Drainage basin sand reduction efficiency evaluation and regulation method based on reservoir group topological structure

Abstract

The invention discloses a basin sand reduction efficiency evaluation and regulation method based on a reservoir group topological structure, and belongs to the field of hydraulic engineering, and the method comprises the steps: S1, inputting basin hydrological data; s2, calculating accumulated runoff sediment transport and drawing a double-accumulation curve; s3, recognizing turning years of human activities on the water-sediment relationship through the double-accumulation curve mutation points, and dividing a natural period and a human influence period by combining the mutation points; s4, analyzing a water-sediment relationship, and calculating a drainage basin sediment reduction amount; s5, determining the topology type of the reservoir; s6, calculating an effective control drainage basin area; s7, establishing a relationship between the effective control basin area and the sand reduction rate; and S8, nonlinear regression equation modeling is carried out. The topology cutting effect theory is applied to reservoir group sand reduction efficiency evaluation, and the error problem of a traditional linear superposition model is solved; dynamic prediction of the long-term sand reduction cumulative effect of the cascade reservoir group under the watershed scale is realized; quantitative decision support is provided for newly-built reservoir site selection and built reservoir group optimization scheduling, and the river channel siltation treatment cost is reduced.

Description

Technical Field

[0001] This invention relates to a watershed sediment reduction assessment and control method, and more particularly to a watershed sediment reduction efficiency assessment and control method based on the topology of reservoir groups. Background Technology

[0002] The continuous increase in reservoir capacity not only alters the distribution of water and sediment within the basin but also changes the sediment-carrying capacity of the river network and channels. Large-scale sediment reduction threatens the stability of the middle and lower reaches of the river, the ecological balance of the river delta, and the sustainable operation of major water conservancy infrastructure. Therefore, the regulation mechanism of sediment reduction by the topology of reservoir groups is a major challenge for basin management.

[0003] The spatiotemporal distribution of sediment reduction is influenced by various factors, including natural distribution characteristics, reservoir capacity distribution within the basin, and inter-reservoir connectivity. In most studies, sediment reduction trends are examined using the MK method, R / S analysis, and moving average method, all of which are applicable to single variables. This study employs the dual-mass curve method to detect abrupt changes in the water-sediment relationship and identify anthropogenic sediment reduction effects. Based on sediment changes over different periods, the water-sediment relationship method is used to characterize the natural sediment-carrying capacity of the river channel.

[0004] While these methods can calculate the short-term sediment retention capacity of a single reservoir, the long-term cumulative sediment reduction effect of cascade reservoir operation in a river network is unclear. Analyzing the impact of reservoir distribution on sediment reduction by linearly superimposing reservoir capacity and the catchment area of ​​reservoirs within the basin neglects the nonlinear sediment transport influenced by the reservoir network in the river network. Furthermore, sediment reduction and reservoir operation have a coupling effect; the cascade of reservoirs on the main stream and tributaries alters the spatial distribution of sediment transport. Therefore, the sediment reduction response mechanism of reservoir distribution in a river network is also unclear. Summary of the Invention

[0005] The purpose of this invention is to provide a method for evaluating and regulating watershed sediment reduction efficiency based on the topology of reservoir groups, so as to solve the problems of spatiotemporal limitations, linear superposition distortion, and lack of scheduling-sediment reduction coupling mechanism in traditional watershed sediment reduction evaluation methods.

[0006] To achieve the above objectives, the specific plan is as follows:

[0007] A method for assessing and regulating watershed sediment reduction efficiency based on reservoir group topology, comprising the following steps:

[0008] S1: Input watershed hydrological data;

[0009] S2: Calculate the cumulative runoff sediment transport using the double cumulative curve method and plot the double cumulative curve;

[0010] S3: Identify the turning points in the impact of human activities (such as reservoir construction) on water and sediment relationships by using abrupt change points on double cumulative curves. Divide the natural period into the period of human influence by combining these abrupt change points.

[0011] S4: Analyze the water-sediment relationship using the water-sediment relationship method and calculate the sediment reduction in the watershed;

[0012] S5: Determine the reservoir topology type;

[0013] S6: Calculate the effective control basin area;

[0014] S7: Establish the relationship between the effective control watershed area and sediment reduction rate using nonlinear regression method;

[0015] S8: Modeling nonlinear regression equations.

