A method for estimating monthly sediment inflow based on small watershed units

Abstract

The application provides a small watershed unit-based monthly scale river-incoming sediment volume estimation method, comprising the following steps: step S1: obtaining DEM data in a watershed range, combining remote sensing images to perform water system extraction and small watershed division; step S2: calculating a slope length factor L of each grid by using the DEM data y , a slope factor S y ; step S3: constructing a 30m resolution monthly scale vegetation coverage dataset by using multi-source remote sensing image data, and calculating a biological measure factor B m ; step S4: calculating a monthly scale rainfall erosion force factor by using monthly rainfall data; step S5: calculating a soil erodibility factor K, an engineering factor E and a tillage factor T; step S6: calculating a sediment transport ratio SDR of each grid in a small watershed unit; and step S7: calculating a monthly scale river-incoming sediment volume A of each small watershed. The technical scheme effectively improves the estimation precision and rationality of the river-incoming sediment volume, and provides a new means for evaluating the obtained river-incoming sediment volume under different time and space characteristics.

Description

Technical Field

[0001] The present invention relates to the technical field of river sediment volume estimation, in particular to a method for estimating monthly river sediment volume based on small watershed units. Background Art

[0002] Currently, there is a significant amount of research and application focused on calculating and spatially distributing soil erosion or soil conservation functions. However, these studies generally focus on interannual regional variations in soil erosion. Significant differences in vegetation cover and precipitation between months make it difficult to rationally calculate soil erosion across the year. Furthermore, there is limited research focused on calculating the amount of sediment entering rivers. Furthermore, watershed water and sediment research often utilizes observational data from hydrological monitoring stations, which are sparsely populated. These observations can only comprehensively reflect water and sediment conditions across larger regions, failing to provide a deep understanding of sediment sources or clarify the contribution of individual watersheds to river sediment inflows. Furthermore, they fail to capture the interdependence and constraints between landscape elements. Summary of the Invention

[0003] In view of this, the purpose of the present invention is to provide a monthly scale river sediment estimation method based on small watershed units, which effectively improves the accuracy and rationality of river sediment estimation and provides a new means for evaluating the river sediment amount under different temporal and spatial characteristics.

[0004] To achieve the above object, the present invention adopts the following technical solution: a method for estimating monthly sediment inflow based on small watershed units, comprising the following steps:

[0005] Step S1: Obtain the DEM data of the watershed range, extract the river system, divide the small watershed, and further determine the accuracy of the river system and small watershed division based on remote sensing images;

[0006] Step S2: Calculate the slope length factor L of each grid using DEM data y , slope factor S y ;

[0007] Step S3: Obtain Landsat series, Sentinel 2A, GF1 WFV multi-source medium-resolution remote sensing image data to construct monthly-scale vegetation coverage FVC m Data, calculate the monthly biological measure factor B m (m=1,2……12);

[0008] Step S4: Calculate the monthly rainfall erosivity factor R using monthly rainfall data m , m=1,2……12;

[0009] Step S5: Calculate the soil erodibility factor K, the engineering factor E and the tillage factor T;

[0010] Step S6: Taking the small watershed as a unit, the slope factor S of the uphill area and downhill area of ​​each grid is calculated. y , biological measures factor B m Numerical value, calculate the sediment transport ratio SDR of each grid;

[0011] Step S7: Taking the small watershed as a unit, calculate the monthly sediment inflow A of each small watershed to form the spatial distribution of the sediment inflow of the entire watershed.

[0012] In a preferred embodiment, the specific steps of step S1 are as follows:

[0013] Step S11: Collect the DEM data of the watershed, and use the hydrological analysis module in the geographic information system software to perform depression filling and cropping processing;

[0014] Step S12: import the processed DEM data into the SWAT model, set the minimum catchment area, and generate the river network;

[0015] Step S13: Select the watershed outlet point according to the actual situation and divide the watershed into small watersheds;

[0016] Step S14: Check the topological relationship as needed, combine remote sensing data, and use human-computer interaction to generate reasonable small watershed vector data. The number of small watershed units is N, and the number of cell grids in each small watershed is N. Sj , j=1,2,……N.

