Method for determining ecological flow process based on runoff variation reconstruction and frequency analysis

Abstract

The application discloses a kind of ecological flow process determination method based on runoff variation reconstruction and frequency analysis, comprising: 1) collecting the long sequence daily runoff observation data of ecological control section in basin, and identifying potential hydrological variation point;2) the runoff sequence is divided into several hydrological variation periods;3) using hydrological model, the observed runoff of each hydrological period is recovered in turn, and the natural daily runoff process is obtained;4) the minimum adaptation period of fish to runoff change is determined;5) the average value of natural runoff in each period is used as the new daily runoff, and the natural daily runoff time series is reconstructed;6) based on daily runoff hydrological frequency curve within a year, select the frequency matched runoff as ecological flow, and construct daily ecological flow process within a year.The calculation result of the method of the application can not only guarantee the dynamic demand of ecological flow to runoff change, but also effectively support the coordinated development goal of sustainable development requirement of water resources and ecological balance under water regime change, and has high popularization and use value.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of hydrological prediction and ecological flow formulation, and particularly relates to a method for determining ecological flow process based on runoff variation reconstruction and frequency analysis. BACKGROUND

[0002] Under the background of rapid economic development, the construction and operation of water conservancy projects have intensified the development and utilization of river water resources by human activities, but often overlook the basic needs of river ecosystems for water resources, leading to signs of degradation in their health. To balance water resource development and ecological protection, while ensuring the needs of economic and social water use, the water quantity required to maintain the normal ecological structure and function of river ecosystems, i.e., ecological flow, should also be met to promote the coordinated development of sustainable use of water resources and ecological balance.

[0003] Currently, there are more than 200 ecological flow calculation methods worldwide, which can be divided into hydrological methods, hydraulic methods, habitat simulation methods, and overall methods. Among them, the hydrological method is widely used globally due to its easy data acquisition and simple calculation. At the same time, with the increasing depth of ecological flow research, the hydrological method is continuously improving and enriching, constantly adapting to new research needs. However, under the influence of climate change and human activities, river hydrological regime is undergoing unprecedented complex changes, which seriously disrupts the normal life rhythm of aquatic organisms. In this complex hydrological environment, the needs of aquatic organism communities for river habitats have become more diverse and sophisticated, no longer limited to simple water quantity guarantee, but more concerned about the characteristics of flow and the continuity of its dynamic process. However, the existing hydrological method generally uses a fixed proportion to set a fixed ecological flow value, which cannot truly reflect the dynamic needs of river ecosystems for runoff changes. Therefore, it is necessary to develop an ecological flow calculation method that can consider the stability of dynamic water demand of river ecosystems under changing hydrological regime. SUMMARY

[0004] The purpose of the present application is to overcome the shortcomings of the prior art and provide a method for determining ecological flow process based on runoff variation reconstruction and frequency analysis, which can accurately reflect and evaluate the annual dynamic process of ecological flow and ensure the dynamic needs of aquatic organisms for runoff changes, improving the calculation accuracy and practical guiding value of ecological flow.

[0005] To achieve the above technical purpose, the present application adopts the following technical solutions.

[0006] A method for determining ecological flow process based on runoff variation reconstruction and frequency analysis, comprising the following steps:

[0007] Step S1, collect long-term daily runoff observation data of the ecological control section of the river basin, and identify potential variation points in the daily runoff time series by using a hydrological process variation diagnosis method;

[0008] Step S2, based on the basic operation data of the upstream water conservancy project regulation and storage of the selected ecological control section, combined with the variation characteristics of historical hydrological and meteorological elements, the potential variation points identified in step S1 are reviewed and verified, and according to the review results, the daily runoff time series is divided into several hydrological variation periods;

[0009] Step S3, select the earliest hydrological variation period least affected by human activities as the natural reference period, and consider the observed runoff data of the natural reference period as the natural daily runoff time series, and use it to construct a meteorological-driven hydrological model to predict the natural daily runoff process of the next hydrological variation period; combined with the sliding reduction principle, along the daily runoff time series, the natural daily runoff process of the subsequent hydrological variation period is restored in turn;

[0010] Step S4, investigate the ecological habits of the main fish species of the ecological control section of the river basin, analyze the correlation between the key life activities of the main fish including reproduction, migration, foraging and runoff changes, and determine the minimum adaptation period of the main fish to runoff changes;

[0011] Step S5, taking the minimum adaptation period as the standard for quantifying continuous runoff changes, calculate the average value of the natural daily runoff in each period of the restored multi-year natural daily runoff time series Q (天然) =(Q 1(天然) ,Q 2(天然) ,...,Q n(天然) ,...,Q N(天然) ), and consider it as the daily runoff of the first day of the corresponding period, and then reconstruct a new natural daily runoff time series;

[0012] Step S6, calculate the daily runoff frequency and the monthly average hydrological frequency in the new natural daily runoff time series by frequency analysis, and determine the annual monthly comprehensive hydrological frequency according to the runoff distribution characteristics in the year, draw the daily runoff frequency curve in the year, select the daily runoff matching the monthly comprehensive hydrological frequency as the ecological flow, and determine the daily ecological flow process in the year.

