Tidal river reach water level and flow relation analysis method based on tidal level harmonic analysis

Abstract

The invention discloses a tidal reach water level and flow relation analysis method based on tidal level harmonic analysis. The method comprises the steps of collecting actually measured water level data, basin river topography and digital elevation data of a tidal reach hydrologic station; characteristic parameters and water surface elevation change characteristics of all partial tides of the tide level of the tidal river reach are obtained on the basis of tide level harmonic analysis, and then independent tide flow and river runoff flow are obtained; establishing a tidal reach one-dimensional hydrodynamic model, and analyzing a flow change process and a water level flow change relation under different water level change scenes; and analyzing the contribution degree of the tidal flow and the river runoff to the actual flow and the change process by utilizing a multivariate regression analysis and drift diameter analysis method to obtain the change characteristics of the water level and flow relationship of the tidal reach. The method has the advantages that the water level and flow relation of the tidal reach can be rapidly analyzed, complex estuary hydrodynamic process simulation is not needed, and the method is also applicable when actually measured flow data is lacked.

Description

Technical Field

[0001] The invention relates to the technical field of hydrological calculation and hydrological data compilation, and in particular to a method for analyzing the relationship between water level and flow in a tidal river section based on tidal level harmonic analysis. Background Art

[0002] The relationship between river water level and flow is one of the key elements of hydrological data compilation. The accuracy and rationality of the relationship between water level and flow will have a direct impact on the reliability and timeliness of hydrological data compilation, and further affect subsequent work such as hydrological forecasting, flood warning, river regulation and reservoir scheduling. The relationship between water level and flow can provide a scientific decision-making basis for comprehensive basin management, water resources development and sustainable utilization, and flood control and drought relief. Therefore, obtaining accurate river water level and flow relationship is of practical significance for improving the quality of hydrological data compilation and optimizing basin water resources development and comprehensive utilization.

[0003] For the monitoring and acquisition of river water level and flow data, due to the complex terrain of natural river channels, the flow velocity and morphology of rivers in different sections are difficult to monitor in real time. Long-term continuous monitoring of river flow data requires a lot of manpower, material and economic resources, while continuous monitoring of river water level data is relatively easy to achieve. Therefore, most hydrological stations usually only continuously monitor river water level data and obtain continuous river flow data through the water level-flow relationship recursion. Under the influence of factors such as riverbed scouring and silting, flood fluctuations, backwater changes, and tidal effects, the water level-flow relationship of natural rivers is mostly expressed as a single or complex rope curve relationship. It is difficult to directly and accurately determine its mathematical function relationship. It is necessary to use single-value processing to construct a stable and single water level-flow relationship curve. At present, the more mature methods for calculating the relationship between river water level and flow include the correction factor method, the drop index method, and the data-driven optimization method. These methods are widely used in the calculation and verification of the water level-flow relationship in river flood processes, and have relatively good calculation accuracy and applicability.

[0004] At present, a relatively complete hydrological data compilation system has been established for the major rivers in my country, forming a relatively complete hydrological data database. However, for some small and medium-sized river basins, the collection and compilation of hydrological data is not perfect, and the river level-discharge relationship has not yet been obtained and calibrated in the basin area. Its hydrological stations can usually only obtain continuous water level data but lack long-term flow data. In addition, most hydrological stations in tidal river sections are tidal stations, which mainly tend to obtain continuous tidal water level data. Against the background of global warming, extreme weather events such as typhoons and storm surges occur frequently, and the tidal upstream and erosion processes in the estuary area are intensified. When conducting numerical simulation analysis of the hydrodynamic process of tidal river sections, it is necessary to use the flow data of tidal river sections to calibrate and verify the model. Due to the limitations of the measured data acquisition process, the flow data of tidal river sections calculated by the hydrodynamic model are currently mainly relied on to analyze the water level-discharge relationship of tidal river sections.

[0005] In view of the above problems, the present invention proposes a technical solution based on tidal harmonic analysis method combined with numerical simulation analysis of hydrodynamic model, which is used to solve the problem of water level and flow relationship analysis in tidal river sections lacking measured flow data. The method of the present invention effectively makes up for the shortcomings of the existing technology and can provide more reliable data and technical support for hydrological analysis and hydrodynamic model research in tidal river sections. Summary of the invention

[0006] The object of the present invention is to provide a method for analyzing the relationship between water level and flow in a tidal river section based on tidal harmonization analysis, thereby solving the above-mentioned problems existing in the prior art.

