Improved hydrological situation change evaluation method for quantifying influence of water conservancy project

Abstract

The invention discloses an improved hydrological situation change evaluation method for quantifying the influence of a water conservancy project, and the evaluation method can more accurately quantify the hydrological situation change degree of the influence of the water conservancy project through the improvement of a change range method based on an IHA index system. The evaluation method comprises the following steps: collecting long-sequence flow data of hydrological stations closer to the downstream of a water conservancy project before and after the construction of the water conservancy project; calculating IHA evaluation indexes of two periods before and after the construction of the water conservancy project; calculating upper and lower target boundaries of each evaluation index before hydraulic engineering construction; analyzing a natural change rule of the flow, and optimizing upper and lower target boundaries of part of evaluation indexes; providing a discrete-variable weight method, and assigning the weight of each evaluation index according to discrete and variable conditions; and calculating the hydrological situation change degree after the construction of the water conservancy project by using a change range method according to the determined upper and lower target boundaries and weights of the final evaluation indexes.

Description

Technical Field

[0001] This invention relates to the field of hydrological situation analysis technology, specifically an improved method for evaluating changes in hydrological situation caused by the quantitative impact of water conservancy projects. Background Technology

[0002] The construction and operation of various reservoirs, sluices, and other water conservancy projects in my country will have a certain impact on the hydrological conditions of the rivers in which they are located. Currently, many scholars have conducted research in this area, mainly using the Indicators of Hydrologic Alteration (IHA) system and the Range of Variation Approach (RVA) proposed by Ritcher et al. to analyze the degree of change in hydrological conditions before and after the construction of water conservancy projects.

[0003] However, the IHA indicator system has many evaluation indicators. In existing range-of-change methods and related studies, the weights are singular or the determination of weights mainly considers the correlation between evaluation indicators, with little consideration for the dispersion and variation of the evaluation indicators themselves, and no consideration for the natural variation law of hydrological conditions. This makes it impossible to accurately quantify the impact of water conservancy projects on changes in hydrological conditions.

[0004] Therefore, it is necessary to propose a method for evaluating changes in hydrological conditions that is applicable to quantifying the impact of water conservancy projects. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides an improved method for evaluating changes in hydrological conditions that quantify the impact of water conservancy projects.

[0006] The technical solution adopted in this invention is: an improved method for evaluating the changes in hydrological conditions caused by the quantitative impact of water conservancy projects, comprising the following steps: Step S1. Collect long-sequence flow data of hydrological stations near the downstream of the water conservancy project before and after its construction; Step S2. Calculate the IHA evaluation index for the two periods before and after the construction of the water conservancy project; Step S3. Based on the principle of the variation range method, calculate the upper and lower target boundaries of each evaluation indicator before the construction of the water conservancy project, and use the values ​​of 25% and 75% of the design frequency as the initial upper and lower target boundaries of each evaluation indicator. Step S4. Analyze the natural variation pattern of hydrological station length sequence flow using linear regression. After determining that there is a significant increase or decrease pattern in the hydrological station length sequence, calculate the ratio of the multi-year average flow before and after the construction of the water conservancy project. Based on the multi-year average flow ratio, scale the upper and lower target boundaries of the monthly average flow and annual extreme flow in the IHA evaluation indicators. Together with the upper and lower target boundaries of other unchanged evaluation indicators, form the final upper and lower target boundaries of each evaluation indicator. Step S5. Calculate and determine the weights of each evaluation index using the discrete-variable weighting method; Step S6. Using the range of variation method, calculate the degree of change in hydrological situation after the construction of water conservancy projects based on the determined upper and lower target boundaries and weights of each final evaluation index.

[0007] Furthermore, the IHA evaluation indicators in step S2 specifically include: average flow from January to December, minimum and maximum average flow on the 1st, 3rd, 7th, 30th, and 90th days of the year, number of days with zero flow, base flow index: minimum flow on the 7th day of the year / average flow of the year, time of occurrence of the maximum and minimum flow of the year, number of low flow pulses, average duration of low flow pulses, number of high flow pulses, average duration of high flow pulses, average flow increase rate, average flow decrease rate, and number of flow reversals per year.

[0008] Furthermore, in step S3, the upper and lower target boundaries of each evaluation indicator before the construction of the water conservancy project are calculated, using the values ​​of 25% and 75% of the design frequency as the initial upper and lower target boundaries of each evaluation indicator; specifically: The values ​​of the design frequency at 25% and 75% were calculated by fitting the hydrological frequency using the P-III curve.