[0013] Specifically, the collection of long-term daily runoff observation data of the ecological control section of the river basin in step S1 has a collection period of not less than 20 years.

[0014] Specifically, the basic operation data of the upstream water conservancy project regulation and storage in step S2 includes construction time, location, scale and regulation operation.

[0015] Specifically, in step S3, the natural daily runoff process of each subsequent hydrological variation period is restored by the following steps:

[0016] In step S31, the daily runoff time series Q of the basin ecological control section in step S2 is divided into N hydrological variation periods, i.e., Period 1, Period 2,..., Period N, and the daily runoff sequence of each period is arranged and the daily meteorological element sequence wherein n = 1, 2,..., N, and j = 1, 2,..., m n N is the total number of hydrological variation periods into which the daily runoff time series is divided; m n is the number of daily runoff data in the nth hydrological variation period;

[0017] In step S32, the earliest hydrological variation period Period 1 with the least human activity impact is selected as the natural baseline period, and Q 1 is regarded as the natural daily runoff sequence and Q 1 is subjected to Pearson correlation analysis with the daily meteorological element sequence considering a maximum lag time of 60 days, wherein d = 1, 2,..., 60, and (T-d) represents d days ago;

[0018] In step S33, in the hydrological variation period Period 1, the top 10 meteorological factors with the largest absolute correlation coefficients are selected as input variables, Q 1 is taken as the target variable, a first meteorological-driven hydrological model is constructed, and the parameters of the first meteorological-driven hydrological model are optimized;

[0019] In step S34, in the hydrological variation period Period 2, the top 10 meteorological factors with the largest absolute correlation coefficients are selected as prediction factors, the first meteorological-driven hydrological model is used to predict the daily runoff process of Period 2, and the prediction result is regarded as the natural daily runoff sequence of the second hydrological variation period

[0020]

[0021] In step S35, in combination with the sliding restoration principle, the daily runoff time series is slid forward by one hydrological variation period, the second meteorological-driven hydrological model is constructed using Q 2 and in Period 2, and the natural daily runoff sequence of the third hydrological variation period is predicted according to the meteorological factors in the hydrological variation period Period 3 The natural daily runoff sequence of each subsequent hydrological variation period is restored in turn

[0022] Further, the daily meteorological element sequence arranged in step S31 should match the daily runoff sequence, and the daily meteorological element includes precipitation.

[0023] Specifically, in step S4, the determination of the minimum adaptation period of the main fish species to the runoff change includes the following steps:

[0024] Step S41, according to the ecological habits of the main fish species at the ecological control section of the basin, one or more of the life activity indexes including spawning amount, migration distance and foraging amount are selected as representative quantitative indexes;

[0025] Step S42, assuming that the adaptation period of the representative life activity of the main fish species to the runoff change is S days, where S = 1, 2,..., 30, the average value of all continuous S-day representative quantitative indexes in a year is calculated and taken as the value of the first day of the corresponding period to form a time sequence where k = 365-S+1;

[0026] Step S43, the average value of all continuous S-day natural daily runoff in a year is calculated and taken as the daily runoff of the first day of the corresponding period to reconstruct a natural daily runoff time sequence based on the adaptation period S

[0027] Step S44, an ecological hydrological response model is constructed to maximize the correlation and minimize S, which is expressed as: wherein, is the correlation coefficient between and

[0028] Step S45, the obtained ecological hydrological response model is solved by using the traversal method to obtain the minimum adaptation period S of the main fish species to the runoff change min .

[0029] Specifically, in step S5, the reconstruction of a new set of natural daily runoff time sequences is as follows:

[0030]

[0031]

[0032]

[0033] In the above formula, i = 1, 2,..., m, n = 1, 2,..., N, j = 1, 2,..., m n , h = 1, 2,..., m-S min +1; Q (天然) ​​Q represents the multi-year natural daily runoff time series of the basin ecological control section recovered in step S3; m is the sequence Q (天然) total number of natural daily runoff data in the middle of the day; N is the total number of hydrological variation periods divided by the daily runoff sequence; m n is the number of natural daily runoff data in the nth hydrological variation period; Q represents the newly formed daily natural runoff of the hth day after reconstruction; S min is the minimum adaptation period determined in step S4; Q represents the multi-year natural daily runoff sequence newly formed after reconstruction.