[0007] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0008] A method for analyzing the relationship between water level and flow in a tidal river section based on tidal harmonic analysis comprises the following steps:

[0009] S1. Tidal harmonization analysis:

[0010] Based on tidal harmonic analysis, characteristic parameters of each tidal level segment and water surface elevation change characteristics of tidal river sections are obtained, and then independent tidal flow and river runoff flow are obtained;

[0011] S2. Real-time flow calculation of one-dimensional hydrodynamic model:

[0012] Discretize and solve the Saint-Venant equations describing the hydrodynamic process of tidal river sections to obtain the water level and flow information of each calculation section; establish a one-dimensional hydrodynamic equation for tidal river sections to analyze the flow change process and the relationship between water level and flow change in tidal river sections under different water level change scenarios;

[0013] S3. Multiple regression analysis and path analysis:

[0014] The tidal flow and runoff flow are set as independent variables, and the actual flow is set as the dependent variable. The partial regression coefficient obtained by multiple regression analysis and the path coefficient obtained by path analysis respectively reflect the contribution of the independent variables to the numerical value and change process of the dependent variable, and the changing characteristics of the water level-flow relationship in tidal river sections are obtained.

[0015] Preferably, step S1 specifically includes the following contents:

[0016] S11. The classical tidal harmonic analysis method assumes that the amplitude and retardation angle of each tide are constants, and the tidal time series function is represented by the linear superposition of a series of cosine functions, each cosine function used for superposition represents a tide;

[0017]

[0018] Where Z(t) is the tide level data observed at time t; σ j , H j , g j are the angular frequency, amplitude and lag angle corresponding to the jth tidal component; j = 1, 2, …, J, J is the total number of tidal components; S0 is the sea level elevation at the current moment;

[0019] S12. Obtain new variable a according to the amplitude and delay angle of the tidal wave j and b j , using the new variable a j and b j Linearized tide level time series function;

[0020]

[0021] a j =H j cosg j

[0022] b j =H j sing j

[0023] Among them, Z(t)' is the new variable a j and b j The tidal data observed at time t after linearization;

[0024] S13. When there are N tide level data observed at each time, N tide level equations can be constructed, and the least square method of multivariate function to find the extreme value is used to solve the variable a. j and b j ;

[0025] S14. Get variable a j and b j After that, the amplitude and delay angle of each tide are,

[0026]

[0027] g j =arctan(b j / a j )

[0028] Among them, the delay angle g j The value range of the inverse tangent function is (0,360°); the result range of the inverse tangent function arctan is (-90°,90°); according to the parameter a j and b j To correct the lag angle g j ;

[0029] S15. Through tidal harmonic analysis and tidal fitting forecasting, the fitting forecast tidal level time series and the sea level elevation change time series for the study period are obtained.

[0030] Preferably, step S13 specifically comprises using matrix operation to solve:

[0031] Z=KU

[0032] Among them, Z is the observed tide data matrix; K is the known coefficient matrix; U is the unknown parameter matrix to be solved;

[0033] The specific form of the above matrix is:

[0034]

[0035] According to the least squares method, the optimal solution of U is,

[0036] U=(K T K) -1 K T Z

[0037] Where T is the transpose of the matrix.

[0038] Preferably, between step S14 and step S15, the following is further included:

[0039] S15. Use the Rayleigh criterion to determine the shortest time series length of the observed tide level required to distinguish each tide component.

[0040]

[0041] Among them, N0 is the length of the observation sequence; t0 is the observation interval; T1 and T2 are the periods of any two tidal components.

[0042] Preferably, step S2 specifically includes the following contents:

[0043] S21. The Saint-Venant equations describing the motion law of shallow one-dimensional non-steady-state gradually changing flow are used to describe the hydrodynamic process of tidal river sections.

[0044] S22, using the four-point eccentric Preissmann implicit difference format, discretize and solve the Saint-Venant equations to obtain the water level and flow information of each calculation section;

[0045] S23. Establish a one-dimensional hydrodynamic model for tidal river sections, and analyze and study the changing process of the water level-discharge relationship under the influence of different influencing factors in the river section;

[0046] S24. Set different calculation scenarios to analyze the relationship between tides, river runoff and the water level and flow in tidal river sections in actual conditions.

[0047] Preferably, in step S23, a one-dimensional hydrodynamic model of a tidal river section is established, which specifically includes the following contents:

[0048] S231. Establish engineering documents;

[0049] S232, draw river systems and import river terrain data;

[0050] S233, setting boundary conditions and initial conditions;

[0051] S234, setting operation parameters;

[0052] S235, model calculation and post-processing.

