Method for calculating ecological flow threshold value of alpine canyon type stream based on hydrology set method

Abstract

The invention discloses a mountain and valley type stream ecological flow threshold value calculation method based on a hydrological set legitimacy, and the method comprises the steps: obtaining the monthly average flow data of a watershed for more than 30 years, determining the boundary node of the periodic change time period of the watershed, and calculating the ecological flow threshold values of different time periods through eight hydrological methods; a hydrology set percentage method and a quantile method are used to carry out calculation and segmentation expression on the threshold set after dividing the boundary nodes; and establishing a comprehensive quantitative index evaluation system of the ecological flow threshold by using a geometric averaging method. The beneficial effects of the method are that through a hydrology set percentage and quantile calculation mode, the periodic change of the drainage basin is finely divided and expressed in a segmented manner, and the calculation precision of the ecological flow threshold value under the seasonal change of the alpine and gorge type stream is improved; and the identification and description capabilities of dynamic change characteristics in an ecological flow threshold period are obviously enhanced.

Description

Technical Field

[0001] The invention relates to the technical field of ecological flow hydrology calculation, in particular to a method for calculating the ecological flow threshold of a high mountain canyon stream based on a hydrology ensemble method. Background Art

[0002] The temporal and spatial distribution of water resources in my country is very uneven, with large differences in inter-annual and intra-annual changes. The degree of ecological flow security of most rivers decreases significantly from main streams to tributaries, and water resources are insufficiently allocated. Under the current background of the Ministry of Water Resources vigorously promoting the recovery of the ecological environment of rivers and lakes, ensuring ecological flow will inevitably require the redistribution of water resources in time and space. Therefore, ensuring the ecological flow of rivers and lakes and continuously strengthening the rigid constraints on water resources are of great significance to supporting high-quality economic and social development.

[0003] The hydrological method is the earliest proposed method to calculate ecological flow using historical hydrological data of rivers. It is widely used because of its simple calculation and principle. The most representative methods include the Tennant method, the 7Q10 method, the average flow method of the driest month in the past 10 years, the annual distribution method, the Lyon method, the minimum monthly average runoff method, etc. Most hydrological methods can propose appropriate ecological flow thresholds based on the seasonal changes in the water regime of the basin and have achieved good results, but there are few reasonable calculation methods for the ecological flow thresholds of alpine canyon streams. How to establish a calculation method for ecological flow thresholds suitable for alpine canyon streams, ensure the adaptability of ecological flow thresholds to changes in natural hydrological conditions, and be at a high level in the comprehensive evaluation system with accuracy, satisfaction and suitability as indicators, is the problem to be solved at present. Summary of the invention

[0004] In view of this, the purpose of the present invention is to provide a method for calculating the ecological flow threshold of high mountain canyon streams based on the hydrological ensemble method, which can accurately reflect the seasonal differences in flow and embody the dynamic change characteristics of the threshold.

[0005] To achieve the above object, the present invention adopts the following technical solution: a method for calculating the ecological flow threshold of alpine canyon streams based on the hydrological ensemble method, comprising the following steps:

[0006] Step S1: Calculate the ecological flow threshold of different months in the basin within a year, collect monthly average runoff data for more than 30 years, and for basins lacking long series of flow data, interpolation and extension are required based on the hydrological station data in the adjacent study area;

[0007] Step S2: Select 8 hydrological methods based on the hydrological data characteristics of the watershed, divide each month of the year into flood season and non-flood season, calculate the ecological flow thresholds of different months respectively, and use all the results as the collective input of step S3 and step S4;

[0008] Step S3: Based on the set of ecological flow thresholds calculated by the eight hydrological methods in step S2, 15% of the sum of the threshold results in the hydrological method set is used as the ecological flow threshold for each month in the flood season, and the upper quartile of the hydrological method set is used as the ecological flow threshold for each month in the non-flood season. The flood season and the non-flood season are distinguished according to the percentage and quantile of the hydrological set to ensure that the subsequent calculation of the ecological flow threshold complies with the basic rule that the flood season flow is larger than the non-flood season flow;

[0009] Step S4: Based on hydrological indicators such as river flow change rate, occurrence time and extreme flow, a comprehensive index evaluation system consisting of the accuracy, satisfaction and suitability of the ecological flow threshold is established. The new method for calculating the ecological flow threshold based on the hydrological set in step S3 and the eight hydrological methods in step S2 are comprehensively evaluated. The evaluation level of each method is determined and compared according to the river health level evaluation standard to ensure the suitability and accuracy of the ecological flow threshold results of the new method.

