Determination method suitable for tidal bifurcated channel improvement line

Abstract

The invention relates to a determination method suitable for a tidal bifurcated river regulation line, which comprises the following steps: establishing a two-dimensional tidal current sediment numerical model, simulating tidal current sediment movement of a regulation river reach under typical hydrological conditions, and calculating the average ebb flow and the average ebb sediment content of each typical section; calculating the suspended sand stop flow velocity and the bed sand stop flow velocity of the regulated river reach; calculating the river width Bi0 corresponding to each typical section; on the basis of the river width Bi0 of each section, drawing up a regulation line for regulating the river reach; simulating the tidal current sediment movement of the regulation reach after the regulation line is implemented, and calculating the average ebb flow and the average ebb sediment content of each typical section after the regulation line is implemented; calculating the river width Bi1 corresponding to the new tidal current sediment condition of each typical section after the regulation line is implemented; comparing the river width Bi1 with the river width Bi0 of the same section; and on the basis of the river width Bi1 of each section, drawing up a final regulation line for regulating the river reach. According to the method, the change of branch channel tidal current power after the regulation project is implemented is considered, and the river regulation line can be determined more accurately.

Description

Technical Field

[0001] The invention relates to the technical field of river channel regulation, and in particular to a method for determining a regulation line for a tidal bifurcated river channel. Background Art

[0002] The regulation line is the boundary line of the river regulation project. River regulation generally includes flood regulation, medium water regulation and low water regulation. Among them, flood regulation mainly controls the safe discharge of flood tides, such as building embankments; medium water regulation mainly controls the direction of river water flow and stabilizes the river flow, such as building levees; low water regulation mainly improves the flow conditions in the dry season and stabilizes the water depth in the dry season, such as building spur dikes. At present, the flood regulation lines of major estuaries in my country have been basically determined, but due to the reduction of sediment in the estuary and the adjustment of river flow, medium water regulation is still an urgent problem to be solved. At present, the medium water regulation line is generally based on the reasonable river width. The reasonable river width of the regulated river section is calculated through a certain river phase relationship, and then the river regulation line is determined. However, this method calculates the reasonable river width using the current tidal sediment parameters in the regulated river section, and does not consider the changes in the tidal sediment parameters in the regulated river section after the implementation of the regulation line, resulting in the proposed bifurcated river regulation line being incompatible with the tidal sediment dynamics of the river section. In particular, for the bifurcated channels of tidal estuaries, the implementation of a regulation project in a channel will cause significant changes in the tidal volume, tidal dynamics, and channel diversion pattern in the channel, resulting in the regulation line determined based on the current tidal sediment parameters not being able to adapt to the channel after regulation. Therefore, it is necessary to develop a method for determining the regulation line of a tidal bifurcated channel that takes into account the changes in tidal dynamics of the channel. Summary of the invention

[0003] In order to overcome the shortcomings of the above-mentioned background technology, the purpose of the present invention is to provide a method for determining the regulation line of a tidal bifurcated river channel, which takes into account the changes in the tidal dynamics of the branch channel after the implementation of the regulation project and can determine the river channel regulation line more accurately.

[0004] To achieve the above object, the present invention is implemented by the following technical solutions:

[0005] The present invention provides a method for determining a regulation line of a tidal bifurcated river channel, comprising the following steps:

[0006] S1: Collect underwater topography and hydrological sediment data of the regulated river section, establish a two-dimensional tidal sediment numerical model, and calibrate and verify the model; select typical hydrological conditions to simulate tidal sediment movement in the regulated river section, and the hydrological conditions include at least one large, medium and small tide; arrange a corresponding number of typical sections along the flow direction of the regulated river section at a certain section spacing, extract the tidal flow and sediment content of each typical section, and calculate the average low tide flow and average low tide sediment content of each typical section within a large, medium and small tide cycle;

[0007] S2: Based on the measured sediment data such as suspended sediment and bed sediment, the representative particle size of suspended sediment and bed sediment in the regulated river section is analyzed, and the stopping flow velocity of suspended sediment and bed sediment is calculated;

[0008] S3: Based on the average ebb flow, average ebb sediment content, suspended sediment stopping velocity, bed sand stopping velocity and other parameters of each section, the Dou Guoren River correlation equation is used to calculate the river width B corresponding to each typical section. i0 ;

[0009] S4: The river width B of each section i0 Based on this, formulate the regulation line of the river section to be regulated;

