Flood calculation method designed by reasoning formula for determining runoff production parameters based on soil classification

Abstract

The invention mainly relates to the technical field of water conservancy and water engineering, and provides an inference formula design flood calculation method for determining runoff production parameters based on soil classification in order to solve the problem that a method for calculating design flood based on an inference formula method is not suitable for regions lack of rainstorm flood observation data. The core idea of the method is as follows: a soil classification database is adopted to classify the soil texture of a corresponding region, software is applied to simulate the soil infiltration process under different rainfall intensities, and the stable infiltration rate after runoff production is obtained as the runoff production parameter of the corresponding region; the confluence parameters and the runoff production parameters of the corresponding soil texture types are substituted into a design flood calculation formula, design flood calculation of different soil texture type areas in corresponding areas is achieved, and the method for calculating the design flood based on the inference formula method can also be suitable for areas lacking rainstorm flood observation data.

Description

Technical Field

[0001] The present invention mainly relates to the technical field of water conservancy and water engineering, and in particular to a flood calculation method designed based on an inference formula for determining runoff parameters based on soil classification. Background Art

[0002] The inference formula method is one of the earliest methods proposed to deduce design floods from rainstorm data. It starts from the formation process of rainfall runoff, generalizes rainfall losses, assumes that the runoff generation and confluence processes are uniform, and the runoff intensity multiplied by the basin area is the flood flow at the outlet section. The inference formula method has made corrections and improvements to the basic formula in different regions according to the local rainstorm and flood characteristics, and it has been widely used in various countries until now. At present, the inference formula method has been applied to various types of water conservancy and hydropower projects such as mountain torrent disaster prevention and control, bridges and culverts, and different industries or departments have their own flood calculation methods based on the inference formula principle. Among them, the water science institute inference formula is the formula of the Hydrology Research Institute of the Water Resources Research Institute, which is applicable to basins with an area of less than 1000km. 2 In the region, the smaller the basin area, the higher the accuracy of the calculation result, and the more it conforms to the assumed premise. Both partial confluence and full confluence can be used. The relevant flood calculation specifications for water conservancy and hydropower engineering design clearly stipulate that the reasoning formula of the Institute of Water Science and Technology is one of the main methods for calculating rainstorm floods in small and medium-sized basins.

[0003] The core concept of the inference formula method is to utilize regional rainstorm and flood observation data, study their patterns, and establish empirical relationships between them and watershed characteristics. This empirical pattern serves as the basis for flood estimation in watersheds lacking data. Due to the general scarcity of observation data in small watersheds, the inference formula calculation methods used in each region are highly empirical and have a limited scope of application. Therefore, domestic research on the inference formula method focuses not only on the derivation of inference formulas but also on the study of runoff generation and runoff calculation parameters. However, the runoff parameter μ varies in some regions due to various factors, such as region, soil texture type, vegetation cover, and rainfall characteristics. Currently, there is no unified fixed value. Therefore, the calculation of cross-sectional flood volumes based on the inference formula method in these regions faces significant limitations. Summary of the Invention

[0004] The technical problem to be solved by the present invention is: the present invention provides a method for calculating design floods based on an inference formula to determine runoff parameters based on soil classification, aiming to solve the problem that the method for calculating design floods based on the inference formula method is not suitable for areas where there is a lack of rainstorm flood observation data.

[0005] The technical solution adopted by the present invention to solve the above technical problems is:

[0006] A flood calculation method is designed based on an inference formula for determining runoff parameters based on soil classification, the method comprising:

[0007] Determine the soil texture type of the target area;

[0008] Through simulation calculation, obtain the runoff generation parameters of different soil texture types in the target area, and determine the confluence parameters of the corresponding soil texture types;

[0009] Substitute the confluence parameters and runoff generation parameters of the corresponding soil texture types into the design flood calculation formula to calculate the design flood of the corresponding area.

[0010] Furthermore, the specific method for obtaining the runoff generation parameters of different soil texture types in the target area through simulation calculation is as follows: Based on Hydrus-1D, simulate the soil infiltration process under different rainfall intensities to obtain the stable infiltration rate after runoff generation, and correct the stable infiltration rate. Take the corrected stable infiltration rate as the runoff generation parameter of the corresponding soil texture type.

[0011] Furthermore, classify the soil texture based on the HWSD soil database and the USDA soil texture classification standard.

[0012] Furthermore, correct the stable infiltration rate simulated by Hydrus-1D based on the dimensionless correction coefficient.

