Improved hydrologic regime change evaluation method for quantifying water conservancy project impact

Abstract

The application discloses an improved hydrological regime change evaluation method for quantifying the influence of water conservancy projects, which is based on an IHA index system and can more accurately quantify the hydrological regime change degree of the influence of water conservancy projects by improving the change range method. The evaluation method comprises the following steps: collecting long sequence flow data of a hydrological station close to a water conservancy project downstream 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 the construction of the water conservancy project; analyzing the natural change law of the flow, and optimizing the upper and lower target boundaries of part of the evaluation indexes; proposing a dispersion-variation weight method, and assigning weights to each evaluation index according to the dispersion and variation; and calculating the hydrological regime change degree after the construction of the water conservancy project by using the change range method according to the determined upper and lower target boundaries and weights of each evaluation index.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of hydrological regime analysis, and particularly relates to an improved hydrological regime change evaluation method for quantifying the influence of water conservancy projects. BACKGROUND

[0002] The use of various reservoirs, sluices and other water conservancy projects in China will have a certain impact on the hydrological regime of the rivers. At present, many scholars have carried out certain research in this regard, mainly using the IHA index system (Indicators of Hydrologic Alteration, IHA) and the range of variability approach (Range of Variability Approach, RVA) proposed by Ritcher et al. to analyze the degree of change of the hydrological regime before and after the construction of water conservancy projects.

[0003] However, the IHA index system has many evaluation indexes, and in the existing range of variability approach and related research, the weight is single or mainly considers the correlation between the evaluation indexes, and the dispersion degree and variation of the evaluation indexes are less considered, and the natural change rule of the hydrological regime is not considered, so that the influence of water conservancy projects on the change of the hydrological regime cannot be accurately quantified.

[0004] Therefore, it is necessary to propose a hydrological regime change evaluation method suitable for quantifying the influence of water conservancy projects. SUMMARY

[0005] In view of the deficiencies in the prior art, the present application provides an improved hydrological regime change evaluation method for quantifying the influence of water conservancy projects.

[0006] The technical scheme adopted by the present application is as follows: an improved hydrological regime change evaluation method for quantifying the influence of water conservancy projects, comprising the following steps:

[0007] Step S1. Collecting long sequence flow data of the hydrological station near the downstream of the water conservancy project before and after the construction of the water conservancy project;

[0008] Step S2. Calculating the IHA evaluation indexes of the two periods before and after the construction of the water conservancy project;

[0009] Step S3. According to the analysis principle of the range of variability approach, calculating the upper and lower target boundaries of each evaluation index before the construction of the water conservancy project, and taking the values of the design frequency of 25% and the design frequency of 75% as the initial upper and lower target boundaries of each evaluation index;

[0010] Step S4. After analyzing the natural variation law of the long sequence of flow of the hydrological station by linear regression method and judging that the long sequence of flow of the hydrological station has obvious increasing or decreasing law, the ratio of the multi-year average flow of the two periods before and after the construction of the water conservancy project is calculated, and the upper and lower target boundaries of the monthly average flow and the annual extreme flow in the IHA evaluation index are scaled according to the ratio of the multi-year average flow; together with the upper and lower target boundaries of other unchanged evaluation indexes, the final upper and lower target boundaries of each evaluation index are formed;

[0011] Step S5. The weight of each evaluation index is calculated by the discrete-variable weight method.

[0012] Step S6. The change degree of the hydrological regime after the construction of the water conservancy project is calculated by the change range method according to the final upper and lower target boundaries of each evaluation index and the weight.

[0013] Further, the IHA evaluation index in step S2 specifically includes: the average flow of January to December, the minimum average flow and the maximum average flow of 1 day, 3 days, 7 days, 30 days and 90 days per year, the number of days of 0 flow, the base flow index: the minimum flow of 7 days per year / the average flow per year, the time of the maximum flow per year and the minimum flow per year, the number of low-flow pulses, the average duration of low-flow pulses, the number of high-flow pulses, the average duration of high-flow pulses, the average increase rate of flow, the average decrease rate of flow, and the number of flow reversals per year.

