A riverbed evolution analysis method

Abstract

The present invention provides a riverbed evolution analysis method, which belongs to the technical field of riverbed evolution. The method starts from the measured topographic data of the study area on a long-term scale, calculates the time series of scouring and silting changes in different blocks of the study river section, statistically analyzes the long-term scouring and silting probabilities of different blocks of the study river section, and draws a scouring and silting probability distribution map based on this. At the same time, the standard deviation of the riverbed elevation distribution is analyzed, and the stability of the riverbed is evaluated according to the size of the standard deviation. This method can not only more intuitively display the historical scouring and silting changes of different blocks in the study area on a long-term scale, but also summarize the historical scouring and silting laws, evaluate the stability of the riverbed, and infer the future topographic evolution trend of the river channel. At the same time, it simplifies the conventional riverbed stability assessment method and more objectively analyzes the scouring and silting evolution laws of the river channel from a quantitative perspective.

Description

Technical Field

[0001] The invention relates to a riverbed evolution analysis method and belongs to the technical field of riverbed evolution. Background Art

[0002] Riverbed evolution generally refers to the process of scouring and silting changes in the riverbed under natural conditions and after the construction and renovation of buildings. Understanding the changing laws of riverbed evolution and making qualitative and quantitative forecasts are important prerequisites for river channel improvement and water-related engineering construction. The riverbed evolution analysis methods mainly include measured data analysis, river channel physical model tests, river channel mathematical model tests, etc. The measured data analysis is mainly based on the measured topographic data of the river channel, and the cross-sections, longitudinal sections (deep channel lines), scouring and silting distribution maps of the river channel in different years are compared. Figure 1 Generally, the riverbed elevation topography of two years is subtracted to obtain the changes in riverbed scouring and deposition, including areas of riverbed scouring, areas of riverbed deposition, and areas where the riverbed is basically stable.

[0003] Due to the influence of human activities and natural factors, riverbed evolution is an extremely complex dynamic process. Over different years, a specific area of ​​the riverbed, or even the entire riverbed, may be constantly silted, eroded, or alternately eroded and silted. Therefore, using traditional erosion and siltation distribution maps to describe riverbed erosion and siltation changes has certain limitations. First, conventional riverbed erosion and siltation distribution maps can only reflect the changes in riverbed erosion and siltation between two different years. Furthermore, when erosion and siltation between two years reach a basic equilibrium, this method cannot accurately describe the erosion and siltation characteristics of the terrain.

[0004] Riverbed stability is a crucial component of riverbed evolution analysis. It is typically assessed using indicators such as the longitudinal stability coefficient, lateral stability coefficient, and comprehensive stability coefficient. Qualitative analysis can also be conducted by comparing riverbed elevation and topographic data from different years. On the one hand, the calculation of riverbed stability indicators requires the use of numerous measured or empirical parameters, such as the average riverbed particle size, river flat depth, bed-forming flow, and river flat width at equivalent bed-forming flow. These parameters are difficult to determine when the riverbed has a complex cross-section or when water levels fluctuate in tidal channels. On the other hand, these indicators primarily assess the overall stability of a river or river section and cannot characterize the stability of a localized region of a river channel or section. Furthermore, qualitative analyses based on riverbed topographic data from different years cannot be quantified using a unified standard and are inherently subjective. Summary of the Invention

[0005] In view of the shortcomings of the prior art, the present invention provides a riverbed evolution analysis method, comprising the following steps:

[0006] 1) Collect information

[0007] Measure or collect underwater terrain elevation data Z1, Z2, Z3..., Z x , unify the elevation and plane coordinate systems of all underwater topographic data from different years;

[0008] 2) Grid division

[0009] The studied river section is divided into m×n grids L using terrain processing software. ij , the grid division accuracy should be reasonably selected with reference to the topographic survey accuracy;

[0010] 3) Terrain interpolation

[0011] Import the terrain data of each year obtained in step 1 into the grid divided in step 2 and perform data interpolation to obtain the terrain elevation of all grid centers in different years of the study river section, thereby generating a digital elevation model. For example, import Z1 into the grid and interpolate to obtain the terrain elevation data Z1L of each grid in the study river section in the first year. 11 、Z1L 12 ,…Z1L 1n , Z1L 21 、Z1L 22 ,…Z1L 2n ,…,Z1L m1 、Z1L m2 ,…Z1L mn Similarly, by importing Z2 into the grid and interpolating it, we can obtain the terrain elevation data Z2L of each grid in the second year of the study river section. 11 、Z2L 12 ,…Z2L 1n , Z2L 21 、Z2L 22 ,…Z2L 2n ,…,Z2L m1 、Z2L m2 ,…Z1L mn By analogy, we can obtain the terrain elevation data Z of each grid in the study river section in the xth year. x L 11 、Z x L 12 ,…Z x L 1n , Z x L 21 、Z x L 22 ,…Z x L 2n ,…,Z x L m1 、Z x L m2 ,…Z x L mn;

