A method for calculating sediment transport in small watersheds

Abstract

The present invention discloses a method for calculating sediment transport in a small watershed, which belongs to the field of sediment transport calculation. The method comprises determining a measuring section; sampling sediment in a riverbed of the measuring section to obtain a particle size distribution of bed load; calculating the bed load sediment transport per unit time based on the particle size distribution of bed load; sampling river water at each water depth of the measuring section to obtain a suspended load sediment transport per unit time; calculating the basin sediment transport according to the bed load sediment transport per unit time and the suspended load sediment transport per unit time, and completing the small watershed sediment transport calculation. The present invention solves the problem of insufficient accuracy of the existing sediment transport calculation method due to insufficient data.

Description

Technical Field

[0001] The invention belongs to the field of sediment transport calculation, and in particular relates to a method for calculating sediment transport in a small watershed. Background Art

[0002] The calculation of sediment transport in small watersheds is one of the important research contents in the field of water resources management and environmental protection. It involves the quantitative description of the source, transport process and deposition law of sediment in the watershed, which is of great significance for understanding the relationship between water and sediment in the watershed, assessing the status of soil erosion, and formulating soil and water conservation measures. The main calculation methods are the sediment transport rate and flow product method. The basic principle of the sediment transport rate and flow product method is that the sediment transport is equal to the product of the sediment transport rate and the flow; this method is suitable for watersheds with measured sediment transport rate and flow data. By measuring the mass of sediment on the riverbed surface per unit cross-sectional area per unit time and the volume of water flow through the cross-section, the sediment transport can be calculated. This method needs to ensure the accuracy and representativeness of the sediment transport rate and flow data. There are also suspended load and bedload calculation methods for calculating sediment transport; suspended load is sediment suspended in water and moves with the water flow. Its sediment transport can be estimated by methods such as measured data, water-sediment relationship interpolation and extension, and checking the sediment transport modulus diagram in the regional hydrological manual. Bedload is sediment moving along the water flow direction on the riverbed surface. Due to lack of data and accuracy issues, the sediment transport volume is often estimated by indirect methods, such as the proportional coefficient method, bed load sediment transport rate formula calculation, etc. This method comprehensively considers the contribution of suspended load and bed load to the sediment transport volume, and more accurately reflects the water-sediment relationship in the basin. Existing calculation methods also include the mathematical model method: using mathematical models and computer technology to simulate the water and sand movement process in the basin, so as to calculate the sediment transport volume. It is suitable for complex basins or basins with insufficient data. By inputting the basin's topography, climate, vegetation and other parameters, the model can simulate the rainfall runoff process, soil erosion process and sediment transport process in the basin, and then calculate the sediment transport volume; this method needs to fully consider the actual situation of the basin and the reliability of the data when establishing the model.

[0003] The calculation of sediment discharge in small watersheds is one of the important research contents in the fields of hydrology and soil erosion. By reasonably selecting the calculation method and considering the influence of influencing factors, the sediment discharge in small watersheds can be accurately calculated, providing an important decision-making basis for water resources management and environmental protection. Summary of the invention

[0004] In view of the above-mentioned deficiencies in the prior art, a method for calculating sediment transport in a small watershed is provided in the present invention, which solves the problem of insufficient accuracy of the existing sediment transport calculation method due to insufficient data.

[0005] In order to achieve the above-mentioned invention object, the technical solution adopted by the present invention is: a method for calculating sediment transport in a small watershed, comprising the following steps:

[0006] S1. Determine the measurement section;

[0007] S2. Sampling the sediment in the riverbed of the measured section to obtain the particle size distribution of the bed load;

[0008] S3. Calculate the sediment transport per unit time of the bed load based on the particle size distribution of the bed load;

[0009] S4. Take river water samples at each water depth of the measurement section to obtain the suspended sediment transport per unit time;

[0010] S5. Calculate the sediment transport in the watershed based on the bed load and suspended load per unit time, and complete the sediment transport measurement in the small watershed.

[0011] Furthermore, the S2 is specifically:

[0012] S201, setting the sampling interval;

[0013] S202, sampling the riverbed sediment of the measured section along the river transverse direction based on the sampling interval to obtain a plurality of sampling data;

[0014] S203, performing sediment particle size statistics on each sampling data to obtain sediment particle size distribution within each sampling interval.