[0053] Preferably, the scenario setting in step S24 specifically includes:

[0054] (1) All flow boundaries are closed, and the downstream water level boundary is set to the tidal data without the influence of river runoff; this is used to simulate and analyze the relationship between water level and flow under the action of tides;

[0055] (2) The flow boundary remains unchanged, and the downstream water level boundary is set to the river water level data after removing the tidal effect; this is used to simulate and analyze the river runoff effect;

[0056] (3) The flow boundary and water level boundary are set as measured data, which are used to simulate the actual situation and the combined effects of tides and runoff.

[0057] Preferably, step S3 specifically includes the following contents:

[0058] S31. Multiple regression analysis: Let y be an observable random variable, affected by n factors x1, x2, …, x n If there is a linear relationship between the two, the expression is:

[0059]

[0060] Among them, α is the intercept; x i is the i-th factor, i=1,2,…,n; β i is the partial regression coefficient; ε is the random error, which is subject to Normal distribution of is the regression variance;

[0061] The multiple regression fitting model expression is:

[0062]

[0063] The calculation formula of the regression equation is the regression square sum Q:

[0064]

[0065] make SS i =∑X i 2 ,SP ij =∑X i Y i ,SP iy =∑X i Y; let the coefficient matrix be A, the partial regression coefficient matrix be b, and the constant matrix be K. According to the least squares method, the relationship between the three matrices is expressed as,

[0066] Ab=K

[0067] in,

[0068]

[0069] The optimal solution of the partial regression coefficient matrix b is,

[0070] b=(A T A) -1 A T K

[0071] After calculating the optimal solution of the partial regression coefficient matrix b, the intercept a is,

[0072]

[0073] S32, Path analysis: Calculate the path coefficient p i ,

[0074]

[0075] Among them, SS y is the total sum of squares of the dependent variable y; the path coefficient p i The value range is (-1,1). The larger the absolute value of the path coefficient is, the greater the influence of the independent variable on the dependent variable is.

[0076] Preferably, before step S1, the step further includes:

[0077] S0. Data collection:

[0078] Collect measured water level data from hydrological stations in tidal river sections, river topography in the basin and digital elevation data, and process these data.

[0079] Preferably, S0 specifically includes the following contents:

[0080] S01. Obtain high-resolution digital elevation data of the watershed area corresponding to the tidal river section from the open source dataset, and perform stitching, cropping, geographic and projection coordinate settings on it;

[0081] S02. Obtain river topographic data of tidal river sections by means of cruise surveying or mobile phone historical hydrological data, and integrate it into the above digital elevation data;

[0082] S03. Collect and organize the long-term measured water level data of hydrological stations in tidal river sections, and perform time-averaging processing on the measured water level data.

[0083] The beneficial effects of the present invention are: 1. The method of the present invention utilizes tidal harmonic analysis and tidal processing to explore the tidal change rules and tidal contributions of tidal river sections, and can obtain real-time tidal change data without the influence of river runoff and river water level change data without the influence of tides. 2. The method of the present invention utilizes a one-dimensional hydrodynamic model to calculate real-time flow to solve the problem of lack of long-term continuous measured flow data at hydrological stations in tidal river sections, and can calculate the real-time flow change process of tidal river sections under the action of tides and river runoff. 3. The method proposed by the present invention utilizes multiple regression analysis and path analysis to analyze the contribution of tidal flow and runoff flow to the numerical size and change process of real-time flow, and realizes a rapid analysis of the water level-flow relationship for tidal river sections lacking measured flow data. BRIEF DESCRIPTION OF THE DRAWINGS

[0084] Figure 1 is a flow chart of an analysis method in an embodiment of the present invention;

[0085] Figure 2 Schematic diagram of the Preissmann implicit difference format in an embodiment of the present invention;

[0086] Figure 3 is a schematic diagram of the water system in the study area in an embodiment of the present invention;

[0087] Figure 4 is a schematic diagram of tidal harmonic analysis results in an embodiment of the present invention;

[0088] Figure 5 is a schematic diagram of the forecast tide level and river runoff water level in an embodiment of the present invention;

[0089] Figure 6 is a schematic diagram of tidal flow and river runoff calculation results in an embodiment of the present invention;

[0090] Figure 7 It is a diagram of the verification results of the multiple regression analysis in the embodiment of the present invention. DETAILED DESCRIPTION

[0091] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings. It should be understood that the specific implementation methods described herein are only used to explain the present invention and are not used to limit the present invention.

