Reservoir ecological flow calculation and discharge scheme determination method based on hydrology method and entropy weight method

Abstract

The invention relates to the field of hydraulic engineering and ecological protection, in particular to a reservoir ecological flow calculation and discharge scheme determination method based on a hydrology method and an entropy weight method. The method comprises the following steps: collecting daily scale runoff data and arranging the daily scale runoff data into a monthly scale; preliminarily calculating an ecological flow threshold value by using five hydrological methods such as a Tennant method and a Qp method; adopting an entropy weight method to give a weight, and comprehensively calculating the most suitable ecological flow; the ecological flow guarantee rate is calculated through a frequency method, and a grade threshold value is set; and designing a discharge scheme based on reservoir characteristics. According to the method, multiple hydrological methods and entropy weight methods are combined, the ecological flow is analyzed from multiple dimensions, the calculation precision and consistency are improved, a flexible drainage strategy is formulated, ecological protection and water demands are balanced, the reservoir management scientificity is improved, and the watershed hydrological and ecological integrity is maintained.

Description

Technical Field

[0001] The present invention relates to the field of ecological environmental technology, and in particular to a method for calculating reservoir ecological flow and determining a discharge scheme based on a hydrology method and an entropy weight method. Background Art

[0002] In the fields of water conservancy projects and ecological protection, the accurate calculation and reasonable discharge of reservoir ecological flow are of great significance to maintaining the ecological balance of the watershed. However, the current ecological flow calculation methods have many technical difficulties that need to be solved. Traditional ecological flow calculation methods usually rely on a single hydrological method, such as the Tennant method, the Qp method, or the Texas method. Although these methods are simple to operate, they only determine the ecological flow from a specific perspective and are difficult to fully consider the complex changes in flow frequency, seasonal differences, and extreme climatic conditions. As a result, the calculation results are inaccurate and cannot fully reflect the dynamic characteristics of ecological water demand. In addition, the ecological flow thresholds obtained by different single methods often vary greatly, making it difficult to form a unified standard in practical applications, which has brought significant problems to water resources management and ecological protection.

[0003] Existing technologies also exhibit significant shortcomings in balancing ecological protection with water demand. During reservoir operations, economic water needs such as power generation and irrigation are often prioritized, while ensuring ecological flow is neglected, exposing downstream ecosystems to the risk of degradation. Furthermore, the lack of accurate ecological flow calculation methods often makes it difficult to balance the needs of all parties when allocating water resources. This leads to the crowding out of ecological water use, frequent ecological problems such as river dry-ups and water quality deterioration. These issues not only affect the healthy functioning of river basin ecosystems but also hinder the sustainable use of water resources.

[0004] Existing technologies are limited in their ability to cope with the complex operational environment of reservoirs. Reservoirs vary in their engineering, hydrological, and ecological requirements, and are susceptible to external factors such as climate change. However, existing ecological flow discharge schemes are mostly static designs, lacking flexibility and dynamic adjustment mechanisms. They cannot be optimized in real-time based on reservoir conditions and changes in the external environment, making it difficult to ensure the integrity of the watershed's hydrological ecology. This limitation not only restricts the sustainable operation of reservoirs but also adversely impacts the healthy development of watershed ecosystems.

[0005] Therefore, developing a method for calculating reservoir ecological flow and determining discharge plans that can integrate multiple hydrological methods, improve the accuracy of ecological flow calculations, and flexibly adapt to complex environments has become a technical challenge that urgently needs to be addressed. It is against this backdrop that this paper proposes an innovative method that combines hydrological methods with the entropy weight method. This method aims to comprehensively analyze ecological flow from a multidimensional perspective, improve the accuracy and consistency of calculation results, and design flexible discharge plans to achieve a dynamic balance between ecological protection and water demand. Summary of the Invention

[0006] This paper addresses existing issues such as inaccurate ecological flow calculations, difficulty balancing ecological protection with water demand, and insufficient reservoir management capacity to cope with complex environments. By proposing a method for calculating reservoir ecological flow and determining discharge plans based on hydrological and entropy weighting methods, this approach combines multiple hydrological and entropy weighting methods to comprehensively analyze ecological flow from a multidimensional perspective, improving the accuracy and consistency of calculation results. It also designs flexible discharge plans to dynamically adapt to reservoir characteristics and external environmental changes.