[0015] Furthermore, the expression of the sediment particle size distribution within each sampling interval in S203 is:

[0016] F(X i )=[f i,1 ,f i,2 ,...,f i,max ]

[0017]

[0018] Among them, F(X i ) is the i-th sampling interval X i The distribution of sediment particle size within the i,1 is the i-th sampling interval X i The specific gravity of the first level of sediment particle size; f i,2 is the i-th sampling interval X i The specific gravity of the second-level sediment particle size; f i,max is the i-th sampling interval X i The specific gravity of the largest sediment particle size within the range; d z is the sediment particle size; M soil is the total amount of sediment currently sampled; N i is the i-th sampling interval X i The number of sampling times; d max-1 is the upper limit of the sediment particle size threshold of the max-1 level; dmax is the upper limit of the sediment particle size threshold of the max level; max is the total number of sediment particle size levels.

[0019] Furthermore, the expression of bed load transport rate in S3 is:

[0020]

[0021] Among them, V 推 N is the bed load per unit time; X is the total number of sampling intervals; ρ s is the density of sediment; ρ is the density of water; τ b is the shear stress of water flow on the bed surface; τ c is the critical bed water shear stress; u is the water flow friction velocity; c 0 is the sedimentation coefficient; ω is the sedimentation velocity; g is the gravitational acceleration; f i,1 is the i-th sampling interval X i The specific gravity of the first level of sediment particle size; f i,max is the i-th sampling interval X i The specific gravity of the largest sediment particle size within the range; a max It is the movement coefficient of sediment of the max-th sediment particle size driven by water flow velocity; max is the total number of sediment particle size grades.

[0022] Furthermore, the S4 is specifically:

[0023] S401, setting a second sampling interval;

[0024] S402, based on the second sampling interval, sampling river water along the river depth at the sampling interval center of each sediment sampling in the measurement section to obtain a plurality of river water sampling data;

[0025] S403, obtaining the distribution of river water sediment content based on a number of river water sampling data;

[0026] S404, obtaining the average flow velocity of the measured section, and calculating the suspended sediment transport per unit time based on the average flow velocity of the measured section and the sediment content of the river water.

[0027] Furthermore, the expression for the distribution of river water sediment content in S403 is:

[0028]

[0029] in, For sediment sampling N X The sediment content of river water at the Mth second sampling interval of river water sampling is calculated at the sampling interval; M is the maximum number of the second sampling interval in river water sampling.

[0030] Furthermore, the expression of suspended sediment transport per unit time in S404 is:

[0031]

[0032] Among them, V 悬 is the suspended sediment transport per unit time; v is the average flow velocity of the measured section; For sediment sampling N X The cross-sectional area formed by the sampling interval and the Mth second sampling interval of river water sampling; For sediment sampling N X At the sampling interval, the sediment content of the river water at the Mth second sampling interval of the river water sampling is calculated.

[0033] Furthermore, the expression of the sediment transport capacity of the watershed in S5 is:

[0034] O=(bV 推 +V 悬 )T

[0035] Where O is the sediment transport in the basin; b is the depth compensation coefficient of bed load transport; V 推 V is the bed load per unit time; 悬 is the suspended sediment transport per unit time; T is the sediment transport duration.

[0036] The beneficial effects of the present invention are as follows: the present invention calculates the sediment transport of a certain section in a short period of time by calculating the sediment transport of bed load and suspended load at a certain moment in the river. The sampling accuracy is improved by dividing the riverbed sediment based on the sampling interval and dividing the river water based on the second sampling interval, and sampling the bed load and suspended load respectively; the time distribution of the sediment transport per unit time of the bed load is performed based on the particle size distribution of the riverbed sediment, which can improve the sediment transport per unit time accuracy within a single sampling interval. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 The present invention is a flow chart of the method. DETAILED DESCRIPTION

[0038] The specific implementation modes of the present invention are described below so that those skilled in the art can understand the present invention. However, it should be clear that the present invention is not limited to the scope of the specific implementation modes. For those of ordinary skill in the art, as long as various changes are within the spirit and scope of the present invention as defined and determined by the attached claims, these changes are obvious, and all inventions and creations utilizing the concept of the present invention are protected.

[0039] like Figure 1 As shown, in one embodiment of the present invention, a method for calculating sediment transport in a small watershed includes the following steps:

[0040] S1. Determine the measurement section;

[0041] S2. Sampling the sediment in the riverbed of the measured section to obtain the particle size distribution of the bed load;

[0042] S3. Calculate the sediment transport per unit time of the bed load based on the particle size distribution of the bed load;

[0043] S4. Take river water samples at each water depth of the measurement section to obtain the suspended sediment transport per unit time;

[0044] S5. Calculate the sediment transport in the watershed based on the bed load and suspended load per unit time, and complete the sediment transport measurement in the small watershed.

