Underwater topography accompanying inversion method and device based on water surface line control

Abstract

The application provides a water surface line control-based underwater terrain accompanying inversion method and device, which can accurately and effectively invert underwater complex terrain and make the inversion result more in line with the actual situation. The method comprises the following steps: step 1, collecting basic parameters for calculating a river channel; step 2, determining a control equation of the river channel calculation model and establishing an objective function; step 2.1, the complex bottom terrain of a natural river channel is represented by a water level z, the whole river channel is divided into small river sections by many sections, and the control equation of the river channel calculation model is established; step 2.2, an objective function is constructed, and an accompanying mode is established; step 3, the water level calculation value is obtained by solving the model equation, the objective function is calculated, and it is judged whether the precision requirement is met; if yes, the river bottom slope of the iteration is output; if not, the next step is performed; step 4, a correction gradient formula of the objective function about the bottom slope is solved, the search direction and search step of the optimization control variable are determined, the bottom slope is corrected, and the step 3 is returned.

Description

Technical Field

[0001] This invention belongs to the field of water conservancy engineering technology, specifically relating to an underwater topographic inversion method and apparatus based on water surface line control. Background Technology

[0002] Rivers are systems composed of water flow and channel boundaries. On the one hand, water flow acts on the channel boundaries, causing changes in boundary conditions; on the other hand, changes in the channel boundaries, in turn, affect the water flow structure. These two aspects are interdependent and mutually restrictive, constituting river evolution and development. For example, after the construction of a reservoir, the backwater effect causes siltation. The resulting topography not only affects the backwater inundation but also the reservoir's efficiency, ultimately threatening its safe operation. Therefore, river topography is often essential data for various studies and engineering projects, directly influencing river evolution, development, and engineering layout.

[0003] Generally, common methods for directly determining and predicting reservoir sedimentation topography include field measurements, mathematical models, and physical models. However, the reservoir area is often surrounded by canyons and mountains, making field measurements difficult and costly. Due to safety and economic constraints, field measurements are often not timely or comprehensive. Mathematical and physical models can only predict topography and often only serve as a reference for reservoir design and operation. This makes determining and studying reservoir sedimentation topography challenging. Furthermore, water level data is often easier to measure than topographic data; therefore, the method of inverting water depth from the water surface to obtain reservoir topography has gradually gained popularity. Among these applications, the most common is the direct inversion of water depth and underwater topography using remote sensing data. This has further evolved to using remote sensing data to analyze the relationships between hydraulic elements and invert river depth measurements, such as using continuous synchronous observations of water level and river width from remote sensing data to estimate river depth, or combining multi-source remote sensing data to extract water level and river width for inverting river depth measurements. However, the accuracy of such methods depends on the resolution of remote sensing data, is easily affected by river characteristics, and has a large error between the estimated riverbed elevation and the actual terrain, making it difficult to adapt to the diverse needs of river terrain determination. Therefore, it is necessary to improve terrain inversion methods to enhance the accuracy of terrain simulation. However, the complex and variable terrain of natural reservoirs and the continuous development of reservoir siltation pose challenges to the application of other inversion methods. Summary of the Invention

[0004] This invention is made to solve the above-mentioned problems, and aims to provide an underwater topography inversion method and apparatus based on water surface line control, which can accurately and effectively invert complex underwater topography and make the inversion results more consistent with the actual situation.

[0005] To achieve the above objectives, the present invention employs the following solution:

[0006] <Method>

[0007] This invention provides an underwater topography inversion method based on water surface line control, comprising the following steps:

[0008] Step 1: Collect and calculate the basic parameters of the river channel, including: topographic cross-sectional morphological features and measured cross-sectional water level data;

[0009] Step 2: Determine the governing equations of the river channel calculation model, establish the objective function, and specify the initial values ​​of the riverbed slope and the accuracy requirements of the objective function;

[0010] Step 2.1: The topography of the natural river channel is complex. The water level z represents the water surface line. The entire river channel is divided into small river segments by many cross sections, and the governing equations of the river channel calculation model are established.

