Analysis method for sediment transportation and deposition in large-spatial-scale watershed

Abstract

The invention discloses an analysis method for sediment transportation and deposition in a large-spatial-scale watershed, and relates to the technical field of sediment deposition analysis. The method comprises the following specific steps: collecting a plurality of sediment sediment samples at each sampling point in a drainage basin; analyzing the sediment sediment sample through particle size grading to obtain a sample particle analysis result; generating a particle size grading distribution curve according to the sample particle analysis result; and through the particle size grading distribution curve, according to the proportion of each particle size component in the particle size grading distribution curve, in combination with the erosion amount and the sediment transportation ratio, carrying out sediment budget calculation. According to the method, sediment budgetary calculation is carried out on the large-spatial-scale watershed by applying a particle size grading analysis method, the heap, deposition and transportation conditions of erosion sediment of different particle size groups in the watershed are obtained, and the calculation result is accurate.

Description

Technical Field

[0001] The invention relates to the technical field of sediment deposition analysis, and in particular to an analysis method for sediment transport and deposition in a large spatial scale watershed. Background Art

[0002] Sediment production from river basin erosion is the process in which sediment that meets hydraulic conditions is discharged through the river basin outlet after erosion, transportation, and deposition. The law of sediment mass conservation runs through this process. Sediment transport ratio is an indicator that reflects the sediment production and transport capacity of river basin erosion, which is of great significance for evaluating the benefits of soil and water conservation and sediment reduction. However, there is little research on river basin sediment transport and deposition analysis based on a large spatial scale in the existing technology. Summary of the invention

[0003] The purpose of the present invention is to provide an analysis method for sediment transport and deposition in a large spatial scale watershed to solve the problems raised in the background technology.

[0004] To achieve the above object, the present invention provides the following scheme: a method for analyzing sediment transport and deposition in a large spatial scale watershed, the specific steps of which include the following:

[0005] Collect multiple sediment samples at each sampling point within the watershed;

[0006] Analyzing the sediment sample by particle size distribution to obtain a sample particle analysis result;

[0007] Generate a particle size distribution curve according to the sample particle analysis results;

[0008] Through the particle size distribution curve, according to the proportion of each particle size component, combined with the erosion amount and sediment transport ratio, sediment estimation is carried out.

[0009] Preferably, the calculation of the erosion amount is carried out using an improved universal soil loss equation, and the various factor indicators include R value, K value, L value, S value, C value and P value.

[0010] Preferably, the calculation formula of the R value is:

[0011]

[0012] Among them, P is the average annual precipitation, P i Monthly precipitation.

[0013] Preferably, the calculation formula of the K value is:

[0014]

[0015] Among them, SAN is the sand content; SIL is the silt content; CLA is the clay content; C represents the organic carbon content; SN1 = 1-SAN / 100.

[0016] Preferably, the calculation formula of the S value is:

[0017]

[0018] Among them, S is the slope factor and θ is the slope.

[0019] Preferably, the calculation formula of the L value is:

[0020]

[0021] Among them, L ij is the slope length factor of the grid cell, A ij-in is the uphill catchment area of ​​the unit, D is the unit width, x ij is the width of the unit perpendicular to the flow direction, and m is the slope length index.

[0022] Preferably, the particle size distribution analysis is completed by mechanical sieving and laser particle size analyzer testing.

[0023] According to the specific embodiments provided by the present invention, the present invention discloses the following technical effects: the present invention applies the particle size grading analysis method to perform sediment estimation on a large spatial scale basin, and obtains the accumulation, deposition and transport conditions of eroded sediment of different particle size groups in the basin, and the estimated results are accurate. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0025] Figure 1 is a flow chart of the method of the present invention;

[0026] Figure 2 This is a scatter plot of the relationship between the proportion of sediment with a particle size less than 1.0 mm and D50 in the present invention. DETAILED DESCRIPTION

[0027] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions 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] The purpose of this invention is to provide a method for analyzing sediment transport and deposition in a large spatial scale watershed. Figure 1 As shown, the specific steps include the following:

[0029] S1. Collect multiple sediment samples at each sampling point in the watershed;

[0030] S2. Analyze the sediment sample by particle size distribution to obtain the sample particle analysis results;

[0031] S3, generating a particle size distribution curve according to the sample particle analysis results;

[0032] S4. Make an approximate estimate of sediment based on the particle size distribution curve, the proportion of each particle size component, and the erosion amount and sediment transport ratio.