[0010] In a preferred embodiment:

[0011] In step S1, interpolation and extension are performed based on the data of hydrological stations closer to the study area. The hydrological analogy method is used, and the formula is as follows:

[0012]

[0013] In the formula, Q 设 and Q 参 They are the flow rates of the design hydrological station and the reference hydrological station, in m 3 / s;P 设 and P 参 are the rainfall at the design hydrological station and the reference hydrological station, in mm; F 设 and F 参 They are the controlled basin areas of the design hydrological station and the reference hydrological station, in km 2 .

[0014] In a preferred embodiment:

[0015] In step S2, the eight commonly used hydrological methods are the annual distribution method, the Lyon method, the monthly minimum flow method, the improved 7Q10 method, the monthly flow variation method, the Tennant method, the Texas method, and the average flow method of the driest month in the past 10 years. The principles of calculating ecological flow by each hydrological method are as follows:

[0016] in

[0017] ① The formula for calculating ecological flow using the annual distribution method is:

[0018]

[0019] In the formula is the average annual runoff over many years, m 3 / s; is the multi-year average monthly flow rate of the ith month, m 3 / s;q min(i) is the multi-year minimum monthly average flow rate of the ith month, m 3 / s;q ij is the average monthly flow in the i-th month of the j-th year, m 3 / s; n is the number of years in the long series; is the minimum annual runoff, m 3 / s; η is the mean ratio of the same period; To calculate the basic ecological flow of the river in each month, m 3 / s.

[0020] ② The monthly minimum flow method takes the minimum value of the multi-year natural monthly average flow series of each month as the ecological flow of the month;

[0021] ③ The improved 7Q10 method selects the runoff data of the driest month in the past years for frequency analysis and draws the P-Ⅲ frequency curve; finally, the flow with a 90% guaranteed rate is calculated from the P-Ⅲ curve as the ecological flow;

[0022] ④ The average flow rate of the driest month in the past 10 years is based on the monthly average flow data of the driest month in the past 10 years. The average of the monthly average flow rates of the driest month in these 10 years is calculated as the ecological flow rate;

[0023] ⑤ The Texas method selects the monthly average flow value under the 50% guarantee rate of each month, and takes its specific percentage as the ecological flow of the month. In the present invention, the specific percentage is 20%;

[0024] ⑥ The formulas for calculating ecological flow using the Lyon method, monthly flow variation method, and Tennant method are:

[0025]

[0026] Where Q LE is the ecological flow calculated by Lyon method, m 3 / s;q M is the monthly median flow, m 3 / s;q m is the average monthly flow, m 3 / s;q a is the average annual flow, m 3 / s;Q ME is the ecological flow calculated by the monthly flow variation method, m 3 / s;Q TE is the ecological flow calculated by Tennant method, m 3 / s.

[0027] In a preferred embodiment:

[0028] In step S3, 15% of the sum of the threshold results in the hydrological method set is used as the ecological flow threshold for each month in the flood season, and the upper quartile of the hydrological method set is used as the ecological flow threshold for each month in the non-flood season;

[0029] The specific formula is as follows:

[0030]

[0031] In the formula, Q ef is the ecological flow threshold calculated by the hydrological ensemble percentage method during the flood season, m 3 / s;Q enf is the ecological flow threshold calculated by the hydrological ensemble quantile method in the non-flood season, m 3 / s;Q i They are the ecological flow thresholds calculated by 8 common hydrological methods, m 3 / s.

[0032] In a preferred embodiment:

[0033] In step S4, in order to comprehensively evaluate the applicability of different calculation methods in the study area, the geometric mean method is used to comprehensively quantify the accuracy, satisfaction and suitability of suitable ecological flow. The calculation formula is:

[0034]

[0035] Where: Z j It represents the comprehensive index. When the comprehensive index is closer to 1, it indicates that the calculated suitable ecological flow threshold is closer to the natural water flow of the river, and the suitable ecological flow threshold is more beneficial to the health of the river. j The numerical definition of the river health level is divided into five levels, which represent extremely poor, poor, moderate, good and excellent levels respectively. The evaluation criteria are shown in Table 1; P j M is the accuracy level; j S is the degree of satisfaction; j for the appropriate degree;