[0011] Step 2.2: Construct the objective function and establish the adjoint pattern;

[0012] The objective function is constructed using the distance between the measured water depth and the calculated water depth at the cross-section to be determined:

[0013]

[0014] Construct a function to describe the dynamic state of the model:

[0015]

[0016]

[0017]

[0018]

[0019] In the formula, h represents the water depth; E s λ represents the specific energy of the cross section; λ is a coefficient; r is a directional parameter, with the control section upstream during rapid flow and r = 1; and downstream during slow flow and r = -1; Δs represents the length of the river section; i represents the slope of the riverbed; subscript d represents the cross section where the water depth is to be determined; superscript obs represents the measured value; and subscript u represents the cross section where the water depth is known.

[0020] Step 2.3: Determine the accuracy requirements of the objective function based on actual engineering needs, and specify the initial bottom slope;

[0021] Step 3: Solve the model equations to obtain the calculated water level value, calculate the objective function and determine whether it meets the accuracy requirements. If it does, output the riverbed slope at this iteration. If it does not, proceed to the next step.

[0022] Step 4: Calculate the corrected gradient formula of the objective function with respect to the bottom slope, determine the search direction and search step size of the optimization control variables, correct the bottom slope and return to step 3;

[0023] Step 4.1: Determine the search direction d for the optimized control variable. k and search step size α k From x k Starting from the beginning, gradually adjust the control variables along the search direction:

[0024] x k+1 =x k +d k α k (4.1-1)

[0025] In the formula, the subscripts k+1 and k represent the current correction and the previous correction, respectively;

[0026] Let the objective function decrease continuously until its calculated model value gets closer to the observed value:

[0027] J(x k +d k α k ) <J(x k (4.1-2)

[0028] In the calculation, the negative gradient direction of equation (2.2-1) with respect to the riverbed slope is taken as d. k The corrected gradient formula for the objective function with respect to the bottom slope i is:

[0029]

[0030] Step 4.2: Correct the riverbed slope based on the determined search step size and search direction:

[0031] i k+1 =i k +α k d k (4.2-1).

[0032] Preferably, in the underwater topography inversion method based on water surface line control provided by the present invention, in step 4.1, the search step size α k The method for determining the step size is as follows: Given an initial step size α0, along d... k Substitute the direction optimization control variables into the objective function, if J(x) k +d k α0) <J(x k Let α1 = ωα0, where ω is a real number greater than 1, and substitute it into the objective function. Repeat this process until J(x) is reached. k +d k α k'+1 )>J(x k At this point, the search step size α can be confirmed. k =α k' , where k' is the k'th search in the kth correction.

[0033] Preferably, in the underwater topography inversion method based on water surface line control provided by the present invention, the topographic cross-sectional morphological features in step 1 include the cross-sectional water-passing area and the variation law of hydraulic radius along water depth.

[0034] Preferably, in the underwater topography inversion method based on water surface line control provided by the present invention, in step 2.1, the length of each small river segment is 1.2 to 1.6 times the river width.

[0035] Preferably, in the underwater topography inversion method based on water surface line control provided by the present invention, in step 2.1, the upstream and downstream cross-sections in a certain small river segment are set as cross-section 1 and cross-section 2, respectively, the river segment length is Δs, and the energy equation is:

[0036] E s2 -E s1 =z b1 -z b2 -h w1-2 (2.1-1)

[0037] In the formula, Z b Indicates the bottom elevation of the trench; subscripts 1 and 2 represent section 1 and section 2 respectively; head loss h w1-2 =h f +h j Including head loss along the route h f and local head loss h j Two parts;

[0038] In the calculation of water surface profiles, sometimes the downstream water depth of a small segment is known, and the upstream water surface profile is calculated; sometimes the opposite is true. The subscript *u* represents a cross-section with a known water depth, and the subscript *d* represents a cross-section with a water depth to be determined. Therefore, the energy equation for non-uniform flow is:

[0039]

[0040] In the formula, This indicates the average hydraulic gradient of the calculated river section;

[0041] Locally abruptly changing sections in natural river channels are included in the head loss along the river by taking into account the roughness value; the formula for calculating the head loss along the river is:

[0042]

[0043] In the formula, To calculate the average hydraulic gradient of the river section; This represents the average flow modulus of the upstream and downstream sections of the river.