[0034] Specifically, in step S6, the determination of the annual daily ecological flow process comprises the following steps:

[0035] Step S61, arrange the multi-year natural daily runoff data of the basin ecological control section after reconstruction in step S5 Let the natural daily runoff of the tth day in the xth month of the yth year be Q y,x,t , where y = 1, 2,..., Y, x = 1, 2,..., X, t = 1, 2,..., K x , Y is the total number of years, X is the number of months per year, X = 12, K x is the total number of days corresponding to the xth month;

[0036] Step S62, determine the hydrological frequency of each natural daily runoff by frequency analysis, and then calculate the multi-year average daily runoff hydrological frequency value of each month in the year respectively:

[0037]

[0038] In the above formula, P y,x,t represents the hydrological frequency value of the tth day in the xth month of the yth year; represents the average daily runoff hydrological frequency value of the xth month of the yth year; represents the multi-year average daily runoff hydrological frequency value of the xth month;

[0039] Step S63, let the basic hydrological frequency of the daily runoff of the basin ecological control section in the flood season and non-flood season in the year be P 汛期 and P 非汛期 , respectively, then superimpose the basic hydrological frequency on P and P , respectively, to determine the comprehensive hydrological frequency of the xth month :

[0040] If the xth month belongs to the flood season, then

[0041] If the xth month belongs to the non-flood season, then

[0042] Step S64: On the theoretical daily runoff frequency curve for the year, select a value that matches... The corresponding daily runoff is used as the ecological flow value for day t of month x. This allows for the determination of the annual ecological flow process.

[0043] Furthermore, in step S63, P 汛期 =50%, P 非汛期 =25%.

[0044] Furthermore, the method for obtaining the theoretical frequency curve of daily runoff within the year as described in step S64 is as follows:

[0045] Step S641: The natural daily runoff Q from multiple years... y,x,t Organized into daily natural daily runoff sequences, i.e., the daily runoff sequence for day t of month x.

[0046] Step S642: Plot the theoretical frequency curve of the daily runoff sequence for the first day of January over multiple years: Q in sequence 1,1,1 Q 2,1,1 ,...,Q Y,1,1 The daily runoff values ​​were sorted from largest to smallest, and the P-III type curve was used to fit the daily runoff sequence of the multi-year period to obtain the theoretical frequency curve of daily runoff on the first day of January.

[0047] Step S643, for multi-year periods Repeat steps S641-S642 for the remaining daily runoff sequences to obtain the theoretical daily runoff frequency curve for day t of month x. Summarize and organize the results to obtain the theoretical daily runoff frequency curve for the whole year.

[0048] Compared with the prior art, the present invention has the following beneficial effects:

[0049] The ecological flow process determination method based on runoff variation reconstruction and frequency analysis provided by the application is significantly different from the traditional hydrology method in ecological flow calculation; the traditional hydrology method generally takes multi-year average runoff, monthly runoff or fixed frequency runoff value as the benchmark of ecological flow, which has great subjectivity and empiricism, and cannot accurately reflect the characteristics of river ecological flow change with runoff; the ecological flow process determination method based on runoff variation reconstruction and frequency analysis proposed by the application restores the natural daily runoff process of the river through runoff variation diagnosis and sliding reduction method, can make it retain the historical runoff change characteristics, further reconstructs the natural daily runoff sequence based on the minimum adaptation period of aquatic organisms to runoff change, can reflect the dynamic response demand of key life activities of aquatic organisms to runoff change, and finally selects the daily runoff corresponding to the comprehensive hydrological frequency as the ecological flow through frequency analysis, which can maximize the dynamic water demand of the river ecological system under the hydrological regime change, is in line with ecological reality, and is convenient to implement; compared with the prior art, the ecological flow process determination method based on runoff variation reconstruction and frequency analysis is first proposed by the application and is applied to river ecological flow calculation, which is an important innovation in the technical field, can guarantee the dynamic demand of ecological flow to runoff change, can effectively support the coordinated development goal of sustainable development of water resources and ecological balance under water regime change, and has certain popularization and use value. BRIEF DESCRIPTION OF DRAWINGS

[0050] In order to more clearly illustrate the technical solutions of the embodiments of the present disclosure, the drawings needed to be used in the embodiments will be briefly introduced below, and it should be understood that the following drawings only show some of the embodiments of the present disclosure, and therefore should not be regarded as a limitation on the scope, and other related drawings can also be obtained by those skilled in the art without creative labor on the premise of not paying creative labor.

[0051] Figure 1 The flow chart of the ecological flow process determination method based on runoff variation reconstruction and frequency analysis of the present application.

[0052] Figure 2 The schematic diagram of reconstructing the natural daily runoff process based on the minimum adaptation period in the embodiment of the present application.