[0016] Further, in step S2, the double cumulative curve method includes:

[0017] The continuous cumulative values ​​of runoff and sediment transport within the watershed over time are calculated using the following formulas:

[0018]

[0019] Plot double cumulative curves with the cumulative values ​​of runoff and sediment transport on the horizontal and vertical axes, respectively.

[0020] Furthermore, in step S4, the water-sediment relationship method includes the following steps:

[0021] Establish the power function relationship between runoff and sediment transport under natural conditions, and fit parameters a and b through regression analysis:

[0022] S i =aQ i b

[0023] Incorporate measured runoff during the human impact period into S i In the calculation of theoretical natural sediment transport:

[0024] S t =aQ t b

[0025] Finally, calculate the interannual sediment reduction:

[0026] ΔS=S t -S i '.

[0027] Furthermore, in step S5, the reservoir topology types include: parallel reservoirs, series reservoirs, and composite connected reservoirs.

[0028] Furthermore, the effective control area of ​​the series-connected reservoirs is the control catchment area of ​​the downstream reservoir:

[0029] A e =max(A1,A2,…,A)n )=A1∪A2∪…∪A n

[0030] The effective catchment area of ​​parallel reservoirs is the sum of the catchment areas of all reservoirs in the river network:

[0031]

[0032] The effective control catchment area of ​​the composite reservoir is calculated recursively through topological relationships, after deducting the influence of the upstream already controlled area:

[0033] A m,n '=A 0,1 ∪A 0,2 ∪…∪A m,n -A 0,1 ∪A 0,2 ∪…∪A i＜m,j＜n .

[0034] Furthermore, in step S7, the nonlinear regression equation in the nonlinear regression method is:

[0035]

[0036] In summary, the present invention has the following advantages over the prior art:

[0037] (1) Apply the theory of topological cutting effect to the evaluation of sediment reduction efficiency of reservoir group to solve the error problem of traditional linear superposition model;

[0038] (2) To achieve dynamic prediction of the long-term sediment reduction cumulative effect of cascade reservoir groups at the watershed scale;

[0039] (3) Provide quantitative decision support for the site selection of new reservoirs and the optimized scheduling of existing reservoir groups, thereby reducing the cost of river siltation control. Attached Figure Description

[0040] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this invention, illustrate exemplary embodiments of the invention and are used to explain the invention, but do not constitute an undue limitation of the invention. In the drawings:

[0041] Figure 1 A flowchart for the calculation of a watershed sediment reduction efficiency assessment and regulation method based on reservoir group topology;

[0042] Figure 2 This is a schematic diagram of a double cumulative curve;

[0043] Figure 3 A schematic diagram for calculating the catchment area controlled by a large reservoir group;

[0044] Figure 4This represents the double cumulative curves of the main streams and tributaries of the upper Yangtze River.

[0045] Figure 5 This is a water-sediment relationship curve;

[0046] Figure 6 The amount of sediment reduction in major tributaries and main streams during each period;

[0047] Figure 7 This relates to the relationship between the sediment reduction rate of the main tributaries and main streams of the upper Yangtze River and the proportion of the effective controlled drainage area. Detailed Implementation

[0048] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0049] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments of the present invention. As used herein, the singular form may also include the plural form unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0050] Unless otherwise specifically stated, the relative arrangement, numerical expressions, and values ​​of the components and steps set forth in these embodiments do not limit the scope of the invention. It should also be understood that, for ease of description, the dimensions of the various parts shown in the drawings are not drawn to actual scale. Techniques, methods, and devices known to those skilled in the art may not be discussed in detail, but where appropriate, such techniques, methods, and devices should be considered part of the specification. In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not as limitations. Therefore, other examples of exemplary embodiments may have different values. It should be noted that similar reference numerals and letters in the following figures denote similar items; therefore, once an item is defined in one figure, it need not be further discussed in subsequent figures.

[0051] See Figure 1 As shown, this invention provides a method for assessing and regulating watershed sediment reduction efficiency based on reservoir group topology, including the following steps:

[0052] S1: Input watershed hydrological data;

[0053] S2: Calculate the cumulative runoff sediment transport using the double cumulative curve method and plot the double cumulative curve;

[0054] As a preferred embodiment, the double cumulative curve method includes:

[0055] Use formulas (1) and (2) to calculate the continuous cumulative values ​​of runoff and sediment transport within the watershed over time.

