A method for characterizing a river channel bar pattern

Abstract

The present application relates to the technical field of hydraulic engineering, and particularly relates to a method for characterizing a river channel beach pattern, comprising the following steps: step one: extracting a geometric figure surrounded by a cross section of a study river section and a bankfull water level; step two: obtaining a center of the geometric figure; step three: determining a center parameter from the center position, and dimensionless the center parameter; step four: according to the geometric figure surrounded by the cross section of the study river section and the bankfull water level corresponding to a time, the variation of the cross section center parameter with time can be obtained. By introducing the concept of the center and obtaining the variation of the cross section center parameter with time through the above steps, the evolution process of the river section with a dramatic adjustment of the beach pattern can be better characterized through the variation of the cross section center parameter with time.

Description

Technical Field

[0001] This invention relates to the field of water conservancy engineering technology, and specifically to a method for characterizing the river channel and floodplain patterns. Background Technology

[0002] Currently, the commonly used parameters for representing the cross-sectional shape of a river channel are cross-sectional area, river width, average water depth, and width-to-depth ratio, which are generally reasonable when studying the overall scouring and sedimentation of a river channel. After the construction of large-scale water conservancy projects, the bends in downstream river channels generally undergo a process of "convex scouring and concave sedimentation," such as cutting off shoals and bends (e.g., the lower reaches of the Han River and the lower Jingjiang River). That is, the convex bank of the bend is eroded and cut down, gradually forming a new river channel; while sedimentation occurs in the deep channels of the concave bank, gradually forming a mid-channel bar.

[0003] Traditional cross-sectional morphology can only represent the average scouring and deposition of the entire cross-section, and cannot capture the dramatic evolution of the river channel pattern. Summary of the Invention

[0004] In view of this, the present invention provides a method for characterizing the channel and floodplain patterns of a river, in order to solve the problem that traditional cross-sectional morphology of water passages cannot capture the dramatic evolution of the channel and floodplain patterns.

[0005] In a first aspect, the present invention provides a method for characterizing river channel and floodplain patterns, comprising the following steps:

[0006] Step 1: Extract the geometric shape enclosed by the cross-section of the river and the flat water level of the river section under study;

[0007] Step 2: Determine the centroid of the geometric figure;

[0008] Step 3: Determine the centroid parameters from the centroid position, and then make the centroid parameters dimensionless;

[0009] Step 4: Based on the geometric figure formed by the cross-section of the river section and the corresponding flat water level at the time of study, the change of the centroid parameter over time can be calculated.

[0010] In one optional implementation, in step two, the centroid position is obtained using the centroid calculation formula:

[0011]

[0012] Where x is the x-coordinate, y is the y-coordinate, and A is the cross-sectional area of ​​the water passage. That is, the centroid coordinates.

[0013] In one alternative implementation, in step two, the centroid position is obtained using drawing software.

[0014] In one optional implementation, the specific steps for obtaining the centroid position are as follows:

[0015] Select the geometric shape enclosed by the cross-section of the water passage and the flat water level, first use the region command REG, and then use the massprop command to obtain the centroid.

[0016] In one optional implementation, in step three, the centroid parameters are determined from the centroid position, specifically as follows:

[0017] The centroid is located at position H below the water surface. c ;

[0018] Point O is the intersection of the concave bank and the flat beach water level, and the lateral distance from the centroid to point O is B. c .

[0019] In one optional implementation, in step three, the dimensionless transformation of the centroid parameter specifically involves:

[0020] The average water depth of the cross-section is H = A / B, where A is the cross-sectional area of ​​the cross-section, B is the river width, and B0 is the river width. c / B and H c / H is the dimensionless centroid parameter.

[0021] In one alternative implementation, the cross-sectional area of ​​the river section under study is extracted by a measurement unit.

[0022] In one alternative implementation, in step four, the time series is a year, a month, or a specific time period.