[0092] Embodiment 1

[0093] like Figure 1 As shown, in this embodiment, a method for analyzing the relationship between water level and flow in a tidal river section based on tidal harmonic analysis is provided, which includes the following four parts:

[0094] 1. Data Collection

[0095] Collect the measured water level data of hydrological stations in tidal river sections (research river sections), river topography and digital elevation data in the basin, and process these data. Specifically, it includes the following contents:

[0096] 1.1. Obtain high-resolution digital elevation data of the watershed area corresponding to the study river section from the open source dataset, and perform operations such as splicing, cropping, geographic and projection coordinate settings on it.

[0097] 1.2. Obtain river topographic data of the study river section by means of cruise surveying or collecting historical hydrological data, and integrate them into the above-mentioned digital elevation data.

[0098] 1.3. Collect and organize the long-term measured water level data of the hydrological stations in the study river section, and perform time-averaging processing on the measured data.

[0099] 2. Tidal harmonization analysis:

[0100] Based on tidal harmonic analysis, the characteristic parameters of each tidal level segment and the water surface elevation change characteristics of the tidal river section are obtained, and then the independent tidal flow and river runoff flow are obtained. Specifically, it includes the following contents:

[0101] 2.1. The classical tidal harmonic analysis method assumes that the amplitude and retardation angle of each tide are constants, and the tidal time series function is represented by the linear superposition of a series of cosine functions, each of which represents a tide.

[0102]

[0103] Where Z(t) is the tide level data observed at time t; σ j , H j , g j are the angular frequency, amplitude and lag angle corresponding to the jth partial tide; j=1,2,…,J, J is the total number of partial tides; S0 is the sea level elevation at the current moment.

[0104] 2.2. Obtain the new variable a according to the amplitude and lag angle of the tidal wave j and b j , using the new variable a j and b j Linearized tide level time series function;

[0105]

[0106] in,

[0107] a j =H j cosg j , b j =H j sing j

[0108] Among them, Z(t)' is the new variable a j and b j The tide level data observed at time t after linearization.

[0109] 2.3. When there are N tide level data observed at each time, N tide level equations can be formed. The least square method of multivariate function to find the extreme value is used to solve the variable a. j and b j ; Specifically, in order to facilitate programming and calculation, matrix operations are used to solve,

[0110] Z=KU (3)

[0111] Among them, Z is the observed tide data matrix; K is the known coefficient matrix; U is the unknown parameter matrix to be solved; the specific form of the above matrix is,

[0112]

[0113]

[0114] According to the least squares method, the optimal solution of U is,

[0115] U=(K T K) -1 K T Z

[0116] Where T is the transpose of the matrix.

[0117] 2.4. Getting variable a j and b j After that, the amplitude and delay angle of each tide are,

[0118]

[0119] Among them, the delay angle g j The value range of the inverse tangent function is (0,360°); the result range of the inverse tangent function arctan is (-90°,90°); it needs to be based on the parameter a j and b j To correct the lag angle g j .

[0120] 2.5. In order to improve the resolution accuracy of the tides, the Rayleigh criterion is used to determine the shortest time series length of the tide level observation required to resolve each tide.

[0121]

[0122] Where N0 is the length of the observation sequence; t0 is the observation interval; T1 and T2 are the periods of any two tidal components;

[0123] 2.6. Through tidal harmonic analysis and tidal fitting forecast, the fitted forecast tidal time series of the study period is obtained, that is, the tidal time series without the influence of river runoff, and the sea level elevation change time series during the study period. For tidal river sections, it can be regarded as the river water level series reflecting the influence of the river's own runoff after removing the influence of tidal effects.

[0124] 3. Real-time flow calculation of one-dimensional hydrodynamic model:

[0125] Discretize and solve the Saint-Venant equations describing the hydrodynamic process of tidal river sections to obtain the water level and flow information of each calculation section; establish a one-dimensional hydrodynamic equation for tidal river sections to analyze the flow change process and the relationship between water level and flow change in tidal river sections under different water level change scenarios. Specifically, it includes the following contents:

[0126] 3.1. The tidal river section has a small drop and a large cross-sectional depth. The Saint-Venant equations describing the motion law of shallow one-dimensional non-steady gradually changing flow are used to describe the hydrodynamic process of the tidal river section. The continuity equation and momentum equation in the Saint-Venant equations are shown in equations (6.a) and (6.b):

[0127]

[0128]

[0129] Among them, t is the time coordinate; x is the space coordinate; A is the cross-sectional area of ​​the river section; Q is the flow rate; q1 is the single-width flow rate of the inflow beside the river section (inflow is positive and outflow is negative); u is the average flow velocity of the section; z is the river water level; g is the gravitational acceleration; n0 is the Manning coefficient; R is the hydraulic radius.