[0036] Table 1 Evaluation criteria for river health level

[0037]

[0038] Among them, the accuracy P j An indicator that reflects the degree of deviation between the appropriate ecological flow threshold and the monthly runoff. The closer the ratio of the appropriate ecological flow threshold to the monthly runoff is to 1, the more reasonable it is. The calculation formula is:

[0039]

[0040] Where: P j is the accuracy of suitable ecological flow in the jth month, Q ej is the ecological flow threshold of the jth month, m 3 / s;Q zj For Q ej The average value of the monthly flow rate of the corresponding month, m 3 / s;

[0041] Satisfaction level j It mainly reflects the index that meets the appropriate ecological flow threshold. The calculation formula is:

[0042]

[0043] Where: M j is the suitable ecological flow satisfaction rate in the jth month; D ij is the number of months in the jth month of the i-th year that meet the suitable ecological flow; D j is the total number of months; Q ij represents the runoff in the jth month of the i-th year, m 3 / s;Q ej is the suitable ecological flow threshold for the jth month, m 3 / s;

[0044] Suitability S j It mainly indicates the degree of dispersion between the suitable ecological flow and the monthly runoff. The more days the suitable ecological flow meets the natural flow, the higher the degree of satisfaction. The calculation formula is:

[0045]

[0046] S j =1-S j ′ / 10 (16)

[0047] Where: S j With S j ' are the dispersion and suitability of suitable ecological flow in the jth month respectively; Q ej With Q j are the suitable ecological flow in the jth month and the multi-year average monthly runoff, m 3 / s;Q 极j With Q 极j ' are the extreme characteristic flow and the minimum characteristic value of monthly runoff in the jth month, m 3 / s; when the suitable ecological flow is completely equal to the natural runoff, the suitability S j =1.

[0048] Compared with the prior art, the present invention has the following beneficial effects: the present invention takes into account the changing laws of seasonal water conditions in the basin, and on the basis of combining several existing hydrological ecological flow threshold calculation methods, aims to propose a method based on the hydrological ensemble method to calculate the ecological flow thresholds of canyon-type streams under the dam of a high mountain reservoir during the flood season and non-flood season, and then uses accuracy, satisfaction and suitability as indicators to comprehensively evaluate the applicability of this method in the basin, which can accurately reflect the differences in seasonal water conditions and embodies the dynamic change characteristics of the threshold. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 Flow chart for implementing the method of the present invention;

[0050] Figure 2 It is the overall structural framework diagram of the present invention;

[0051] Figure 3 Maps of intra-annual changes in ecological flow thresholds calculated for a variety of hydrological methods;

[0052] Figure 4 Situational plot of the comprehensive index levels of ecological flow thresholds calculated for different hydrological approaches. DETAILED DESCRIPTION

[0053] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0054] It should be noted that the following detailed descriptions are illustrative and are intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present application belongs.

[0055] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application; as used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or their combinations.

[0056] Please refer to Figure 1 , Figure 1 The present invention is a flowchart for implementing the method.

[0057] The present invention provides a method for calculating the ecological flow threshold of a high mountain canyon stream based on a hydrological ensemble method, comprising the following steps:

[0058] S1. In order to take into account the changing patterns of seasonal water conditions in the basin and calculate the ecological flow thresholds of different months in the basin, it is necessary to collect monthly average flow data for more than 30 years. For basins that lack long series of flow data, it is necessary to find hydrological station data in neighboring study areas and interpolate and extend them according to the hydrological analogy method.

[0059] It should be noted that when performing interpolation and extension, the formula of the hydrological analogy method is as follows:

[0060]

[0061] In the formula, Q 设 and Q 参 They are the flow rates of the design hydrological station and the reference hydrological station, in m 3 / s.P 设 and P 参 They are the rainfall at the design hydrological station and the reference hydrological station, in mm. 设 and F 参 They are the controlled basin areas of the design hydrological station and the reference hydrological station, in km 2 .

[0062] S2, based on eight hydrological methods, including annual distribution method, Lyon method, monthly minimum flow method, improved 7Q10 method, monthly flow change method, Tennant method, Texas method and average flow method of the driest month in the past 10 years, each month of the year is divided into flood season and non-flood season, and the ecological flow thresholds of different months are calculated respectively. At the same time, all their results are used as the collective input of S3 and S4.

[0063] It should be noted that the principles and formulas for calculating ecological flow using various hydrological methods are shown below.