[0045] The S2 is specifically:

[0046] S201, setting the sampling interval;

[0047] S202, sampling the riverbed sediment of the measured section along the river transverse direction based on the sampling interval to obtain a plurality of sampling data;

[0048] S203, performing sediment particle size statistics on each sampling data to obtain sediment particle size distribution within each sampling interval.

[0049] The expression of the sediment particle size distribution within each sampling interval in S203 is:

[0050] F(X i )=[f i,1 ,f i,2 ,...,f i,max ]

[0051]

[0052] Among them, F(X i ) is the i-th sampling interval X i The distribution of sediment particle size within the i,1 is the i-th sampling interval X i The specific gravity of the first level of sediment particle size; f i,2 is the i-th sampling interval X i The specific gravity of the second-level sediment particle size; f i,max is the i-th sampling interval X i The specific gravity of the largest sediment particle size within the range; d z is the sediment particle size; M soil is the total amount of sediment currently sampled; N i is the i-th sampling interval X i The number of sampling times; d max-1 is the upper limit of the sediment particle size threshold of the max-1 level; d maxis the upper limit of the sediment particle size threshold of the max level; max is the total number of sediment particle size levels.

[0053] In this embodiment, multiple sampling is performed at each sampling interval, or after the first sampling, multiple sampling is performed in the first sampling pile ( N i,1,B For the Bth sampling, the i-th sampling interval X i The amount of sediment with the first-level sediment particle size; N soil,B is the total amount of sediment at the Bth sampling time); based on the pre-set sediment particle size classification, the sediment particle size distribution is statistically analyzed.

[0054] The expression of bed load transport rate in S3 is:

[0055]

[0056] Among them, V 推 N is the bed load per unit time; X is the total number of sampling intervals; ρ s is the density of sediment; ρ is the density of water; τ b is the shear stress of water flow on the bed surface; τ c is the critical bed water shear stress; u is the water flow friction velocity; c 0 is the sedimentation coefficient; ω is the sedimentation velocity; g is the gravitational acceleration; f i,1 is the i-th sampling interval X i The specific gravity of the first level of sediment particle size; f i,max is the i-th sampling interval X i The specific gravity of the largest sediment particle size within the range; a max It is the movement coefficient of sediment of the max-th sediment particle size driven by water flow velocity; max is the total number of sediment particle size grades.

[0057] In this embodiment, a max The acquisition process is as follows:

[0058] ① Ignore the water depth, obtain the velocity of different sediment particle sizes under the water flow velocity, and obtain the fitting equation of sediment particle size-sediment velocity;

[0059] ②According to the fitting equation of sediment particle size-sediment velocity, the sediment velocity under the current water flow velocity is obtained, and [(1+the ratio of the sediment velocity under the current water flow velocity and the water flow velocity) divided by 2] is used as a max .

[0060] In this embodiment

[0061] The S4 is specifically:

[0062] S401, setting a second sampling interval;

[0063] S402, based on the second sampling interval, sampling river water along the river depth at the sampling interval center of each sediment sampling in the measurement section to obtain a plurality of river water sampling data;

[0064] S403, obtaining the distribution of river water sediment content based on a number of river water sampling data;

[0065] S404, obtaining the average flow velocity of the measured section, and calculating the suspended sediment transport per unit time based on the average flow velocity of the measured section and the sediment content of the river water.

[0066] The expression of the river water sediment content distribution in S403 is:

[0067]

[0068] in, For sediment sampling N X The sediment content of river water at the Mth second sampling interval of river water sampling is calculated at the sampling interval; M is the maximum number of the second sampling interval in river water sampling.

[0069] In this embodiment, sediment sampling is performed linearly in the riverbed; river water sampling is performed in the horizontal and vertical directions, and the obtained M×N X sampling data; river water sampling is the same as sediment sampling, with multiple sampling at each sampling interval, or after the first sampling, multiple sampling is performed in the first sampling pile.

[0070] The expression of suspended sediment transport per unit time in S404 is:

[0071]

[0072] Among them, V 悬 is the suspended sediment transport per unit time; v is the average flow velocity of the measured section; For sediment sampling N X The cross-sectional area formed by the sampling interval and the Mth second sampling interval of river water sampling; For sediment sampling N X At the sampling interval, the sediment content of the river water at the Mth second sampling interval of the river water sampling is calculated.

