Ecological flow process determination method based on runoff variation reconstruction and frequency analysis

Abstract

The invention discloses an ecological flow process determination method based on runoff variation reconstruction and frequency analysis, and the method comprises the steps: 1) collecting long-sequence daily runoff observation data of an ecological control section of a drainage basin, and recognizing potential hydrological variation points; 2) dividing the runoff sequence into a plurality of hydrological variation periods; 3) sequentially recovering the observed runoff of each hydrological period by using the hydrological model to obtain a natural daily runoff process; 4) determining the minimum adaptation period of the fish to runoff change; 5) using the average value of the natural runoff in each period as a new daily runoff volume, and reconstructing a natural daily runoff time sequence; and 6) based on the annual day-by-day runoff hydrological frequency curve, the runoff volume matched with the frequency is selected as the ecological flow volume, and an annual day ecological flow volume process is constructed. The calculation result of the method not only can ensure the dynamic demand of ecological flow on runoff change, but also can effectively support the coordinated development goal of sustainable development requirements of water resources and ecological balance under water regimen change, and has very high popularization and use values.

Description

Technical Field

[0001] The present invention belongs to the technical field of hydrological prediction and hydrological ecological flow formulation, and specifically relates to a method for determining an ecological flow process based on runoff variation reconstruction and frequency analysis. Background Art

[0002] In the context of rapid economic development, the construction and operation of water conservancy projects have intensified the intensity of human activities in the development and utilization of river water resources, but the basic needs of river ecosystems for water resources are often ignored, resulting in signs of degradation in their health. In order to balance water resource development and ecological protection, while ensuring that economic and social water needs are met, the amount of water required by river ecosystems to maintain normal ecological structure and functions, namely ecological flow, should also be met, so as to promote the coordinated development of sustainable use of water resources and ecological balance.

[0003] At present, there are more than 200 ecological flow calculation methods at home and abroad, which can be divided into hydrological method, hydraulic method, habitat simulation method and holistic method. Among them, the hydrological method has been widely used worldwide because of its easy data acquisition and simple and convenient calculation. At the same time, with the deepening of ecological flow research, the hydrological method is also continuously improving and enriching, and constantly adapting to new research needs. However, under the dual influence of climate change and human activities, the river hydrological situation is undergoing unprecedented complex changes, which seriously disrupts the normal life rhythm of aquatic organisms. In this complex hydrological environment, the demand of aquatic communities for river habitats has become more diversified and refined, no longer limited to simple water supply, but more concerned with the characteristics of flow and the continuity of its dynamic process. However, the existing hydrological method generally uses a fixed ratio to set a fixed ecological flow value, which cannot truly reflect the dynamic demand of river ecosystems for runoff changes. Therefore, it is necessary to develop an ecological flow calculation method that can take into account the dynamic water demand stability of river ecosystems under changing hydrological conditions. Summary of the invention

[0004] The purpose of the present invention is to address the deficiencies in the prior art and provide a method for determining the ecological flow process based on runoff variation reconstruction and frequency analysis. This method can not only accurately reflect and evaluate the annual dynamic process of ecological flow, but also ensure the dynamic demand of aquatic organisms for runoff changes, thereby improving the accuracy of ecological flow calculation and its practical guiding value.

[0005] In order to achieve the above technical objectives, the present invention adopts the following technical solutions.

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

[0007] Step S1, collecting the daily runoff observation data of the long historical sequence of the ecological control section of the watershed, and using the hydrological process variation diagnosis method to identify the potential variation points in the runoff time series;

[0008] Step S2: Based on the basic engineering data of the upstream water conservancy project of the selected ecological control section and the change characteristics of historical hydrological and meteorological elements, the potential variation points identified in step S1 are verified; and according to the verification results, the runoff time series is divided into several hydrological variation periods;

[0009] Step S3, select the earliest hydrological period that is least affected by human activities as the natural reference period, regard its observed runoff data as the natural runoff sequence, and construct a meteorological-driven hydrological model to predict the natural daily runoff process of the next hydrological period; combine the sliding restoration principle, slide forward along the time series, and restore the natural daily runoff process of subsequent hydrological periods in turn;

[0010] Step S4, investigating the ecological habits of the main fish species in the ecological control section of the watershed, analyzing the correlation between the key life activities of the main fish, including reproduction, migration, and foraging, and runoff changes in combination with the biohydrological response model, and determining the minimum adaptation period of the main fish to runoff changes;

[0011] Step S5, taking the minimum adaptation period as the standard for quantifying the continuous runoff change, respectively calculating the average value of the natural daily runoff in each period in the entire sequence, and treating it as the daily runoff on the first day of the corresponding period, and then reconstructing a set of new natural daily runoff time series;

[0012] Step S6, calculate the daily runoff hydrological frequency in the new sequence and the average hydrological frequency of each month in the year through frequency analysis; divide the flood season and non-flood season according to the runoff distribution characteristics of the year, and determine the comprehensive hydrological frequency of each month in the year; draw the daily runoff frequency curve of the year, select the daily runoff that matches the monthly comprehensive hydrological frequency as the ecological flow, and determine the daily ecological flow process of the year.

