Method for analyzing evolution characteristics of secondary hanging river

Abstract

The invention relates to the technical field of secondary suspension river treatment and comprehensive lifting treatment of wandering river channels and mud flat areas, in particular to a secondary suspension river evolution characteristic analysis method. Comprising the following steps: S1, collecting long-time sequence data; and S2, carrying out trend analysis on the long-time sequence data through a Tuyer-Sen slope estimation method, and respectively and directly giving the trends of the data in different periods. And S3, judging the periodicity of long-time sequence data through a wavelet analysis method, carrying out multi-scale refined analysis on data signals, carrying out strict diagnosis on mutation points, and meanwhile, giving information on two aspects of phase and amplitude of time sequence change. The long-time sequence data is the tidal land transverse gradient. According to the method, the Tuyer-Sesson slope estimation method and the wavelet analysis method are utilized, the analysis effect is good, and the credibility of secondary river evolution characteristic analysis is high. The method has very important theoretical significance and practical value for second-level suspension river treatment and comprehensive lifting treatment of wandering river channels and mud flat areas in the future.

Description

Technical Field

[0001] The present invention relates to the technical field of secondary suspended river management, wandering river channel and beach comprehensive improvement management, and in particular to a secondary suspended river evolution characteristic analysis method. Background Art

[0002] The Yellow River has a lot of water and sediment, and the relationship between water and sediment is not harmonious. The high sediment characteristics of the Yellow River have caused the lower reaches to be in a state of intense siltation. The riverbed rises by an average of 0.05 to 0.10 meters per year. The current riverbed is generally 4 to 6 meters higher than the ground on both sides of the river. As a result, the lower reaches of the Yellow River have become a world-famous "hanging river on the ground". Since the 1960s, with the completion and operation of the Sanmenxia Reservoir and the construction of production dikes, the relationship between water and sediment in the lower reaches of the Yellow River has become extremely unbalanced. The lower reaches of the riverbed have continued to silt up and shrink, causing the main river channel to gradually rise above the beach near the dike, forming a "secondary hanging river" with "high channel, low beach, and sunken dike root". Since the mid-to-late 1980s, the Yellow River has been in a relatively dry period, with reduced runoff in the downstream and a significant increase in industrial and agricultural water use along the river. The probability of major floods has decreased, and siltation on the beach caused by floods has decreased. The number of small flow processes has greatly increased, changing the natural distribution of lateral siltation and fundamentally changing the location of lateral siltation in the river channel, further reducing the height difference between the beach and the channel, and making the "secondary suspended river" situation extremely severe.

[0003] Since the Xiaolangdi Reservoir was built and put into use in 2000, the process of water and sediment entering the downstream has changed significantly. Under the condition of continuous scouring, the siltation of the downstream river channel has been alleviated, but the situation of "high trough, low beach, and depression at the root of the dike" still exists, and the most serious river section is the Dongbatou to Taochengpu section. The whole river water and sediment regulation with Xiaolangdi Reservoir as the core has slowed down the development of the secondary suspended river to a certain extent, but there are problems such as insufficient follow-up power in the Xiaolangdi Reservoir water and sediment regulation. After the Xiaolangdi Reservoir's sediment retention capacity is full, if no other backbone projects are put into use, the lower reaches of the Yellow River will be seriously silted up again, the already formed middle water channel will shrink rapidly, and the secondary suspended river will also develop rapidly. At that time, once a large flood occurs, when the horizontal gradient of the river channel beach is much greater than the vertical gradient, the flow ratio of the beach area will increase, increasing the possibility of the mainstream colliding with the dike, causing flooding along the dike, and the control and guidance project losing its function of controlling the mainstream, and even the possibility of "rolling river", which directly threatens the safety of the Yellow River dike and seriously threatens the safety of life and property of the people in the beach area. Therefore, studying the evolution characteristics of secondary hanging rivers has important engineering significance for flood control safety in the lower reaches of the Yellow River.

[0004] For a long time, Yellow River control workers have conducted a lot of research on the causes of the formation of secondary suspended rivers, and believe that the occurrence and development of secondary suspended rivers are closely related to the changes in the water and sediment conditions of the river and the boundary conditions of the river channel. However, due to the many controversial issues in the management of secondary suspended rivers, some major issues and key technologies have not been studied clearly. Therefore, how to adopt effective technical means to study the evolution characteristics of the secondary suspended rivers in the lower reaches of the Yellow River under long-term series is a key technical problem that urgently needs to be solved. Summary of the invention

[0005] In order to solve the deficiencies in the prior art, the present invention provides a method for analyzing the evolution characteristics of a secondary suspended river.