[0130] 3.2, using the four-point eccentric Preissmann implicit difference format (such as Figure 2 As shown in the figure, the Saint-Venant equations (Equation (6.a) and Equation (6.b)) are discretized and solved. The discrete equations are shown in Equation (7.a) to Equation (7.d), and the water level and flow information of each calculation section are obtained.

[0131]

[0132] Where i is the section number; t is the time step; △t is the discrete time step; x i is the spatial step length; △x is the discrete spatial step length; θ is the eccentricity coefficient; n is the calculation time; q is the dependent variables such as flow rate and water level in the Saint-Venant equations; Represents the discrete variable of section i at time n. Substituting the above finite difference discrete equation into the Saint-Venant equations can obtain a multi-dimensional linear equation system. Solving the coefficients of the linear equation system can obtain the water level and flow information of each calculation section.

[0133] 3.3. Establish a one-dimensional hydrodynamic model for tidal river sections, and analyze and study the changing process of the water level-discharge relationship under the influence of different influencing factors in the river section. The process of establishing the one-dimensional hydrodynamic model is as follows:

[0134] (1) Establish project documents.

[0135] (2) Draw river systems and import river terrain data.

[0136] (3) Set boundary conditions and initial conditions.

[0137] (4) Set the operation parameters.

[0138] (5) Model calculation and post-processing.

[0139] 3.4. Set different calculation scenarios to analyze the relationship between tides, river runoff and water level and flow in tidal river sections in actual conditions. The specific scenarios are as follows:

[0140] ① Close all flow boundaries, and set the downstream water level boundary to the tidal data without the influence of river runoff; this is used to simulate and analyze the relationship between water level and flow under the action of tides;

[0141] ② The flow boundary does not change, and the downstream water level boundary is set to the river water level data after removing the tidal effect; it is used to simulate and analyze the river runoff effect;

[0142] ③ The flow boundary and water level boundary are set as measured data; they are used to simulate the actual situation and the combined effects of tides and runoff.

[0143] 4. Multiple regression analysis and path analysis:

[0144] The tidal flow and runoff flow are set as independent variables, and the actual flow is set as the dependent variable. The partial regression coefficient obtained by multivariate regression analysis and the path coefficient obtained by path analysis respectively reflect the contribution of the independent variable to the value and change process of the dependent variable, and obtain the changing characteristics of the water level and flow relationship in the tidal river section, so as to realize the rapid analysis of the water level and flow relationship in the tidal river section. Specifically, it includes the following contents:

[0145] 4.1. Multiple regression analysis:

[0146] Let y be an observable random variable affected by n factors x1, x2, …, x n If there is a linear relationship between the two, the expression is:

[0147]

[0148] Among them, α is the intercept; x i is the i-th factor, i=1,2,…,n; β i is the partial regression coefficient; ε is the random error, which is subject to Normal distribution of is the regression variance;

[0149] The multiple regression fitting model expression is:

[0150]

[0151] The calculation formula of the regression equation is the regression square sum Q:

[0152]

[0153] make SS i =∑X i 2 ,SP ij =∑X i Y i ,SP iy =∑X i Y; let the coefficient matrix be A, the partial regression coefficient matrix be b, and the constant matrix be K. According to the least squares method, the relationship between the three matrices is expressed as,

[0154] Ab=K (11)

[0155] in,

[0156]

[0157] The optimal solution of the partial regression coefficient matrix b is,

[0158] b=(A T A) -1 A T K

[0159] After calculating the optimal solution of the partial regression coefficient matrix b, the intercept a is,

[0160]

[0161] 4.2 Path analysis:

[0162] Calculate the path coefficient p i ,

[0163]

[0164] Among them, SS y is the total sum of squares of the dependent variable y; the path coefficient p i The value range is (-1,1). The larger the absolute value of the path coefficient, the greater the influence of the independent variable on the dependent variable. The partial regression coefficient and path coefficient obtained by multiple regression analysis respectively reflect the influence of the independent variable on the value and degree of change of the dependent variable.