[0013] Specifically, the step S1 is to collect a long-term historical sequence of daily runoff observation data of the watershed ecological control section, and the period of collecting the observation data is no less than 20 years.

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

[0015] Specifically, in step S3, the process of restoring the natural daily runoff process in each subsequent hydrological period includes the following steps:

[0016] Step S31: Assume that the daily runoff time series Q of the ecological control section of the watershed in multiple years in step S2 is iDivide into N hydrological variation periods, namely Period 1, Period 2, …, Period N, and sort out the daily runoff series of each period Daily meteorological element sequence where i = 1, 2, ..., m, n = 1, 2, ..., N, j = 1, 2, ..., m n , m is the total number of daily runoff data, m n is the number of daily runoff data in the nth hydrological period;

[0017] Step S32: Select the earliest hydrological variation period, Period 1, which is least affected by human activities, as the natural baseline period. Considered as a natural daily runoff series And compare it with the daily meteorological element series with the maximum lag time of 60 days in the same period Pearson correlation analysis was performed, where d = 1, 2, ..., 60, and (td) represents the meteorological element value d days ago;

[0018] Step S33: In the hydrological variation period Period 1, the top 10 meteorological factors with the absolute value of correlation coefficient are selected as input variables. As the target variable, the first meteorological-driven hydrological model was constructed and its parameters were optimized;

[0019] Step S34: In the hydrological variation period Period 2, the top 10 meteorological factors with the highest absolute value of correlation coefficient are selected as prediction factors, and the daily runoff process of Period 2 is predicted using the first meteorological-driven hydrological model. The prediction results are regarded as the natural daily runoff sequence of this period.

[0020] Step S35: Combine the sliding restoration principle and slide forward one hydrological period along the time series, that is, use the and The second meteorological-driven hydrological model was constructed, and then its natural daily runoff sequence was predicted based on the meteorological factors in the hydrological variation period Period 3. By analogy, the natural daily runoff process of subsequent hydrological periods is restored.

[0021] Furthermore, the daily meteorological element sequence sorted in step S31 should match the daily runoff sequence, and the daily meteorological element must include precipitation.

[0022] Specifically, in step S4, determining the minimum adaptation period of the main fish species to the runoff change includes the following steps:

[0023] Step S41, according to the ecological habits of the main fish species in the ecological control section of the watershed, one or more life activity indicators including spawning amount, migration distance, and foraging amount are selected as representative quantitative indicators;

[0024] Step S42: Assume that the adaptation period of the representative life activities of the main fish species to the runoff change is S days, where S = 1, 2, ..., 30, calculate the average value of the representative quantitative indexes for all S consecutive days in a year, and regard it as the value of the first day of the corresponding period to form a time series Where k = 365 - S + 1;

[0025] Step S43: Calculate the average of all the natural daily runoffs for S consecutive days in a year, and regard it as the daily runoff on the first day of the corresponding period, and reconstruct a new natural daily runoff time series.

[0026] Step S44: construct an eco-hydrological response model. and The goal is to maximize the correlation and minimize S, which can be expressed as: in, express and The correlation coefficient between

[0027] Step S45: Use the traversal method to solve the obtained eco-hydrological response model to obtain the minimum adaptation period S of the main fish to the runoff change. min .

[0028] Specifically, in step S5, the reconstruction forms a new set of natural daily runoff time series, and the process is as follows:

[0029]

[0030] In the above formula, i = 1, 2, ..., m, n = 1, 2, ..., N, j = 1, 2, ..., m n ,h=1,2,...,mS min +1; represents the multi-year natural daily runoff time series of the ecological control section of the watershed after restoration in step S3; m is the total number of natural daily runoff data in the sequence; N is the number of hydrological periods into which the daily runoff sequence is divided; m n is the number of natural daily runoff data in the nth hydrological period; represents the natural runoff on day h newly formed after reconstruction; S min is the minimum adaptation period determined in step S4; Represents the newly formed multi-year natural daily runoff series after reconstruction.