[0014] Further, the upper and lower target boundaries of each evaluation index before the construction of the water conservancy project in step S3 are calculated, and the values of the design frequency of 25% and the design frequency of 75% are taken as the initial upper and lower target boundaries of each evaluation index; specifically:

[0015] The P-III curve is used to fit the hydrological frequency to calculate the values of the design frequency of 25% and the design frequency of 75% of each evaluation index.

[0016] Further, the monthly average flow and the annual extreme flow in the IHA evaluation index in step S4 are specifically:

[0017] The average flow of January to December, the minimum average flow and the maximum average flow of 1 day, 3 days, 7 days, 30 days and 90 days per year;

[0018] The calculation formula is:

[0019] ;

[0020] ;

[0021] ;

[0022] 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;

[0023] 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.

[0024] 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:

[0025] ;

[0026] ;

[0027] ;

[0028] 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.

[0029] Furthermore, the calculation formula for the range of variation method in step S6 is as follows:

[0030] ;

[0031] ;

[0032] ;

[0033] 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.

[0034] 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

[0035] Fig. 1 This is a schematic diagram of the operation of the present invention.

[0036] Fig. 2 This is a graph showing the annual average flow rate trend according to an embodiment of the present invention. Detailed Implementation

[0037] like Figs. 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:

[0038] Step S1. Collect long-sequence flow data of hydrological stations near the downstream of the water conservancy project before and after its construction;

[0039] Step S2. Calculate the IHA evaluation index for the two periods before and after the construction of the water conservancy project;

[0040] 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.

[0041] 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.

[0042] Step S5. Calculate and determine the weights of each evaluation index using the discrete-variable weighting method;

[0043] 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.

[0044] 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.

[0045] 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:

[0046] The values ​​of the design frequency at 25% and 75% were calculated by fitting the hydrological frequency using the P-III curve.

[0047] Furthermore, the monthly average flow and annual extreme flow in the IHA evaluation indicators in step S4 are as follows:

[0048] Average flow from January to December, minimum and maximum average flow over the 1st, 3rd, 7th, 30th and 90th days of the year;

[0049] The calculation formula is:

[0050] ;

[0051] ;

[0052] ;

[0053] 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;

[0054] 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.

[0055] 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:

[0056] ;

[0057] ;

[0058] ;

[0059] 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.

[0060] Furthermore, the calculation formula for the range of variation method in step S6 is as follows:

[0061] ;

[0062] ;

[0063] ;

[0064] 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.

[0065] 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.

[0066] An improved method for evaluating changes in hydrological conditions caused by the quantitative impact of water conservancy projects is adopted, comprising the following steps:

[0067] Step S1. Collect long-sequence flow data of hydrological stations located near the 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.

[0068] 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.

[0069] Table 1. Calculation Results of Evaluation Indicators for Hydrological Stations in the Three Gorges (II)

[0070]

[0071] 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, using the values ​​of 25% and 75% 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% design frequency for each evaluation indicator.

[0072] 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.

[0073] Table 2. Calculation Results of Upper and Lower Target Boundaries for Initial and Final Evaluation Indicators at the Xiajiang (II) Hydrological Station

[0074]

[0075] Step S5. The discrete-variable weighting method is proposed to calculate and determine the weights of each evaluation index.

[0076] 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.

[0077] 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.

[0078] Table 3 Calculation Results of Hydrological Situation Change at the Xiajiang (II) Hydrological Station

[0079]

[0080] 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. 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 upper and lower target boundaries of the other unchanged evaluation indicators, form the final upper and lower target boundaries of each evaluation indicator. 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 degree of 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 evaluation indicator, which is the proportion of the maximum number of years that are 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.

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 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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