[0023] The method for characterizing river channel and floodplain patterns provided by this invention has the following advantages:

[0024] 1. The present invention provides a method for characterizing river channel and floodplain patterns, comprising the following steps:

[0025] Step 1: Extract the geometric shape enclosed by the cross-section of the river and the flat water level of the river section under study;

[0026] Step 2: Determine the centroid of the geometric figure;

[0027] Step 3: Determine the centroid parameters from the centroid position, and then make the centroid parameters dimensionless;

[0028] Step 4: Based on the geometric figure formed by the cross-section of the river section under study and the corresponding flat water level at the time, the change of the centroid parameter over time can be calculated.

[0029] This method for characterizing river channel and floodplain patterns introduces the concept of a centroid. It extracts a geometric figure enclosed by the cross-section of the river section under study and the floodplain water level, then determines the centroid position based on this figure. The centroid parameter is then determined from this position and made dimensionless. Furthermore, based on the geometric figure enclosed by the cross-section of the river section under study and the corresponding floodplain water level over time, the change of the centroid parameter over time can be calculated. Therefore, by observing the change of the cross-sectional centroid parameter over time, the evolution process of river cross-sections undergoing dramatic adjustments in floodplain and floodplain patterns can be effectively characterized.

[0030] 2. The method for characterizing river channel patterns provided by this invention can capture the dramatic evolution of river channels and shoals in downstream bend sections after the construction of large-scale water conservancy projects. Traditional cross-sectional morphology parameters can only capture the overall scouring and deposition process of the cross-section and cannot reflect the channel pattern. Furthermore, the method for determining the centroid of the cross-section in this invention is simple and applicable not only to bend sections but also to any river cross-section, providing high reference value and practical significance for waterway, bank protection, and water intake projects. Attached Figure Description

[0031] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0032] Figure 1 This is a schematic diagram of the centroid obtained in the method for characterizing the river channel and floodplain pattern provided in the embodiments of the present invention.

[0033] Figure 2 A schematic diagram illustrating the changes in the cross-section of the shunting bend before and after the construction of the Three Gorges Dam.

[0034] Figure 3 This is a schematic diagram comparing the changes in the values ​​of traditional cross-sectional morphology parameters (cross-sectional area, river width, and width-to-depth ratio) and the cross-sectional centroid parameters of this invention for the cross-section before and after the construction of the Three Gorges Dam. Detailed Implementation

[0035] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0036] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicating orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance. In addition, the technical features involved in the different embodiments of the invention described below can be combined with each other as long as they do not conflict with each other.

[0037] Example

[0038] Currently, commonly used parameters for representing the cross-sectional morphology of river channels include cross-sectional area, river width, average water depth, and width-to-depth ratio, which are generally reasonable for studying the overall scouring and deposition of river channels. However, after the construction of large-scale water conservancy projects, downstream river bends typically undergo a process of "convex scouring and concave deposition," where the convex bank of the bend is eroded and cuts down, gradually forming a new channel; while the concave bank and deep channel accumulate sediment, gradually forming a mid-channel shoal. Traditional cross-sectional morphology can only represent the average scouring and deposition of the entire cross-section and cannot capture the dramatic changes in the channel pattern.

[0039] Therefore, this embodiment provides a method for characterizing river channel and floodplain patterns, including the following steps:

[0040] Step 1: Extract the geometric shape enclosed by the cross-section of the river and the flat water level of the river section under study;

[0041] Step 2: Determine the centroid of the geometric figure;

[0042] Step 3: Determine the centroid parameters based on the centroid position, and then make the centroid parameters dimensionless;

[0043] Step 4: Based on the geometric figure formed by the cross-section of the river section and the corresponding flat water level at the time of study, the change of the centroid parameter of the cross-section over time can be calculated.

[0044] In this embodiment, the concept of centroid is introduced. A geometric figure enclosed by the cross-section of the river section under study and the floodplain water level is extracted. The centroid position of this geometric figure is then determined, and its parameters are made dimensionless. Furthermore, based on the geometric figure enclosed by the cross-section of the river section under study and the corresponding floodplain water level over time, the change of the centroid parameters over time can be calculated. This change in the centroid parameters over time can effectively characterize the evolution process of the river cross-section undergoing drastic adjustments in the channel and floodplain patterns.