[0031] Specifically, in step S6, the process of determining the daily ecological flow in a year includes the following steps:

[0032] Step S61: Arrange the natural daily runoff data of the watershed ecological control section reconstructed in step S5 for multiple years Assume that the daily runoff on the tth day of the xth month of the yth year is 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 in each year, X = 12, K x is the total number of days corresponding to the xth month;

[0033] Step S62: Determine the hydrological frequency of each daily runoff through frequency analysis, and then calculate the multi-year average daily runoff hydrological frequency value for each month of the year:

[0034]

[0035] In the above formula, P y,x,t It represents the hydrological frequency value of runoff on the tth day of the xth month of the yth year; It represents the average daily runoff hydrological frequency value of the xth month of the yth year; It represents the multi-year average daily runoff hydrological frequency value of the xth month;

[0036] Step S63: Assume that the basic hydrological frequencies of daily runoff in the flood season and non-flood season of the watershed ecological control section are P 汛期 and P 非汛期 , then compare it with Superimpose to determine the comprehensive hydrological frequency of the xth month

[0037] If month x is a flood season, then

[0038] If month x is a non-flood season, then

[0039] Step S64: select the frequency curve of daily runoff theory in the year The matched daily runoff is taken as the ecological flow value on the tth day of the xth month Then determine the ecological flow process within the year.

[0040] Furthermore, in step S63, the basic hydrological frequencies of daily runoff in the flood season and non-flood season of the watershed ecological control section are P and 汛期 and P 非汛期 , P 汛期 =50%, P 非汛期 =25%.

[0041] Furthermore, the method for obtaining the theoretical frequency curve of daily runoff in a year in step S64 is as follows:

[0042] Step S641: The natural daily runoff Q of multiple years is y,x,t Arranged into a daily natural runoff sequence, that is, the daily runoff sequence on the tth day of the xth month

[0043] Step S642: Draw the theoretical frequency curve of the daily runoff sequence on the first day of January in multiple years: Q in sequence 1,1,1 ,Q 2,1,1 ,...,Q Y,1,1 The daily runoff values ​​were sorted from large to small, and the P-Ⅲ curve was used to fit the daily runoff series of multiple years to obtain the theoretical frequency curve of daily runoff on the first day of January.

[0044] Step S643: The remaining daily runoff sequences in the sequence repeat steps S641-S642 to obtain the daily runoff theoretical frequency curve on the tth day of the xth month, and the daily runoff theoretical frequency curve for the year is obtained by summarizing and collating.

[0045] Compared with the prior art, the present invention has the following beneficial effects:

[0046] The method for determining an ecological flow process based on runoff variation reconstruction and frequency analysis provided by the present invention is significantly different from traditional hydrological methods in ecological flow calculation; traditional hydrological methods generally use multi-year average runoff, monthly runoff or fixed-frequency runoff values ​​as the benchmark for ecological flow, which is not only highly subjective and empirical, but also unable to accurately reflect the characteristics of river ecological flow changing with runoff; the method for determining an ecological flow process based on runoff variation reconstruction and frequency analysis proposed by the present invention restores the natural daily runoff process of the river through runoff variation diagnosis and sliding restoration methods, so that it can fully retain the historical runoff variation characteristics, and at the same time further reconstructs the natural daily runoff sequence based on the minimum adaptation period of aquatic organisms to runoff changes. , which can reflect the dynamic response needs of key life activities of aquatic organisms to runoff changes. Finally, through frequency analysis, the daily runoff corresponding to the comprehensive hydrological frequency is scientifically selected as the ecological flow, which can maximize the dynamic water demand of the river ecosystem under changing hydrological conditions, which is both in line with ecological reality and easy to implement. Compared with the existing technology, the present invention proposes for the first time 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 this technical field. The calculation results can not only guarantee the dynamic needs of ecological flow for runoff changes, but also effectively support the coordinated development goals of sustainable development requirements of water resources and ecological balance under water conditions changes, and have certain promotion and use value. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] In order to more clearly illustrate the technical solutions of the embodiments of the present disclosure, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present disclosure and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying creative work.

[0048] Figure 1 The present invention is a flow chart of the method for determining the ecological flow process based on runoff variation reconstruction and frequency analysis.

[0049] Figure 2 It is a schematic diagram of reconstructing the natural daily runoff process based on the minimum adaptation period in an embodiment of the present invention.

[0050] Figure 3 1 is the theoretical frequency curve of runoff on January 1 of Lijiadu Station in many years in the embodiment of the present invention.