[0017] In a preferred embodiment, the specific steps of step S2 are as follows:

[0018] Step S21: Calculate the slope length factor L based on the DEM data obtained in step S1 y ; Slope length factor L y calculate:

[0019]

[0020] λ=λ x cosθ (1)

[0021]

[0022] Where λ is the horizontal projection slope length of the calculation unit, m. When λ≤100m, it is calculated according to the actual value; when λ>100m, it is calculated as 100m; θ is the slope of the calculation unit; n is the slope length index; L y is the slope length of the calculation unit; x is the slope length of the calculation unit;

[0023] Step S22: Calculate the slope factor S based on the DEM data obtained in step S1 y ; Slope factor Sy calculate:

[0024]

[0025] Where e is the base of natural logarithm, which is 2.72.

[0026] In a preferred embodiment, in step S3, the monthly vegetation coverage FVC m and vegetation cover factor B m The calculation method is as follows:

[0027] Step S31: Using multi-source medium-resolution remote sensing data such as Landsat series, Sentinel 2A and GF1 WFV, the monthly NDVI index with a resolution of 30 m is calculated through CCDC and spatiotemporal fusion methods;

[0028] Step S32: Calculate the monthly vegetation coverage FVC using the pixel binary model m ;

[0029] Step S33: Based on the existing land use classification results and monthly vegetation coverage FVC m Conduct monthly biological measures of factor B m , where forest land, orchard, grassland, and bare land are calculated using formula (5), tea garden, cultivated land, and terraced fields are assigned a value of 1, and water bodies and impervious surfaces are assigned a value of 0;

[0030]

[0031] In a preferred embodiment, in step S4, the monthly rainfall erosivity factor R m The calculation method is as follows:

[0032] R m =0.183*P m 1.995 (6)

[0033] Where R m is the rainfall erosivity factor in month m; P m is the rainfall in month m.

[0034] In a preferred embodiment, in step S5, the specific steps of calculating the engineering measure factor E, the soil erodibility factor K, and the tillage factor T are as follows:

[0035] Step S51: Collect data on whether soil and water conservation measures have been taken in the runoff areas within the study area, and calculate the engineering measure factors E of tea gardens and terraces to be 0.118 and 0.414 respectively, and 1 for other land types;

[0036] Step S52: Using soil attribute data, calculate the soil erodibility factor K based on the erosion-productivity impact calculation model EPIC:

[0037]

[0038] Where: SAN is sand content; SIL is silt content; CLA is clay content; c is organic carbon content; SN1 = 1-SAN / 100;

[0039] Step S53: Based on the T factor calculation method provided by the farming measures and the crop rotation system in different regions, the farming measure factors T for cultivated land and terraced fields are 0.15516 and 0.17964 respectively; when the calculation unit is not cultivated land or terraced field, the T factor is assigned a value of 1.

[0040] In a preferred embodiment, in step S6, the sediment transport ratio SDR of each grid is calculated based on the small watershed as a unit. i The specific steps are as follows:

[0041]

[0042] Where: SDR max The value of the maximum theoretical sediment transport ratio is usually set to 0.5, IC0 and k are calibration parameters, and IC i is the connectivity index, defined as:

[0043]

[0044] Where: D up is the upslope component of the ith pixel in the small watershed unit, indicating the potential for sediment transport from upstream to downstream. dn is the downslope component of the i-th pixel in the small watershed unit, indicating the possibility of sediment reaching the sink through the flow path, and is defined as:

[0045]

[0046] Where: represents the average value of the biological measure factor in the upslope sediment-producing area, is the average slope of the upslope sediment-producing area, A is the area of ​​the upslope sediment-producing area, d i is the length of water flow in the i-th unit along the steepest downslope direction, B th 、S th Defined as:

[0047]

[0048] In a preferred embodiment, in step S7, the specific steps for calculating the monthly sediment inflow A of each small watershed are as follows:

[0049] Step S71: Calculate the monthly soil erosion modulus of each grid point i in the small watershed using the CSLE formula. The formula is as follows:

[0050] CSLE i =R i K i LS i B i E i T i (14)

