A method for determining the friction coefficient of the bottom bed in tidal river sections

Abstract

The present invention provides a method for determining the friction coefficient of the bottom bed of a tidal river section, by setting a number of observation points in the tidal river section, measuring the water surface elevation data of all observation points at a number of times; establishing a partial reflection wave theory, constructing a water surface elevation equation of the tidal wave propagation characteristics of the tidal river section; fitting the measured data according to the water surface elevation equation, inferring the tidal wave reflection coefficient, tidal wave number and damping modulus, and calculating the instantaneous hydraulic gradient; combining the maximum flow velocity and hydraulic radius measured at the designated observation point, substituting into the Manning formula, calculating the Manning coefficient n of the designated measurement point of the tidal river section as the friction coefficient of the bottom bed at the designated measurement point. The present invention is not only applicable to tidal river sections with non-constant non-uniform flow, but also to river sections with constant uniform flow; improving the calculation accuracy of the friction coefficient of the bottom bed, while reducing the time and labor costs of scientific researchers.

Description

Technical Field

[0001] The invention relates to the technical field of river section bottom bed friction coefficient calculation, and in particular to a method for calculating the bottom bed friction coefficient of a tidal river section based on the Manning equation. Background Art

[0002] Tidal reaches of the Estuary are the interface between rivers and the ocean. They are rich in ecological resources, provide sufficient food and water, and are important channels for transportation between the inland and the ocean. Therefore, they are often densely populated areas. Important cities and famous commercial ports in the world are all located on the banks of tidal rivers. Before carrying out relevant regulation work on tidal reaches, it is necessary to first understand and master the characteristics of its hydrological changes. Therefore, hydrodynamic analysis of tidal reaches is very important. Generally, in the hydrological analysis of tidal reaches at the estuary, most of them directly use the Manning formula to calculate the flow velocity (Tidal current velocity), and use the surface water level elevation change as its hydraulic gradient, and use the bed particle size method to estimate the Manning coefficient value.

[0003] However, the elevation change of the tidal water surface in the tidal river section is attenuated by the friction resistance of the bottom bed, and is bulged due to the constriction and reflection of the river channel, that is, the change of the water surface elevation is the combined effect of friction attenuation and reflection bulging, so its flow condition is a complex non-steady non-uniform flow condition, and its water surface elevation change is a non-linear curve function; precisely because the tidal wave in the tidal river section is an unsteady non-uniform flow, the calculation result error of the existing method is very large.

[0004] Moreover, if the method of estimating the Manning coefficient based on the particle size of the bottom bed in tidal river sections is used, in addition to collecting on-site tidal observation data at full tide, it is also necessary to collect and measure the particle size of the bottom bed in the entire river section at the estuary. This consumes a huge amount of manpower, material resources and time, and usually requires the organization of water conservancy public sector institutions to conduct long-term observation and collection, or the support of long-term project funds to complete, which is not something that ordinary university teachers and professional research scholars can afford. Summary of the invention

[0005] In view of the above technical problems, the present invention proposes a method for determining the friction coefficient of the bottom bed of a tidal river section, by setting a number of observation points in the tidal river section, measuring the water surface elevation data of all observation points at a number of times, establishing a partial reflection wave theory, and constructing a water surface elevation equation of the tidal wave propagation characteristics of the tidal river section; fitting and calculating the tidal wave reflection coefficient ω, the tidal wave number κ, and the damping modulus μ, and calculating the instantaneous hydraulic gradient S t(Instantaneous Hydraulic Slope); Combined with the measured maximum flow velocity and hydraulic radius, the Manning's coefficient n value is calculated based on the Manning formula as the bottom bed friction coefficient of the tidal river section. The present invention improves the calculation accuracy of the bottom bed friction coefficient of the tidal river section and reduces the time and labor costs of scientific researchers.

[0006] Specifically, a method for determining the friction coefficient of the bottom bed of a tidal river section is based on the Manning formula and is characterized by comprising the following steps:

[0007] S1 sets N observation points x in the tidal river section i , at T time t j Measure the water surface elevation data η of all observation points ij ;

[0008] S2 establishes the partial reflection wave theory and constructs the water surface elevation equation η(x i );

[0009] S3: the water surface elevation data n ij According to the water surface elevation equation η(x i ) fitting, calculate the instantaneous hydraulic gradient equation S tj ;

[0010] S4 measures the designated measuring point x of the tidal river section m Low tide or high tide time max Maximum flow velocity V and hydraulic radius R;

[0011] S5 converts the instantaneous hydraulic gradient S tmax (x m ), the maximum flow velocity V and the hydraulic radius R are substituted into the Manning formula The Manning coefficient n of the designated measuring point is calculated as the bottom bed friction coefficient of the designated measuring point.