[0051] Figure 4 It is a comparison diagram between the method of the present invention and the Tennant method. DETAILED DESCRIPTION

[0052] In order to facilitate those of ordinary skill in the art to understand and implement the present invention, the following detailed description is given to each step of the method proposed by the present invention, and it should be understood that these embodiments are only used to illustrate the present invention and are not used to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of the present application.

[0053] Example

[0054] See also Figure 1 In this embodiment, taking a sub-basin ecological control section of the 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 invention is specifically described, including the following steps:

[0055] Step S1, collecting daily runoff observation data from 1953 to 2018 for a sub-basin ecological control section of the Poyang Lake Basin, and using a hydrological process variation diagnosis method to identify potential variation points in the runoff time series;

[0056] In this embodiment, the sliding t-test method is used to diagnose potential variation points of the runoff time series. In other regions or embodiments, other hydrological process variation diagnosis methods can be selected or multiple variation diagnosis methods can be combined for comprehensive analysis. The process of variation diagnosis based on the sliding t-test method is specifically as follows:

[0057] The daily runoff observation data is organized into an annual runoff time series, and the runoff volume in the yth year is represented by 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), two samples with capacity 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 that G1(Q)=G2(Q) is tested:

[0058]

[0059] In the above formula, the statistic t follows a distribution with degrees of freedom of (v1+v2-2). For a given significance level α, the critical value t is obtained by looking up the t distribution table. α , if |t|>t α , reject the original hypothesis, that is, a mutation occurs at the sliding point y, otherwise it is believed that there is no significant difference between the two sequences before and after the sliding point y;

[0060] After inspection, it was found that the annual runoff sequence of the ecological control section of the basin mutated in 1962, 1984 and 2002, which were years of significant mutation.

[0061] Step S2: Based on the basic engineering data of the upstream water conservancy project of the selected ecological control section and the change characteristics of historical hydrological and meteorological elements, the potential variation points identified in step S1 are reviewed and verified to identify the variation points;

[0062] According to the review results, the runoff time series is divided into four hydrological variation periods, namely, January 1, 1953 to December 31, 1961, January 1, 1962 to December 31, 1983, January 1, 1984 to December 31, 2001, and January 1, 2002 to December 31, 2018, denoted as Period 1, Period 2, Period 3, and Period 4, respectively.

[0063] Step S3, select the earliest hydrological period that is least affected by human activities as the natural reference period, regard its observed runoff data as the natural runoff sequence, and construct a meteorological-driven hydrological model to predict the natural daily runoff process of the next hydrological period; combine the sliding restoration principle, slide forward along the time series, and restore the natural daily runoff process of subsequent hydrological periods in turn;

[0064] In this embodiment, daily precipitation monitoring data from 1953 to 2018 are collected, and a meteorological-driven hydrological model is constructed based on runoff data and meteorological element data. In this embodiment, a gated circulation 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. The specific selection depends on the actual applicability. The construction process of the gated circulation unit model is as follows:

[0065] Suppose the hidden state (u t ) and cell status (c t ) are merged into a state information u t (c t ), the two control gates are update gate (z t ) and reset gate (r t ), where: z t Used to control the u of the previous time step t-1 t-1 (c t-1 ) into the current time step t, z t The larger the value of , the more state information of the previous time step is written; t Used to control the state information of the previous time step to be written into the current candidate set The degree of t The smaller the value of , the less state information from the previous time step is written.

[0066] In the structure of the gated recurrent unit, the update equation is calculated as follows:

[0067] z t =σ(W xz x t +W hz u t-1 +b z )

[0068] r t =σ(W xr x t +W hr u t-1 +b r )

[0069]

[0070] u t =c t

[0071] In the above formula, σ is the sigmoid activation function, W xz and W hz , W xr and W xr , Wxc and W hc are the weight matrices of the update gate, reset gate and candidate set, respectively, and b z 、b r and b c They are the update gate, reset gate and bias vector of the candidate set respectively.