[0006] The technical solution of the present invention is:

[0007] A method for analyzing the evolution characteristics of a secondary hanging river comprises the following steps:

[0008] S1: Collect long time series data.

[0009] S2: The trend analysis of long time series data is carried out through the Theil-Sen slope estimation method, which directly gives the trend of data in different periods.

[0010] S3: The periodicity of long time series data is judged by wavelet analysis method, and the mutation points are strictly diagnosed by multi-scale refinement analysis of data signals, and the phase and amplitude information of time series changes are given at the same time.

[0011] Furthermore, the long time series data is the horizontal gradient of the beach.

[0012] Furthermore, the calculation formula of the Theil-Sen slope estimation method is as follows:

[0013]

[0014] In the formula, Median represents the median value;

[0015] x j ,x i are the sample data corresponding to time j and time i (j>i) respectively;

[0016] k is the trend degree parameter of the time series. When k>0, the time series shows an upward trend, and when k<0, it shows a downward trend.

[0017] Furthermore, the wavelet function used in the wavelet analysis method is the Complex Morlet (cmor) wavelet.

[0018] Furthermore, for the wavelet function Ψ(t) that satisfies certain conditions, the time series f(t)∈L 2The wavelet transform of (R) can be calculated by the following formula:

[0019]

[0020] Where W f (a, b) are wavelet transform coefficients;

[0021] f(t) is a signal or an integrable function;

[0022] a is the scale factor of extension and shortening;

[0023] b is the time factor of the time series, reflecting the time shift of the series;

[0024] for The complex conjugate function of ;

[0025] W f (a,b) is a binary function that changes with parameters a and b, with b as the horizontal coordinate, a as the vertical coordinate, and the coefficient value as the vertical coordinate. A three-dimensional surface graph can be drawn. Wavelet analysis displays its projection by drawing a two-dimensional contour map on a plane, while the wavelet transform is presented as a three-dimensional surface graph and a contour map. These graphs reflect the time-frequency variation characteristics of the time series. When the scale a remains unchanged, the wavelet coefficients change with time, revealing the variation characteristics of the time series at this scale. Analysis of the wavelet coefficients can reveal the periodic variation characteristics of the time series at multiple time scales.

[0026] Furthermore, the real part of the Cmor wavelet coefficient reflects the periodic changes of the beach cross gradient time series within different time scales. The modulus of the wavelet coefficient reflects the distribution of energy density in the time domain corresponding to the change period of different time scales. Wavelet coefficients with larger modulus values ​​indicate that the corresponding time scale has strong periodicity in this period, which appears as warm colors in the three-dimensional surface map and contour map. The square of the wavelet coefficient modulus is equivalent to the wavelet energy spectrum, which can be used to analyze the oscillation energy of different periods and infer the performance of periodicity in the time domain at different time scales.

[0027] Furthermore, in order to determine the main time scale of the time series, the square of the wavelet coefficient modulus can be integrated in the time domain to obtain the wavelet variance:

[0028]

[0029] Where W f (a, b) are wavelet transform coefficients.

[0030] Furthermore, the wavelet variance diagram represents the change process of the wavelet variance with the scale a, which can be used to determine the relative strength of different scale disturbances in the signal and the main time scale, that is, the main period. The larger the extreme point, the greater the contribution to the wavelet variance, and the stronger the oscillation on the time series scale. According to the results of the wavelet variance test, the main period trend diagram of the flat beach flow in the study area is drawn, which reflects the change process of the wavelet coefficient of the first main period of the flat beach flow, that is, the average period and quasi-oscillation change characteristics on the time scale of the main period.

[0031] The beneficial effects achieved by the present invention are:

[0032] 1. The present invention uses the Theil-Sen slope estimation method and the wavelet analysis method to study the evolution trend and evolution characteristics of the secondary suspended river in the serious secondary suspended river section of the lower reaches of the Yellow River under the long time series. The Theil-Sen slope estimation method can perform trend analysis on the long time series data and directly give the trend of the data in different periods; the wavelet analysis method can judge the periodicity of the long time series data, and conduct strict diagnosis of the mutation points by performing multi-scale refinement analysis on the data signal, and at the same time give the characteristics of the phase and amplitude of the time series change, so that the analysis of the evolution characteristics of the secondary suspended river under the long time series of the lower reaches of the Yellow River is more accurate.