[0012] 4) Calculate the time series of erosion and siltation changes

[0013] Starting from the second year, the elevation difference between each year and the elevation of the first year is calculated to obtain the elevation change of the study river section between the two years, and then x-1 sets of elevation differences can be obtained. Let this value be △Z k L ij △Z k L ij >0 means the river is silted up, △Z k L ij <0 indicates that the river channel has been eroded, thus obtaining the time series of erosion and deposition changes of all grids in the study river section on a long time scale;

[0014] 5) Calculate the probability of erosion and siltation

[0015] By counting the time series of scouring and silting changes of each grid, the number of scouring events of each grid can be obtained. According to the ratio of the number of scouring events of each grid to the number of overall elevation changes, the long-term scouring probability of each grid in the time series can be obtained. For example, there are 20 sets of elevation difference data. When counting the number of grids L 11 When the probability of erosion and deposition is k L 11 There are 5 groups of data <0, △Z k L 11 There are 15 groups of data >0, then L 11 The probability of erosion in 20 years is 5 / 20*100%=25%, and the probability of sedimentation is 15 / 20*100%=75%;

[0016] 6) Draw a probability distribution map of erosion and siltation

[0017] The probability of erosion and deposition of each grid is plotted according to the grid position to obtain the distribution of erosion and deposition probability of the studied river section;

[0018] 7) Calculate the standard deviation of each grid according to the statistical standard deviation formula. The standard deviation calculation formula is as follows:

[0019]

[0020] Where n is the statistical year, x i is the terrain elevation value of a grid in year i, is the average terrain elevation for that grid cell over a specific timescale. This formula can be used to calculate the standard deviation for all grid cells over a long timescale. Smaller standard deviations indicate more clustered terrain data and smaller variations in riverbed erosion and deposition, indicating greater riverbed stability. Larger standard deviations indicate more discrete terrain data and more drastic variations in riverbed erosion and deposition, indicating weaker riverbed stability. By plotting the standard deviation of each grid cell against its position, we can obtain the distribution of standard deviations for the study section, and thus the distribution of riverbed stability.

[0021] Preferably, in step 1), x represents the elevation measurement time and x≥2.

[0022] Preferably, in step 2), the terrain processing software is MIKE21, SMS or Arcgis.

[0023] Preferably, in step 2), i=1, 2, 3, ..., m; j=1, 2, 3, ..., n.

[0024] Preferably, in step 4), ΔZ k L ij =Z k L ij -Z1L ij , k=2, 3...x; i=1, 2, 3..., m; j=1, 2, 3..., n.

[0025] The present invention provides a riverbed evolution analysis method. Compared with the existing technology, the technical solution of the present invention has at least the following beneficial effects: ① The historical elevation changes in the study area are statistically analyzed, the probability of scouring and silting in different blocks of the study area is calculated, and the scouring and silting probability distribution map is drawn. This can not only more intuitively display the historical scouring and silting changes in different blocks of the study area over a long period of time, but also infer the future evolution trend of the river channel topography. ② From a statistical point of view, the stability of the riverbed is evaluated by the standard deviation of the riverbed elevation distribution, and the stability level of the study river section is divided accordingly, and the degree of stability of different blocks of the study river section can be quantitatively determined. ③ The conventional riverbed stability assessment method is simplified, and the scouring and silting evolution law of the river channel can be analyzed more objectively from a quantitative perspective. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 Grid division diagram of the studied river section.

[0027] Figure 2 This is the measured elevation point map of the study river section in 2005.

[0028] Figure 3 The topographic elevation map of the river section in 2005 was used for the study.

[0029] Figure 4 To study the probability distribution map of river section sedimentation.

[0030] Figure 5 To study the probability distribution map of scour in the river section.

[0031] Figure 6 This is the standard deviation distribution map of each grid in the study river section. DETAILED DESCRIPTION

[0032] The present invention will be described in detail below with reference to the accompanying drawings.

[0033] Example 1

[0034] (1) Collect and study the terrain elevation data of a river from 2005 to 2020 for 15 years. x (x=1, 2, 3…15).

[0035] (2) Based on the scope of the studied river channel and the accuracy of topographic survey, the studied river section is divided into 3×4 grids, such as Figure 1 shown.

[0036] (3) Import the terrain elevation data of 15 years into the grid and interpolate them in sequence to obtain the terrain elevation of each grid center in the 15 years, as shown in the following example: Figures 2 and 3 As shown in Table 1.

[0037] Table 1

[0038]

[0039]

[0040]

[0041] (4) Subtract the terrain elevation of each year from the elevation of the first year to obtain the elevation difference data △Z k L ij (k=2, 3…14) as shown in Table 2.

[0042] Table 2

[0043]

[0044]

[0045]

[0046]

[0047] (5) Count the number of times siltation occurs in each grid, as shown in Table 3.