[0072] Based on the constructed meteorological driven hydrological model and the sliding restoration principle, the natural daily runoff process of each hydrological period is restored in sequence by sliding forward along the time series, such as Figure 2 As shown, the specific process is:

[0073] Step S31: According to the hydrological variation period divided in step S2, the daily runoff time series Q of the ecological control section of the watershed for multiple years are converted into i and daily meteorological element time series C i , sorted into daily runoff series for each period Daily meteorological element sequence where i = 1, 2, ..., m, n = 1, 2, ..., N, j = 1, 2, ..., m n , m is the total number of daily runoff data, m n is the number of daily runoff data in the nth hydrological period;

[0074] Step S32: Select the earliest hydrological variation period, Period 1, which is least affected by human activities, as the natural baseline period. Considered as a natural daily runoff series And compare it with the daily meteorological element series with the maximum lag time of 60 days in the same period Pearson correlation analysis was performed, where d = 1, 2, ..., 60, and (td) represents the meteorological element value d days ago;

[0075] Step S33: In the hydrological variation period Period 1, the top 10 meteorological factors with the absolute value of correlation coefficient are selected as input variables. As the target variable, the first meteorological-driven hydrological model was constructed and its parameters were optimized;

[0076] Step S34: In the hydrological variation period Period 2, the top 10 meteorological factors with the highest absolute value of correlation coefficient are selected as prediction factors, and the daily runoff process of Period 2 is predicted using the first meteorological-driven hydrological model. The prediction results are regarded as the natural daily runoff sequence of this period.

[0077] Step S35: Combine the sliding restoration principle and slide forward one hydrological period along the time series, that is, use the and The second meteorological-driven hydrological model was constructed, and then its natural daily runoff sequence was predicted based on the meteorological factors in the hydrological variation period Period 3. By analogy, the natural daily runoff process of subsequent hydrological periods is restored.

[0078] Step S4, the main fish species in the selected watershed ecological control section are black carp, grass carp, silver carp and bighead carp, among which black carp has the greatest ecological and economic value, and then the key life habits of black carp such as spawning amount, migration distance and foraging amount are investigated; combined with the biohydrological response model, the correlation between the reproductive activity of black carp and runoff changes is analyzed to determine the minimum adaptation period of black carp to runoff changes;

[0079] Step S41, in this embodiment, the spawning amount of black carp is selected as the representative life activity quantitative index. Of course, in other regions or embodiments, other key life activity indicators of other aquatic organisms can also be selected as representative quantitative indicators. The selection of specific indicators should be determined according to actual conditions;

[0080] Step S42: Assume that the adaptation period of the black carp's reproductive activity to the runoff change is S days, where S = 1, 2, ..., 30, calculate the average of all S consecutive days of spawning in a year, and regard it as the value of the first day of the corresponding period to form a time series Where k = 365 - S + 1;

[0081] Step S43: Calculate the average of all the natural daily runoffs for S consecutive days in a year, and regard it as the daily runoff on the first day of the corresponding period, and reconstruct a new natural daily runoff time series.

[0082]

[0083] Step S44: construct an eco-hydrological response model. and The goal is to maximize the correlation and minimize S, which can be expressed as: in, express and The correlation coefficient between

[0084] Step S45: Use the traversal method to solve the obtained eco-hydrological response model to obtain the minimum adaptation period S of black carp to runoff changes. min .

[0085] Step S5: Taking the minimum adaptation period as the standard for quantifying the continuous runoff change, the average value of the natural daily runoff in each period in the entire sequence is calculated respectively, and it is regarded as the daily runoff on the first day of the corresponding period, and then a new set of natural daily runoff time series is reconstructed, specifically:

[0086]

[0087] In the above formula, i = 1, 2, ..., m, n = 1, 2, ..., N, j = 1, 2, ..., m n ,h=1,2,…,mS min +1; represents the multi-year natural daily runoff time series of the ecological control section of the watershed after restoration in step S3; m is the total number of natural daily runoff data in the sequence; N is the number of hydrological periods into which the daily runoff sequence is divided; m n is the number of natural daily runoff data in the nth hydrological period; represents the natural runoff on day h newly formed after reconstruction; S min is the minimum adaptation period determined in step S4; Represents the newly formed multi-year natural daily runoff series after reconstruction.

[0088] Step S6, by frequency analysis, calculate the daily runoff hydrological frequency in the new sequence and the average hydrological frequency of each month in the year; divide the flood season and the non-flood season according to the runoff distribution characteristics of the year, and determine the comprehensive hydrological frequency of each month in the year; draw the daily runoff frequency curve of the year, select the daily runoff that matches the monthly comprehensive hydrological frequency as the ecological flow, and determine the daily ecological flow process of the year;

[0089] Step S61: Arrange the natural daily runoff data of the watershed ecological control section reconstructed in step S5 for multiple years Assume that the daily runoff on the tth day of the xth month of the yth year is 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 in each year, X = 12, K x is the total number of days corresponding to the xth month;

[0090] Step S62: Calculate the daily runoff hydrological frequency and the average hydrological frequency of each month in the new sequence through frequency analysis; specifically:

[0091]