[0053] Figure 3 The runoff theoretical frequency curve of January 1 of the Lijiadu Station in multiple years in the embodiment of the present application.

[0054] Figure 4 The comparison chart of the method of the present application and the Tennant method. DETAILED DESCRIPTION

[0055] For the convenience of those skilled in the art to understand and implement the present application, the steps of the method of the present application are described in detail below, and it should be understood that these examples are only used to illustrate the present application and not to limit the scope of the present application. In addition, it should be understood that those skilled in the art can make various modifications or changes to the present application after reading the content taught by the present application, and these equivalent forms also fall within the scope defined by the claims attached to the present application.

[0056] Embodiments

[0057] Please refer to Figure 1 In this embodiment, taking an ecological control section of a sub-basin of Poyang Lake Basin as an example, the method for determining the ecological flow process based on runoff variation reconstruction and frequency analysis provided by the present application is specifically described, which comprises the following steps:

[0058] Step S1, collect the daily runoff observation data of the ecological control section of the sub-basin of Poyang Lake Basin from 1953 to 2018, and identify the potential mutation point in the daily runoff time series by using the hydrological process variation diagnosis method;

[0059] In this embodiment, the sliding t-test method is used to diagnose the potential mutation point in the daily runoff time series, and in other regions or embodiments, other hydrological process variation diagnosis methods or a combination of multiple variation diagnosis methods can also be used for comprehensive analysis. The process of variation diagnosis based on the sliding t-test method is specifically as follows:

[0060] The daily runoff observation data is arranged into an annual runoff time series, and the runoff of the yth year is denoted as Q y (y = 1, 2,..., 66), the distribution functions of the two sequences before and after the sliding point y are G1(Q) and G2(Q), respectively, and two samples with capacities v1 and v2 are extracted from the two distribution functions, and the average values of the two sequences are and The standard deviations are D1 and D2, respectively. The original hypothesis G1(Q) = G2(Q) is tested:

[0061]

[0062] In the above formula, the statistic t follows a distribution with degrees of freedom (v1 + v2 - 2), and for a given significance level a, the critical value t α is obtained by looking up the t distribution table, if |t| > t α , the original hypothesis is rejected, that is, a mutation occurs at the sliding point y, otherwise it is considered that there is no significant difference between the two sequences before and after the sliding point y;

[0063] Through the test, the annual runoff sequence of the basin ecological control section has mutations in 1962, 1984 and 2002, which are significant mutation years.

[0064] Step S2, based on the basic working condition data of the water conservancy project regulation and storage upstream of the selected ecological control section, combined with the change characteristics of historical hydrological and meteorological elements, the potential mutation points identified in step S1 are reviewed and verified, and the mutation points are identified;

[0065] According to the review results, the daily runoff time series is divided into four hydrological variation periods, which are 1953.1.1-1961.12.31, 1962.1.1-1983.12.31, 1984.1.1-2001.12.31 and 2002.1.1-2018.12.31, respectively, which are Period 1, Period 2, Period 3 and Period 4.

[0066] Step S3, select the earliest hydrological variation period least affected by human activities as the natural baseline period, and consider the observed runoff data of the natural baseline period as the natural runoff sequence, and use it to build a meteorological-driven hydrological model to predict the natural daily runoff process of the next hydrological variation period; combined with the sliding reduction principle, along the time sequence sliding forward, the natural daily runoff process of each subsequent hydrological variation period is restored in turn;

[0067] In this embodiment, daily precipitation monitoring data from 1953 to 2018 is collected, and based on runoff data and meteorological element data, a meteorological-driven hydrological model is constructed. In this embodiment, a gated recurrent unit model is selected as the basic hydrological model. Of course, in other embodiments, other data-driven models or physical models can also be selected, and the specific selection is determined by actual applicability. The construction process of the gated recurrent unit model is as follows:

[0068] The hidden state (u t ) and cell state (c t ) in the gated recurrent unit model are combined into a state information u t (c t ), and two control gates are update gate (z t ) and reset gate (r t ), wherein: z t is used to control the degree of bringing u t-1 (c t-1 ) of the previous time step t-1 into the current time step t, the greater the value of z t , the more state information of the previous time step is written; r t is used to control the degree of writing the state information of the previous time step into the current candidate set , the smaller the value of r t , the less state information of the previous time step is written.

[0069] In the structure of the gated recurrent unit, the calculation mode of the update equation is specifically:

[0070] z t =σ(W xz x t +W hz u t-1 +b z )

[0071] r t =σ(W xr x t +W hr u t-1 +b r )

[0072]

[0073]

[0074] u t =c t

[0075] In the above formula, σ is a sigmoid activation function, W xz and W hz , W xr and W xr , W xc and W hc are weight matrices of update gate, reset gate and candidate set respectively, b z , b r and b c are bias vectors of update gate, reset gate and candidate set respectively.