[0033] The following is an explanation of the principle and application steps of the particle size distribution analysis method:

[0034] The basic principle of sediment particle size distribution analysis is the conservation of basin sediment mass, and the relationship is:

[0035] S E =S D +S Y ;

[0036] Among them, S E is the total annual soil erosion in the area above the drainage outlet control section, S D is the total amount of sediment deposited in the area above the drainage outlet control section each year, S Y It is the total amount of sediment carried by water through the outlet control section each year.

[0037] According to the size of the sediment particles, the particles are divided into n particle size groups D1~D2, D2~D3, D3~D4,..., where the subscripts 1, 2, 3, 4,... are sequential numbers. ΔP i The particle size is between D i ~D i+1 The percentage of sediment in the total sediment volume. The particle size of sediment deposited above the control section of the basin outlet is between D i ~D i+1 The amount of sediment between can be calculated as follows:

[0038]

[0039] S E Obtained from existing data or soil erosion calculation method; S Y It is calculated based on the flow, suspended sediment concentration and bed load transport rate measured at the hydrological station; (ΔP i ) EThe representative particle size distribution S of the sediment eroded from the upper reaches of the basin m Get, S m It can be roughly estimated by the following method: take the average value of the particle size distribution of multiple representative upstream slopes, riverbeds and debris flow ditch sediments as S a ; Since part of the original sediment has been transported into rivers in the form of suspended matter after erosion, the representative particle size distribution of the eroded sediment needs to take this part of the sediment into account and be calculated using the following formula:

[0040] S m =q%S a +r%S sy ;

[0041] Among them, q% and r% are the proportion of sediment deposited above the control section of the basin outlet and the proportion of sediment transported through the control section in the total erosion, respectively. sy The particle size distribution of the total sediment transported at the outlet control section can be obtained from hydrological data. sy It can be calculated that (ΔP i ) Y .

[0042] The particle size distribution analysis method of the present invention is S E It is mainly calculated by the universal soil loss equation (RUSLE); the basin sediment transport S Y The data are obtained from the hydrological yearbook of the corresponding outlet control station; the sediment transport ratio (SDR) can be obtained by knowing the erosion and sediment transport data, and then q and r can be obtained; S of different sediment particle size components a Obtained from field sampling and screening statistics, S sy Obtained from the statistics of hydrological yearbook data.

[0043] In this embodiment, the Daning River Basin is taken as an example to perform sediment estimation.

[0044] Basin Overview: Daning River is one of the main first-level tributaries of the Yangtze River in the Three Gorges Reservoir area. It is located on the north bank of the Yangtze River. It originates from the southern foot of Daba Mountain and flows from north to south. It flows into the Yangtze River at the west entrance of Wu Gorge. The main stream is about 162km long and the basin area is 4181km. 2 The lithology of the basin is mainly lithocrystal rock (dolomite, limestone), and the main soil types are lime soil, yellow-brown soil, brown soil and purple soil. Due to the internal geological action and the strong erosion, denudation and dissolution in the later period, the basin has formed a landscape with steep terrain, developed karst, dense gullies and deep canyons.

[0045] A field survey was conducted on the Daning River in the Three Gorges Reservoir area. Samples of eroded slope deposits, channel deposits, and riverbed sediments were collected from the main tributaries and tributaries of the Daning River. After regional merging, multiple samples were collected at each sampling point to obtain the average value of the particle size distribution. The gradation analysis was completed using mechanical screening and laser particle size analyzer testing. The particle size distribution curve was generated based on the sample particle analysis results. Based on the results, the median particle size D50 of the sampled sediment in the Daning River basin and the percentage of sediment with a particle size less than 1.00 mm in the sand sample were statistically calculated, as shown in Table 1.

[0046]

[0047]

[0048] Table 1

[0049] In the logarithmic coordinate system, the slope deposit points with obviously larger particle sizes are eliminated, and the distribution curves of the last two columns of characteristic values ​​of the sampling points in the table are drawn, as shown in the figure. Figure 2 As shown in the figure, the curve takes the proportion of sediment with a particle size less than 1.0 mm as the vertical axis and D50 as the horizontal axis. It can be seen that with the increase of D50, the proportion of sediment with a particle size less than 1.0 mm gradually decreases, and the two are negatively correlated.

[0050] The Daning River is mainly eroded by hydraulic forces, and a large amount of suspended sediment comes mainly from surface erosion. Therefore, the calculation of erosion in the Daning River basin is carried out using the improved universal soil loss equation (RUSLE). The calculation methods for each factor index are as follows:

[0051] R value: Rainfall erosivity is an indicator that quantitatively characterizes the potential for soil erosion caused by rainfall. Its classic formula is the product of total rainfall kinetic energy (E) and maximum 30-minute rainfall intensity (I30). However, this calculation method requires continuous recording of rainfall time and cumulative rainfall, and sequentially determining the duration and rainfall of each rainfall. Data acquisition and calculation are relatively difficult. Therefore, various correction algorithms have also emerged. After partial calculation and comparison, the present invention adopts the following simplified algorithm to calculate rainfall erosivity:

[0052]

[0053] Among them, P is the average annual precipitation, P i Monthly precipitation.