[0045] In this embodiment, the geometric figure enclosed by the cross-section of the river section and the flat water level in step one is based on the cross-section results proposed by the hydrological bureau and other measurement units, and then the cross-section and the flat water level are used to form a geometric figure.

[0046] Generally speaking, the cross-section of major rivers, especially the bends, is mostly composite, consisting of a main channel and side banks. The water level at the flat banks is the water level that just submerges the side banks.

[0047] In this embodiment, in step two, the centroid position is obtained using the following centroid calculation formula:

[0048]

[0049] Where x is the x-coordinate, y is the y-coordinate, and A is the cross-sectional area of ​​the water passage. That is, the centroid coordinates.

[0050] Alternatively, the centroid location can also be obtained using drawing software. For example, the centroid location can be obtained using the centroid search command in software such as AutoCAD. For instance, the specific steps for obtaining the centroid location using AutoCAD are as follows: select the geometric shape enclosed by the water-crossing section and the flat water level, first use the region command REG, and then use the massprop command to obtain the centroid.

[0051] In this embodiment, in step three, the centroid parameters are determined by the centroid position, specifically: the position of the centroid below the water surface is H. c Point O is the intersection of the concave bank and the flat beach water level, and the lateral distance from the centroid to point O is B. c .

[0052] In this embodiment, in step three, the dimensionless transformation of the centroid parameter specifically involves:

[0053] The average water depth across the cross-section is H = A / B, where A is the cross-sectional area, B is the river width, and B' is the cross-sectional area. c / B and H c / H refers to the dimensionless morphocentric ginseng.

[0054] Specifically, such as Figure 1 As shown, Figure 1 The location of the centroid is at point Q.

[0055] In this embodiment, the concave bank is used as point O because the concave bank of the bend suffers from severe bank erosion and generally has revetment and dike projects, so the bank boundary is relatively fixed. On the other hand, the convex bank of the bend has a more developed side beach, which undergoes more drastic erosion and sedimentation, and the bank boundary is unstable.

[0056] In this embodiment, in step four, the time series is annual, monthly, or a specific time period. The specific time period is: based on the drastic evolution of the river channel cross-section during a certain time period, several time points are selected within this time period, and the geometric figure formed by the cross-section of the study river section at these time points and the corresponding flat water level is obtained, and the change of the centroid parameter over time is calculated accordingly.

[0057] To further illustrate this point, this embodiment takes the section of the Diaoguan bend in the Xiajingjiang River section downstream of the Three Gorges Reservoir as an example to compare the morphological parameters of the two sections. Figure 2 The diagram shows the changes in the cross-section of the channel before and after the construction of the Three Gorges Dam.

[0058] The Three Gorges Project began impounding water in 2003. For example... Figure 2 As shown, from 1998 to 2003, the main characteristic of the bend's evolution was the scouring and downcutting of the deep channel on the concave bank, and the increasing siltation and elevation of the convex bank's sidebars, a typical "concave scouring and convex siltation" process. From 2003 to 2008, the deep channel on the concave bank silted up, gradually forming a mid-channel bar; the convex bank's sidebars were scoured and downcut, forming a new channel, a typical "convex scouring and concave siltation" evolution process. From 2008 to 2012, siltation continued on the concave bank, the mid-channel bar continued to rise, and the convex bank's sidebars experienced slight scouring. From 2012 to 2016, the scouring and siltation on the concave bank did not change much; the main adjustment process occurred within the new channel on the convex bank, with scouring and downcutting near the concave bank and siltation near the convex bank. In the absence of a major flood that significantly altered the entire cross-section, the channel and bar pattern did not change much, with most adjustments occurring within the new channel.

[0059] Figure 3 This is a schematic diagram comparing the changes in the values ​​of traditional cross-sectional morphological parameters (cross-sectional area, river width, width-to-depth ratio) and the cross-sectional centroid parameters in this embodiment for the curve cross-section before and after the construction of the Three Gorges Dam.