[0010] S5: Using the tidal sediment model established in S1 and the selected hydrological conditions, simulate the tidal sediment movement of the regulated river section after the regulation line is implemented, extract the tidal flow and sediment content process of each typical section arranged in S1, and calculate the average ebb tidal flow and average ebb tidal sediment content of each typical section in a large, medium and small tidal cycle;

[0011] S6: Based on the average ebb flow and average ebb sediment content of each typical section calculated in S5, the corresponding river width B of each typical section is calculated using the Dou Guoren River correlation formula i1 ;

[0012] S7: The river width B of the same section i1 With B i0 Compare; if the river width of each section|(B i1 —B i0 ) / B i0 |≤1%, then B i1 The river width is the reasonable river width of section i; if the river width of a section|(B i1 —B i0 ) / B i0 |>1%, repeat S4 (this time with B i1 Based on the proposed regulation line, B i0 =B i1 ), S5 and S6, until all sections|(B i1 —B i0 ) / B i0 |≤1%;

[0013] S8: The river width B of each section i1 Based on this, the final regulation line of the river section is formulated.

[0014] In the above technical solution, in step S1, the underwater topographic data refers to the river system topographic data measured in recent years in the regulated river section, and the hydrological sediment data includes at least two measured tide levels, flow velocities, tidal volumes, sediment content and other data. The underwater topographic data and the hydrological sediment data test period should be basically consistent. The control equations of the two-dimensional tidal sediment numerical model are composed of the water flow continuity equation, the water flow motion equation, the sediment transport equation, etc. The relevant equations can be expressed as:

[0015] 1) Continuity equation of water flow

[0016]

[0017] 2) Equation of water flow

[0018]

[0019] 3) Sediment transport equation

[0020]

[0021] in,

[0022]

[0023] Where: x and y are Cartesian coordinates, u and v are the components of the vertical average velocity in the x and y directions respectively; h = d + η is the total water depth, d is the static water depth, η is the water level; g is the gravitational acceleration; ρ0 is the density of water; f is the Coriolis force coefficient; τ bx , τ by is the bottom stress in the x and y directions, τ sx , τ sy is the surface stress in the x and y directions; T xx , T xy , T yy is the horizontal viscous stress; c is the vertical average sediment concentration; D x , D y is the sediment diffusion coefficient; E is the bed scour term; D is the bed sediment term; w s is the sediment settling velocity, c b is the suspended sediment concentration near the bottom, p d is the probability of settlement, ε is the bed scour coefficient, τ b is the bed shear stress, τ ce is the critical scour shear stress of the bed surface, n is the scour index, τ cd is the critical settlement shear stress of the bed surface.

[0024] In the above technical solution, in step S1, typical hydrological conditions refer to hydrological conditions that are compatible with the changes in the river flow of the regulated river section, and generally can be hydrological conditions of a normal water year or equivalent to the average ebb tide over many years. The section spacing is determined based on the width of the regulated river section and the length of the regulated river section, and is generally (0.5 to 2) times the river width. The average ebb flow and average ebb sediment content of the section in step S1 are calculated according to the flow and sediment content of the section during the ebb of large, medium and small tides according to the following formula.

[0025] Average ebb flow The calculation formula is

[0026]

[0027] Where: Q i , Q i+1 For adjacent t i , t i+1 The ebb flow at time t1, t n+1 It is the time for rest during growth and the time for rest during growth.

[0028] Average sand content The calculation formula is

[0029]

[0030] Where: c i , c i+1 For adjacent t i , t i+1 The sand content at low tide at each moment.

[0031] In the above technical solution, in step S2, the representative particle size refers to the particle size of the sediment larger and smaller than a certain particle size that accounts for 50% of the total weight of the sand sample, and is expressed as d 50 The suspended sediment stopping velocity is calculated using the representative particle size of the suspended sediment, U cs =9.01d 12 The bottom sand stopping velocity is calculated using the bottom sand representative particle size U cb =9.01d 12 .

[0032] In the above technical solution, in step S3, the river width calculation formula in the Dou Guoren River correlation is as follows:

[0033]

[0034] Where b is the proportionality coefficient, which is 0.15; β is the tidal coefficient, which is 1.0 for the river section without tidal bore; g is the gravitational acceleration, which is 9.81 m / s 2 ; U cs is the suspended sand stopping velocity; is the average low tide sediment content in a calculation period; is the average ebb flow in a calculation period; k is the sediment entrainment coefficient, which is taken as 4.0; α is the relative stability coefficient of the river bank and river bottom soil, which is taken as 1.0; U cb is the bottom sand stopping flow velocity;

[0035] In the above technical solution, in step S3, the river width B corresponding to each typical section i0 , subscript i is the section number, generally represented as 1, 2, 3..., and subscript 0 represents the initial condition. i0 Generally represented as B 10 , B 20 , B 30 , B 40 ...B n0 .