[0054] The calculated R unit is 100 ft·t·in·ac -1 ·h -1 ·a -1The data are monthly rainfall data of 154 stations in the upper reaches of the Yangtze River and its surrounding areas from 1956 to 2010. The rainfall erosivity data of each station can be obtained through Kriging spatial interpolation to obtain the rainfall erosivity raster map of the upper reaches of the Yangtze River, and then the rainfall erosivity map of the Daning River Basin can be obtained through the clip tool of GIS.

[0055] K value: Soil erodibility indicates the sensitivity of soil to erosion, and reflects the ease with which soil is separated, washed away and transported by rainfall. The usual methods for calculating K value are: direct measurement method, nomogram method and formula method. The direct measurement method is generally believed to be able to obtain more reliable first-hand data, but it takes a lot of time and money; the erodibility nomogram method requires basic information on soil structure level and soil permeability level, and the existing soil background data in my country cannot meet this requirement. Therefore, the erodibility factor of most soil types still needs to be calculated by formula. The K value method in the EPIC model is used for calculation, and the influence of gravel content on K is taken into account, and necessary corrections are made to the original algorithm. The calculation formula of K value is:

[0056]

[0057] Among them, SAN is the sand content; SIL is the silt content; CLA is the clay content; C represents the organic carbon content; SN1 = 1-SAN / 100. The conversion formula for gravel soil erodibility is:

[0058]

[0059] Among them, Sr is the relative amount of soil erosion, Rm is the soil gravel content, and the soil erodibility grid map is obtained after the calculation is completed.

[0060] The LS value is the slope length and slope factor, which reflects the effect of topographic features on soil erosion. At present, the formula for calculating the LS factor is mainly obtained from slope experimental data and belongs to an empirical model. The structure and parameter size of these models are somewhat different. There are also many methods for calculating terrain factors, especially slope length, using DEM data. In my country, regions are divided according to the graded merging of slopes and directions, or the relationship between slope length and landform type is obtained through field surveys, or assumptions are set for the termination of slope length calculation. Taking into account a considerable proportion of steep slopes in the reservoir area and comparing the calculation results of some formulas, the slope factor S in the present invention is calculated using the following formula:

[0061]

[0062] Among them, S is the slope factor and θ is the slope.

[0063] The slope length factor uses a slope length factor calculation formula based on DEM data. This formula is consistent with the process on the slope from upslope to downslope. As the catchment area increases, the runoff increases, and the erosion force increases. The required DEM data comes from SRTM.

[0064] The calculation formula of L value is:

[0065]

[0066] Among them, L ij is the slope length factor of the grid cell, A ij-in is the uphill catchment area of ​​the unit, D is the unit width, x ij is the width of the unit perpendicular to the flow direction, and m is the slope length index.

[0067]

[0068] C value and P value: Vegetation cover and management factor C refers to the ratio of soil loss of a specific crop or vegetation cover to soil loss of bare land under the same other conditions; soil and water conservation measures factor P refers to the ratio of soil loss after taking water conservation measures to soil loss when planting along the slope. The assignment method is used to assign values ​​to various land use types in the 1:100,000 national land use map in 2000. C value and P value grid maps can be generated from the assignment of various land use types and land use maps.

[0069] Output of lithology factor (Ro): There are many landslides in the reservoir area, and their contribution to suspended sediment should also be considered. Lithology is closely related to landslides. Its control of the spatial distribution and development of soil erosion has an important impact on the erosion and sediment production in the Daning River Basin. Since there are few studies on the relationship between lithology and soil erosion in China, and most of them remain at the qualitative description, the expert scoring method is used to assign the erodibility of the main soil-forming parent rocks distributed in the upper reaches of the Yangtze River. When scoring, first determine the lithology, then determine the structural occurrence, and then score according to the erodibility assignment table of soil-forming parent rocks in the Daning River Basin, and finally complete the rasterization in GIS.

[0070] After obtaining the calculation results of the above factors, the factors were multiplied and superimposed in GIS to obtain the soil erosion of the Daning River. According to calculations, the average soil erosion modulus of the Daning River basin for many years is about 2000t / a.km 2 The total soil erosion is about 8.4 million t / a.