[0165] Embodiment 2

[0166] In this implementation case, Shizui Station, a tidal station in the tidal river section of the Tanjiang River, is taken as an example to specifically illustrate the specific implementation process and results of the present invention. Shizui Station of Tanjiang River is located in the lower reaches of the Tanjiang River. It is a national basic tidal (water) station with long-sequence tidal (water) level measurement data. The main water systems of the Tanjiang River are distributed as follows: Figure 3 The steps and benefit analysis of this implementation case are as follows:

[0167] 1. Data Collection

[0168] Collect the measured tide (water) level data of Shizui Station in 2023, the topographic data of the main channel of Tanjiang River, the digital elevation data of Tanjiang River Basin, and the discharge flow of Heshan Sluice from March 25 to April 18, 2023. Use GIS tools to process and integrate the topographic data; average the measured tide (water) level data of Shizui Station in 2023 into hourly water level data.

[0169] 2. Tidal harmonization analysis

[0170] In this embodiment, the main information of each tidal component considered is shown in Table 1. The tidal harmonic analysis calculation process is implemented by the S_TIDE toolkit of Matlab language. First, the "s_tide" function in S_TIDE is used to perform a harmonic analysis on the measured tidal data of Shizui Station in 2023. The contribution of each tidal component is analyzed by sorting the tidal amplitude, and the tidal amplitude and lag angle of the 11 tidal components considered are calculated. The calculation results of the tidal harmonic analysis are shown in Table 2. The "s_consturct2" function is used to predict the tidal changes from March 26 to April 18, considering both all tidal components and the above 11 tidal components. The prediction results are as follows: Figure 4 As shown. The root mean square error RMSE considering all tidal conditions is 0.067m, and the Nash efficiency coefficient NSE is 0.98; the root mean square error RMSE considering 11 tidal conditions is 0.122m, and the Nash efficiency coefficient NSE is 0.93, indicating that the tidal level prediction results of the two cases are close to the measured values. On this basis, the tidal level change results after removing the influence of river runoff and the river water level change results after removing the tidal effect are obtained (see Figure 5 ).

[0171] Table 1 Main tidal information

[0172]

[0173] Table 2 Tidal harmonic analysis results

[0174]

[0175] 3. Real-time flow calculation of one-dimensional hydrodynamic model

[0176] In this embodiment, the HEC-RAS software is used to establish a one-dimensional hydrodynamic model. In order to analyze the impact and contribution of tidal flow and river runoff on the flow change of Shizui section, the following three scenarios are set for analysis:

[0177] ① Close all flow boundaries, and set the downstream water level boundary to the tidal data that removes the influence of river runoff;

[0178] ② The flow boundary remains unchanged, and the downstream water level boundary is set to the river water level data after removing the tidal effect;

[0179] ③The flow boundary and water level boundary are set as measured data.

[0180] The flow calculation results of scenario ① and scenario ② are as follows: Figure 6As shown. For the tidal flow calculated in scenario ①, the water level-flow relationship shows an obvious rope-loop type non-stable single-valued corresponding relationship, and the instantaneous water level-flow shows an alternating fluctuation characteristic; for the river runoff flow calculated in scenario ②, the flow changes relatively stably over time, and the flow-water-level-flow relationship shows a stable non-single-valued corresponding relationship. Under the action of river runoff, the movement form of the water flow is a non-moving wave. In this implementation case, the water level-flow relationship of Shizui Station is affected by both the tidal flow of the rope-loop type non-stable non-single-valued relationship and the river runoff of the stable non-single-valued relationship.

[0181] 4. Multiple regression analysis and path analysis

[0182] In this implementation case, the flow calculation results of scenarios ① and ② are set as independent variables, and the flow calculation results of scenario ③ are set as dependent variables, so as to conduct multiple regression analysis and path analysis. The results of multiple regression analysis are shown in Appendix 3, and the verification results are shown in Figure 7 As shown. For the verification results, the square residual coefficient R2 is 0.9095 and the root mean square error RMSE is 139.9m 3 / s, the relative standard deviation RSD is 21.0%, the Nash efficiency coefficient NSE is 0.92, and the partial regression coefficient obtained by the multiple regression analysis can better reflect the influence of river runoff and tidal flow on the actual flow size. For the path analysis, the path coefficient of tidal flow is 0.9446, and the path coefficient of river runoff is 0.0710, which shows that the direct influence of tidal flow on the actual flow in this embodiment is much greater than that of river runoff, and the change process of real-time flow in the tidal river section is mainly controlled by the change process of tidal flow.