[0044] The equations governing the water depth at the desired cross-section, i.e., the model governing equations, are as follows:

[0045]

[0046] <device>

[0047] Furthermore, the present invention also provides an underwater topography cascading inversion device based on water surface line control for automatically implementing the above-mentioned <method>, characterized in that it includes:

[0048] The acquisition department acquires the basic parameters of the calculated river channel, including: topographic cross-sectional morphological features and measured cross-sectional water level data;

[0049] The model establishment section determines the governing equations of the river channel calculation model according to steps 2.1 to 2.3, establishes the objective function, and gives the initial value of the riverbed slope and the accuracy requirements of the objective function.

[0050] Step 2.1: The topography of the natural river channel is complex. The water level z represents the water surface line. The entire river channel is divided into small river segments by many cross sections, and the governing equations of the river channel calculation model are established.

[0051] Step 2.2: Construct the objective function and establish the adjoint pattern;

[0052] The objective function is constructed using the distance between the measured water depth and the calculated water depth at the cross-section to be determined:

[0053]

[0054] Construct a function to describe the dynamic state of the model:

[0055]

[0056]

[0057]

[0058]

[0059] In the formula, h represents the water depth; E s λ represents the specific energy of the cross section; λ is a coefficient; r is a directional parameter, with the control section upstream during rapid flow and r = 1; and downstream during slow flow and r = -1; Δs represents the length of the river section; i represents the slope of the riverbed; subscript d represents the cross section where the water depth is to be determined; superscript obs represents the measured value; and subscript u represents the cross section where the water depth is known.

[0060] Step 2.3: Determine the accuracy requirements of the objective function based on actual engineering needs, and specify the initial bottom slope;

[0061] The solution section solves the model equations to obtain the calculated water level value, calculates the objective function and determines whether it meets the accuracy requirements. If it does, it outputs the riverbed slope it has iterated to this point; otherwise, it enters the correction section for correction.

[0062] The correction section calculates the corrected gradient formula of the objective function with respect to the bottom slope according to steps 4.1 to 4.2, determines the search direction and search step size of the optimization control variables, corrects the bottom slope, and returns to the solution section.

[0063] Step 4.1: Determine the search direction d for the optimized control variable. k and search step size α k From x k Starting from the beginning, gradually adjust the control variables along the search direction:

[0064] x k+1 =x k +d k α k (4.1-1)

[0065] In the formula, the subscripts k+1 and k represent the current correction and the previous correction, respectively;

[0066] Let the objective function decrease continuously until its calculated model value gets closer to the observed value:

[0067] J(x k +d k α k ) <J(x k (4.1-2)

[0068] In the calculation, the negative gradient direction of equation (2.2-1) with respect to the riverbed slope is taken as d. k The corrected gradient formula for the objective function with respect to the bottom slope i is:

[0069]

[0070] Step 4.2: Correct the riverbed slope based on the determined search step size and search direction:

[0071] i k+1 =i k +α k d k (4.2-1)

[0072] The control unit communicates with the acquisition unit, model building unit, solution unit, and correction unit, and controls their operation.

[0073] Preferably, the underwater topography inversion device based on water surface line control provided by the present invention may further include: an input display unit, which is communicatively connected to the control unit, allowing the user to input operation commands, and displaying the input, output, and intermediate processing data of the corresponding unit in the form of text, tables, graphics, or three-dimensional dynamic models according to the operation commands.

[0074] Preferably, the underwater topography inversion device based on water surface line control provided by the present invention may further include: an underwater topography generation unit, which is communicatively connected to the control unit and generates underwater topography based on the riverbed slope output by the solver unit; and a dredging unit, which is communicatively connected to the control unit and determines the reservoir siltation situation based on the underwater topography generated by the underwater topography generation unit, and then determines the reservoir dredging scheme.

[0075] Preferably, in the underwater topography inversion device based on water surface line control provided by the present invention, the search step size α in the correction unit is... k Determination of: Given an initial step size α0, along d k Substitute the direction optimization control variables into the objective function, if J(x) k +d k α0) <J(x k Let α1 = ωα0, where ω is a real number greater than 1, and substitute it into the objective function. Repeat this process until J(x) is reached. k +d k α k'+1 )>J(x k At this point, the search step size α can be confirmed. k =α k' , where k' is the k'th search in the kth correction.