[0036] In the above technical solution, in step S4, the regulation line is planned to be based on the river width B i0 Based on, appropriately smooth.

[0037] In the above technical solution, in step S6, the river width B corresponding to each typical section i1 , subscript i is the section number, generally represented as 1, 2, 3..., subscript 1 represents the initial regulation line after the tidal sediment dynamics change. i0 Generally represented as B 11 , B 21 , B 31 , B 41 ...B n1 .

[0038] In the above technical solution, in step S7, repeating S4 is to increase the river width B of each section i1 Re-assume the new B i0 Based on this river width, the regulation line of the regulated river section is drawn up, and then S5 and S6 are repeated to obtain the new B i1 .

[0039] Compared with the prior art, the present invention has the following beneficial effects:

[0040] (1) The present invention takes into account that after the implementation of the regulation project in a tidal bifurcated river channel, the tidal dynamics in the channel will change significantly. The regulation line formulated on the basis of fully considering this change is closer to reality. The traditional method does not consider the change of tidal sediment dynamics, and the formulated regulation line will not be able to adapt to the tidal sediment dynamic conditions of the river channel after regulation, resulting in the river channel after regulation failing to form a relatively good river channel morphology.

[0041] (2) The technical route of the present invention is clear, the technical method is relatively simple, and there is no complicated processing process. After collecting the basic hydrological and sediment data of the regulated river section, the river regulation line can be quickly determined with high accuracy according to the process of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 The present invention is a flow chart of a method for determining a tidal bifurcation river regulation line.

[0043] Figure 2 This is the grid map of the two-dimensional tidal sediment model of the Yangtze River Estuary.

[0044] Figure 3 This is a map of the current status of the northern branch of the Yangtze River estuary.

[0045] Figure 4 This is a schematic diagram of the research on the regulation line of the northern branch of the Yangtze River Estuary. DETAILED DESCRIPTION

[0046] The exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although the exemplary embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided to enable a more thorough understanding of the present disclosure and to fully convey the scope of the present disclosure to those skilled in the art.

[0047] like Figure 1 As shown, this implementation case is mainly used to determine the regulation line of the northern branch of the Yangtze River Estuary, including the following steps:

[0048] Step S1: Collect underwater topographic data of the Yangtze River estuary in 2016 and hydrological sediment data in 2016 and 2017, and establish a two-dimensional tidal sediment numerical model for the Yangtze River estuary (see Figure 2 ); calibrate and verify the tidal current, tidal level and sediment content of the two-dimensional tidal sediment numerical model of the Yangtze River Estuary using the hydrological and sediment data of 2016 and 2017; select September 15 to September 30, 2002 as the typical hydrological conditions to carry out the two-dimensional tidal sediment model simulation of the Yangtze River Estuary; Figure 3 ) One section was arranged every 5 km, with a total of 5 typical sections. The tidal flow process and sediment content process of the 5 typical sections under the working conditions in September 2002 were extracted, and the average ebb tidal flow and average ebb tidal sediment content corresponding to the 5 typical sections in a large, medium and small tidal cycle were calculated.

[0049] Step S2: Based on the measured suspended sediment and bed sediment data in 2016 and 2017, the representative particle size of suspended sediment and the representative particle size of bed sediment in the regulated river section are analyzed, and the suspended sediment stop flow velocity and the bed sediment stop flow velocity are calculated.

[0050] Step S3: Based on the average ebb flow, average ebb sediment content, suspended sediment stopping velocity and bed sediment stopping velocity of each section, the Douguoren River correlation equation is used to obtain the river width corresponding to the five typical sections (B from upstream to downstream, respectively). 10 , B 20 , B 30 , B 40 , B 50 ) are 3830m, 4370m, 5040m, 5880m and 6950m respectively.

[0051] Step S4: Take the river width B i0 Based on this, the regulation line of the river section to be regulated is drawn up (see Figure 4 ).