[0076] Based on the constructed meteorological driving hydrological model, combined with the sliding reduction principle, along the time sequence sliding forward, the natural daily runoff process of each hydrological variation period is recovered in turn, as shown in Figure 2 , the specific process is:

[0077] Step S31, according to the hydrological variation period divided in step S2, the daily runoff time series Q i and daily meteorological element time series C i of the ecological control section of the basin in multiple years are arranged into daily runoff sequence and daily meteorological element sequence of each period, where n=1, 2,..., N, j=1, 2,..., m n , N is the total number of hydrological variation periods divided by daily runoff time series; m n is the number of daily runoff data in the nth hydrological variation period;

[0078] Step S32, selecting the hydrological variation period Period 1 affected least by human activities and earliest as the natural reference period, taking Q 1 as the natural daily runoff sequence and taking Q 1 as the daily meteorological element sequence considering the maximum lag time of 60 days in the same period performing Pearson correlation analysis, where d = 1, 2,..., 60, and (T-d) represents d days ago;

[0079] Step S33, in the hydrological variation period Period 1, selecting the top 10 meteorological factors in terms of absolute value of correlation coefficient as input variables, taking Q 1 as the target variable, constructing a first meteorological-driven hydrological model, and optimizing parameters of the first meteorological-driven hydrological model;

[0080] Step S34, in the hydrological variation period Period 2, selecting the top 10 meteorological factors in terms of absolute value of correlation coefficient as prediction factors, predicting the daily runoff process of Period 2 by using the first meteorological-driven hydrological model, and taking the prediction result as the natural daily runoff sequence of the second hydrological variation period

[0081]

[0082] Step S35, combining the sliding reduction principle, sliding one hydrological variation period forward along the daily runoff time sequence, constructing a second meteorological-driven hydrological model by using Q 2 and in Period 2, and predicting the natural daily runoff sequence of the third hydrological variation period according to the meteorological factors in the hydrological variation period Period 3 and so on, to restore the natural daily runoff sequence of each subsequent hydrological variation period

[0083] Step S4, the main fish species of the selected ecological control section of the basin is blue carp, grass carp, silver carp and bighead carp, among which the blue carp has the most ecological and economic value, and the key life habits such as spawning quantity, migration distance and foraging quantity of the blue carp are further investigated; combining a biological hydrological response model, the correlation between the reproductive activity of the blue carp and the runoff change is analyzed to determine the minimum adaptation period of the blue carp to the runoff change;

[0084] The step S4 includes the following steps:

[0085] Step S41, in the present embodiment, the spawning quantity of the blue carp is selected as the representative life activity quantitative index, and of course in other regions or embodiments, other key life activity indexes of other aquatic organisms can also be selected as the representative quantitative index, and the specific index selection should be determined according to the actual situation;

[0086] Step S42, the adaptation period of the breeding activity of the blue fish to the runoff change is S days, where S = 1, 2,..., 30, the average value of the egg production amount of all consecutive S days in a year is calculated, and the average value is regarded as the value of the first day of the corresponding period to form a time series where k = 365-S+1;

[0087] Step S43, the average value of the natural daily runoff of all consecutive S days in a year is calculated, and the average value is regarded as the daily runoff of the first day of the corresponding period to reconstruct a new natural daily runoff time series

[0088] Step S44, an ecological hydrological response model is constructed to maximize the correlation and minimize S, which is expressed as: where, is the correlation coefficient between and

[0089] Step S45, the obtained ecological hydrological response model is solved by using the traversal method to obtain the minimum adaptation period S of the blue fish to the runoff change min .

[0090] Step S5, taking the minimum adaptation period as the standard for quantifying continuous runoff change, the average value of the natural daily runoff in each period in the restored multi-year natural daily runoff time series Q (天然) =(Q 1(天然) ,Q 2(天然) ,...,Q n(天然) ,...,Q N(天然) ) is calculated, and the average value is regarded as the daily runoff of the first day of the corresponding period, and then a new natural daily runoff time series is reconstructed, which is specifically:

[0091]

[0092]

[0093]

[0094] In the above formula, i = 1, 2,..., m, n = 1, 2,..., N, j = 1, 2,..., m n , h = 1, 2,..., m-S min +1; Q (天然) represents the multi-year natural daily runoff time series of the ecological control section of the basin after restoration in step S3; m is the total number of natural daily runoff data in the sequence Q (天然) ; N is the total number of hydrological variation periods into which the daily runoff sequence is divided; m n ​​the number of natural daily runoff data in the nth hydrological variation period; represents the newly formed hth daily natural runoff after reconstruction; S min is the minimum adaptation period determined in step S4; represents the newly formed multi-year daily natural runoff sequence after reconstruction.