[0183] Table 3 Multiple regression analysis results parameter analysis

[0184]

[0185] ANOVA

[0186]

[0187]

[0188] In summary, the method for analyzing the relationship between water level and flow in tidal river sections based on tidal harmonization analysis proposed in the present invention can quickly and conveniently analyze the relationship between water level and flow in tidal river sections without going through complex simulation of estuary hydrodynamic processes. It is also applicable to water level stations in tidal river sections that lack long-term measured flow data, and is helpful to improve the collection and compilation of hydrological data in small and medium-sized river basins and tidal river sections.

[0189] By adopting the above technical solution disclosed in the present invention, the following beneficial effects are obtained:

[0190] The present invention provides a method for analyzing the relationship between water level and flow in a tidal river section based on tidal harmonization analysis: The method of the present invention uses tidal harmonization analysis and tidal division processing to explore the tidal level change law and tidal contribution of tidal river sections, and can obtain real-time tidal level change data without the influence of river runoff and river water level change data without the influence of tides. The method of the present invention uses a one-dimensional hydrodynamic model to calculate the real-time flow to solve the problem of the lack of long-term continuous measured flow data at hydrological stations in tidal river sections, and can calculate the real-time flow change process of tidal river sections under the action of tides and river runoff. The method proposed by the present invention uses multiple regression analysis and path analysis to analyze the contribution of tidal flow and runoff flow to the numerical size and change process of real-time flow, and realizes a rapid analysis of the relationship between water level and flow in tidal river sections that lack measured flow data.

[0191] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be considered as the scope of protection of the present invention.

Claims

1. A method for analyzing the relationship between water level and flow in a tidal river section based on tidal harmonic analysis, characterized in that: The following steps are included: S1. Tidal harmonization analysis: Based on tidal harmonic analysis, characteristic parameters of each tidal level segment and water surface elevation change characteristics of tidal river sections are obtained, and then independent tidal flow and river runoff flow are obtained; S2. Real-time flow calculation of one-dimensional hydrodynamic model: Discretize and solve the Saint-Venant equations describing the hydrodynamic process of tidal river sections to obtain the water level and flow information of each calculation section; establish a one-dimensional hydrodynamic equation for tidal river sections to analyze the flow change process and the relationship between water level and flow change in tidal river sections under different water level change scenarios; S3. Multiple regression analysis and path analysis: The tidal flow and runoff flow are set as independent variables, and the actual flow is set as the dependent variable. The partial regression coefficient obtained by multiple regression analysis and the path coefficient obtained by path analysis respectively reflect the contribution of the independent variables to the numerical value and change process of the dependent variable, and the changing characteristics of the water level-flow relationship in tidal river sections are obtained.

2. The method for analyzing the relationship between water level and flow in a tidal river section based on tidal harmonic analysis according to claim 1 is characterized by: Step S1 specifically includes the following contents: S11. The classical tidal harmonic analysis method assumes that the amplitude and retardation angle of each tide are constants, and the tidal time series function is represented by the linear superposition of a series of cosine functions, each cosine function used for superposition represents a tide; Where Z(t) is the tide level data observed at time t; σ j , H j , g j are the angular frequency, amplitude and lag angle corresponding to the jth tidal component; j = 1, 2, …, J, J is the total number of tidal components; S0 is the sea level elevation at the current moment; S12. Obtain a new variable a based on the amplitude and lag angle of the tide j and b j , using the new variable a j and b j Linearized tide level time series function; a j =H j cost j b j =H j sing j Among them, Z(t)' is the new variable a j and b j The tidal data observed at time t after linearization; S13. When there are N tide level data observed at each time, N tide level equations can be constructed, and the least square method of multivariate function to find the extreme value is used to solve the variable a. j and b j ; S14. Get variable a j and b j After that, the amplitude and delay angle of each tide are, g j =arctan(b j / a j ) Among them, the delay angle g j The value range of the inverse tangent function is (0,360°); the result range of the inverse tangent function arctan is (-90°,90°); according to the parameter a j and b j To correct the lag angle g j ; S15. Through tidal harmonic analysis and tidal fitting forecasting, the fitting forecast tidal level time series and the sea level elevation change time series for the study period are obtained.

3. The method for analyzing the relationship between water level and flow in a tidal river section based on tidal harmonic analysis according to claim 2 is characterized by: Step S13 specifically involves using matrix operations to solve: Z=KU Among them, Z is the observed tide data matrix; K is the known coefficient matrix; U is the unknown parameter matrix to be solved; The specific form of the above matrix is: According to the least squares method, the optimal solution of U is, U=(K T K) -1 K T Z Where T is the transpose of the matrix.