[0052] Step S5: Using the two-dimensional tidal sediment model of the Yangtze River Estuary, calculate the tidal sediment movement of the northern branch of the Yangtze River Estuary after the implementation of the initial regulation line under the conditions from September 15 to September 30, 2002, extract the tidal flow process and sediment content process of five typical sections, and calculate the average ebb tidal flow and average ebb tidal sediment content of each typical section within a large, medium and small tidal cycle.

[0053] Step S6: Based on the average ebb flow and average ebb sediment content of each section calculated in S5, the Dou Guoren River correlation formula is used to calculate the reasonable river width corresponding to each typical section after the regulation line is implemented. The river width corresponding to the five typical sections (B 11 , B 21 , B 31 , B 41 , B 51 ) are 3720m, 4220m, 4790m, 5420m and 6250m respectively.

[0054] Step S7: Compare the river width B of the same section i1 With B i0 , at this time |(B 51 —B 50 ) / B 50 |=8%>1%,repeat steps S4, S5 and S6. Repeat step S4, i.e., take the river width B of each section as i0 Basic, B i0 The regulation lines are 3720m, 4220m, 4790m, 5410m and 6230m respectively; repeat steps S5 and S6 to obtain the new river width B corresponding to the five typical sections. i1 (i.e. B 11 , B 21 , B 31 , B 41 , B 51 ) are 3720m, 4220m, 4790m, 5400m, and 6210m respectively. At this time, |(Bi1 —B i0 ) / B i0 |All less than 1%.

[0055] Step S8: Take the river width B of each section i1 (3720m, 4220m, 4790m, 5400m, 6210m ) Based on the above, the final control line of the river section is formulated ( Figure 4 ).

[0056] The present invention proposes a technical method for calculating the regulation river width and arranging the regulation line based on the change of tidal sediment dynamics after the implementation of the tidal bifurcated river regulation line. The regulation line of the tidal bifurcated river can be accurately determined, and the technical method is relatively simple and can be applied to the determination of various tidal bifurcated river regulation lines.

[0057] The above are only preferred embodiments of the present invention. It should be noted that the above preferred embodiments should not be regarded as limiting the present invention, and the protection scope of the present invention should be based on the scope defined by the claims. For ordinary technicians in this technical field, several improvements and modifications can be made without departing from the spirit and scope of the present invention, and these improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. A method for determining a regulation line for a tidal bifurcation river channel, characterized in that: The steps include: S1: Establish a two-dimensional tidal sediment numerical model, select typical hydrological conditions to simulate the tidal sediment movement in the regulated river section; arrange a corresponding number of typical sections along the flow direction of the regulated river section at a certain section spacing, and calculate the average low tide flow and average low tide sediment content of each typical section; S2: Based on the measured sediment data of suspended sediment and bed sediment, the representative particle size of suspended sediment and bed sediment in the regulated river section is analyzed, and the suspended sediment stop flow velocity and bed sediment stop flow velocity in the regulated river section are calculated; S3: Based on the average ebb flow, average ebb sediment content, and suspended sediment stopping velocity and bed sand stopping velocity parameters of each typical section, the Dou Guoren River correlation equation is used to calculate the river width B corresponding to each typical section. i0 ; S4: The river width B of each typical section i0 Based on this, formulate the regulation line of the river section to be regulated; S5: Based on the two-dimensional tidal sediment numerical model established in step S1 and the selected typical hydrological conditions, simulate the tidal sediment movement of the regulated river section after the regulation line is implemented, and calculate the average low tide flow and average low tide sediment content of each typical section after the regulation line is implemented; S6: Based on the average ebb current flow and average ebb current sediment content calculated in step S5, the corresponding river width B of each typical section is calculated using the Dou Guoren River correlation equation. i1 ; S7: Comparison of river widths B in the same typical section i1 With B i0 , if the river width of each typical section|(B i1 —B i0 ) / B i0 |≤1%, then B i1 The river width is the reasonable river width of section i; If the river width of a typical section|(B i1 —B i0 ) / B i0 |>1%, repeat steps S4, S5 and S6 until all typical sections|(B i1 —B i0 ) / B i0 |≤1%; S8: The river width B of each typical section i1 Based on this, the final regulation line of the river section is formulated.

2. The method for determining a regulation line for a tidal bifurcation river channel according to claim 1, characterized in that: In step S1, a two-dimensional tidal sediment numerical model is established by collecting underwater topography and hydrological sediment data of the regulated river section, and the model is calibrated and verified; wherein, the underwater topography data refers to the river system topography data of the regulated river section measured in recent years, and the hydrological sediment data includes at least two measured tide levels, flow velocities, tidal volumes, and sediment content data, and the test periods of the underwater topography data and the hydrological sediment data should be basically consistent.