[0064] The formula for calculating ecological flow using the annual distribution method is:

[0065]

[0066] In the formula is the multi-year average monthly flow rate of the ith month, m 3 / s;q min(i) is the multi-year minimum monthly average flow rate of the ith month, m 3 / s;q ij is the average monthly flow in the i-th month of the j-th year, m 3 / s; n is the number of years in the long series.

[0067] The monthly minimum flow method takes the minimum value of the multi-year natural monthly average flow series for each month as the ecological flow for that month.

[0068] The improved 7Q10 method selects the runoff data of the driest month in previous years for frequency analysis and draws a P-Ⅲ frequency curve; finally, the flow with a 90% guaranteed rate is calculated from the P-Ⅲ curve as the ecological flow.

[0069] The average flow rate of the driest month in the past 10 years is based on the average monthly flow rate data of the driest month in the past 10 years. The average of the average monthly flow rates of the driest month in these 10 years is calculated as the ecological flow.

[0070] The Texas method selects the monthly average flow value under the 50% guarantee rate in each month, and takes a specific percentage thereof as the ecological flow of the month. In the present invention, the specific percentage is 20%.

[0071] The formulas for calculating ecological flow using the Lyon method, monthly flow variation method, and Tennant method are:

[0072]

[0073] Where Q LE is the ecological flow calculated by Lyon method, m 3 / s;q M is the monthly median flow, m 3 / s;q m is the average monthly flow, m 3 / s;q a is the average annual flow, m 3 / s;Q ME is the ecological flow calculated by the monthly flow variation method, m 3 / s;Q TE is the ecological flow calculated by Tennant method, m 3 / s.

[0074] S3. In order to more accurately reflect the average level of the eight hydrological methods, the ecological flow threshold set calculated by the eight hydrological methods in S2 is used. In each month of the flood season, 15% of the sum of the threshold results in the hydrological method set is used as the ecological flow threshold, and in each month of the non-flood season, the upper quartile of the hydrological method set is used as the ecological flow threshold.

[0075] It should be noted that the formula for calculating the ecological flow thresholds during the flood season and non-flood season using the percentage and quantile of the hydrological set is as follows:

[0076]

[0077] In the formula, Q ef is the ecological flow threshold calculated by the hydrological ensemble percentage method during the flood season, m 3 / s.Q enf is the ecological flow threshold calculated by the hydrological ensemble quantile method in the non-flood season, m 3 / s.Qi They are the ecological flow thresholds calculated by 8 common hydrological methods, m 3 / s.

[0078] S4. With reference to the "Guidelines for River and Lake Health Assessment (Trial)" and other relevant technical documents issued by the River Chief Office of the Ministry of Water Resources, based on hydrological indicators such as river flow change rate, occurrence time and extreme flow, a comprehensive index evaluation system consisting of the accuracy, satisfaction and suitability of ecological flow thresholds is established, and the calculation results of 8 hydrological methods and the hydrological ensemble method proposed in this invention are evaluated.

[0079] It should be noted that in order to comprehensively evaluate the applicability of different calculation methods in the study area, the geometric mean method was used to comprehensively quantify the accuracy, satisfaction and suitability of suitable ecological flow. The calculation formula is:

[0080]

[0081] Where: Z j It represents the comprehensive index. The closer the comprehensive index is to 1, the closer the calculated suitable ecological flow threshold is to the natural water flow of the river, and the more beneficial the suitable ecological flow threshold is to the health of the river. j The numerical definition of the river health level is divided into five levels, which represent extremely poor, poor, moderate, good and excellent levels respectively. The evaluation criteria are shown in Table 2; P j M is the accuracy level; j S is the degree of satisfaction; j To the appropriate degree.

[0082] Table 2 Evaluation criteria for river health level

[0083]

[0084] Among them, the accuracy P j It mainly reflects the degree of deviation between the appropriate ecological flow threshold and the monthly runoff. The closer the ratio of the appropriate ecological flow threshold to the monthly runoff is to 1, the more reasonable it is. The calculation formula is:

[0085]

[0086] Where: P j is the accuracy of suitable ecological flow in the jth month, Q ej is the ecological flow threshold of the jth month, m 3 / s;Q zj For Q ej The average value of the monthly flow rate of the corresponding month, m 3 / s.