[0012] The observation point x i Specifically, let the estuary of the tidal river be the starting point, and mark the observation points in sequence as i, i = 1, 2, ..., N, x i is the distance between the observation point and the starting point, and the propagation from the estuary to the upstream of the river is +x i Direction, the reflection from the upstream of the river to the estuary is -x i direction.

[0013] The water surface elevation data η ij Specifically, mark the observation time sequence as j, j = 1, 2, ..., T, t j is the measurement time, at the same time tj Measure all observation points x1, x2, ...x N The water surface elevation η of observation point i at observation time j is η ij .

[0014] The water surface elevation equation η(x i ), specifically:

[0015] η(x i )=η1(x i )+η2(x i ),

[0016]

[0017]

[0018] In the above formula, η1(x i ) is the water surface elevation equation of the incident wave entering the estuary from the open sea, η2(x i ) is the water surface elevation equation for the reflected wave from the open sea to the estuary; ω is the tidal wave reflection coefficient, κ is the tidal wave number, μ is the damping modulus, a0 is a constant, and σ is the time period; Substitute into the water surface elevation equation η(x i ) i The value is +x i .

[0019] The value range of the tidal wave reflection coefficient ω is 0 to 1, for example, ω=0 is a forward wave, and ω=1 is a fully reflected wave.

[0020] Furthermore, the instantaneous hydraulic gradient equation S tj , specifically:

[0021]

[0022] The S tmax (x m ) is specifically: the x of the specified observation point m and the measurement time t max , substitute into the instantaneous hydraulic gradient equation S tj Calculate S tmax (x m ).

[0023] Furthermore, the present invention is not only applicable to tidal river sections with non-steady non-uniform flow, but also to river sections with steady uniform flow, but is not limited thereto.

[0024] The present invention provides a method for determining the friction coefficient of the bottom bed of a tidal river section, by setting a number of observation points in the tidal river section, measuring the water surface elevation data of all observation points at a number of times; establishing a partial reflection wave theory, constructing a water surface elevation equation of the tidal wave propagation characteristics of the tidal river section; fitting the measured data according to the water surface elevation equation, calculating the instantaneous hydraulic gradient; combining the measured maximum flow velocity and hydraulic radius, substituting into the Manning formula, calculating the Manning coefficient n of the designated measurement point of the tidal river section, that is, the friction coefficient of the bottom bed at the designated measurement point. The present invention improves the calculation accuracy of the friction coefficient of the bottom bed, while reducing the time and labor costs of scientific researchers.

[0025] The beneficial effect of the present invention is that it overcomes the problem of large calculation errors caused by directly adopting the Manning formula because the tidal waves in the tidal river section are non-constant and non-uniform flows, while reducing the time and labor costs of scientific researchers; and the present invention can further compile the method steps, and parameters such as tidal observation values, tidal velocity, and Manning coefficient into a software program, embed it in hydrological measuring instruments such as tide meters, or integrate it into a mobile phone app, so as to conduct a more comprehensive, real-time and sustainable development study on the hydrological analysis of the tidal river section at the estuary. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 The present invention is a flow chart of a method for determining the friction coefficient of the bottom bed of a tidal river section. DETAILED DESCRIPTION

[0027] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0028] like Figure 1 As shown, specifically, a method for determining the friction coefficient of the bottom bed of a tidal river section is based on the Manning formula and is characterized by comprising the following steps:

[0029] S1 sets N observation points x in the tidal river section i , at T time t j Measure the water surface elevation data η of all observation points ij ;

[0030] The observation point x i Specifically, let the estuary of the tidal river be the starting point, and mark the observation points in sequence as i, i = 1, 2, ..., N, x iis the distance between the observation point and the starting point, and the propagation from the estuary to the upstream of the river is +x i Direction, the reflection from the upstream of the river to the estuary is -x i direction;

[0031] The water surface elevation data η ij Specifically, mark the observation time sequence as j, j = 1, 2, ..., T, t j is the measurement time, at the same time t j Measure all observation points x1, x2, ...x N The water surface elevation η of observation point i at observation time j is η ij .