[0073] The expression of the sediment transport capacity in the watershed in S5 is:

[0074] O=(bV 推 +V 悬 )T

[0075] Where O is the sediment transport in the basin; b is the depth compensation coefficient of bed load transport; V 推 V is the bed load per unit time; 悬is the suspended sediment transport per unit time; T is the sediment transport duration.

Claims

1. A method for calculating sediment transport in a small watershed, characterized in that: The following steps are involved: S1. Determine the measurement section; S2. Sampling the sediment in the riverbed of the measured section to obtain the particle size distribution of the bed load; S3. Calculate the bed load sediment transport per unit time based on the bed load particle size distribution; the expression of bed load sediment transport rate in S3 is: Among them, V 推 N is the bed load per unit time; X is the total number of sampling intervals; ρ s is the density of sediment; ρ is the density of water; τ b is the shear stress of water flow on the bed surface; τ c is the critical bed surface water flow shear stress; u is the water flow friction velocity; c0 is the sedimentation coefficient; ω is the sedimentation velocity; g is the gravity acceleration; f i,1 is the i-th sampling interval X i The specific gravity of the first level of sediment particle size; f i,max is the i-th sampling interval X i The specific gravity of the largest sediment particle size within the range; a max is the movement coefficient of the sediment of the max-th sediment particle size driven by the water flow velocity; max is the total number of sediment particle size levels; S4. Take river water samples at each water depth of the measurement section to obtain the suspended sediment transport per unit time; S5. Calculate the sediment transport of the basin according to the sediment transport per unit time of the bed load and the suspended load, and complete the sediment transport measurement of the small basin. The expression of the sediment transport of the basin in S5 is: O=(bV 推 +V 悬 )T Where O is the sediment transport in the basin; b is the depth compensation coefficient of bed load transport; V 推 V is the sediment transport per unit time of bed load; 悬 is the suspended sediment transport per unit time; T is the sediment transport duration.

2. The method for calculating sediment transport in a small watershed according to claim 1, characterized in that: The S2 is specifically: S201, setting the sampling interval; S202, sampling the riverbed sediment of the measured section along the river transverse direction based on the sampling interval to obtain a plurality of sampling data; S203, performing sediment particle size statistics on each sampling data to obtain sediment particle size distribution within each sampling interval.

3. The method for calculating sediment transport in a small watershed according to claim 2 is characterized in that: The expression of the sediment particle size distribution within each sampling interval in S203 is: F(X i )=[f i,1 ,f i,2 ,...,f i,max ] Among them, F(X i ) is the i-th sampling interval X i The distribution of sediment particle size within the i,1 is the i-th sampling interval X i The specific gravity of the first level of sediment particle size; f i,2 is the i-th sampling interval X i The specific gravity of the second-level sediment particle size; f i,max is the i-th sampling interval X i The specific gravity of the largest sediment particle size within the range; d z is the sediment particle size; M soil is the total amount of sediment currently sampled; N i is the i-th sampling interval X i The number of sampling times; d max-1 is the upper limit of the sediment particle size threshold of the max-1 level; d max is the upper limit of the sediment particle size threshold of the max level; max is the total number of sediment particle size levels.

4. The method for calculating sediment transport in a small watershed according to claim 1, characterized in that: The S4 is specifically: S401, setting a second sampling interval; S402, based on the second sampling interval, sampling river water along the river depth at the sampling interval center of each sediment sampling in the measurement section to obtain a plurality of river water sampling data; S403, obtaining the distribution of river water sediment content based on a number of river water sampling data; S404, obtaining the average flow velocity of the measured section, and calculating the suspended sediment transport per unit time based on the average flow velocity of the measured section and the sediment content of the river water.

5. The method for calculating sediment transport in a small watershed according to claim 4, characterized in that: The expression of the river water sediment content distribution in S403 is: in, For sediment sampling N X The sediment content of river water at the Mth second sampling interval of river water sampling is calculated at the sampling interval; M is the maximum number of the second sampling interval in river water sampling.

6. The method for calculating sediment transport in a small watershed according to claim 4, characterized in that: The expression of suspended sediment transport per unit time in S404 is: Among them, V 悬 is the suspended sediment transport per unit time; v is the average flow velocity of the measured section; For sediment sampling N X The cross-sectional area formed by the sampling interval and the Mth second sampling interval of river water sampling; For sediment sampling N X At the sampling interval, the sediment content of the river water at the Mth second sampling interval of the river water sampling is calculated.

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