[0087] Satisfaction level jIt mainly reflects the index that meets the appropriate ecological flow threshold. The calculation formula is:

[0088]

[0089] Where: M j is the suitable ecological flow satisfaction rate in the jth month; D ij is the number of months in the jth month of the i-th year that meet the suitable ecological flow; D j is the total number of months; Q ij represents the runoff in the jth month of the i-th year, m 3 / s;Q ej is the suitable ecological flow threshold for the jth month, m 3 / s.

[0090] Suitability S j It mainly indicates the degree of dispersion between the suitable ecological flow and the monthly runoff. The more months the suitable ecological flow meets the natural flow, the higher the degree of satisfaction. The calculation formula is:

[0091]

[0092] S j =1-S j ′ / 10 (16)

[0093] Where: S j With S j ' are the dispersion and suitability of suitable ecological flow in the jth month respectively; Q ej With Q j are the suitable ecological flow in the jth month and the multi-year average monthly runoff, m 3 / s;Q 极j With Q 极j ' are the extreme characteristic flow and the minimum characteristic value of monthly runoff in the jth month, m 3 / s; Q of the present invention 极j With Q ej When the suitable ecological flow is completely equal to the natural runoff, the suitability S j =1.

[0094] In order to better explain the specific process of the present invention, the method flow is as follows ( Figure 1 ), the implementation method of the present invention is described in detail in combination with specific implementation cases:

[0095] This case takes the Muyang River Basin, a high mountain canyon stream with a high degree of development, as an example, and calculates the ecological flow threshold for the Zhouning Power Station in the basin.

[0096] There is a Qibu hydrological station in the Qibuxi basin, a tributary of Muyangxi, which is close to the case area and has a long series of hydrological observation data from 1960 to 2022. It can be used as a representative station for the case. The monthly average flow data of Qibu Station from 1960 to 2022 are selected, and the monthly average runoff data of Zhouning Power Station are interpolated and extended to obtain the annual monthly average flow data of Zhouning Power Station from 1960 to 2022 as the basis for calculation.

[0097] Based on eight hydrological methods, namely, annual distribution method, Lyon method, monthly minimum flow method, improved 7Q10 method, monthly flow variation method, Tennant method, Texas method and average flow method of the driest month in the past 10 years, the ecological flow thresholds of different months were calculated respectively, and all the results were used as the ensemble results of the hydrological methods in this study. In order to more accurately reflect the average level of the eight hydrological methods, 15% of the sum of the threshold results in the hydrological method ensemble was taken as the ecological flow threshold for the flood season month, and the upper quartile of the hydrological method ensemble was used as the ecological flow threshold for the non-flood season month. The ecological flow thresholds for the flood season and the non-flood season were determined according to the specific percentage and quantile of the hydrological ensemble, respectively, reflecting the basic water regime that the flood season flow in the basin is greater than the non-flood season flow. Figure 3 The annual change chart of ecological flow thresholds calculated by various hydrological methods shows that the principles of different hydrological methods are different, and the change trends of their results are also inconsistent. Except for the average flow method of the driest month in the past 10 years, the improved 7Q10 method, and the Tennant method, the distribution law and overall change trend of the ecological flow thresholds of each month of the remaining calculation methods are basically consistent with the multi-year average runoff of each month, which is also consistent with the changing characteristics of seasonal rainfall recharge and runoff surplus and shortage in the Muyang River Basin. The suitable ecological flow threshold for the dam site of Zhouning Power Station calculated by the hydrological ensemble method fluctuates with the seasonal changes of water conditions, and its demand in the flood season is significantly greater than that in the non-flood season.

[0098] In actual projects, there are significant differences in the hydrological characteristics and flow data of different river basins. In order to verify the rationality of the calculation method of ecological flow threshold based on hydrological ensemble and its superiority compared with other hydrological methods, the Ministry of Water Resources River Chief Office "River and Lake Health Assessment Guide (Trial)" and other relevant technical documents were referred to. Based on hydrological indicators such as river flow change rate, occurrence time and extreme flow, a comprehensive index evaluation system consisting of the accuracy, satisfaction and suitability of ecological flow threshold was established, and the calculation results of 8 hydrological methods and hydrological ensemble method were evaluated. Figure 4The figure shows the level of comprehensive index of ecological flow threshold calculated by various hydrological methods. It can be seen from the figure that compared with a single hydrological method, the comprehensive index of suitable ecological flow threshold calculated by the hydrological ensemble method proposed in the present invention is between 0.54 and 0.84; the comprehensive index of ecological flow in the non-flood season is between 0.66 and 0.84, and the river health status is "excellent" or "very excellent", which has strong adaptability to alpine canyon streams and can be used as a method for calculating suitable ecological flow threshold for Zhouning Power Station.