[0092] In the above formula, P y,x,t It represents the hydrological frequency value of runoff on the tth day of the xth month of the yth year; It represents the average daily runoff hydrological frequency value of the xth month of the yth year; It represents the multi-year average daily runoff hydrological frequency value of the xth month;

[0093] Step S63: divide the flood season into March to July and the non-flood season into August to February of the following year according to the annual runoff distribution characteristics. In this embodiment, considering the large runoff volume and high ecological demand during the flood season, the frequency value of 50% for distinguishing between flood and dry hydrological events is selected as the basic hydrological frequency of the flood season, that is, P 汛期 =50%, and the runoff in the non-flood season is low, but for the selected basin ecological control section, the ecological demand guarantee degree is still high, so the minimum frequency value of flood events in the non-flood season is selected as the basic hydrological frequency in the non-flood season, that is, P 非汛期 =25%. Of course, in other regions or embodiments, other frequency values ​​may be set. In actual selection, the historical hydrological conditions and ecological protection goals of the selected river shall prevail. On this basis, the comprehensive hydrological frequency of each month in the year is determined, specifically:

[0094] The multi-year average daily runoff hydrological frequency value of the xth month in the watershed ecological control section is By superimposing the corresponding basic hydrological frequency, the comprehensive hydrological frequency of the xth month can be determined.

[0095] If month x is a flood season, then

[0096] If month x is a non-flood season, then

[0097] Step S64: Obtain the theoretical frequency curve of daily runoff in the year and select The matched daily runoff is taken as the ecological flow value on the tth day of the xth month Then determine the ecological flow process within the year.

[0098] Among them, the method for obtaining the theoretical frequency curve of daily runoff in a year is as follows:

[0099] Step S641: The natural daily runoff Q of multiple years is y,x,t Arranged into a daily natural runoff sequence, that is, the daily runoff sequence on the tth day of the xth month

[0100] Step S642: Draw the theoretical frequency curve of the daily runoff sequence on the first day of January in multiple years: Q in sequence 1,1,1 ,Q 2,1,1 ,...,Q Y,1,1 The daily runoff values ​​were sorted from large to small, and the P-Ⅲ curve was used to fit the daily runoff series of multiple years, as shown in the following figure: Figure 3 As shown, the theoretical frequency curve of daily runoff on the first day of January is obtained;

[0101] Step S643: The remaining daily runoff sequences in the sequence repeat steps S641-S642 to obtain the daily runoff theoretical frequency curve on the tth day of the xth month, and the daily runoff theoretical frequency curve for the year is obtained by summarizing and collating.

[0102] In this example, in order to verify that the annual ecological flow process constructed by the method of the present invention is reasonable, the obtained results are compared with the Tennant method. Figure 4 As shown, the method of this embodiment calculates that the average daily ecological flow of the river in the flood season from March to July accounts for 42.00% of the multi-year daily average runoff, reaching the "good" range level of the Tennant method, and when the runoff reaches its peak in June, the activity of the river ecosystem is reduced due to the impact of floods, and the proportion of ecological flow also decreases accordingly; the average daily ecological flow of the river in the non-flood season from September to February of the following year accounts for 24.23% of the multi-year daily average runoff, also reaching the "good" range level of the Tennant method, and when the runoff is at a low level, the self-regulation activity of the river ecosystem is enhanced, and the proportion of ecological flow increases slightly.

[0103] In summary, it can be seen that the annual ecological flow process constructed by this method can achieve a relatively good flow level in both the flood season and the non-flood season, and can provide an excellent living condition for the river ecosystem. At the same time, the method of the present invention takes into account the dynamic demand of the river ecological coefficient for runoff changes, and can capture the changes in the river hydrological situation to the maximum extent and make adaptive adjustments, rather than setting a subjective and empirical fixed ecological flow ratio like some hydrological methods represented by the Tennant method. In comparison, the present invention proposes for the first time an ecological flow process determination method based on runoff variation reconstruction and frequency analysis, and applies it to the calculation of river ecological flow. It is an important innovation in this technical field. The calculation results can not only guarantee the dynamic demand of ecological flow for runoff changes, but also effectively support the coordinated development goals of sustainable development requirements of water resources and ecological balance under water conditions changes, and has a certain value of promotion and use.

[0104] The above is only a preferred embodiment of the present invention, and does not limit the present invention in other forms. Any technician familiar with the profession may use the above disclosed technical content to change or modify it into an equivalent embodiment with equivalent changes. However, any simple modification, equivalent change and modification made to the above embodiment according to the technical essence of the present invention without departing from the technical solution of the present invention still belongs to the protection scope of the technical solution of the present invention.