[0033] 2. The present invention uses a wavelet variance diagram to represent the change process of the wavelet variance over time scale, which is used to determine the relative strength of disturbances of different scales in the signal and the main time scale, that is, the main period. The larger the extreme point, the greater the contribution to the wavelet variance, and the stronger the oscillation on the time series scale. The main period trend diagram is a diagram of the change process of the wavelet coefficients of the first main period of the evolution of the secondary suspended river in the study area, which is drawn according to the results of the wavelet variance test. It can reflect the average period and quasi-oscillation change characteristics existing on the time scale of the main period; and then the contour map of the real part of the wavelet coefficient is used to verify the result of the strongest period of the evolution of the secondary suspended river. Facts have proved that this method has good analysis effect and high credibility in the analysis of the evolution characteristics of the secondary suspended river. It has very important theoretical significance and practical value for the future management of secondary suspended rivers, wandering rivers and comprehensive improvement of beach areas. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a trend chart of horizontal gradient change.

[0035] Figure 2 It is a three-dimensional surface diagram of the real part of the wavelet of the time series of the horizontal gradient of the beach (Dongbaitou-Gaocun river section).

[0036] Figure 3 It is the contour map of the real part of the wavelet of the time series of the horizontal gradient of the beach (Dongbaitou-Gaocun river section).

[0037] Figure 4It is a three-dimensional surface diagram of the wavelet coefficient modulus of the time series of the lateral gradient of the beach (Dongbaitou-Gaocun river section).

[0038] Figure 5 It is the contour map of the wavelet coefficient modulus of the time series of the lateral gradient of the beach (Dongbaitou-Gaocun river section).

[0039] Figure 6 It is a three-dimensional surface diagram of the beach horizontal gradient time series as the modulus square of the wavelet coefficient (Dongbaitou-Gaocun river section).

[0040] Figure 7 It is the contour map of the horizontal gradient time series of the beach as the modulus square of the wavelet coefficient (Dongbaitou-Gaocun river section).

[0041] Figure 8 It is the wavelet variance diagram of the lateral gradient of the beach.

[0042] Fig. 9 It is the main cycle trend chart. DETAILED DESCRIPTION

[0043] To facilitate those skilled in the art to understand the present invention, specific implementations of the present invention are described below with reference to the accompanying drawings.

[0044] The horizontal gradient of the beach is an important parameter reflecting the development degree of the secondary suspended river and an important indicator reflecting the flood risk of the river. The change law of the horizontal gradient is an important manifestation of the evolution law of the riverbed in the lower reaches of the Yellow River. This example takes the Dongbaitou to Gaocun section as an example to study the evolution characteristics of the secondary suspended river in this section under the long time series.

[0045] Figure 1 The evolution of the horizontal gradient of the left bank of the Dongbaitou to Gaocun section is given. Overall, before the operation of the Xiaolangdi Reservoir in 2000, the evolution trend of the average horizontal gradient of the beach had experienced many ups and downs, and was generally in a trend of gradual increase. The Theil–Sen Estimator was used to analyze its changing trend, and its trend degree was expressed by the k value, which can be divided into four stages: ①1960-1973, the horizontal gradient trend of the beach k=0.03, this period belongs to the initial formation period of the secondary suspended river; ②1974-1986, k=0.04, this period belongs to the slow development period of the secondary suspended river; ③1987-1999, k=0.18, this period belongs to the rapid development period of the secondary suspended river; ④2000-2021, k=0.03, this period belongs to the stable development period of the secondary suspended river. Among them, the first three periods are before the operation of the Xiaolangdi Reservoir, and the fourth period is after the operation of the Xiaolangdi Reservoir. It can be seen that in the early stage of the operation of Xiaolangdi Reservoir, the secondary hanging river had developed to a very serious degree. After the water and sand regulation of Xiaolangdi Reservoir, the siltation of the downstream river channel was reduced, and the development trend of the secondary hanging river was alleviated to a certain extent.