4. The method for analyzing the relationship between water level and flow in a tidal river section based on tidal harmonic analysis according to claim 2 is characterized by: Also included between step S14 and step S15, S15. Use the Rayleigh criterion to determine the shortest time series length of the observed tide level required to distinguish each tide component. Among them, N0 is the length of the observation sequence; t0 is the observation interval; T1 and T2 are the periods of any two tidal components.

5. The method for analyzing the relationship between water level and flow in a tidal river section based on tidal harmonic analysis according to claim 1 is characterized by: Step S2 specifically includes the following contents: S21. The Saint-Venant equations describing the motion law of shallow one-dimensional non-steady-state gradually changing flow are used to describe the hydrodynamic process of tidal river sections. S22, using the four-point eccentric Preissmann implicit difference format, discretize and solve the Saint-Venant equations to obtain the water level and flow information of each calculation section; S23. Establish a one-dimensional hydrodynamic model for tidal river sections, and analyze and study the changing process of the water level-discharge relationship under the influence of different influencing factors in the river section; S24. Set different calculation scenarios to analyze the relationship between tides, river runoff and the water level and flow in tidal river sections in actual conditions.

6. The method for analyzing the relationship between water level and flow in a tidal river section based on tidal harmonic analysis according to claim 5 is characterized by: In step S23, a one-dimensional hydrodynamic model of the tidal river section is established, which specifically includes the following contents: S231. Establish engineering documents; S232, draw river systems and import river terrain data; S233, setting boundary conditions and initial conditions; S234, setting operation parameters; S235, model calculation and post-processing.

7. The method for analyzing the relationship between water level and flow in a tidal river section based on tidal harmonic analysis according to claim 5 is characterized by: The scenario setting in step S24 specifically includes: (1) All flow boundaries are closed, and the downstream water level boundary is set to the tidal data without the influence of river runoff; this is used to simulate and analyze the relationship between water level and flow under the action of tides; (2) The flow boundary remains unchanged, and the downstream water level boundary is set to the river water level data after removing the tidal effect; this is used to simulate and analyze the river runoff effect; (3) The flow boundary and water level boundary are set as measured data, which are used to simulate the actual situation and the combined effects of tides and runoff.

8. The method for analyzing the relationship between water level and flow in a tidal river section based on tidal harmonic analysis according to claim 1 is characterized by: Step S3 specifically includes the following contents: S31. Multiple regression analysis: Let y be an observable random variable, affected by n factors x1, x2, …, x n If there is a linear relationship between the two, the expression is: Among them, α is the intercept; x i is the i-th factor, i=1,2,…,n; β i is the partial regression coefficient; ε is the random error, which is subject to Normal distribution of is the regression variance; The multiple regression fitting model expression is: The calculation formula of the regression equation is the regression square sum Q: make SP ij =∑X i Y i ,SP iy =∑X i Y; let the coefficient matrix be A, the partial regression coefficient matrix be b, and the constant matrix be K. According to the least squares method, the relationship between the three matrices is expressed as, Ab=K in, The optimal solution of the partial regression coefficient matrix b is, b=(A T A) -1 A T K After calculating the optimal solution of the partial regression coefficient matrix b, the intercept a is, S32, Path analysis: Calculate the path coefficient p i , Among them, SS y is the total sum of squares of the dependent variable y; the path coefficient p i The value range is (-1,1). The larger the absolute value of the path coefficient is, the greater the influence of the independent variable on the dependent variable is.

9. The method for analyzing the relationship between water level and flow in a tidal river section based on tidal harmonic analysis according to any one of claims 1 to 8, characterized in that: Before step S1, the method further includes: S0. Data collection: Collect measured water level data from hydrological stations in tidal river sections, river topography in the basin and digital elevation data, and process these data.

10. The method for analyzing the relationship between water level and flow in a tidal river section based on tidal harmonic analysis according to claim 9, characterized in that: S0 specifically includes the following contents: S01. Obtain high-resolution digital elevation data of the watershed area corresponding to the tidal river section from the open source dataset, and perform stitching, cropping, geographic and projection coordinate settings on it; S02. Obtain river topographic data of tidal river sections by means of cruise surveying or mobile phone historical hydrological data, and integrate it into the above digital elevation data; S03. Collect and organize the long-term measured water level data of hydrological stations in tidal river sections, and perform time-averaging processing on the measured water level data.

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