Claims

1. A method for determining ecological flow processes based on runoff variation reconstruction and frequency analysis, characterized in that: The following steps are involved: Step S1, collecting the daily runoff observation data of the long historical sequence of the ecological control section of the watershed, and using the hydrological process variation diagnosis method to identify the potential variation points in the runoff time series; Step S2: Based on the basic engineering data of the upstream water conservancy project of the selected ecological control section and the change characteristics of historical hydrological and meteorological elements, the potential variation points identified in step S1 are verified; and according to the verification results, the runoff time series is divided into several hydrological variation periods; Step S3, select the earliest hydrological period that is least affected by human activities as the natural reference period, regard its observed runoff data as the natural runoff sequence, and construct a meteorological-driven hydrological model to predict the natural daily runoff process of the next hydrological period; combine the sliding restoration principle, slide forward along the time series, and restore the natural daily runoff process of subsequent hydrological periods in turn; Step S4, investigating the ecological habits of the main fish species in the ecological control section of the watershed, analyzing the correlation between the key life activities of the main fish, including reproduction, migration, and foraging, and runoff changes in combination with the biohydrological response model, and determining the minimum adaptation period of the main fish to runoff changes; Step S5, taking the minimum adaptation period as the standard for quantifying the continuous runoff change, respectively calculating the average value of the natural daily runoff in each period in the entire sequence, and treating it as the daily runoff on the first day of the corresponding period, and then reconstructing a set of new natural daily runoff time series; Step S6, calculate the daily runoff hydrological frequency in the new sequence and the average hydrological frequency of each month in the year through frequency analysis; divide the flood season and non-flood season according to the runoff distribution characteristics of the year, and determine the comprehensive hydrological frequency of each month in the year; draw the daily runoff frequency curve of the year, select the daily runoff that matches the monthly comprehensive hydrological frequency as the ecological flow, and determine the daily ecological flow process of the year.

2. The method for determining ecological flow process based on runoff variation reconstruction and frequency analysis according to claim 1 is characterized in that: In step S3, the process of restoring the natural daily runoff process in each subsequent hydrological period includes the following steps: Step S31: Assume that the daily runoff time series Q of the ecological control section of the watershed in multiple years in step S2 is i Divide into N hydrological variation periods, namely Period 1, Period 2, …, Period N, and sort out the daily runoff series of each period Daily meteorological element sequence where i = 1, 2, ..., m, n = 1, 2, ..., N, j = 1, 2, ..., m n , m is the total number of daily runoff data, m n is the number of daily runoff data in the nth hydrological period; Step S32: Select the earliest hydrological variation period, Period 1, which is least affected by human activities, as the natural baseline period. Considered as a natural daily runoff series And compare it with the daily meteorological element series with the maximum lag time of 60 days in the same period Pearson correlation analysis was performed, where d = 1, 2, ..., 60, and (td) represents the meteorological element value d days ago; Step S33: In the hydrological variation period Period 1, the top 10 meteorological factors with the absolute value of correlation coefficient are selected as input variables. As the target variable, the first meteorological-driven hydrological model was constructed and its parameters were optimized; Step S34: In the hydrological variation period Period 2, the top 10 meteorological factors with the highest absolute value of correlation coefficient are selected as prediction factors, and the daily runoff process of Period 2 is predicted using the first meteorological-driven hydrological model. The prediction results are regarded as the natural daily runoff sequence of this period. Step S35: Combine the sliding restoration principle and slide forward one hydrological period along the time series, that is, use the and The second meteorological-driven hydrological model was constructed, and then its natural daily runoff sequence was predicted based on the meteorological factors in the hydrological variation period Period 3. By analogy, the natural daily runoff process of subsequent hydrological periods is restored.

3. The method for determining ecological flow process based on runoff variation reconstruction and frequency analysis according to claim 1 is characterized in that: In step S4, determining the minimum adaptation period of the main fish species to the runoff change includes the following steps: Step S41, according to the ecological habits of the main fish species in the ecological control section of the watershed, one or more life activity indicators including spawning amount, migration distance, and foraging amount are selected as representative quantitative indicators; Step S42: Assume that the adaptation period of the representative life activities of the main fish species to the runoff change is S days, where S = 1, 2, ..., 30, calculate the average value of the representative quantitative indexes for all S consecutive days in a year, and regard it as the value of the first day of the corresponding period to form a time series Where k = 365-S+1; Step S43: Calculate the average of all the natural daily runoffs for S consecutive days in a year, and regard it as the daily runoff on the first day of the corresponding period, and reconstruct a new natural daily runoff time series. Step S44: construct an eco-hydrological response model. and The goal is to maximize the correlation and minimize S, which can be expressed as: in, express and The correlation coefficient between Step S45: Use the traversal method to solve the obtained eco-hydrological response model to obtain the minimum adaptation period S of the main fish to the runoff change. min .