[0071] Sediment estimation: Based on the field sampling data of the Daning River Basin, the average sediment particle size distribution curve of the basin is obtained. According to the proportion of each particle size component, combined with the erosion amount and sediment transport ratio, the S of the corresponding particle size component can be further calculated. aAccording to the long-term sediment transport data and calculation results of the Daning River Basin, the long-term sediment transport in the basin is about 1.95 million t / a, and the erosion is about 8.4 million t / a. The average sediment transport ratio SDR is 0.23, from which r% is 1-0.23=0.77=77%, and q% is 23%.

[0072] By removing the singular values ​​of the slope (and riverbed) sampling and river sediment grading results, the representative particle size gradation Sm of different grading components can be calculated, and then according to the formula, the mass proportion distribution of different grading components of eroded unit volume of sediment can be obtained. The approximate calculation table of sediment in the Daning River basin based on the particle size analysis method is as follows:

[0073] As shown in Table 2:

[0074]

[0075]

[0076] Table 2

[0077] From Table 2, we can see that of the annual average soil erosion of 8.4 million tons in the Daning River Basin, 6.468 million tons of sediment are deposited on the river bank or slope foot, and 1.932 million tons enter the river for transport. Among them, the sediment with a particle size between 2mm and 1mm (i.e. D1-D2, the same below) is about 187,000 tons, which is basically deposited on the river bank or slope foot; the sediment between D0.5-D1 is about 604,000 tons, of which 589,000 tons are deposited on the river bank or slope foot, and 15,000 tons enter the river for transport; the sediment between D0.25-D0.5 is about 1.017 million tons, of which 1.001 million tons are deposited on the river bank. The sediment between D0.1-D0.25 is about 1.17 million tons, of which 874,000 tons are deposited on the river bank or the foot of the slope, and 296,000 tons are transported into the river; the sediment between D0.05-D0.1 is about 845,000 tons, of which 480,000 tons are deposited on the river bank or the foot of the slope, and 365,000 tons are transported into the river; The sediment between D0.05 and D0.05 is about 913,000 tons, of which 556,000 tons are deposited on the river bank or the foot of the slope, and 357,000 tons enter the river for transportation; the sediment between D0.01-D0.025 is about 1,105,000 tons, of which 647,000 tons are deposited on the river bank or the foot of the slope, and 458,000 tons enter the river for transportation; the sediment between D0.005-D0.01 is about 376,000 tons, of which 27. 70,000 tons are deposited on the river bank or foot of the slope, and 139,000 tons enter the river for transportation; the sediment between D0.005-D0.002 is about 376,000 tons, of which 221,000 tons are deposited on the river bank or foot of the slope, and 155,000 tons enter the river for transportation; the clay below D0.002 is about 1.772 million tons, of which 1.637 million tons are deposited on the river bank or foot of the slope, and 135,000 tons enter the river for transportation.

[0078] The principles and implementation methods of the present invention are described in this article using specific examples. The description of the above embodiments is only used to help understand the method and core idea of ​​the present invention. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A method for analyzing sediment transport and deposition in a large spatial scale basin, characterized in that: The specific steps include the following: Collect multiple sediment samples at each sampling point within the watershed; Analyzing the sediment sample by particle size distribution to obtain a sample particle analysis result; Generate a particle size distribution curve according to the sample particle analysis results; Through the particle size distribution curve, according to the proportion of each particle size component, combined with the erosion amount and sediment transport ratio, sediment estimation is carried out.

2. The method for analyzing sediment transport and deposition in a large spatial scale basin according to claim 1 is characterized in that: The calculation of the erosion amount is carried out using an improved universal soil loss equation, and the various element indicators include R value, K value, L value, S value, C value and P value.

3. The method for analyzing sediment transport and deposition in a large spatial scale basin according to claim 2 is characterized in that: The calculation formula of the R value is: Among them, P is the average annual precipitation, P i Monthly precipitation.

4. The method for analyzing sediment transport and deposition in a large spatial scale basin according to claim 2 is characterized in that: The calculation formula of the K value is: Among them, SAN is the sand content; SIL is the silt content; CLA is the clay content; C represents the organic carbon content; SN1 = 1-SAN / 100.

5. The method for analyzing sediment transport and deposition in a large spatial scale basin according to claim 2 is characterized in that: The calculation formula of the S value is: Among them, S is the slope factor and θ is the slope.

6. The method for analyzing sediment transport and deposition in a large spatial scale basin according to claim 2 is characterized in that: The calculation formula of the L value is: Among them, L ij is the slope length factor of the grid cell, A ij-in is the uphill catchment area of ​​the unit, D is the unit width, x ij is the width of the unit perpendicular to the flow direction, and m is the slope length index.

7. The method for analyzing sediment transport and deposition in a large spatial scale basin according to claim 1 is characterized in that: The particle size distribution analysis is completed by mechanical screening method and laser particle size analyzer test.

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