[0051] Where: CSLE i is the actual soil erosion modulus of grid i, R i is the rainfall erosion factor of grid i, K i is the soil erodibility factor of grid i, LS i is the slope length and slope factor of grid i, B i is the biological measure factor of grid i, E i is the engineering measure factor of grid i, T i is the tillage measure factor of grid i;

[0052] Step S72: Calculate the actual amount of sediment A entering the river at grid i that contributes to the sediment entering the river under the condition of sediment interception. The formula is as follows:

[0053] A i =CSLE i SDR i (15)

[0054] Where: A i is the actual sediment yield of grid i, SDR i is the sediment transport ratio under the conditions of vegetation cover factor and soil and water conservation measures at grid i;

[0055] Step S73: Calculate the monthly sediment inflow A of each small watershed j Sj , the formula is as follows:

[0056]

[0057] Where: A i is the actual sediment yield of grid i, N Sj is the number of grids in the small watershed that contribute to river inflow;

[0058] Step S74: Calculate the amount of sediment entering the river A for each small watershed unit in the watershed Sj , j = 1, 2, ... N, forming the spatial distribution of sediment entering the river in the basin.

[0059] Compared with the existing technology, the present invention has the following beneficial effects: by integrating remote sensing data with multiple temporal and spatial resolutions, constructing 30m-level medium-resolution monthly-scale vegetation cover time series data, and taking into account the actual temporal and spatial changes of rainfall and the differences in the water and soil interception capabilities of different surface covers, a monthly-scale basin-wide sediment inflow estimation model with small watersheds as units is established. The estimation results can not only accurately depict the spatial distribution of sediment inflow into the river, but also effectively reflect the changing characteristics between months within a year; the results are not only beneficial to water and soil conservation and management planning in the basin, but also have important significance for improving the ecosystem service functions of the basin. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] Figure 1 This is a flow chart of a method for estimating monthly river sediment inflow based on small watershed units according to a preferred embodiment of the present invention. DETAILED DESCRIPTION

[0061] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0062] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present application belongs.

[0063] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application; as used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form, and it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or their combinations.

[0064] like Figure 1 As shown in FIG, a flowchart of a method for estimating monthly sediment inflow based on a small watershed unit of the present invention includes the following steps:

[0065] Step S1: Obtain the DEM data of the watershed range, extract the river system, divide the small watershed, and further determine the accuracy of the river system and small watershed division based on remote sensing images;

[0066] The specific steps of step S1 are as follows:

[0067] Step S11: Collect the DEM data of the watershed, and use the hydrological analysis module in ArcGIS software to perform depression filling and cropping;

[0068] Step S12: import the processed DEM data into the SWAT model, set the minimum catchment area, and generate the river network;

[0069] Step S13: Select the watershed exit point and divide the watershed into small watersheds;

[0070] Step S14: Check the topological relationship as needed, combine remote sensing data, and use human-computer interaction to generate reasonable small watershed vector data. The number of small watershed units is N, and each small watershed grid unit is N. Sj (j=1,2,……N).

[0071] Step S2: Calculate the slope length factor L based on the DEM data obtained in step S1 y , slope factor S y ;

[0072] The specific steps of step S2 are as follows:

[0073] Step S21: Calculate the slope length factor L based on the DEM data obtained in step S1 y ;

[0074] Slope length factor L y calculate:

[0075]

[0076] λ=λ x cosθ (2)

[0077]

[0078] Where λ is the horizontal projection slope length of the calculation unit, m (when λ≤100m, calculate according to the actual value; when λ>100m, calculate according to 100m); θ is the slope of the calculation unit, (°); n is the slope length index; L y is the slope length of the calculation unit, m; λ x is the slope length of the calculation unit, m.

[0079] Step S22: Calculate the slope factor S based on the DEM data obtained in step S1 y ;

[0080] Slope factor S y calculate:

[0081]

[0082] Where e is the base of natural logarithm, which can be 2.72.