[0056]

[0057] In the formula, Q' is the continuous cumulative value of the watershed runoff (100 million m³). 3 ), Q i For the watershed runoff (in billions of m³) in the i-th year of the statistical sequence 3 ), where n is the sample size of the statistical sequence. S' is the continuous cumulative value of sediment transport in the basin (hundred million tons), S i Let be the sediment load (in billions of tons) of the basin in the i-th year of the statistical sequence.

[0058] Plot the double cumulative curves with the cumulative values ​​of runoff and sediment transport on the horizontal and vertical axes, respectively, as shown below. Figure 2 As shown, the slope of the double cumulative curve represents the ratio of runoff to sediment transport within the watershed. When the double cumulative curve deflects upward, the sediment transport corresponding to the same runoff increases; conversely, when the curve deflects downward, the runoff sediment transport capacity within the watershed decreases.

[0059] S3: Identify the turning points in the impact of human activities (such as reservoir construction) on water and sediment relationships by using abrupt change points on double cumulative curves. Divide the natural period into the period of human influence by combining these abrupt change points.

[0060] S4: Analyze the water-sediment relationship using the water-sediment relationship method and calculate the sediment reduction in the watershed;

[0061] As a preferred method, the water-sediment relationship method quantitatively assesses the sediment interception effect of reservoirs and other engineering projects by separating the impacts of natural and human activities on sediment transport. The core of this method is to establish a baseline formula using natural period data, then compare the theoretical and actual values ​​during periods of human influence to ultimately determine the amount of sediment reduction.

[0062] First, a power function relationship between runoff and sediment transport under natural conditions is established, and parameters a and b are fitted through regression analysis:

[0063] S i =aQ i b (3)

[0064] In the formula, S i Q represents the sediment load of the basin under natural conditions (in billions of tons). i Watershed runoff under natural conditions (100 million m³) 3 ), where a is a coefficient reflecting the runoff and sediment production characteristics of the basin, and b is an index reflecting the sediment transport characteristics of the river.

[0065] Then, substitute the measured runoff during the period of human impact into Formula 3 to calculate the theoretical natural sediment transport:

[0066] S t =aQ t b (4)

[0067] In the formula, Q t Watershed runoff during the period of human impact (100 million m³) 3 ), S t The theoretical natural sediment transport volume (in billions of tons) during the period of human impact.

[0068] Finally, calculate the interannual sediment reduction:

[0069] ΔS=S t -S i (5)

[0070] In the formula, ΔS represents the reduction in sediment in the watershed (hundred million tons), and S... i 'This refers to the sediment load in the basin during the period of human impact (in billions of tons).

[0071] S5: Determine the reservoir topology type (parallel, series, composite);

[0072] As a preferred option, such as Figure 3 As shown, based on the connection type of large reservoirs, the influence of the topological structure of a large reservoir group on watershed sediment regulation is explained by the controlled catchment area of ​​the reservoirs. In a cascade reservoir system, the total sediment reduction caused by a large reservoir is related to the effectively controlled catchment area, i.e., the control catchment area of ​​the last reservoir. The larger the effectively controlled catchment area, the greater the amount of water and sediment transported into the reservoir, and the greater the regulating effect of the reservoir.

[0073] (1) Series of reservoirs: The effective control area is the control basin area of ​​the downstream reservoir.

[0074] A e =max(A1,A2,…,A) n )=A1∪A2∪…∪A n (7)

[0075] In the formula, A e The effective control drainage area of ​​the reservoir (km²) 2 A n The controlled catchment area (km²) of the nth reservoir 2 ).

[0076] (2) Parallel reservoirs: The effective controlled catchment area is the sum of the controlled catchment areas of all reservoirs in the river network.

[0077]

[0078] (3) Composite interconnected reservoirs: In composite interconnected reservoirs, due to the complex interconnection types, the effective controlled catchment area varies greatly among different stations. By recursively calculating through topological relationships and deducting the influence of the upstream controlled area, the effective controlled catchment area can be calculated.

[0079] A m,n '=A 0,1 ∪A 0,2 ∪…∪A m,n -A 0,1 ∪A 0,2 ∪…∪A i＜m,j＜n (9)

[0080] In the formula, A m,n 'The effective control drainage area (km²) of the m-th tributary and the n-th reservoir 2 A i,j The effective control drainage area (km²) of the j-th reservoir on the i-th tributary 2 ).