[0076] Preferably, the underwater topography inversion device based on water surface line control provided by the present invention, in the model building section, sets the upstream and downstream cross-sections as cross-section 1 and cross-section 2 respectively in a certain small river segment, the river segment length as Δs, and the energy equation as:

[0077] E s2 -E s1 =z b1 -z b2 -h w1-2 (2.1-1)

[0078] In the formula, Z b Indicates the bottom elevation of the trench; subscripts 1 and 2 represent section 1 and section 2 respectively; head loss h w1-2 =h f +h j Including head loss along the route h f and local head loss h j Two parts;

[0079] In the calculation of water surface profiles, sometimes the downstream water depth of a small segment is known, and the upstream water surface profile is calculated; sometimes the opposite is true. The subscript *u* represents a cross-section with a known water depth, and the subscript *d* represents a cross-section with a water depth to be determined. Therefore, the energy equation for non-uniform flow is:

[0080]

[0081] In the formula, This indicates the average hydraulic gradient of the calculated river section;

[0082] Locally abruptly changing sections in natural river channels are included in the head loss along the river by taking into account the roughness value; the formula for calculating the head loss along the river is:

[0083]

[0084] In the formula, To calculate the average hydraulic gradient of the river section; This represents the average flow modulus of the upstream and downstream sections of the river.

[0085] The equations governing the water depth at the desired cross-section, i.e., the model governing equations, are as follows:

[0086]

[0087] The role and effect of invention

[0088] The underwater topography inversion method and apparatus based on water surface line control provided by this invention first generalizes the river channel topography, then constructs an objective function using the distance between the measured and calculated water depths at the desired cross-section. Next, it constructs a function describing the dynamic state of the model and proposes a modified gradient formula. Using the negative gradient direction of the riverbed slope as the search direction, the modified gradient formula is used to continuously search and optimize the riverbed slope (river channel topography slope) according to the accuracy requirements of the objective function until the accuracy requirements are met, thus obtaining the optimal riverbed slope. Ultimately, it achieves the inversion of reservoir topography based on the measured water surface line, with good agreement between the inverted and measured topography and small errors. This invention provides a scientific tool for the inversion of deep-thalveolar elevations in natural and silted river channels, enabling rapid and accurate determination of underwater topography, and subsequently, control of reservoir siltation and engineering layout. Attached Figure Description

[0089] Figure 1 This is a flowchart of an underwater topography inversion method based on water surface line control, as described in an embodiment of the present invention.

[0090] Figure 2 This is a schematic diagram of the deep-water iteration process of a certain river section involved in an embodiment of the present invention, wherein (a) is the BDS~BD0 river section, and (b) is the BD15-1~BD16 river section;

[0091] Figure 3 This is a schematic diagram showing the comparison between the calculation results and the measured terrain involved in the embodiments of the present invention. Detailed Implementation

[0092] The following description, in conjunction with the accompanying drawings, details the underwater topography inversion method and apparatus based on water surface line control that relates to the present invention.

[0093] <Example 1>

[0094] like Figure 1 As shown, the underwater topography inversion method based on water surface line control provided in this embodiment includes the following steps:

[0095] Step 1: Collect and calculate the basic parameters of the river channel, including: topographic cross-sectional morphological characteristics, such as the water-passing area, the variation law of hydraulic radius with water depth, and measured cross-sectional water level data;

[0096] Step 2: Determine the model control equations, establish the objective function, and specify the initial values ​​of the riverbed slope and the accuracy requirements of the objective function;

[0097] Step 2.1: Based on the energy equation of the open channel steady flow, the objective function is further determined. The natural river channel has complex bottom topography, and the water level z represents the water surface. In the calculation, the entire river section is first divided into many smaller river segments using cross-sections. In this embodiment, the length of each smaller river segment is approximately 1.5 times the river width.