[0095] Step S6, calculate the daily runoff hydrological frequency in the new natural daily runoff time series and the monthly average hydrological frequency in the year by frequency analysis; divide the flood season and the non-flood season according to the runoff distribution characteristics in the year, determine the monthly comprehensive hydrological frequency, draw the daily runoff frequency curve in the year, select the daily runoff matching the monthly comprehensive hydrological frequency as the ecological flow, and determine the daily ecological flow process in the year;

[0096] Step S61, arrange the multi-year natural daily runoff data of the reconstructed ecological control section of the basin in step S5 Let the natural daily runoff of the xth month of the yth year on the tth day be Q y,x,t , where y = 1, 2,..., Y, x = 1, 2,..., X, and t = 1, 2,..., K x , Y is the total number of years, X is the number of months per year, X = 12, and K x is the total number of days corresponding to the xth month;

[0097] Step S62, calculate the hydrological frequency of the natural daily runoff in the new sequence and the average daily runoff hydrological frequency in each month of the year by frequency analysis; specifically:

[0098]

[0099] In the above formula, P y,x,t represents the hydrological frequency value of the natural daily runoff of the xth month of the yth year on the tth day; represents the average daily runoff hydrological frequency value of the xth month of the yth year; represents the multi-year average daily runoff hydrological frequency value of the xth month;

[0100] Step S63, divide the flood season as March to July and the non-flood season as August to the following February according to the runoff distribution characteristics in the year; in this embodiment, considering that the runoff in the flood season is large and the ecological demand is high, the frequency value 50% that distinguishes the wet and dry hydrological events is selected as the basic hydrological frequency of the flood season, that is, P 汛期 = 50%, while the runoff in the non-flood season is low, but the ecological demand guarantee degree is still high for the selected ecological control section of the basin, so the minimum frequency value 25% of the wet event in the non-flood season is selected as the basic hydrological frequency of the non-flood season, that is, P 非汛期=25%, of course, other frequency values ​​can be set in other regions or embodiments. In actual selection, the historical hydrological conditions and ecological protection goals of the selected river should be taken into account. Based on this, the comprehensive hydrological frequency for each month of the year is determined as follows:

[0101] The multi-year average daily runoff hydrological frequency value of the watershed ecological control section for month x is... By superimposing the corresponding basic hydrological frequency, the comprehensive hydrological frequency for month x can be determined. :

[0102] If month x falls within the flood season, then

[0103] If month x is outside the flood season, then

[0104] Step S64: On the theoretical daily runoff frequency curve obtained within the year, select the... The corresponding daily runoff is used as the ecological flow value for day t of month x. This allows for the determination of the annual ecological flow process.

[0105] The method for obtaining the theoretical frequency curve of daily runoff within the year is as follows:

[0106] Step S641: The natural daily runoff Q from multiple years... y,x,t Organized into daily natural daily runoff sequences, i.e., the daily runoff sequence for day t of month x.

[0107] Step S642: Plot the theoretical frequency curve of the daily runoff sequence for the first day of January over multiple years: Q in sequence 1,1,1 Q 2,1,1 ,...,Q Y,1,1 The daily runoff values ​​were sorted from largest to smallest, and the multi-year daily runoff series was fitted using P-III type curves, such as... Figure 3 As shown, the theoretical frequency curve of daily runoff on the first day of January is obtained;

[0108] Step S643, for multi-year periods Repeat steps S641-S642 for the remaining daily runoff sequences to obtain the theoretical daily runoff frequency curve for day t of month x. Summarize and organize the results to obtain the theoretical daily runoff frequency curve for the whole year.

[0109] In this embodiment, to verify the rationality of the annual ecological flow process constructed by the method of the present invention, the results are compared with those obtained by the Tennant method, such as... Figure 4As shown, the method of the embodiment calculates that the daily average ecological flow of the river in the flood season from March to July accounts for 42.00% of the daily average runoff in many years, reaches the "good" range level of the Tennant method, and in June when the runoff reaches the peak, the river ecosystem activity is reduced due to the influence of flood, and the ecological flow accounts for a corresponding decrease; the daily average ecological flow of the river in the non-flood season from September to the next February accounts for 24.23% of the daily average runoff in many years, also reaches the "good" range level of the Tennant method, and when the runoff is at a lower level, the river ecosystem itself adjusts the activity to be enhanced, and the ecological flow accounts for a slight increase.