[0009] Furthermore, the monthly average flow and annual extreme flow in the IHA evaluation indicators in step S4 are as follows: Average flow from January to December, minimum and maximum average flow over the 1st, 3rd, 7th, 30th and 90th days of the year; The calculation formula is: ; ; ; In the formula: , These are the upper and lower target boundaries of the scaled j-th evaluation index, respectively. , ... , These represent the multi-year average flow rates downstream before and after the construction of the water conservancy project; The scaled upper and lower target boundaries of each evaluation indicator, together with the unchanged upper and lower target boundaries of other evaluation indicators, form the final upper and lower target boundaries of each evaluation indicator.

[0010] Furthermore, in step S5, the discrete-variable weighting method is used to calculate and determine the weights of each evaluation index. The weights are calculated using data from before the construction of the water conservancy project, and the calculation formula is as follows: ; ; ; In the formula: Let be the dispersion of the j-th evaluation index; is the multi-year average of the j-th indicator; The maximum number of consecutive years within the upper and lower target boundaries during the calculation period for the j-th evaluation indicator; This refers to the change in the j-th indicator, specifically the proportion of the maximum number of years continuously within the upper and lower target boundaries to the total number of years. Let be the weight of the j-th evaluation indicator; The total number of years to be calculated; The number of evaluation indicators.

[0011] Furthermore, the calculation formula for the range of variation method in step S6 is as follows: ; ; ; In the formula: The degree of change of the j-th evaluation indicator; and , respectively, represent the actual and predicted values ​​of the upper and lower target boundaries of the j-th evaluation index after the impact of the water conservancy project, where each evaluation index falls within the final target boundary; r is the proportionality coefficient, taken as 50%; The total number of years for the evaluation of the impact of water conservancy projects; This represents the overall degree of change in the hydrological situation.

[0012] Compared to existing technologies, the advantages of this invention are that it can more accurately and objectively quantify the degree of hydrological situation change caused by water conservancy projects. First, by analyzing the natural variation patterns of flow, the upper and lower target boundaries of each evaluation indicator in the variation range method are optimized, which reduces the impact of natural variation patterns on the evaluation results and improves the accuracy of the evaluation results. Second, in the original variation range method, the weights of each evaluation indicator are consistent in the analysis and calculation. Related studies mainly consider the correlation between the evaluation indicators, with less consideration for the evaluation indicators themselves. This invention proposes a discrete-variable weighting method to assign weights to each evaluation indicator, arguing that the greater the data dispersion of the evaluation indicator and the smaller the variation, the greater the weight should be assigned, thus improving the objectivity of the evaluation results. Attached Figure Description

[0013] Figure 1 This is a schematic diagram of the operation of the present invention.

[0014] Figure 2 This is a graph showing the annual average flow rate variation trend according to an embodiment of the present invention. Detailed Implementation

[0015] like Figures 1-2 As shown, an improved method for evaluating changes in hydrological conditions caused by the quantitative impact of water conservancy projects includes the following steps: Step S1. Collect long-sequence flow data of hydrological stations near the downstream of the water conservancy project before and after its construction; Step S2. Calculate the IHA evaluation index for the two periods before and after the construction of the water conservancy project; Step S3. Based on the principle of the variation range method, calculate the upper and lower target boundaries of each evaluation indicator before the construction of the water conservancy project, and use the values ​​of 25% and 75% of the design frequency as the initial upper and lower target boundaries of each evaluation indicator. Step S4. Analyze the natural variation pattern of hydrological station length sequence flow using linear regression. After determining that there is a significant increase or decrease pattern in the hydrological station length sequence, calculate the ratio of the multi-year average flow before and after the construction of the water conservancy project. Based on the multi-year average flow ratio, scale the upper and lower target boundaries of the monthly average flow and annual extreme flow in the IHA evaluation indicators. Together with the upper and lower target boundaries of other unchanged evaluation indicators, form the final upper and lower target boundaries of each evaluation indicator. Step S5. Calculate and determine the weights of each evaluation index using the discrete-variable weighting method; Step S6. Using the range of variation method, calculate the degree of change in hydrological situation after the construction of water conservancy projects based on the determined upper and lower target boundaries and weights of each final evaluation index.

[0016] Furthermore, the IHA evaluation indicators in step S2 specifically include: average flow from January to December, minimum and maximum average flow on the 1st, 3rd, 7th, 30th, and 90th days of the year, number of days with zero flow, base flow index: minimum flow on the 7th day of the year / average flow of the year, time of occurrence of the maximum and minimum flow of the year, number of low flow pulses, average duration of low flow pulses, number of high flow pulses, average duration of high flow pulses, average flow increase rate, average flow decrease rate, and number of flow reversals per year.

[0017] Furthermore, in step S3, the upper and lower target boundaries of each evaluation indicator before the construction of the water conservancy project are calculated, using the values ​​of 25% and 75% of the design frequency as the initial upper and lower target boundaries of each evaluation indicator; specifically: The values ​​of the design frequency at 25% and 75% were calculated by fitting the hydrological frequency using the P-III curve.