[0032] The propagation characteristics of tidal waves in tidal river sections should not be just standing waves or forward waves. It is necessary to consider the damping of tidal waves entering the estuary. Due to the influence of factors such as river channel constriction, steep channel slope or closed terrain, such as gates or artificial structures, tidal wave reflection occurs. At the same time, the amplitude of tidal waves is damped and attenuated by the friction effect of the bottom bed. On this basis, the partial reflection wave theory is established to construct the water surface elevation equation η(x i );

[0033] The water surface elevation equation η(x i ), specifically:

[0034] η(x i )=η1(x i )+η2(x i ),

[0035]

[0036]

[0037] In the above formula, η1(x i ) is the water surface elevation equation of the incident wave entering the estuary from the open sea, η2(x i ) is the water surface elevation equation of the reflected wave entering the estuary from the open sea; ω is the tidal wave reflection coefficient, κ is the tidal wave number, and the value of ω ranges from 0 to 1, for example, ω=0 is a forward wave, and ω=1 is a fully reflected wave; μ is the damping modulus, a0 is a constant, and σ is the number of time periods; let substituted into the water surface elevation equation η(x i ) i The value is +x i .

[0038] S3: the water surface elevation data n ij According to the water surface elevation equation η(x i ) fitting, calculate the instantaneous hydraulic gradient equation S tjThe instantaneous hydraulic gradient S tj , specifically:

[0039]

[0040] S4 measures the designated measuring point x of the tidal river section m Low tide or high tide time max Maximum flow velocity V and hydraulic radius R;

[0041] S5: x of the specified observation point m and the measurement time t max , substitute into the instantaneous hydraulic gradient equation S tj The instantaneous hydraulic gradient S is calculated tmax (x m ), the instantaneous hydraulic gradient S tmax (x m ), the maximum flow velocity V and the hydraulic radius R are substituted into the Manning formula The Manning coefficient n of the designated measuring point is calculated as the bottom bed friction coefficient of the designated measuring point.

[0042] Furthermore, the present invention is not only applicable to tidal river sections with non-constant non-uniform flow, but also to river sections with constant uniform flow, but is not limited thereto.

[0043] Preferably, the present invention selects the tidal section of Keelung River as the calculation object of the method, because the riverbed slope of Keelung River is gentle and the catchment area is low-lying, so its tidal section is longer; according to the analysis data from 2004 to 2018, the n value of the tidal section of Keelung River from the estuary to the upstream is 0.02 to 0.045, and the roughness of the riverbed has shown a stable trend; the present invention adopts the time t1 of the tidal section of Keelung River as June 22, 2005 (May 16 of the lunar calendar, high tide), and the time t2 as September 13, 2006 (July 21 of the lunar calendar, low tide), combines the data of multiple observation stations of Keelung River, takes Bailingqiao Station as the observation point, and calculates the bottom friction coefficient of the tidal section of Keelung River.

[0044] At time t1, 14.89 hr on June 22, 2005, the maximum flow velocity at low tide observed at Bailingqiao Station was 0.6452 m / s. The water surface elevations of each tide station at that time are shown in Table 1:

[0045] Table 1 Water surface elevation at the time of maximum tidal velocity at each tidal station in the tidal section of Keelung River (low tide on June 22, 2005)

[0046]

[0047] According to the water surface elevation data of various observation stations on the Keelung River on June 22, 2005, the K1 value was fitted to be 4.826×10-5 1 / m, μ1 value is 4.337×10 -5 1 / m and the tidal wave reflection coefficient ω1 is 0.75, and the maximum tidal velocity corresponds to the time σt M1 The value is 1.418, and the hydraulic gradient St1 is 3.388×10 -5 1 / m.

[0048] On June 22, 2005, at the Bailing Bridge Station on the Keelung River, x m The value is 6.3km, the observed maximum tidal velocity value V1 is 0.6452 m / s, and the hydraulic radius R1 is expressed as 5.63m at low tide. Substituting the hydraulic gradient St1 value, the maximum tidal velocity value V1 and the hydraulic radius R1 into the Manning formula, the Manning coefficient n1 value of the Bailing Bridge Station of Keelung River is calculated to be 0.0286s / m 1 / 3 .

[0049] Furthermore, at time t2, 20.85 hr on September 13, 2006, the maximum ebb velocity observed at the Bailingqiao station was 0.6261 m / s. The water surface elevations of each tidal station at that time are shown in Table 2:

[0050] Table 2 Water surface elevations at the time of maximum tidal velocity at each tidal station in the tidal section of Keelung River (low tide on September 13, 2006)

[0051]

[0052] Based on the water surface elevation data of the Keelung River at various observation stations on September 13, 2006, the K2 value was fitted to be 5.014×10 -5 1 / m, μ2 value is 4.556×10 -5 1 / m and the tidal wave reflection coefficient ω2 is 0.63, and the maximum tidal velocity corresponds to the time σt M2 The value is 1.649, and the hydraulic gradient St2 is 3.683×10 -5 1 / m.