[0060] Depend on Figure 3It can be seen that due to the implementation of the bank protection project in the lower Jingjiang bend section, the river width did not change significantly, remaining around 1300m in 1998 before the reservoir was built. After the Three Gorges Dam was built, the river width increased somewhat, but remained within the range of 1500-1600m, with little change. The cross-sectional area represents the total scour and sedimentation volume of the cross-section. From 1998 to 2008, the cross-sectional area did not change much, indicating that the total scour and sedimentation volume was relatively small. After 2008, the cross-sectional area increased somewhat, indicating that the cross-section was generally undergoing scour. The width-to-depth ratio was slightly less than 4.0 before the reservoir was built, and increased somewhat after the reservoir was built, but remained basically within the range of 4.0-5.0. Traditional cross-sectional morphology parameters can only reflect the total scour and sedimentation volume of the cross-section and the degree of widening or narrowing of the river width, and cannot characterize the bend cross-section where the shoal and channel patterns are drastically adjusted. However, the total cross-sectional centroid parameters in this embodiment can better capture the shoal and channel patterns. Before the construction of the Three Gorges Dam, the evolution was a typical "concave-convex siltation" pattern, with deep channels eroding and cutting down along the concave bank, and correspondingly, the convex bank's side beaches silted up. c / B decreases, H c / H increases. After the construction of the Three Gorges Dam, especially in the five years before the dam was filled (2003-2008), the channel and shoal pattern underwent drastic adjustments. The convex bank shoals were significantly eroded and incised, while the concave bank silted up to form mid-channel shoals. The cross-section tended to develop into a "W" symmetrical shape, hence B c / B increases, H c / H decreases. This beach-channel pattern has not changed significantly since 2008, therefore B... c / B and H c The / H values ​​did not change significantly.

[0061] Therefore, by introducing the concept of centroid in this embodiment, the evolution of river cross-sections undergoing drastic adjustments in the channel-shoal pattern can be better characterized. This allows for the capture of the dramatic evolution of the channel-shoal pattern in downstream bend sections after the construction of large-scale water conservancy projects. Traditional cross-sectional morphology parameters, on the other hand, can only capture the overall scouring and deposition process of the cross-section and cannot reflect the channel-shoal pattern. Furthermore, the centroid calculation method in this embodiment is simple and applicable not only to bend sections but also to any river cross-section, providing high reference value and practical significance for waterway, bank protection, and water intake projects.

[0062] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for characterizing river channel and floodplain patterns, characterized in that, Includes the following steps: Step 1: Extract the geometric figure enclosed by the cross-section of the river and the flat water level of the river section under study; Step 2: Determine the centroid of the geometric figure; Step 3: Determine the centroid parameters from the centroid position, and then make the centroid parameters dimensionless; Step 4: Based on the geometric figure formed by the cross-section of the river section and the corresponding flat water level at the time, the change of the centroid parameter over time can be calculated. In step three, the centroid parameters are determined based on the centroid position, specifically as follows: The centroid is located at position H below the water surface. c ; Point O is the intersection of the concave bank and the flat beach water level, and the lateral distance from the centroid to point O is B. c ; In step three, the dimensionless transformation of the centroid parameter specifically involves: The average water depth of the cross-section is H=A / B, where A is the cross-sectional area, B is the river width, and Bc / B and Hc / H are dimensionless centroid parameters.

2. The method for characterizing river channel and floodplain patterns according to claim 1, characterized in that, In step two, the centroid position is obtained using the centroid calculation formula: ， ； Where x is the x-coordinate, y is the y-coordinate, and A is the cross-sectional area of ​​the water passage. (i.e., centroid coordinates).

3. The method for characterizing river channel and floodplain patterns according to claim 1, characterized in that, In step two, the centroid position is obtained using drawing software.

4. The method for characterizing river channel and floodplain patterns according to claim 3, characterized in that, The specific steps to obtain the centroid position are as follows: Select the geometric shape enclosed by the cross-section of the water passage and the flat water level, first use the region command REG, and then use the massprop command to obtain the centroid.

5. The method for characterizing river channel and floodplain patterns according to any one of claims 1-4, characterized in that, In step one, the cross-sectional area of ​​the river section under study is extracted by the measurement unit.

6. The method for characterizing channel and floodplain patterns according to any one of claims 1-4, characterized in that, In step four, the time series is annual, monthly, or a specific time period.

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