[0110] As can be seen from the above, the ecological flow process constructed by the method can reach a good flow level in the flood season and the non-flood season, and can provide a good survival condition for the river ecosystem. At the same time, the method considers the dynamic demand of the river ecosystem for runoff change, can maximize the adaptive adjustment of the river hydrological regime change, and is not like some hydrology methods represented by the Tennant method to set a subjective and empirical fixed ecological flow ratio. In comparison, the present application first proposes an ecological flow process determination method based on runoff variation reconstruction and frequency analysis, and applies it to the calculation of river ecological flow, which is an important innovation in the technical field, can guarantee the dynamic demand of ecological flow for runoff change, and can effectively support the coordinated development goal of sustainable development of water resources and ecological balance under the change of water regime, and has certain popularization and use value.

[0111] The above is only a preferred embodiment of the present application, and is not intended to limit the present application in other forms. Any person skilled in the art can modify or change the above disclosed technical content to equivalent embodiments. However, any simple modification, equivalent change and modification made according to the technical essence of the present application without departing from the technical solution content of the present application still belongs to the protection scope of the present application.

Claims

1. A method for determining ecological flow process based on runoff variation reconstruction and frequency analysis, characterized in that, The method comprises the following steps: Step S1, collecting daily runoff observation data of a long sequence of historical runoff of an ecological control section of a river basin, and identifying potential variation points in the daily runoff time series by using a hydrological process variation diagnosis method; Step S2, based on the basic operation data of the upstream water conservancy project regulation and storage of the selected ecological control section, combined with the variation characteristics of historical hydrological and meteorological elements, the potential variation points identified in step S1 are reviewed and verified, and according to the review result, the daily runoff time series is divided into several hydrological variation periods; Step S3, selecting the earliest hydrological variation period least affected by human activities as the natural baseline period, regarding the observed runoff data of the natural baseline period as the natural daily runoff time series, and using the meteorological-driven hydrological model to predict the natural daily runoff process of the next hydrological variation period; combined with the sliding reduction principle, the natural daily runoff process of each subsequent hydrological variation period is restored in turn along the daily runoff time series; The step S3 comprises the following steps: Step S31, divide the daily runoff time series Q of the catchment ecological control section in step S2 for multiple years into N hydrological variation periods, i.e. Period 1, Period 2,..., Period N, and then arrange the daily runoff sequence of each period and the daily meteorological element sequence wherein n = 1, 2,..., N, and j = 1, 2,..., m n N is the total number of hydrological variation periods into which the daily runoff time series is divided; m n is the number of daily runoff data in the nth hydrological variation period; Step S32, select the hydrological variation period Period 1 affected least by human activities and earliest as the natural reference period, and take Q 1 as the natural daily runoff sequence and the daily meteorological element sequence of the maximum lag time 60 days in the same period 1 Pearson correlation analysis is performed, where d = 1, 2,..., 60, and (T-d) represents d days ago;​ Step S33, in the hydrological variation period Period 1, the top 10 meteorological factors with the largest absolute value of correlation coefficient are selected as input variables to Q 1 a first meteorological-driven hydrological model is constructed, and parameters of the first meteorological-driven hydrological model are optimized; Step S34, in the hydrological variation period Period 2, the top 10 meteorological factors with the largest absolute values of correlation coefficients are selected as the prediction factors, the daily runoff process of Period 2 is predicted by using the first meteorological-driven hydrological model, and the prediction result is regarded as the natural daily runoff sequence of the second hydrological variation period Step S35, combined with the sliding reduction principle, along the daily runoff time series forward sliding a hydrological variation period, using the Q 2 and Construct the second meteorological driving hydrological model, and then predict the natural daily runoff sequence of the third hydrological variation period according to the meteorological factors in the hydrological variation period Period 3 In turn, restore the natural daily runoff sequence of the subsequent hydrological variation period Step S4, investigating the ecological habits of the main fish species of the ecological control section of the river basin, analyzing the correlation between the key life activities of the main fish including reproduction, migration, foraging and runoff change by using the biohydrological response model, and determining the minimum adaptation period of the main fish to the runoff change; The step S4 comprises the following steps: Step S41, according to the ecological habits of the main fish of the ecological control section of the river basin, selecting one or more life activity indicators including spawning amount, migration distance and foraging amount as representative quantitative indicators; Step S42, the adaptation period of the representative life activities of the main fish species to the runoff change is S days, wherein S = 1, 2,..., 30, the average value of the representative quantitative indicators of all consecutive S days in a year is calculated, and the average value is regarded as the value of the first day of the corresponding period to form a time series wherein k = 365-S+1; Step S43, calculate the average of all continuous S-day natural daily runoff in the year, and take it as the daily runoff of the first day of the corresponding period, and reconstruct the natural daily runoff time series based on the adaptation period S Step S44, constructing an eco-hydrological response model to with the largest correlation and the smallest S as the target, expressed as: wherein, represents the correlation coefficient between and Step S45, the ecological hydrological response model is solved by using the traversal method to obtain the minimum adaptation period S of the main fish to the runoff change min ; Step S5, taking the minimum adaptation period as the standard for quantifying the change of continuous runoff, the average value of natural daily runoff in each period of the restored multi-year natural daily runoff time series Q (天然) 1(天然) 2(天然) n(天然) N(天然) is calculated, which is regarded as the daily runoff of the first day of the corresponding period, and then a new set of natural daily runoff time series is reconstructed.​​​​ Step S6, calculating the daily runoff hydrological frequency in the new natural daily runoff time series and the monthly average hydrological frequency in a year by frequency analysis; according to the runoff distribution characteristics in a year, dividing the flood season and the non-flood season, determining the monthly comprehensive hydrological frequency in a year; drawing the daily runoff frequency curve in a year, selecting the daily runoff that matches the monthly comprehensive hydrological frequency as the ecological flow, and determining the daily ecological flow process in a year.