[0053] September 13, 2006 at the Bailing Bridge Station on the Keelung River, x m The value is 6.3km, the observed maximum tidal velocity value V2 is 0.6261 m / s, and the hydraulic radius R2 is expressed at a low tide depth of 5.20m. Substituting the hydraulic gradient St2 value, the maximum tidal velocity value V2 and the hydraulic radius R2 into the Manning formula, the Manning coefficient n2 value of the Keelung River Bailing Bridge Station is calculated to be 0.0286s / m 1 / 3 .

[0054] The Manning coefficient n value at the Bailing Bridge Station on the Keelung River was calculated to be 0.025 to 0.030 s / m by using the method of estimating the Manning coefficient based on the particle size.1 / 3 , which is very close to the Manning coefficient n1 and n2 values ​​calculated by the present invention. The comparison results fully illustrate the beneficial effects of the present invention: it overcomes the problem of large calculation errors caused by directly using the Manning formula due to the non-constant and non-uniform flow of tidal waves in tidal river sections, while reducing the time and labor costs of scientific researchers.

[0055] The above-mentioned embodiment only expresses one implementation mode of the present invention, and its description is relatively specific and detailed, but it cannot be understood as limiting the scope of the patent of the present invention. It should be pointed out that for ordinary technicians in this field, several modifications and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be based on the attached claims.

Claims

1. A method for determining the coefficient of friction of the bottom bed in a tidal river section. It is characterized in that The following steps are involved: S1 sets N observation points x in the tidal river section i , at T time t j Measure the water surface elevation data η of all observation points ij ; S2 establishes the partial reflection wave theory and constructs the water surface elevation equation η(x i ); S3 the water surface elevation data n ij According to the water surface elevation equation η(x i ) fitting, calculate the instantaneous hydraulic gradient equation S tj ; S4 measures the designated measuring point x of the tidal river section m Low tide or high tide time max Maximum flow velocity V and hydraulic radius R; S5 converts the instantaneous hydraulic gradient S tmax (x m ), the maximum flow velocity V and the hydraulic radius R are substituted into the Manning formula Calculate and obtain the Manning coefficient n of the designated measuring point as the bottom bed friction coefficient of the designated measuring point; The water surface elevation equation η(x i ), specifically: the(x i )=η 1 (x i )+η 2 (x i ), In the above formula, η 1 (x i ) is the water surface elevation equation of the incident wave entering the estuary from the open sea, η 2 (x i ) is the water surface elevation equation of the reflected wave from the open sea to the estuary; ω is the tidal wave reflection coefficient, κ is the tidal wave number, μ is the damping modulus, and a 0 is a constant, σ is the number of time cycles; let it be substituted into the water surface elevation equation η(x i ) i The value is +x i .

2. A method for determining the friction coefficient of the bottom bed of a tidal river section according to claim 1, It is characterized in that The observation point x i , specifically: Let the estuary of the tidal river be the starting point, and mark the observation points in sequence as i, i = 1, 2, ..., N, x i is the distance between the observation point and the starting point, and the propagation from the estuary to the upstream of the river is +x i Direction, the reflection from the upstream of the river to the estuary is -x i direction.

3. A method for determining the friction coefficient of the bottom bed of a tidal river section according to claim 2, It is characterized in that The water surface elevation data η ij , specifically: Mark the observation time sequence as j, j = 1, 2, ..., T, t j is the measurement time, at the same time t j Measure all observation points x 1 、x 2 ,...x N The water surface elevation η of observation point i at observation time j is η ij .

4. A method for determining the friction coefficient of the bottom bed of a tidal river section according to claim 1, It is characterized in that The value range of the tidal wave reflection coefficient ω is 0 to 1.

5. A method for determining the friction coefficient of the bottom bed of a tidal river section according to claim 4, It is characterized in that Place The instantaneous hydraulic gradient equation S tj , specifically:

6. A method for determining the friction coefficient of the bottom bed of a tidal river section according to claim 5, It is characterized in that The S tmax (x m ) specifically: The x of the specified measurement point m and the measurement time t max , substitute into the instantaneous hydraulic gradient equation S tj Calculate S tmax (x m ).

7. A method for determining the friction coefficient of the bottom bed of a tidal river section according to claim 6, It is characterized in that It is applicable to at least one of tidal river sections with non-constant non-uniform flow or river sections with constant uniform flow.

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