[0081] S6: Calculate the effective control basin area;

[0082] S7: Establish the relationship between the effective control watershed area and sediment reduction rate using nonlinear regression method;

[0083] As a preferred approach, the effective control area ratio refers to the effective catchment area controlled by the reservoirs divided by the total target catchment area, representing the proportion of the catchment area actually intercepted by the reservoir group through its topological structure relative to the entire target catchment area. The sediment reduction rate is the annual sediment reduction amount divided by the theoretical natural sediment transport, representing the interception efficiency of the reservoir group on sediment transport. Using the effective control area ratio as the x-axis and the sediment reduction rate as the y-axis, the relationship between the two is constructed to quantify the dynamic relationship between the effective control area ratio and the sediment reduction rate under different topological structures. A nonlinear regression method is used to establish the two-variable relationship:

[0084]

[0085] In the formula, A a Total area of ​​the target watershed (km²) 2 ), k is the sediment reduction efficiency coefficient, reflecting the interception capacity per unit controlled area (related to geology and reservoir scheduling strategies), α is the nonlinear exponent, characterizing the spatial superposition effect of topological structure (α>1 indicates superlinear growth, α=1 indicates linear relationship), and c is the sediment reduction coefficient (such as the contribution of soil and water conservation projects).

[0086] S8: Modeling nonlinear regression equations.

[0087] Using the watershed sediment reduction efficiency assessment and regulation method based on reservoir group topology proposed in this patent, the sediment reduction amount and effective control area of ​​the upper Yangtze River basin are calculated, and a quantitative model of the two is constructed.

[0088] The upper reaches of the Yangtze River are located in western China, extending from Geladandong Peak on the Qinghai-Tibet Plateau to Yichang, Hubei Province, with a total length of approximately 4,500 kilometers. It covers seven provinces and municipalities, including Qinghai, Tibet, and Sichuan, with an area of ​​about 1 million square kilometers. The core source is located at Geladandong Peak in the Tanggula Mountains of the Qinghai-Tibet Plateau, and its major tributaries include the Jinsha River, Min River, Jialing River, and Wujiang River.

[0089] Using double cumulative curves to find abrupt changes in the watershed's water-sediment relationship, such as... Figure 4 As shown, the cumulative runoff and cumulative sediment load of different rivers exhibit a linear trend, with a goodness of fit R0. 2 All values ​​are greater than 0.9. The significantly reduced linear slope of the double cumulative curves indicates a decreasing trend in the river's runoff-sediment transport relationship.

[0090] like Figure 5 As shown, the natural stage and the period of human activity impact are divided according to the abrupt change point of the double cumulative curve, water-sediment relationship curves are constructed, and water-sediment equations are fitted.

[0091] like Figure 6 As shown, the runoff during the period of human impact is substituted into the water-sediment relationship curve of the natural stage to calculate the theoretical natural sediment transport. The difference between the theoretical natural sediment transport and the sediment transport during the period of human impact is used to calculate the sediment reduction of the main tributaries of the upper Yangtze River at each stage.

[0092] The effective controlled drainage area of ​​each river basin was calculated using formulas (7) to (9), as shown in Table 1. From 1999 to 2022, the controlled drainage area of ​​major tributaries such as the Jinsha River and Min River continued to rise, with the Jinsha River section experiencing a surge in controlled area to 458,800 km² after 2011. 2 This represents a 293% increase compared to the initial period; the Minjiang River basin's controlled area reached 126,862 km² in 2017. 2 This represents a 66% increase compared to 1985. However, as the controlled drainage areas of tributaries continue to increase, the controlled area of ​​the Yangtze River main stream is steadily decreasing. The controlled area of ​​the Yangtze River main stream has decreased from 817,543 km² in the baseline period. 2 It continues to shrink, and by 2022 it will only have 182,400 km remaining. 2 The decrease was as high as 77.7%.