3. The method for determining a regulation line for a tidal bifurcation river channel according to claim 1 or 2, characterized in that: In step S1, the control equations of the two-dimensional tidal sediment numerical model include the water flow continuity equation (1), the water flow motion equations (2) and (3), and the sediment transport equation (4), which can be expressed as: in: In the above formula: x and y are Cartesian coordinates, u and v are the components of the vertical average velocity in the x and y directions respectively; h = d + η is the total water depth, d is the static water depth, η is the water level; g is the gravitational acceleration; ρ0 is the density of water; f is the Coriolis force coefficient; τ bx , τ by is the bottom stress in the x and y directions, τ sx , τ sy is the surface stress in the x and y directions; T xx , T xy , T yy is the horizontal viscous stress; c is the vertical average sediment concentration; D x , D y is the sediment diffusion coefficient; E is the bed scour term; D is the bed sediment term; w s is the sediment settling velocity, c b is the suspended sediment concentration near the bottom, p d is the probability of settlement, ε is the bed scour coefficient, τ b is the bed shear stress, τ ce is the critical scour shear stress of the bed surface, n is the scour index, τ cd is the critical settlement shear stress of the bed surface.

4. The method for determining a regulation line for a tidal bifurcation river channel according to claim 1, characterized in that: In step S1, typical hydrological conditions refer to hydrological conditions that are compatible with changes in river flow in the regulated river section, and adopt hydrological conditions in a normal water year or equivalent to the multi-year average low tide; typical hydrological conditions include at least one large, medium and small tide.

5. The method for determining the regulation line of a tidal bifurcation river according to claim 1, characterized in that: In step S1, the section spacing is determined comprehensively based on the width of the regulated river section and the length of the regulated river section, and is 0.5 to 2 times the river width.

6. The method for determining the regulation line of a tidal bifurcation river according to claim 4 or 5, characterized in that: In step S1, the average ebb flow and average ebb sediment content of each typical section are calculated according to the flow and sediment content of the section during the ebb tides of high, medium and low tides according to the following formula: Average ebb flow The calculation formula is: Where: Q i , Q i+1 For adjacent t i , t i+1 The ebb flow at time t1, t n+1 It is the time for rising and falling; Average sand content The calculation formula is: Where: c i , c i+1 For adjacent t i , t i+1 The sand content at low tide at each moment.

7. The method for determining the regulation line of a tidal bifurcation river according to claim 1, characterized in that: In step S2, the representative particle size refers to the particle size of the sediment whose weight is greater than and less than a certain particle size and accounts for 50% of the total weight of the sand sample, and is expressed as d 50 The suspended sediment stopping velocity is calculated using the representative particle size of the suspended sediment, U cs =9.01d 12 The bottom sand stopping velocity is calculated using the bottom sand representative particle size U cb =9.01d 12 .

8. The method for determining the regulation line of a tidal bifurcated river channel according to claim 1, characterized in that: In step S3, the river width B in the Douguoren River correlation equation is calculated as follows: Where: b is the proportionality coefficient, which is 0.15; β is the tidal coefficient, which is 1.0 for the river section without tidal bore; g is the gravitational acceleration, which is 9.81 m / s 2 ; U cs is the suspended sand stopping velocity; is the average low tide sediment content in a calculation period; is the average ebb flow in a calculation period; k is the sediment entrainment coefficient, which is taken as 4.0; α is the relative stability coefficient of the river bank and river bottom soil, which is taken as 1.0; U cb The bottom sand stopping flow velocity.

9. The method for determining the regulation line of a tidal bifurcation river according to claim 1, characterized in that: In step S3, the river width B corresponding to each typical section i0 , subscript i is the section number, represented as 1, 2, 3..., and subscript 0 represents the initial condition; In step S6, the river width B corresponding to each typical section i1 , subscript i is the section number, represented as 1, 2, 3..., and subscript 1 represents the initial regulation line after the tidal sediment dynamics change is implemented.

10. The method for determining the regulation line of a tidal bifurcation river according to claim 1, characterized in that: In step S7, repeating step S4 means that the river width B of each section is i1 Re-assume the new B i0 Based on this river width, the regulation line of the regulated river section is drawn up, and then steps S5 and S6 are repeated to obtain a new B i1 .

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