4. The method for determining ecological flow process based on runoff variation reconstruction and frequency analysis according to claim 1 is characterized in that: In step S5, the reconstruction forms a new set of natural daily runoff time series, and the process is as follows: In the above formula, i = 1, 2, ..., m, n = 1, 2, ..., N, j = 1, 2, ..., m n ,h=1,2,...,mS min +1; represents the multi-year natural daily runoff time series of the ecological control section of the watershed after restoration in step S3; m is the total number of natural daily runoff data in the sequence; N is the number of hydrological periods into which the daily runoff sequence is divided; m n is the number of natural daily runoff data in the nth hydrological period; represents the natural runoff on day h newly formed after reconstruction; S min is the minimum adaptation period determined in step S4; Represents the newly formed multi-year natural daily runoff series after reconstruction.

5. The method for determining ecological flow process based on runoff variation reconstruction and frequency analysis according to claim 1 is characterized in that: In step S6, the process of determining the daily ecological flow in a year includes the following steps: Step S61: Arrange the natural daily runoff data of the watershed ecological control section reconstructed in step S5 for multiple years Assume that the daily runoff on the tth day of the xth month of the yth year is 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 in each year, X = 12, K x is the total number of days corresponding to the xth month; Step S62: Determine the hydrological frequency of each daily runoff through frequency analysis, and then calculate the multi-year average daily runoff hydrological frequency value for each month of the year: In the above formula, P y,x,t represents the hydrological frequency value of runoff on the tth day of the xth month of the yth year; P y,x It represents the average daily runoff hydrological frequency value of the xth month of the yth year; It represents the multi-year average daily runoff hydrological frequency value of the xth month; Step S63: Assume that the basic hydrological frequencies of daily runoff in the flood season and non-flood season of the watershed ecological control section are P 汛期 and P 非汛期 , then compare it with Superimpose to determine the comprehensive hydrological frequency of the xth month If month x is a flood season, then If month x is a non-flood season, then Step S64: select the frequency curve of daily runoff theory in the year The matched daily runoff is taken as the ecological flow value on the tth day of the xth month Then determine the ecological flow process within the year.

6. The method for determining ecological flow process based on runoff variation reconstruction and frequency analysis according to claim 1 is characterized in that: The step S1 is to collect a long-term historical sequence of daily runoff observation data of the watershed ecological control section, and the period of collecting the observation data is not less than 20 years.

7. The method for determining ecological flow process based on runoff variation reconstruction and frequency analysis according to claim 1 is characterized in that: The basic engineering data of the upstream water conservancy project in step S2 includes the construction time, location, scale and engineering data of the upstream water conservancy project.

8. The method for determining ecological flow process based on runoff variation reconstruction and frequency analysis according to claim 2 is characterized in that: The daily meteorological element sequence sorted in step S31 should match the daily runoff sequence, and the daily meteorological element must include precipitation.

9. The method for determining ecological flow process based on runoff variation reconstruction and frequency analysis according to claim 5 is characterized in that: In step S63, the basic hydrological frequencies of daily runoff in the flood season and non-flood season of the watershed ecological control section are respectively P 汛期 and P 非汛期 , P 汛期 =50%, P 非汛期 =25%.

10. The method for determining ecological flow process based on runoff variation reconstruction and frequency analysis according to claim 5 is characterized in that: The method for obtaining the theoretical frequency curve of daily runoff in a year in step S64 is as follows: Step S641: The natural daily runoff Q of multiple years is y,x,t Arranged into a daily natural runoff sequence, that is, the daily runoff sequence on the tth day of the xth month Step S642: Draw the theoretical frequency curve of the daily runoff sequence on the first day of January in multiple years: Q in sequence 1,1,1 ,Q 2,1,1 ,...,Q Y,1,1 The daily runoff values ​​were sorted from large to small, and the P-Ⅲ curve was used to fit the daily runoff series of multiple years to obtain the theoretical frequency curve of daily runoff on the first day of January. Step S643: The remaining daily runoff sequences in the sequence repeat steps S641-S642 to obtain the daily runoff theoretical frequency curve on the tth day of the xth month, and the daily runoff theoretical frequency curve for the year is obtained by summarizing and collating.

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