[0018] Furthermore, the monthly average flow and annual extreme flow in the IHA evaluation indicators in step S4 are as follows: Average flow from January to December, minimum and maximum average flow over the 1st, 3rd, 7th, 30th and 90th days of the year; The calculation formula is: ; ; ; In the formula: , These are the upper and lower target boundaries of the scaled j-th evaluation index, respectively. , ... , These represent the multi-year average flow rates downstream before and after the construction of the water conservancy project; The scaled upper and lower target boundaries of each evaluation indicator, together with the unchanged upper and lower target boundaries of other evaluation indicators, form the final upper and lower target boundaries of each evaluation indicator.

[0019] Furthermore, in step S5, the discrete-variable weighting method is used to calculate and determine the weights of each evaluation index. The weights are calculated using data from before the construction of the water conservancy project, and the calculation formula is as follows: ; ; ; In the formula: Let be the dispersion of the j-th evaluation index; is the multi-year average of the j-th indicator; The maximum number of consecutive years within the upper and lower target boundaries during the calculation period for the j-th evaluation indicator; This refers to the change in the j-th indicator, specifically the proportion of the maximum number of years continuously within the upper and lower target boundaries to the total number of years. Let be the weight of the j-th evaluation indicator; The total number of years to be calculated; The number of evaluation indicators.

[0020] Furthermore, the calculation formula for the range of variation method in step S6 is as follows: ; ; ; In the formula: The degree of change of the j-th evaluation indicator; and , respectively, represent the actual and predicted values ​​of the upper and lower target boundaries of the j-th evaluation index after the impact of the water conservancy project, where each evaluation index falls within the final target boundary; r is the proportionality coefficient, taken as 50%; The total number of years for the evaluation of the impact of water conservancy projects; This represents the overall degree of change in the hydrological situation.

[0021] The implementation example takes the impact assessment of the hydrological situation after the construction of the Xiajiang Hydropower Project on the main stream of the Ganjiang River in XX Province as the implementation object. The Xiajiang Hydropower Project is located in the middle reaches of the Ganjiang River in XX Province and was completed in 2012.

[0022] An improved method for evaluating changes in hydrological conditions caused by the quantitative impact of water conservancy projects is adopted, comprising the following steps: Step S1. Collect long-sequence flow data from hydrological stations located downstream of the water conservancy project before and after its construction. Specifically, collect the daily average flow data of the Xiajiang (II) hydrological station from 1957 to 2022 after the construction of the Xiajiang Water Conservancy Project. The Xiajiang (II) hydrological station is located approximately 4.3 km downstream of the Xiajiang Water Conservancy Project, with no tributaries flowing into it.

[0023] Step S2. Calculate the IHA evaluation indicators for the two periods before and after the construction of the water conservancy project. Specifically, this includes the evaluation indicators for the Xiajiang (II) hydrological station from 1957 to 2011 and from 2013 to 2022. Since the river section has never experienced a flow interruption, the "number of days with zero flow" indicator is not included in the evaluation in this embodiment.

[0024] Table 1. Calculation Results of Evaluation Indicators for Hydrological Stations in the Three Gorges (II)

[0025] Step S3. Based on the principle of the range-of-changes method, calculate the upper and lower target boundaries of each evaluation indicator before the construction of the water conservancy project, using the values ​​of 25% and 75% of the design frequency as the initial upper and lower target boundaries of each evaluation indicator. Use P-III curve fitting to the hydrological frequency to calculate the values ​​of 25% and 75% of the design frequency for each evaluation indicator.

[0026] Step S4. Analyze the natural variation pattern of flow using linear regression, calculate the ratio of the multi-year average flow between the two periods before and after the construction of the water conservancy project, and scale the upper and lower target boundaries of the monthly average flow and annual extreme flow in the IHA evaluation indicators according to this ratio. Together with the upper and lower target boundaries of other unchanged evaluation indicators, form the final upper and lower target boundaries of each evaluation indicator.

[0027] Table 2. Calculation Results of Upper and Lower Target Boundaries for Initial and Final Evaluation Indicators at the Xiajiang (II) Hydrological Station

[0028] Step S5. The discrete-variable weighting method is proposed to calculate and determine the weights of each evaluation index.

[0029] Step S6. Using the range of variation method, calculate the degree of change in hydrological situation after the construction of water conservancy projects based on the determined upper and lower target boundaries and weights of each final evaluation index.

[0030] The actual values ​​of each evaluation indicator falling into the upper and lower target boundaries after the impact of the Xiajiang Water Conservancy Project are statistically analyzed. The predicted values ​​of each evaluation indicator falling into the upper and lower target boundaries after the impact of the water conservancy project are calculated, and the degree of change of each evaluation indicator is calculated.