[0013] Furthermore, the soil texture types in the Tibet region obtained based on the HWSD soil database and the USDA soil texture classification standard include: clay, silty clay, silty loam, loam, sandy clay loam, sandy loam.

[0014] The beneficial effects of the present invention are as follows: The design flood calculation method based on the reasoning formula for determining runoff generation parameters according to soil classification in the present invention classifies the soil in the corresponding area using the soil classification database, and uses software to simulate the soil infiltration process under different rainfall intensities, obtains the stable infiltration rate after runoff generation as the runoff generation parameter of the corresponding area, and obtains the confluence parameter of the corresponding area. Substitute the confluence parameters and runoff generation parameters of different soil texture types into the design flood calculation formula to achieve the design flood calculation for different regions in the corresponding area, and improve the applicability of the method for calculating design flood based on the reasoning formula method in areas lacking storm flood observation data. Description of the Drawings

[0015] Figure 1 It is a triangular coordinate diagram for USDA soil geology classification. Detailed Embodiment

[0016] Soil plays a crucial regulatory role in the hydrological cycle. Its hydraulic properties (water-holding and water-transporting capacities) and hydrological state (water content and its distribution) are directly related to the redistribution effect of rainfall reaching the ground, affecting the proportion of surface runoff and infiltration, and determining the soil water storage and groundwater recharge. The particle size, arrangement, and composition ratio of the soil particles that make up the soil are called soil texture, which determines the water-transporting characteristics and water-holding capacity of the soil and is related to the movement law of water in the soil.

[0017] Soil texture classification takes the percentage of each particle size in the soil as the standard. In this invention, the USDA standard as shown in Figure 1 is used to classify the soil geology. As shown in Table 1, according to the different composition ratios of sand grains (particle size 0.02 - 2 mm), silt grains (particle size 0.002 - 0.02 mm), and clay grains (particle size < 0.002 mm), the USDA standard divides the soil texture types into 12 types such as sandy soil, loamy sand, sandy loam, etc.

[0018] Table 1 USDA Soil Texture Classification

[0019]

[0020]

[0021] HWSD (Harmonized World Soil Database) is a world soil dataset jointly developed by the Food and Agriculture Organization of the United Nations (FAO) and the International Soil Reference and Information Centre (ISRIC).

[0022] In this embodiment, the rational formula design flood calculation method for determining runoff parameters based on soil classification described in this invention is explained by taking the design flood calculation of the rational formula method in the Tibet region as an example. Combining the HWSD data, the soil in the Tibet region is classified according to the USDA soil texture classification standard. The USDA soil texture classification in the Tibet region is shown in Table 2, mainly including 6 types such as clay, silty clay, silty loam, loam, sandy clay loam, and sandy loam. Among them, the proportion of sandy loam and loam reaches 93.0%, the proportion of loam and sandy loam is 56.6%, the proportion of loam is 36.4%, and the proportion of other types of soil + water bodies, glaciers, etc. is only 7.0%.

[0023] Table 2 USDA Soil Geology Classification in the Tibet Region

[0024]

[0025]

[0026] After determining the soil texture type, based on the Hydrus-1D software, simulate the stable infiltration rate after runoff generation corresponding to each soil texture type. The stable infiltration rate after runoff generation obtained from the Hydrus-1D simulation is data at a single point in an ideal state. When applied to an actual watershed, the underlying surface conditions are more complex, and there are certain differences between the two. Therefore, a dimensionless correction coefficient needs to be introduced to correct the stable infiltration rate simulated by Hydrus-1D, and the corrected stable infiltration rate is used as the runoff generation parameter for calculating the design flood of the cross-section. In the present invention, the dimensionless correction coefficients for clay, silty clay, and silt loam are 1, the dimensionless correction coefficient for loam and sandy clay loam is taken as 0.8, and the dimensionless correction coefficient for sandy loam is taken as 0.4. The comprehensive stable runoff generation parameter of the watershed is calculated by weighted average of the runoff generation parameters corresponding to the areas of different soil texture types.

[0027] In this embodiment, the runoff generation parameters μ of various types of soil in the Tibet region are shown in Table 3.