[0046] Figure 2 to Figure 9 This is the wavelet coefficient diagram of the horizontal gradient of the left bank beach from Dongbatou to Gaocun. Figure 2 and Figure 3 The three-dimensional surface map and real part contour map of the wavelet reflect the distribution of the horizontal gradient of the beach in the time scale and the periodic changes in different time domains. It can be seen from the figure that the wavelet coefficient fluctuates in the time scales of 25 to 32 years, 15 to 25 years, 10 to 15 years, and 5 to 10 years, indicating that the horizontal gradient has multi-time scale characteristics. There are quasi-three oscillations of alternating rise and fall on the time scale of 25 to 32 years, and 4.5 oscillations on the time scale of 15 to 25 years. The wavelet coefficients change most dramatically on these two time scales, which can best represent the fluctuation law of the horizontal gradient of the beach. Figure 4 and Figure 5 It is a three-dimensional surface map and contour map of the wavelet coefficient modulus of the beach transverse gradient, reflecting the periodicity intensity of the corresponding time scale in the period. Warm colors indicate strong periodicity, and cold colors indicate weak periodicity. It can be seen from the figure that in the process of the evolution of the transverse gradient, the modulus values ​​of the time scales of 15 to 25 years and 25 to 32 years are the largest, indicating that the beach transverse gradient cycle is the strongest in these two time scales, and the modulus values ​​of the periodic changes of other time scales are small, indicating that the beach transverse gradient cycle is not obvious in other time scales. Figure 6 and Figure 7 It is a three-dimensional surface diagram and contour diagram of the modulus square of the wavelet coefficient of the horizontal slope of the beach, which is used to analyze the oscillation energy of different periods. Figure 4 and Figure 5 The difference is that this figure can further clearly reflect the time scale of the strongest cycle. It can be seen from the figure that the energy of the 15-25 year time scale is stronger, and the time domain is distributed after 2000; the energy of the 25-32 year time scale is slightly weaker, and the time domain is distributed between 1975 and 2000.

[0047] Figure 8 and Fig. 9 It is the variance diagram of the wavelet coefficient of the beach transverse gradient and the main period trend diagram, which respectively reflect the main period and evolution trend of the beach transverse gradient evolution. Figure 8 It can be seen that there are two obvious peaks in the wavelet variance diagram of the lateral gradient of the beach, namely the first main cycle and the second main cycle. The first main cycle corresponds to a time scale of 31 years, and the second main cycle corresponds to a time scale of 21 years. Fig. 9 It can be seen that in the first main cycle of 31 years, the horizontal slope has experienced quasi-three oscillations, and its evolution cycle is 20 years; in the second main cycle of 21 years, the horizontal slope has experienced 4.5 oscillations, and its evolution cycle is 13 to 14 years. Figures 1 to 9It can be seen that the first main cycle and the second main cycle correspond to two different time scales. Taking 2000 as the boundary, it is divided into two stages, the first main cycle is distributed before 2000, and the second main cycle is distributed after 2000. This shows that after 2000, the construction and operation of Xiaolangdi Reservoir changed the original periodic evolution structure of the horizontal gradient of the beach.

[0048] The above-described embodiments of the present invention do not constitute a limitation on the protection scope of the present invention. Any modification, equivalent substitution and improvement made within the spirit and principle of the present invention shall be included in the protection scope of the claims of the present invention.

Claims

1. A method for analyzing the evolution characteristics of a secondary suspended river, characterized in that: The steps include: S1: Collect long time series data; S2: The trend analysis of long time series data is carried out through the Theil-Sen slope estimation method, and the trend of data in different periods is directly given; S3: The periodicity of long time series data is judged by wavelet analysis method, and the mutation points are strictly diagnosed by multi-scale refinement analysis of data signals, and the phase and amplitude information of time series changes are given at the same time.

2. A method for analyzing the evolution characteristics of a secondary suspended river according to claim 1, characterized in that: The long time series data is the horizontal gradient of the beach.

3. A method for analyzing the evolution characteristics of a secondary suspended river according to claim 1, characterized in that: The calculation formula of the Theil-Sen slope estimation method is as follows: In the formula, Median represents the median value; x j ,x i are the sample data corresponding to time j and time i (j>i) respectively; k is the trend degree parameter of the time series. When k>0, the time series shows an upward trend, and when k<0, it shows a downward trend.

4. A method for analyzing the evolution characteristics of a secondary suspended river according to claim 1, characterized in that: The wavelet function used in the wavelet analysis method is Complex Morlet (cmor) wavelet.

5. A method for analyzing the evolution characteristics of a secondary suspended river according to claim 4, characterized in that: For the wavelet function Ψ(t) that satisfies certain conditions, the time series f(t)∈L 2 The wavelet transform of (R) can be calculated by the following formula: Where W f (a, b) are wavelet transform coefficients; f(t) is a signal or an integrable function; a is the scale factor of extension and shortening; b is the time factor of the time series, reflecting the time shift of the series; for The complex conjugate function of ; W f (a,b) is a binary function that changes with parameters a and b, with b as the horizontal coordinate, a as the vertical coordinate, and the coefficient value as the vertical coordinate.

6. A method for analyzing the evolution characteristics of a secondary suspended river according to claim 5, characterized in that: In order to determine the main time scale of the time series, the square of the wavelet coefficient modulus can be integrated in the time domain to obtain the wavelet variance: Where W f (a, b) are wavelet transform coefficients.

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