[0083] Step S3: Obtain medium-resolution remote sensing image data from multiple sources such as Landsat series, Sentinel 2A, and GF1 WFV to construct monthly vegetation coverage FVC m Data, calculate the monthly biological measure factor B m(m=1,2……12);

[0084] The specific steps of step S3 are as follows:

[0085] Step S31: Calculate the monthly NDVI index with a resolution of 30 m using multi-source remote sensing data such as Landsat series, Sentinel 2A, and GF1 WFV through CCDC and spatiotemporal fusion methods;

[0086] Step S32: Calculate the monthly vegetation coverage FVC using the pixel binary model m ;

[0087] Step S33: Based on the existing land use classification results and monthly vegetation coverage FVC m Conduct monthly biological measures of factor B m The calculation of forest land, orchard, grassland and bare land is calculated using Formula 5, tea garden, cultivated land and terraced fields are assigned a value of 1, and water bodies and impervious surfaces are assigned a value of 0.

[0088]

[0089] Step S4: Calculate the monthly rainfall erosivity factor R m (m=1,2……12);

[0090] The specific steps of step S4 are as follows:

[0091] R m =0.183*P m 1.995 (6)

[0092] Where R m is the rainfall erosivity factor in month m (MJ·mm / (hm 2 ·h));P m is the rainfall in month m (mm).

[0093] Step S5: Calculate the soil erodibility factor K, the engineering factor E and the tillage factor T;

[0094] The specific steps of step S5 are as follows:

[0095] Step S51: Collect data on whether soil and water conservation measures have been taken in the runoff areas within the study area, and calculate the engineering measures factor E of tea gardens and terraces to be 0.118 and 0.414 respectively, and 1 for other land types;

[0096] Step S52: Using soil attribute data, calculate the soil erodibility factor K based on the erosion-productivity impact calculation model EPIC:

[0097]

[0098] where SAN is the sand content (%); SIL is the silt content (%); CLA is the clay content (%); c is the organic carbon content (%); and SN1 = 1 - SAN / 100.

[0099] Step S53: A calculation method of T factor is provided according to the tillage measures and the crop rotation system of different regions. The tillage measure factor T of the tillage and terrace is 0.15516 and 0.17964 respectively, and it is provided that the T factor is assigned as 1 when the calculation unit is non-tillage and terrace.

[0100] Step S6: The slope factor S y , the biological measure factor B m are calculated.

[0101] The specific steps of the step S6 are as follows:

[0102]

[0103] where SDR max is the maximum theoretical sediment transport ratio, IC0 and k are calibration parameters, IC i is the connectivity index, and is defined as:

[0104]

[0105] where D up is the upslope component, indicating the potential of the upstream sediment to be transported to the downstream channel, and D dn is the downslope component, indicating the possibility of the sediment to reach the confluence point after passing through the flow path, and are respectively defined as:

[0106]

[0107] where: is the average value of the biological measure factor of the upslope sediment-producing area, is the average value of the slope of the upslope sediment-producing area, A is the area of the upslope sediment-producing area, d i is the flow length of the i-th unit along the steepest downslope direction, B th , S th are defined as:

[0108]

[0109] Step S7: The monthly scale river-incoming sediment amount A of each small watershed is calculated to form the spatial distribution of the river-incoming sediment amount of the entire watershed.

[0110] The specific steps of the step S7 are as follows:

[0111] Step S71: Calculate the monthly soil erosion modulus of each grid point i in the small watershed using the CSLE formula. The formula is as follows:

[0112] CSLE i =R i K i LS i B i E i T i (14)

[0113] Where: CSLE i is the actual soil erosion modulus of grid i, R i is the rainfall erosion factor of grid i, K i is the soil erodibility factor of grid i, LS i is the slope length and slope factor of grid i, B i is the biological measure factor of grid i, E i is the engineering measure factor of grid i, T i is the tillage measure factor of grid i.

[0114] Step S72: Calculate the actual amount of sediment A entering the river at grid i that contributes to the sediment entering the river under the condition of sediment interception. The formula is as follows:

[0115] A i =CSLE i SDR i (15)

[0116] Where: A i is the actual sediment yield of grid i, SDR i is the sediment transport ratio under the conditions of vegetation cover factor and soil and water conservation measures at grid i.

[0117] Step S73: Calculate the monthly sediment inflow A of each small watershed j Sj , the formula is as follows:

[0118]

[0119] Where: A i is the actual sediment yield of grid i, N Sj is the number of grids in the small watershed that contribute to the river flow.