[0099] The beneficial effects of the present invention are as follows: the percentages and quantiles of the ecological flow set calculated based on a variety of hydrological methods are used to determine the ecological flow thresholds for high mountain canyon streams during the flood season and non-flood season, respectively. The calculation results of this hydrological set method can accurately reflect the seasonal water situation differences and change characteristics of the flow within the year, and compared with the comprehensive evaluation index of a single hydrological method, the ecological flow threshold has better suitability and more accurate results, which not only reflects the dynamic change characteristics of the threshold within the year, but also can better serve the sustainable development, utilization and management practices of water resources in similar basins.

[0100] For those skilled in the art, the above examples are only used to illustrate the technical solutions and effects of the present invention, and do not limit the present invention. The present invention can be implemented in other specific forms without departing from the spirit or basic features of the present invention. Any changes made within the spirit and principles of the present invention should be included in the present invention, and any figure mark in the claims should not be regarded as limiting the claims involved.

Claims

1. A method for calculating the ecological flow threshold of alpine canyon streams based on the hydrological ensemble method, characterized by: The following steps are involved: Step S1: Calculate the ecological flow threshold of different months in the basin within a year, collect monthly average runoff data for more than 30 years, and for basins lacking long series of flow data, interpolation and extension are required based on the hydrological station data in the adjacent study area; Step S2: Select 8 hydrological methods based on the hydrological data characteristics of the watershed, divide each month of the year into flood season and non-flood season, calculate the ecological flow thresholds of different months respectively, and use all the results as the collective input of step S3 and step S4; Step S3: Based on the set of ecological flow thresholds calculated by the eight hydrological methods in step S2, 15% of the sum of the threshold results in the hydrological method set is used as the ecological flow threshold for each month in the flood season, and the upper quartile of the hydrological method set is used as the ecological flow threshold for each month in the non-flood season. The flood season and the non-flood season are distinguished according to the percentage and quantile of the hydrological set to ensure that the subsequent calculation of the ecological flow threshold complies with the basic rule that the flood season flow is larger than the non-flood season flow; Step S4: Based on hydrological indicators such as river flow change rate, occurrence time and extreme flow, a comprehensive index evaluation system consisting of the accuracy, satisfaction and suitability of the ecological flow threshold is established. The new method for calculating the ecological flow threshold based on the hydrological set in step S3 and the eight hydrological methods in step S2 are comprehensively evaluated. The evaluation level of each method is determined and compared according to the river health level evaluation standard to ensure the suitability and accuracy of the ecological flow threshold results of the new method.

2. A method for calculating the ecological flow threshold of alpine canyon streams based on the hydrological ensemble method as claimed in claim 1, characterized in that: In step S1, interpolation and extension are performed based on the data of hydrological stations closer to the study area. The hydrological analogy method is used, and the formula is as follows: In the formula, Q 设 and Q 参 They are the flow rates of the design hydrological station and the reference hydrological station, in m 3 / s;P 设 and P 参 are the rainfall at the design hydrological station and the reference hydrological station, in mm; F 设 and F 参 They are the controlled basin areas of the design hydrological station and the reference hydrological station, in km 2 .