[0098] In a certain river segment, the upstream and downstream cross-sections are designated as cross-section 1 and cross-section 2, respectively, and the river segment length is Δs. The energy equation is:

[0099]

[0100] In the formula, z1 and z2 are the water levels at the upstream and downstream sections of the calculated river segment, in meters (m); α1 and α2 are the kinetic energy correction coefficients at the upstream and downstream sections of the calculated river segment; and the head loss is h. w1-2 =h f +h j The head loss includes two parts: friction head loss and local head loss. Natural river channels often have localized abrupt changes in direction, but the local head loss in general bends and narrow sections is small and is included in the friction head loss by taking the roughness coefficient. The formula for calculating friction head loss is:

[0101]

[0102] In the formula, The Chezy formula can be used to calculate the average hydraulic gradient of a river section. is the average flow modulus of the upstream and downstream sections of the river; A is the cross-sectional area, C is the Chezy coefficient, and R is the hydraulic radius;

[0103] The water level elevation z of the open channel is taken from the bottom elevation z of the channel. b Let the water depth h represent the following:

[0104] z = z b +hcosθ (3)

[0105] The energy equation for steady non-uniform flow in an open channel is:

[0106]

[0107] In the formula, cosθ is the cosine of the longitudinal inclination angle of the open channel bottom, and the calculation formula is as follows: The cross-sectional specific energy E is obtained by subtracting the bottom elevation of the channel from the total head. S That is:

[0108]

[0109] Therefore, equation (1) can be written as the energy equation for steady open channel flow in the form of cross-sectional specific energy:

[0110] E s2 -E s1 =z b1 -z b2 -h w1-2 (6)

[0111] In the calculation of water surface lines, sometimes the downstream water depth of a small segment is known, and the upstream water surface line is calculated; sometimes the opposite is true. Therefore, if the subscript u represents a cross-section with known water depth, and the subscript d represents a cross-section with the water depth to be calculated, then equation (4) can be rewritten as:

[0112]

[0113] In the formula, Let be the average hydraulic gradient of the micro-segment, which can be approximated as the average of the hydraulic gradients of the two cross-sections; r is a direction parameter, with the control section upstream during rapid flow, r = 1; and downstream during slow flow, r = -1. Therefore, the equation for the water depth of the cross-section to be determined can be obtained, that is, the model governing equation is:

[0114]

[0115] Step 2.2: Construct the objective function and establish the adjoint mode.

[0116] The objective function is constructed using the distance between the measured water depth and the calculated water depth at the cross-section to be determined:

[0117]

[0118] The function describing the dynamic state of the model is constructed as follows:

[0119]

[0120]

[0121]

[0122]

[0123] Step 2.3: Determine the accuracy requirement of the objective function based on actual engineering needs, and specify the initial bottom slope (river channel slope i). In this embodiment, the accuracy requirement is set to 10. -4 m, initial bottom slope is 0.003.

[0124] Step 3: Solve the model equations to obtain the calculated values ​​(calculate the water level), calculate the objective function and determine whether it meets the accuracy requirements. If it does, output the riverbed slope at this iteration. If it does not meet the requirements, proceed to the next step. Figure 3 By comparing the final output of step 3 after step 4 correction in the selected case of this invention with the measured river topography, it can be found that the two are in good agreement.

[0125] Step 4: Calculate the corrected gradient formula of the objective function with respect to the variable to be solved (bottom slope), determine the search direction and search step size of the optimization control variable, correct the variable to be solved (bottom slope), and return to step 3. Figure 2 The iterative correction process of the riverbed slope in the selected case of this invention is described.

[0126] Step 4.1: When the objective function does not meet the accuracy requirements, the riverbed slope needs further optimization. Optimization methods are used to find the optimal control variables, and the search direction d for optimizing the control variables is determined. k and search step size α k From x k Starting from the beginning, gradually adjust the control variables along the search direction.

