateral elevation data consists of elevation values from multiple riverbed measuring points arranged along the width of the river channel. Each elevation value is the straight-line distance from the measuring point to the water surface. The process of dividing the target river channel cross-section into multiple scour and deposition sections based on the lateral elevation data specifically includes: The elevation values of the multiple riverbed measuring points are differentially calculated along the width of the river channel to obtain a transverse difference curve; Identify multiple abrupt change points in the lateral difference curve; Based on the multiple mutation points, the lateral difference curve is divided into multiple difference segments; The multiple differential segments are restored into multiple lateral elevation segments, and the target river channel section is divided into multiple scour and deposition sections according to the multiple lateral elevation segments, wherein one lateral elevation segment corresponds to one scour and deposition section.
3. The method according to claim 2, characterized in that, The identification of multiple abrupt change points in the lateral difference curve specifically includes: Using the target river section as the center, obtain the lateral difference curves of multiple adjacent river sections within a preset river length range; Multiple abrupt change points of the transverse difference curve of each adjacent river section are identified to obtain the set of abrupt change point locations for each adjacent river section. The positions of multiple abrupt change points in the target river section are compared with the sets of multiple abrupt change point positions in the longitudinal direction of the river to obtain a set of continuous points of multiple abrupt change points in the target river section along the longitudinal direction of the river. If the number of points in the continuous set of the first mutation point of the target river section is greater than or equal to a preset threshold, then the first mutation point is determined to be a valid mutation point, and the first mutation point is any one of the multiple mutation points.
4. The method according to claim 1, characterized in that, The hydraulic parameters include the roughness coefficient. The process of allocating the discharge flow of the siltation-promoting dam according to the hydraulic parameters of multiple scour and sedimentation sections to obtain the cross-sectional flow corresponding to each of the multiple scour and sedimentation sections specifically includes: Based on the lateral elevation data, the hydraulic radii corresponding to each of the multiple scour and deposition sections are calculated; Based on the roughness coefficient and hydraulic radius of each of the aforementioned scour and deposition cross sections, the average flow velocity of each of the aforementioned scour and deposition cross sections is calculated using the Manning formula. Based on the ratio of the average flow velocities of each of the aforementioned scour and siltation sections, the discharge flow of the siltation-promoting dam is proportionally allocated to obtain the cross-sectional flow of each of the aforementioned scour and siltation sections.
5. The method according to claim 4, characterized in that, The method of proportionally distributing the discharge flow of the siltation-promoting dam according to the ratio of the average flow velocities of each of the aforementioned scour and siltation sections to obtain the cross-sectional flow of each of the aforementioned scour and siltation sections specifically includes: Calculate the velocity difference between the average flow velocity of the first scour and sedimentation section and the average flow velocity of the second scour and sedimentation section, wherein the first scour and sedimentation section and the second scour and sedimentation section are any two adjacent scour and sedimentation sections among the plurality of scour and sedimentation sections. Obtain the elevation values at the intersection point of the first scour and siltation section and the second scour and siltation section; Based on the velocity difference between the first and second scour sections and the elevation at the junction, the momentum transfer ratio between the first and second scour sections is calculated. Based on the momentum transfer ratio, the cross-sectional flow rates of the first scour and siltation section and the second scour and siltation section are corrected respectively.
6. The method according to claim 5, characterized in that, The step of correcting the cross-sectional flow rates of the first and second scour-siltation sections according to the momentum transfer ratio further includes: Obtain the proportion of sand particles of different sizes in a unit volume of water in the sediment-laden water flow discharged from the siltation dam; From the preset damping coefficient table, various damping coefficients for different particle sizes can be obtained; Based on the damping coefficients of various particle sizes, the momentum transfer correction coefficient of the current sediment-laden water flow is calculated. The momentum transfer ratio is corrected based on the momentum transfer correction coefficient.
7. The method according to claim 1, characterized in that, The step of fusing the time-series curves of scour and sedimentation volume from each of the aforementioned scour and sedimentation cross-sections to obtain and output the time-series curve of scour and sedimentation volume for the target river channel cross-section specifically includes: Based on the lateral elevation data, calculate the average lateral elevation of multiple scour and siltation sections; The scour and siltation section with the smallest mean lateral elevation among the multiple scour and siltation sections is selected as the benchmark scour and siltation section. Starting from the current moment, the cross-correlation coefficient between the time series curve of the scour and siltation volume of the third scour and siltation section and the time series curve of the scour and siltation volume of the reference scour and siltation section is calculated by shifting the curves one by one through historical time points. The third scour and siltation section is any one of the multiple scour and siltation sections. If, when the third scour and siltation section is shifted to the first moment, the cross-correlation coefficient between the scour and siltation volume time series curve of the third scour and siltation section and the scour and siltation volume time series curve of the reference scour and siltation section is greater than a preset cross-correlation coefficient threshold, then the time difference between the first moment and the current moment is calculated. The time series curve of scour and siltation volume of the third scour and siltation section is shifted forward by the time difference between the first moment and the current moment to obtain the time series shift curve of scour and siltation volume of the third scour and siltation section. The time-series translation curves of scour and sedimentation volume of multiple scour and sedimentation sections are summed to obtain the time-series curve of scour and sedimentation volume of the target river section.
8. A system for assessing the impact of silt-promoting dams on the scouring and deposition of the lower Yellow River channel under different flow rates, characterized in that, The system is a riverbed scour and sedimentation monitoring system, which includes an acquisition module (1), a processing module (2), and an output module (3), wherein: The acquisition module (1) is used to acquire the discharge flow of the siltation dam and the lateral elevation data of the downstream target river section, and to divide the target river section into multiple scour and siltation sections according to the lateral elevation data. The processing module (2) is used to acquire the hydraulic parameters of multiple scour and siltation sections, and allocate the discharge flow of the siltation dam according to the hydraulic parameters of multiple scour and siltation sections to obtain the cross-sectional flow corresponding to each of the multiple scour and siltation sections. The cross-sectional flow rate of each of the aforementioned scour and sedimentation sections is used as a boundary condition to drive a preset one-dimensional water and sediment model to calculate the time series curve of the scour and sedimentation volume of each of the aforementioned scour and sedimentation sections. The output module (3) is used to fuse the time series curves of scour and sedimentation of each of the scour and sedimentation sections to obtain and output the time series curve of scour and sedimentation of the target river section.
9. An electronic device, characterized in that, The device includes a processor (301), a memory (305), a user interface (303), and a network interface (304). The memory (305) is used to store instructions. The user interface (303) and the network interface (304) are used to communicate with other devices. The processor (301) is used to execute the instructions stored in the memory (305) to cause the electronic device (300) to perform the method as described in any one of claims 1 to 7.
10. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores instructions that, when executed, perform the method as described in any one of claims 1 to 7.