[0120] Step S74: Calculate the amount of sediment entering the river A for each small watershed unit in the watershed Sj (j=1,2,……N), forming the spatial distribution of sediment entering the river in the basin.

[0121] In this embodiment, in order to more clearly show the quantitative different months of each small watershed into the river sediment situation, the image data of each month of A river basin in 2020 is obtained respectively, and the above steps are used to calculate the river sediment of the 12 months. For the small watershed divided in the study area and the DEM data, each small watershed unit contains different land objects, has different interception ability for sediment, effectively reflects the interaction relationship between land objects, and is helpful to the subsequent calculation of more accurate river sediment. From the river sediment of each small watershed of A river from January to December 2020, it can be seen that in May, the province with more annual rainfall, the river sediment is increased compared with other months, and in the area where human activities cause frequent surface disturbance, the river sediment is more, and in the months with less rainfall from October to December, the river sediment is greatly reduced, which is consistent with the reality. In this embodiment, the spatial and temporal distribution of the river sediment, the rationality of the quantitative estimation of the river sediment and the like are evaluated by using field investigation, hydrological station data and the like. The results show that the spatial and temporal distribution of the monthly river sediment of each watershed of A river in 2020 is consistent with the actual situation, and the small watershed with large contribution to the river sediment can be accurately located, which provides a strong basis for scientifically managing the small watershed and improving the environment.

[0122] The above is the preferred embodiment of the present application, any changes made according to the technical solutions of the present application, as long as the generated function does not exceed the scope of the technical solutions of the present application, belongs to the protection scope of the present application.

Claims

1. A method for estimating monthly sediment inflow based on small watershed units, characterized by: The steps include: Step S1: Obtain the DEM data of the watershed range, extract the river system, divide the small watershed, and further determine the accuracy of the river system and small watershed division based on remote sensing images; Step S2: Calculate the slope length factor L of each grid using DEM data y , slope factor S y ; Step S3: Obtain Landsat series, Sentinel 2A, GF1 WFV multi-source medium-resolution remote sensing image data to construct a 30m resolution monthly scale vegetation cover FVC m Data, calculate the monthly biological measure factor B m , m=1,2……12; Step S4: Calculate the monthly rainfall erosivity factor R using monthly rainfall data m , m＝1,2……12； Step S5: Calculate the soil erodibility factor K, the engineering factor E and the tillage factor T; Step S6: Taking the small watershed as a unit, the slope factor S of the uphill area and downhill area of ​​each grid is calculated. y , biological measures factor B m Numerical value, calculate the sediment transport ratio SDR of each grid; Step S7: Taking the small watershed as a unit, calculate the monthly sediment inflow A of each small watershed to form the spatial distribution of the sediment inflow of the entire watershed; The specific steps of step S1 are as follows: Step S11: Collect the DEM data of the watershed, and use the hydrological analysis module in the geographic information system software to perform depression filling and cropping processing; Step S12: import the processed DEM data into the SWAT model, set the minimum catchment area, and generate the river network; Step S13: Select the watershed outlet point according to the actual situation and divide the watershed into small watersheds; Step S14: Check the topological relationship as needed, combine remote sensing images, and use human-computer interactive editing to generate reasonable small watershed vector data. The number of small watershed units is N, and the number of cell grids in each small watershed is N. Sj , j=1,2,……N; The specific steps of step S2 are as follows: Step S21: Calculate the slope length factor L based on the DEM data obtained in step S1 y ; Slope length factor L y calculate: λ=λ x cosθ (2) Where λ is the horizontal projection slope length of the calculation unit. When λ≤100m, it is calculated according to the actual value; when λ>100m, it is calculated as 100m; θ is the slope of the calculation unit; n is the slope length index; L y is the slope length of the calculation unit; x is the slope length of the calculation unit; Step S22: Calculate the slope factor S based on the DEM data obtained in step S1 y ; Slope factor S y calculate: Where e is the base of natural logarithm, which is 2.

72.