[0127] x k+1 =x k +d k α k (14)

[0128] The objective function is continuously reduced until its calculated model value gets closer to the observed value, i.e.:

[0129] J(x k +d k α k ) <J(x k (15)

[0130] In the calculation, the negative gradient direction of the objective function with respect to the control variables is taken as the search direction, that is, the negative gradient direction of equation (9) with respect to the riverbed slope is taken as d. k To solve this problem, we first need to combine equations (12) and (13) to obtain the corrected gradient formula of the objective function with respect to the bottom slope i:

[0131]

[0132] Search step size α kThe method for determining the initial step size is as follows: A very small initial step size α0 is given (in this embodiment, the initial step size is 10). -6 ), along d k Substitute the direction optimization control variables into the objective function, if J(x) k +d k α0) <J(x k Let α1 = ωα0, where ω is a real number greater than 1, and substitute it into the objective function. Repeat this process until J(x) is reached. k +d k α k'+1 )>J(x k At this point, the search step size can be confirmed as α. k' .

[0133] Step 4.2: Correct the riverbed slope based on the determined search step size and search direction, i.e.:

[0134] i k+1 =i k +α k d k (17)

[0135] <Example 2>

[0136] Furthermore, this second embodiment provides an underwater topography inversion device based on water surface line control that can automatically implement the above method. The device includes an acquisition unit, a model building unit, a solution unit, a correction unit, an underwater topography generation unit, a dredging unit, an input display unit, and a control unit.

[0137] The acquisition department performs the steps described in step 1 above to obtain the basic parameters for calculating the river channel.

[0138] The model establishment section performs the steps described in step 2 above, determines the governing equations of the river channel calculation model, establishes the objective function, and specifies the initial values ​​of the riverbed slope and the accuracy requirements of the objective function.

[0139] The solver performs the steps described in step 3 above, solves the model equations to obtain the calculated water level, calculates the objective function and determines whether it meets the accuracy requirements. If it does, it outputs the riverbed slope it has iterated to this point; otherwise, it enters the correction section for correction.

[0140] The correction unit performs the steps described in step 4 above, calculates the corrected gradient formula of the objective function with respect to the bottom slope, determines the search direction and search step size of the optimization control variables, corrects the bottom slope, and returns to the solution unit.

[0141] The underwater terrain generation unit can generate underwater terrain based on the riverbed slope output by the solver.

[0142] The dredging department can determine the reservoir siltation situation based on the underwater topography generated by the underwater topography generation department, and then determine the reservoir dredging plan.

[0143] The input display unit is used to allow users to input operation commands and to display the input, output, and intermediate processing data of the corresponding units in the form of text, tables, graphics, or three-dimensional dynamic models according to the operation commands.

[0144] The control unit is connected in communication with the acquisition unit, model building unit, solution unit, correction unit, underwater terrain generation unit, dredging unit, and input display unit, and controls their operation.

[0145] The above embodiments are merely illustrative examples of the technical solutions of the present invention. The underwater topography inversion method and apparatus based on water surface line control involved in the present invention are not limited to the contents described in the above embodiments, but are defined by the scope of the claims. Any modifications, additions, or equivalent substitutions made by those skilled in the art based on these embodiments are within the scope of protection claimed by the claims of the present invention.