2. The method according to claim 1, wherein, In step S5, the reconstruction forms a new set of natural daily runoff time series, and the process is as follows: In the formula, i = 1, 2, …, m, n = 1, 2, …, N, j = 1, 2, …, m n , h = 1, 2, …, m-S min + 1; Q (天然) represents the multi-year natural daily runoff time series of the watershed ecological control section after recovery in step S3; m is the total number of natural daily runoff data in sequence Q (天然) ; N is the total number of hydrological variation periods into which the daily runoff sequence is divided; m n is the number of natural daily runoff data in the nth hydrological variation period; represents the newly formed hth day natural runoff after reconstruction; S min is the minimum adaptation period determined in step S4; represents the multi-year natural daily runoff sequence newly formed after reconstruction.

3. The method according to claim 1, wherein, In step S6, the determination of the daily ecological flow process in a year comprises the following steps: Step S61, collate the reconstructed flow ecological control section multi-year natural daily runoff data in step S5 Let the natural daily runoff of the xth month of the yth year on the tth day be Q y,x,t , wherein y = 1, 2, …, Y, x = 1, 2, …, X, t = 1, 2, …, K x , Y is the total number of years, X is the number of months per year, X = 12, K x is the total number of days corresponding to the xth month; Step S62, determining the hydrological frequency of each natural daily runoff by frequency analysis, and then calculating the multi-year average daily runoff hydrological frequency value of each month in a year: In the above formula, P y,x,t represents the hydrological frequency value of natural daily runoff on the tth day of the xth month of the yth year; represents the average daily runoff hydrological frequency value of the xth month of the yth year; represents the multi-year average daily runoff hydrological frequency value of the xth month; Step S63, set the basic hydrological frequency of the daily runoff of the flood season and the non-flood season of the ecological control section of the river basin in a year as P 汛期 and P 非汛期 respectively, then superimpose the basic hydrological frequency respectively with to determine the comprehensive hydrological frequency of the xth month If the xth month belongs to the flood season, then If the xth month belongs to the non-flood season, then Step S64, on the daily runoff theoretical frequency curve in the year, select the daily runoff matching the ecological flow value of the xth month and the tth day Further determine the ecological flow process in the year.​ 4. The method according to claim 1, wherein, In step S1, the collection of the daily runoff observation data of a long sequence of historical runoff of an ecological control section of a river basin, the observation data collected for more than 20 years.

5. The method according to claim 1, wherein, In step S2, the basic operation data of the upstream water conservancy project regulation and storage includes construction time, location, scale and regulation operation data.

6. The method according to claim 1, wherein, In step S31, the daily meteorological element sequence should match the daily runoff sequence, and the daily meteorological element includes precipitation.

7. The method according to claim 3, wherein, In step S63, P 汛期 = 50%, P 非汛期 = 25%.

8. The method according to claim 3, wherein, In step S64, the method for obtaining the daily runoff theoretical frequency curve in a year is as follows: Step S641, the multi-year natural daily runoff Q y,x,t arranging into a daily natural daily runoff sequence, i.e. a daily runoff sequence of the xth month and the tth day Step S642, draw the theoretical frequency curve of the multi-year January 1st daily runoff sequence: take Q 1,1,1 Q 2,1,1 Q Y,1,1 Sort the daily runoff values from large to small, and use the P-III curve to fit the multi-year daily runoff sequence to obtain the January 1st daily runoff theoretical frequency curve; Step S643, for multi-year periods Repeat steps S641-S642 for the remaining daily runoff sequences to obtain the theoretical daily runoff frequency curve for day t of month x. Summarize and organize the results to obtain the theoretical daily runoff frequency curve for the whole year.

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