[0048] Table 3

[0049]

[0050] Based on this, the ratio of the number of siltation events to the number of elevation changes (14 in this example) for each grid is calculated, which is the siltation probability of each grid from 2005 to 2020. Furthermore, the scour probability of each grid from 2005 to 2020 can be obtained, as shown in Tables 4 and 5.

[0051] Table 4

[0052]

[0053] Table 5

[0054]

[0055] (6) The probability of sedimentation of each grid is plotted in a bar graph according to the grid position, and the probability distribution of sedimentation in the study section can be obtained. Similarly, the probability distribution of scour in the study section can be obtained, such as Figures 4 and 5 shown.

[0056] (7) Calculate the standard deviation of each grid according to the formula, as shown in Table 6.

[0057] Table 6

[0058]

[0059] Based on this, the standard deviation distribution map of each grid is drawn, that is, the riverbed stability distribution map, such as Figure 6 shown.

[0060] The above-described embodiments merely represent preferred embodiments of the present invention, and their descriptions are relatively specific and detailed. However, the present invention is not limited to these embodiments. It should be noted that it is within the skill of a person skilled in the art to understand the present invention. Any modifications made without departing from the spirit of the present invention are within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be determined by the appended claims.

Claims

1. A riverbed evolution analysis method, characterized in that: The following steps are involved: 1) Collect information Measure or collect underwater terrain elevation data Z1, Z2, Z3..., Z x , unify the elevation and plane coordinate systems of all underwater topographic data from different years; 2) Grid division The studied river section is divided into m×n grids L using terrain processing software. ij , i=1, 2, 3…, m; j=1, 2, 3…, n, the grid division accuracy should be reasonably selected with reference to the topographic survey accuracy; 3) Terrain interpolation Import the terrain data of each year obtained in step 1 into the grid divided in step 2 and perform data interpolation to obtain the terrain elevation of all grid centers in different years of the study river section, thereby generating a digital elevation model; import Z1 into the grid and interpolate to obtain the terrain elevation data Z1L of each grid in the study river section in the first year 11 、Z1L 12 ,…Z1L 1n , Z1L 21 、Z1L 22 ,…Z1L 2n ,…,Z1L m1 、Z1L m2 ,…Z1L mn Similarly, by importing Z2 into the grid and interpolating it, we can obtain the terrain elevation data Z2L of each grid in the second year of the study river section. 11 、Z2L 12 ,…Z2L 1n , Z2L 21 、Z2L 22 ,…Z2L 2n ,…,Z2L m1 、Z2L m2 ,…Z1L mn ; By analogy, we can obtain the terrain elevation data Z of each grid in the study river section in the xth year x L 11 、Z x L 12 ,…Z x L 1n , Z x L 21 、Z x L 22 ,…Z x L 2n ,…,Z x L m1 、Z x L m2 ,…Z x L mn ; 4) Calculate the time series of erosion and deposition changes Starting from the second year, the terrain elevation of each year is subtracted from the elevation of the first year to obtain the terrain elevation change of the study river section between the two years, and then x-1 groups of elevation differences can be obtained; Let this value be △Z k L ij △Z k L ij >0 means the river is silted up, △Z k L ij <0 indicates that the river channel has been eroded, thus obtaining the time series of erosion and deposition changes of all grids in the study river section on a long time scale; 5) Calculate the probability of erosion and siltation The time series of scouring and deposition changes of each grid is counted to obtain the number of scouring events in each grid. The long-term scouring probability of each grid under this time series can be obtained based on the ratio of the number of scouring events in each grid to the number of overall elevation changes. 6) Draw a probability distribution map of erosion and siltation The probability of erosion and deposition of each grid is plotted according to the grid position to obtain the distribution of erosion and deposition probability of the studied river section; 7) Calculate the standard deviation of each grid according to the statistical standard deviation formula. The standard deviation calculation formula is as follows: ； Where n is the statistical year, is the terrain elevation value of a grid in year i, is the average terrain elevation of the grid within a certain time scale. The standard deviation of all grids in a long time scale can be calculated from this formula. The smaller the standard deviation, the more concentrated the terrain data is, and the smaller the amplitude of riverbed scouring and deposition changes is, that is, the stronger the riverbed stability is. The larger the standard deviation, the more discrete the terrain data is, and the amplitude of riverbed scouring and deposition changes is drastic, that is, the weaker the riverbed stability is. By plotting the standard deviation of each grid according to the grid position, the standard deviation distribution of the studied river section can be obtained, that is, the distribution of riverbed stability.

2. A riverbed evolution analysis method according to claim 1, characterized in that: In step 1), x represents the elevation measurement time and x≥2.

3. A riverbed evolution analysis method according to claim 1, characterized in that: In step 2), the terrain processing software is MIKE21, SMS or Arcgis.

4. A riverbed evolution analysis method according to claim 1, characterized in that: In step 4), △Z k L ij =Z k L ij -Z1L ij , k=2, 3...x; i=1, 2, 3..., m; j=1, 2, 3..., n.

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