3. The method for calculating the ecological flow threshold of alpine canyon streams based on the hydrological ensemble method according to claim 1, characterized in that: In step S2, the eight commonly used hydrological methods are the annual distribution method, the Lyon method, the monthly minimum flow method, the improved 7Q10 method, the monthly flow variation method, the Tennant method, the Texas method, and the average flow method of the driest month in the past 10 years. The principles of calculating ecological flow by each hydrological method are as follows: in ① The formula for calculating ecological flow using the annual distribution method is: In the formula is the average annual runoff over many years, m 3 / s; is the multi-year average monthly flow rate of the ith month, m 3 / s;q min(i) is the multi-year minimum monthly average flow rate of the ith month, m 3 / s;q ij is the average monthly flow in the i-th month of the j-th year, m 3 / s; n is the number of years in the long series; is the minimum annual runoff, m 3 / s; η is the mean ratio of the same period; To calculate the basic ecological flow of the river in each month, m 3 / s. ② The monthly minimum flow method takes the minimum value of the multi-year natural monthly average flow series of each month as the ecological flow of the month; ③ The improved 7Q10 method selects the runoff data of the driest month in the past years for frequency analysis and draws the P-Ⅲ frequency curve; finally, the flow with a 90% guaranteed rate is calculated from the P-Ⅲ curve as the ecological flow; ④ The average flow rate of the driest month in the past 10 years is based on the monthly average flow data of the driest month in the past 10 years. The average of the monthly average flow rates of the driest month in these 10 years is calculated as the ecological flow rate; ⑤ The Texas method selects the monthly average flow value under the 50% guarantee rate of each month, and takes its specific percentage as the ecological flow of the month. In the present invention, the specific percentage is 20%; ⑥ The formulas for calculating ecological flow using the Lyon method, monthly flow variation method, and Tennant method are: Where Q LE is the ecological flow calculated by Lyon method, m 3 / s;q M is the monthly median flow, m 3 / s;q m is the average monthly flow, m 3 / s;q a is the average annual flow, m 3 / s;Q ME is the ecological flow calculated by the monthly flow variation method, m 3 / s;Q TE is the ecological flow calculated by Tennant method, m 3 / s.

4. The method for calculating the ecological flow threshold of alpine canyon streams based on the hydrological ensemble method according to claim 1, characterized in that: In step S3, 15% of the sum of the threshold results in the hydrological method set is used as the ecological flow threshold for each month in the flood season, and the upper quartile of the hydrological method set is used as the ecological flow threshold for each month in the non-flood season; The specific formula is as follows: In the formula, Q ef is the ecological flow threshold calculated by the hydrological ensemble percentage method during the flood season, m 3 / s;Q enf is the ecological flow threshold calculated by the hydrological ensemble quantile method in the non-flood season, m 3 / s;Q i They are the ecological flow thresholds calculated by 8 common hydrological methods, m 3 / s.

5. The method for calculating the ecological flow threshold of alpine canyon streams based on the hydrological ensemble method according to claim 1, characterized in that: In step S4, in order to comprehensively evaluate the applicability of different calculation methods in the study area, the geometric mean method is used to comprehensively quantify the accuracy, satisfaction and suitability of suitable ecological flow. The calculation formula is: Where: Z j It represents the comprehensive index. When the comprehensive index is closer to 1, it indicates that the calculated suitable ecological flow threshold is closer to the natural water flow of the river, and the suitable ecological flow threshold is more beneficial to the health of the river. j The numerical definition of the river health level is divided into five levels, which represent extremely poor, poor, moderate, good and excellent levels respectively. The evaluation criteria are shown in Table 1; P j is the accuracy; M j S is the degree of satisfaction; j for the appropriate degree; Table 1 Evaluation criteria for river health level Among them, the accuracy P j An indicator that reflects the degree of deviation between the appropriate ecological flow threshold and the monthly runoff. The closer the ratio of the appropriate ecological flow threshold to the monthly runoff is to 1, the more reasonable it is. The calculation formula is: Where: P j is the accuracy of suitable ecological flow in the jth month, Q ej is the ecological flow threshold of the jth month, m 3 / s;Q zj For Q ej The average value of the monthly flow rate of the corresponding month, m 3 / s; Satisfaction level j It mainly reflects the index that meets the appropriate ecological flow threshold. The calculation formula is: Where: M j is the suitable ecological flow satisfaction rate in the jth month; D ij is the number of months in the jth month of the i-th year that meet the suitable ecological flow; D j is the total number of months; Q ij represents the runoff in the jth month of the i-th year, m 3 / s;Q ej is the suitable ecological flow threshold for the jth month, m 3 / s; Suitability S j It mainly indicates the degree of dispersion between the suitable ecological flow and the monthly runoff. The more days the suitable ecological flow meets the natural flow, the higher the degree of satisfaction. The calculation formula is: S j =1-S j ′ / 10 (16) Where: S j With S j ' are the dispersion and suitability of suitable ecological flow in the jth month respectively; Q ej With Q j are the suitable ecological flow in the jth month and the multi-year average monthly runoff, m 3 / s;Q 极j With Q 极j ' are the extreme characteristic flow and the minimum characteristic value of monthly runoff in the jth month, m 3 / s; when the suitable ecological flow is completely equal to the natural runoff, the suitability S j =1.

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