2. The method for estimating monthly sediment inflow based on small watershed units according to claim 1 is characterized in that: In step S3, the monthly vegetation coverage FVC m and vegetation cover factor B m The calculation method is as follows: Step S31: Using Landsat series, Sentinel 2A and GF1 WFV multi-source medium-resolution remote sensing data, the monthly NDVI index with a resolution of 30m is calculated through CCDC and spatiotemporal fusion methods; Step S32: Calculate the monthly vegetation coverage FVC using the pixel binary model m ; Step S33: Based on the existing land use classification results and monthly vegetation coverage FVC m Conduct monthly biological measures of factor B m , where forest land, orchard, grassland, and bare land are calculated using formula (5), tea garden, cultivated land, and terraced fields are assigned a value of 1, and water bodies and impervious surfaces are assigned a value of 0; 3. The method for estimating monthly sediment inflow based on small watershed units according to claim 1 is characterized in that: In step S4, the monthly rainfall erosivity factor R m The calculation method is as follows: R m =0.183*P m 1.995 (6) Where R m is the rainfall erosivity factor in month m; P m is the rainfall in month m.

4. The method for estimating monthly sediment inflow based on small watershed units according to claim 1 is characterized in that: In step S5, the specific steps for calculating the engineering measure factor E, the soil erodibility factor K, and the tillage factor T are as follows: Step S51: Collect data on whether soil and water conservation measures have been taken in the runoff areas within the study area, and calculate the engineering measure factors E of tea gardens and terraces to be 0.118 and 0.414 respectively, and 1 for other land types; Step S52: Using soil attribute data, calculate the soil erodibility factor K based on the erosion-productivity impact calculation model EPIC: Where: SAN is sand content; SIL is silt content; CLA is clay content; c is organic carbon content; SN1 = 1-SAN / 100; Step S53: Based on the T factor calculation method provided by the farming measures and the crop rotation system in different regions, the farming measure factors T for cultivated land and terraced fields are 0.15516 and 0.17964 respectively; when the calculation unit is not cultivated land or terraced field, the T factor is assigned a value of 1.

5. The method for estimating monthly sediment inflow based on small watershed units according to claim 1 is characterized in that: In step S6, the sediment transport ratio SDR of each grid is calculated based on the small watershed as a unit. i The specific steps are as follows: Where: SDR max The maximum theoretical sediment transport ratio is set to 0.5, IC0 and k are calibration parameters, and IC i is the connectivity index, defined as: Where: D up is the upslope component of the ith pixel in the small watershed unit, indicating the potential for sediment transport from upstream to downstream. dn is the downslope component of the i-th pixel in the small watershed unit, indicating the possibility of sediment reaching the sink through the flow path, and is defined as: Where: represents the average value of the biological measure factor in the upslope sediment-producing area, is the average slope of the upslope sediment-producing area, A is the area of ​​the upslope sediment-producing area, d i is the length of water flow in the i-th unit along the steepest downslope direction, B th 、S th Defined as:

6. The method for estimating monthly sediment inflow based on small watershed units according to claim 1 is characterized in that: In step S7, the specific steps for calculating the monthly sediment inflow A of each small watershed are as follows: Step S71: Calculate the monthly soil erosion modulus of each grid point i in the small watershed using the CSLE formula. The formula is as follows: CSLE i =R i K i LS i B i E i T i (14) Where: CSLE i is the actual soil erosion modulus of grid i, R i is the rainfall erosion factor of grid i, K i is the soil erodibility factor of grid i, LS i is the slope length and slope factor of grid i, B i is the biological measure factor of grid i, E i is the engineering measure factor of grid i, T i is the tillage measure factor of grid i; Step S72: Calculate the actual amount of sediment A entering the river at grid i that contributes to the sediment entering the river under the condition of sediment interception. The formula is as follows: A i =CSLE i ·SDR i (15) Where: A i is the actual sediment yield of grid i, SDR i is the sediment transport ratio of grid i under the conditions of vegetation cover factor and soil and water conservation measures; Step S73: Calculate the monthly sediment inflow A of each small watershed j Sj , the formula is as follows: Where: A i is the actual sediment yield of grid i, N Sj is the number of grids in the small watershed that contribute to river inflow; Step S74: Calculate the amount of sediment entering the river A for each small watershed unit in the watershed Sj , j = 1, 2, ... N, forming the spatial distribution of sediment entering the river in the basin.

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