Claims

1. An underwater topographic inversion method based on water surface line control, characterized in that, Includes the following steps: Step 1: Collect and calculate the basic parameters of the river channel, including: topographic cross-sectional morphological features and measured cross-sectional water level data; Step 2: Determine the governing equations of the river channel calculation model, establish the objective function, and specify the initial values ​​of the riverbed slope and the accuracy requirements of the objective function; Step 2.1: The topography of the natural river channel is complex. The water level z represents the water surface line. The entire river channel is divided into small river segments by many cross sections, and the governing equations of the river channel calculation model are established. Step 2.2: Construct the objective function and establish the adjoint pattern; The objective function is constructed using the distance between the measured water depth and the calculated water depth at the cross-section to be determined: Construct a function to describe the dynamic state of the model: In the formula, h represents the water depth; E s λ represents the specific energy of the cross section; λ is a coefficient; r is a directional parameter, with the control section upstream during rapid flow and r = 1; and downstream during slow flow and r = -1; Δs represents the length of the river section; i represents the slope of the riverbed; subscript d represents the cross section where the water depth is to be determined; superscript obs represents the measured value; subscript u represents the cross section where the water depth is known. Step 2.3: Determine the accuracy requirements of the objective function based on actual engineering needs, and specify the initial bottom slope; Step 3: Solve the model equation to obtain the calculated water level value, calculate the objective function and determine whether it meets the accuracy requirements. If it does, output the riverbed slope at this iteration. If it does not, proceed to the next step. Step 4: Calculate the corrected gradient formula of the objective function with respect to the bottom slope, determine the search direction and search step size of the optimization control variables, correct the bottom slope and return to step 3; Step 4.1: Determine the search direction d for the optimized control variable. k and search step size α k From x k Starting from the beginning, gradually adjust the control variables along the search direction: x k+1 =x k +d k a k (4.1-1) In the formula, the subscripts k+1 and k represent the current correction and the previous correction, respectively; Let the objective function decrease continuously until its calculated model value gets closer to the observed value: J(x k +d k a k ) <J(x k ) (4.1-2) In the calculation, the negative gradient direction of equation (2.2-1) with respect to the riverbed slope is taken as d. k The corrected gradient formula for the objective function with respect to the bottom slope i is: Step 4.2: Correct the riverbed slope based on the determined search step size and search direction: i k+1 =i k +α k d k (4.2-1)。 2. The underwater topography inversion method based on water surface line control according to claim 1, characterized in that: in, In step 4.1, the search step size α k The method for determining the step size is as follows: Given an initial step size α0, along d... k Substitute the direction optimization control variables into the objective function, if J(x) k +d k α0) <J(x k Let α1 = ωα0, where ω is a real number greater than 1, and substitute it into the objective function. Repeat this process until J(x) is reached. k +d k α k'+1 )>J(x k At this point, the search step size α can be confirmed. k =α k' , where k' is the k'th search in the kth correction.

3. The underwater topography inversion method based on water surface line control according to claim 1, characterized in that: in, In step 1, the topographic cross-sectional morphological characteristics include the cross-sectional water-passing area and the variation law of hydraulic radius along water depth.

4. The underwater topography inversion method based on water surface line control according to claim 1, characterized in that: in, In step 2.1, the length of each small river segment is 1.2 to 1.6 times the river width.

5. The underwater topography inversion method based on water surface line control according to claim 1, characterized in that: in, In step 2.1, let the upstream and downstream sections of a certain small river segment be section 1 and section 2, respectively, and the river segment length be Δs. The energy equation is: E s2 -E s1 =with b1 -with b2 -h w1-2 (2.1-1) In the formula, Z b Indicates the bottom elevation of the trench; subscripts 1 and 2 represent section 1 and section 2 respectively; head loss h w1-2 =h f +h j Including head loss along the route h f and local head loss h j Two parts; In the calculation of water surface profiles, sometimes the downstream water depth of a small segment is known, and the upstream water surface profile is calculated; sometimes the opposite is true. The subscript *u* represents a cross-section with a known water depth, and the subscript *d* represents a cross-section with a water depth to be determined. Therefore, the energy equation for non-uniform flow is: In the formula, This indicates the average hydraulic gradient of the calculated river section; Locally abruptly changing sections in natural river channels are included in the head loss along the river by taking into account the roughness value; the formula for calculating the head loss along the river is: In the formula, To calculate the average hydraulic gradient of the river section; This represents the average flow modulus of the upstream and downstream sections of the river. The equations governing the water depth at the desired cross-section, i.e., the model governing equations, are as follows:

6. An underwater topographic inversion device based on water surface line control, characterized in that, include: The acquisition department acquires the basic parameters of the calculated river channel, including: topographic cross-sectional morphological features and measured cross-sectional water level data; The model establishment section determines the governing equations of the river channel calculation model according to steps 2.1 to 2.3, establishes the objective function, and gives the initial value of the riverbed slope and the accuracy requirements of the objective function. Step 2.1: The topography of the natural river channel is complex. The water level z represents the water surface line. The entire river channel is divided into small river segments by many cross sections, and the governing equations of the river channel calculation model are established. Step 2.2: Construct the objective function and establish the adjoint pattern; The objective function is constructed using the distance between the measured water depth and the calculated water depth at the cross-section to be determined: Construct a function to describe the dynamic state of the model: In the formula, h represents the water depth; E s λ represents the specific energy of the cross section; λ is a coefficient; r is a directional parameter, with the control section upstream during rapid flow and r = 1; and downstream during slow flow and r = -1; Δs represents the length of the river section; i represents the slope of the riverbed; subscript d represents the cross section where the water depth is to be determined; superscript obs represents the measured value; subscript u represents the cross section where the water depth is known. Step 2.3: Determine the accuracy requirements of the objective function based on actual engineering needs, and specify the initial bottom slope; The solution section solves the model equations to obtain the calculated water level value, calculates the objective function and determines whether it meets the accuracy requirements. If it does, it outputs the riverbed slope it has iterated to this point; otherwise, it enters the correction section for correction. The correction section calculates the corrected gradient formula of the objective function with respect to the bottom slope according to steps 4.1 to 4.2, determines the search direction and search step size of the optimization control variables, corrects the bottom slope, and returns to the solution section. Step 4.1: Determine the search direction d for the optimized control variable. k and search step size α k From x k Starting from the beginning, gradually adjust the control variables along the search direction: x k+1 =x k +d k a k (4.1-1) In the formula, the subscripts k+1 and k represent the current correction and the previous correction, respectively; Let the objective function decrease continuously until its calculated model value gets closer to the observed value: J(x k +d k a k ) <J(x k ) (4.1-2) In the calculation, the negative gradient direction of equation (2.2-1) with respect to the riverbed slope is taken as d. k The corrected gradient formula for the objective function with respect to the bottom slope i is: Step 4.2: Correct the riverbed slope based on the determined search step size and search direction: i k+1 =i k +α k d k (4.2-1) The control unit communicates with the acquisition unit, model building unit, solution unit, and correction unit, and controls their operation.

7. The underwater topography inversion device based on water surface line control according to claim 6, characterized in that, Also includes: The input display unit is connected to the control unit in communication, allowing the user to input operation commands and displaying the input, output, and intermediate processing data of the corresponding unit in the form of text, tables, graphics, or three-dimensional dynamic models according to the operation commands.

8. The underwater topography inversion device based on water surface line control according to claim 6, characterized in that, Also includes: The underwater topography generation unit communicates with the control unit and generates underwater topography based on the riverbed slope output by the solver unit. The dredging unit, which is connected to the control unit, determines the reservoir siltation situation based on the underwater topography generated by the underwater topography generation unit, and then determines the reservoir dredging plan.

9. The underwater topography inversion device based on water surface line control according to claim 6, characterized in that: in, In the correction section, the search step size α k Determination of: Given an initial step size α0, along d k Substitute the direction optimization control variables into the objective function, if J(x) k +d k α0) <J(x k Let α1 = ωα0, where ω is a real number greater than 1, and substitute it into the objective function. Repeat this process until J(x) is reached. k +d k α k'+1 )>J(x k At this point, the search step size α can be confirmed. k =α k' , where k' is the k'th search in the kth correction.

10. The underwater topography inversion device based on water surface line control according to claim 6, characterized in that: in, In the model establishment section, in a certain river segment, the upstream and downstream cross-sections are set as cross-section 1 and cross-section 2, respectively, and the river segment length is Δs. The energy equation is: E s2 -E s1 =with b1 -with b2 -h w1-2 (2.1-1) In the formula, Z b Indicates the bottom elevation of the trench; subscripts 1 and 2 represent section 1 and section 2 respectively; head loss h w1-2 =h f +h j Including head loss along the route h f and local head loss h j Two parts; In the calculation of water surface profiles, sometimes the downstream water depth of a small segment is known, and the upstream water surface profile is calculated; sometimes the opposite is true. The subscript *u* represents a cross-section with a known water depth, and the subscript *d* represents a cross-section with a water depth to be determined. Therefore, the energy equation for non-uniform flow is: In the formula, This indicates the average hydraulic gradient of the calculated river section; Locally abruptly changing sections in natural river channels are included in the head loss along the river by taking into account the roughness value; the formula for calculating the head loss along the river is: In the formula, To calculate the average hydraulic gradient of the river section; This represents the average flow modulus of the upstream and downstream sections of the river. The equations governing the water depth at the desired cross-section, i.e., the model governing equations, are as follows:

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