[0093] Table 1. Area of ​​the main tributaries and main streams of the upper reaches of the Yangtze River controlled by different time periods (unit: km²) 2 )

[0094]

[0095]

[0096] A dynamic relationship was established between the proportion of effectively controlled area and the sediment reduction rate. The relationship between the effectively controlled basin area and sediment reduction in the upper reaches of the Yangtze River is as follows: Figure 7 As shown, the relationship between sediment reduction rate and the proportion of the effective controlled catchment area in the main stream exhibits significant variability. The sediment reduction rate of the tributary system (Jinsha River, Min River, Jialing River, and Wujiang River) is significantly positively correlated with the proportion of the reservoir-controlled area, with the scattering points distributed along the y=x baseline, indicating that the expansion of the reservoir group has a linear response characteristic to sediment interception efficiency. The continuously increasing proportion of the reservoir-controlled area in the tributary system indicates that the construction of the reservoir group is continuously developing in the downstream of the basin, achieving increased sediment interception efficiency through gradient interception.

[0097] The systematic development of tributary reservoirs has led to the interception of sediment transport. The effective control area of ​​the main stream reservoirs has been continuously shrinking, decreasing from 0.992 in 1999-2004 to 0.971 in 2017-2022, with the sediment reduction rate of the main stream showing a trend of first increasing and then decreasing. With the operation of the Three Gorges Reservoir in 2003, most of the sediment in the main stream was intercepted, significantly increasing the interception rate. However, with the operation of the tributary reservoir group, the amount of sediment entering the main stream has decreased significantly, leading to a decline in the sediment reduction rate.

[0098] The dynamic changes in sediment reduction rate reveal the reconstruction of natural sedimentation processes by human activities. The topological structure of the middle-level reservoir group in the upper Yangtze River controls the spatiotemporal variation of sediment reduction rate through spatial interception and temporal dynamic regulation. This study provides theoretical experience for the study of sediment regulation topology in large global watersheds and is of great significance for studying the coupling mechanism between reservoir engineering and natural processes.

[0099] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for assessing and regulating watershed sediment reduction efficiency based on reservoir group topology, characterized in that, Including the following steps: S1: Input watershed hydrological data; S2: Calculate the cumulative runoff sediment transport using the double cumulative curve method and plot the double cumulative curve; S3: Identify the turning point years of human activities on the water-sediment relationship by the abrupt change points of the double cumulative curves, and divide the natural period and the period of human influence by combining the abrupt change points; S4: Analyze the water-sediment relationship using the water-sediment relationship method and calculate the sediment reduction in the watershed; S5: Determine the reservoir topology type; S6: Calculate the effective control basin area; S7: Establish the relationship between the effective control watershed area and sediment reduction rate using nonlinear regression method; S8: Modeling nonlinear regression equations.

2. The method for assessing and regulating watershed sediment reduction efficiency based on reservoir group topology as described in claim 1, characterized in that, In step S2, the double cumulative curve method includes: The continuous cumulative values ​​of runoff and sediment transport within the watershed over time are calculated using the following formulas: Plot double cumulative curves with the cumulative values ​​of runoff and sediment transport on the horizontal and vertical axes, respectively.

3. The method for assessing and regulating watershed sediment reduction efficiency based on reservoir group topology as described in claim 1, characterized in that, In step S4, the water-sediment relationship method includes the following steps: Establish the power function relationship between runoff and sediment transport under natural conditions, and fit parameters a and b through regression analysis: S i =aQ i b Incorporate measured runoff during the human impact period into S i In the calculation of theoretical natural sediment transport: S t =aQ t b Finally, calculate the annual sediment reduction: ΔS=S t -S i ' 。 4. The method for assessing and regulating watershed sediment reduction efficiency based on reservoir group topology as described in claim 1, characterized in that, In step S5, the reservoir topology types include: parallel reservoirs, series reservoirs, and composite connected reservoirs.

5. The method for evaluating and regulating watershed sediment reduction efficiency based on reservoir group topology as described in claim 4, characterized in that, The effective control area of ​​the series of reservoirs is the control catchment area of ​​the downstream reservoir: A e =max(A1,A2,…,A n )=A1∪A2∪…∪A n The effective control catchment area of ​​the parallel reservoirs is the sum of the control catchment areas of all reservoirs in the river network: The combined connected reservoirs are calculated recursively based on topological relationships, and the influence of the upstream controlled area is deducted to calculate the effective control basin area: A m,n '=A 0,1 ∪A 0,2 ∪…∪A m,n -A 0,1 ∪A 0,2 ∪…∪A i＜m,j＜n 。 6. The method for assessing and regulating watershed sediment reduction efficiency based on reservoir group topology as described in claim 1, characterized in that, In step S7, the nonlinear regression equation in the nonlinear regression method is:

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