[0028] Table 3 Runoff generation parameters μ of various types of soil in the Tibet region

[0029] Soil texture type Runoff generation parameter μ (mm / min) Runoff generation parameter μ (mm / h) Clay 0.033 1.98 Silty clay 0.0033 0.20 Silt loam 0.075 4.50 Loam 0.138 8.30 Sandy clay loam 0.174 10.5 Sandy loam 0.258 15.5

[0030] To calculate the design flood based on the design flood calculation formula, it is also necessary to determine the concentration parameter m. The concentration parameter m is a parameter that reflects the characteristics of flood concentration. It is related to the regulation effect of the river network in the watershed, hydraulic characteristics, and climate conditions, etc. In small and medium-sized watersheds, this parameter is mainly affected by the underlying surface factors, and the main influencing factors include the natural geographical conditions and rainstorm characteristics of the watershed, and are related to factors such as vegetation, terrain, river network distribution, river channel cross-section shape, and river channel roughness. In China, the m-θ (θ is the watershed characteristic parameter, related to F, L, J, etc.) relationship is usually established for regional synthesis, where θ = L / J 1 / 3 or θ = L / (J 1 / 3 F 1 / 4 ) is the regional synthesis formula of the rational formula parameters that have been established in each province (autonomous region, municipality directly under the Central Government) of China.

[0031] In this embodiment, based on the formula θ = L / J 1 / 3 and the watershed characteristic parameter θ of the design watershed, determine the concentration parameters m of different soil texture types. Combining the soil characteristics in the "Hydraulic Design Manual (2nd Edition)" (Volume 2 Planning, Hydrology, Geology), the specific results of the concentration parameter m in the Tibet region are shown in Table 4.

[0032] Table 4 Concentration parameter m in the Tibet region

[0033]

[0034] Set the hypothetical conditions for the design flood calculation:

[0035] (1) Assume that the storm intensity and runoff coefficient are uniformly distributed in time and space, i.e., the runoff generation intensity is a constant;

[0036] (2) Assume that the change rate of the catchment area with time is a constant, i.e., the confluence velocity is a constant;

[0037] (3) Assume that the water quality particles at the farthest point of the catchment form the maximum flow of the catchment when they reach the outlet section of the catchment;

[0038] (4) Assume that there is no flood regulation in the catchment;

[0039] (5) Assume that the base flow of flood is zero. From the above five basic assumptions, it can be seen that the rational formula method is applicable to mountainous areas with a catchment area of less than 1000 km2, and the hydrometeorological conditions and natural geographical conditions in each region of the catchment are relatively similar.

[0040] Based on the assumption conditions, substitute the corresponding confluence parameter m and runoff generation parameter μ into the design flood peak flow Q mP In the calculation formula, if complete confluence (tc≥τ), then If partial confluence (tc<τ), then Where In the formula: h τ is the maximum net rainfall within the confluence duration τ, in mm; h R is the maximum net rainfall within the runoff generation duration tc, in mm; τ is the confluence duration, in h; F is the catchment area, in km 2 ; S P is the storm rainfall intensity or 1h rainfall intensity, in mm / h; n is the storm attenuation index; μ is the runoff generation parameter, in mm / h; t c is the runoff generation duration, in h; L is the catchment river length, in km; J is the catchment slope (in decimal); m is the confluence parameter.

Claims

1. A method for calculating design flood using an inference formula to determine runoff parameters based on soil classification, characterized in that, The method includes: Determine the soil texture type of the target area; Simulate and calculate the runoff generation parameters of different soil texture types in the target area, and determine the confluence parameters of the corresponding soil texture types; Substitute the confluence parameters and runoff generation parameters of the corresponding soil texture types into the design flood calculation formula to calculate the design flood of the corresponding area.

2. The flood calculation method for the design flood by using the rational formula for determining the runoff generation parameters based on soil classification according to claim 1, characterized in that, The specific method for simulating and calculating the runoff generation parameters of different soil texture types in the target area is as follows: Based on Hydrus-1D, simulate the soil infiltration process under different rainfall intensities to obtain the stable infiltration rate after runoff generation, and correct the stable infiltration rate. Take the corrected stable infiltration rate as the runoff generation parameter of the corresponding soil texture type.

3. The flood calculation method based on the reasoning formula for determining runoff generation parameters according to soil classification as described in claim 1, characterized in that Classify the soil texture based on the HWSD soil database and the USDA soil texture classification standard.

4. The flood calculation method based on the reasoning formula for determining runoff generation parameters according to soil classification as claimed in claim 2, characterized in that Correct the stable infiltration rate simulated by Hydrus-1D based on the dimensionless correction coefficient.

5. The flood calculation method for the design of the runoff generation parameter inference formula based on soil classification according to claim 3, characterized in that, The soil texture types in the Tibet region obtained based on the HWSD soil database and the USDA soil texture classification standard include: clay, silty clay, silt loam, loam, sandy clay loam, sandy loam.

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