[0031] Table 3 Calculation Results of Hydrological Situation Change at the Xiajiang (II) Hydrological Station

[0032] Calculate the overall degree of change in hydrological conditions. Calculations show that after the construction of the Three Gorges Dam, the overall degree of change in downstream hydrological conditions is 49.04%.

Claims

1. An improved method for evaluating changes in hydrological conditions that quantify the impact of water conservancy projects, characterized in that, Includes the following steps: Step S1. Collect long-sequence flow data of hydrological stations near the downstream of the water conservancy project before and after its construction; Step S2. Calculate the IHA evaluation index for the two periods before and after the construction of the water conservancy project; Step S3. Based on the principle of the variation range method, calculate the upper and lower target boundaries of each evaluation indicator before the construction of the water conservancy project, and use the values ​​of 25% and 75% of the design frequency as the initial upper and lower target boundaries of each evaluation indicator. Step S4. Analyze the natural variation law of hydrological station length sequence flow using linear regression method. After determining that there is a significant increase or decrease law in the hydrological station length sequence, calculate the ratio of the multi-year average flow before and after the construction of the water conservancy project. Based on the multi-year average flow ratio, scale the upper and lower target boundaries of the monthly average flow and annual extreme flow in the IHA evaluation index. Together with the upper and lower target boundaries of the other unchanged evaluation indicators, they form the final upper and lower target boundaries of each evaluation indicator. Step S5. Calculate and determine the weights of each evaluation index using the discrete-variable weighting method; Step S6. Using the range of variation method, calculate the degree of change in hydrological situation after the construction of water conservancy projects based on the determined upper and lower target boundaries and weights of each final evaluation index.

2. The improved method for evaluating the hydrological situation changes caused by the quantitative impact of water conservancy projects according to claim 1, characterized in that, The IHA evaluation indicators in step S2 specifically include: Average flow from January to December; minimum and maximum average flow on the 1st, 3rd, 7th, 30th, and 90th days of the year; number of days with zero flow; base flow index: minimum flow on the 7th day of the year / average flow of the year; time of occurrence of the maximum and minimum flow of the year; number of low flow pulses; average duration of low flow pulses; number of high flow pulses; average duration of high flow pulses; average flow increase rate; average flow decrease rate; number of flow reversals per year.

3. The improved method for evaluating the hydrological situation changes in relation to the quantitative impact of water conservancy projects according to claim 2, characterized in that, Step S3 involves calculating the upper and lower target boundaries of each evaluation indicator before the construction of the water conservancy project, using the values ​​of 25% and 75% of the design frequency as the initial upper and lower target boundaries for each evaluation indicator; specifically: The values ​​of the design frequency at 25% and 75% were calculated by fitting the hydrological frequency using the P-III curve.

4. The improved method for evaluating the hydrological situation changes in relation to the quantitative impact of water conservancy projects according to claim 3, characterized in that, The monthly average flow and annual extreme flow in the IHA evaluation indicators in step S4 are as follows: Average flow from January to December, minimum and maximum average flow over the 1st, 3rd, 7th, 30th and 90th days of the year; The calculation formula is: ； ； ； In the formula: , These are the upper and lower target boundaries of the scaled j-th evaluation index, respectively. , ... , These represent the multi-year average flow rates downstream before and after the construction of the water conservancy project; The scaled upper and lower target boundaries of each evaluation indicator, together with the unchanged upper and lower target boundaries of other evaluation indicators, form the final upper and lower target boundaries of each evaluation indicator.

5. An improved method for evaluating the hydrological situation changes caused by the quantitative impact of water conservancy projects according to claim 1, characterized in that, In step S5, the discrete-variable weighting method is used to calculate and determine the weights of each evaluation index. The weights are calculated using data from before the construction of the water conservancy project, and the calculation formula is as follows: ； ； ； In the formula: Let be the dispersion of the j-th evaluation index; is the multi-year average of the j-th indicator; The maximum number of consecutive years within the upper and lower target boundaries during the calculation period for the j-th evaluation indicator; This refers to the change in the j-th indicator, specifically the proportion of the maximum number of years continuously within the upper and lower target boundaries to the total number of years. Let be the weight of the j-th evaluation indicator; The total number of years to be calculated; The number of evaluation indicators.

6. The improved method for evaluating the hydrological situation changes in relation to the quantitative impact of water conservancy projects according to claim 1, characterized in that, The formula for calculating the range of variation in step S6 is as follows: ； ； ； In the formula: The degree of change of the j-th evaluation indicator; and , respectively, represent the actual and predicted values ​​of the upper and lower target boundaries of the j-th evaluation index after the impact of the water conservancy project, where each evaluation index falls within the final target boundary; r is the proportionality coefficient, taken as 50%; The total number of years for the evaluation of the impact of water conservancy projects; This represents the overall degree of change in the hydrological situation.

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