[0007] The present invention provides a method for calculating reservoir ecological flow and determining a discharge scheme based on a hydrological method and an entropy weight method, the specific steps of which are as follows:

[0008] S1: Obtain historical daily runoff data from each hydrological station in the basin and compile them into monthly data. Linear interpolation is used to fill in missing data to ensure data integrity and continuity. Monthly data are generated by taking the arithmetic mean of the daily runoff data within each month for subsequent ecological flow calculations.

[0009] S2: Based on daily or monthly runoff data, preliminary calculations of ecological flow thresholds are performed using five key hydrological methods (Tennant, Qp, Texas, driest month average flow, and cumulative frequency curve). In extreme climatic conditions (e.g., once-in-a-century torrential rain or prolonged drought), alternative methods (e.g., the 7Q10 method or the intra-annual spread method) may be used for supplementary calculations. However, these methods must adhere to the same overall framework and principles as the five original hydrological methods to ensure the reliability and comparability of the results.

[0010] Furthermore, the combination of the five hydrological methods was not randomly selected but was based on an in-depth analysis of the topography, climate characteristics, ecosystem types, and historical runoff data of the Jiaojiang River Basin in Zhejiang Province. The Tennant method provides a baseline threshold estimate based on flow ratio; the Qp method focuses on ecological flow at a specific flow frequency; the Texas method reflects seasonal differences in flow demand; the driest month average flow method effectively ensures a baseline for ecological flow during the dry season; and the cumulative frequency curve method refines the threshold range definition from a probabilistic and statistical perspective.

[0011] S3: Based on the data obtained in S2, the entropy weight method is used to assign weights to the calculation results of the five hydrological methods to comprehensively calculate the optimal ecological flow threshold. The specific implementation of the entropy weight method includes the following steps: First, the monthly ecological flow guarantee rate results calculated by the five hydrological methods are sorted and recorded as \(X_1,X_2,X_3,X_4,X_5\), where each \(X_i\) is a sequence containing multiple data points, representing the ecological flow value at different time points calculated by the \(i\)th hydrological method.

[0012] Secondly, in order to eliminate the influence of different dimensions and orders of magnitude, the five sets of data are standardized using the range standardization method. The formula is as follows:

[0013] \[Z_{ij}=\frac{X_{ij}-\min(X_j)}{\max(X_j)-\min(X_j)}\]

[0014] Where Zij is the normalized value, Xij is the jth data point for the i-th hydrological method, and max(Xj) and min(Xj) are the maximum and minimum values for the j-th hydrological method, respectively. After normalization, five sets of data are obtained. Next, the information entropy of each indicator is calculated. The information entropy calculation formula is as follows:

[0015] \[e_j=-k\sum_{i=1}^{n}p_{ij}\ln(p_{ij})\]

[0016] Where, \(p_{ij}=\frac{Z_{ij}}{\sum_{i=1}^{n}Z_{ij}}\) is the weight of the \(i\)th data point under the \(j\)th hydrological method, \(k=\frac{1}{\ln(n)}\) is the coefficient, and \(n\) is the total number of data points.

[0017] Then, the entropy weight of each hydrological method is calculated based on the information entropy, and the formula is as follows:

[0018] \[w_j=\frac{1-e_j}{\sum_{j=1}^{m}(1-e_j)}\]

[0019] Where wj is the entropy weight of the jth hydrological method, and m is the number of hydrological methods. Finally, the final ecological flow is determined based on the entropy weights. The ecological flow calculated by each hydrological method is multiplied by its corresponding entropy weight, and the five weighted ecological flow results are summed to obtain the final ecological flow value. The formula is as follows:

[0020] \[Q_{\text{final}}=\sum_{j=1}^{5}w_j\cdot Q_j\]

[0021] Among them, \(Q_j\) is the ecological flow value calculated by the \(j\)th hydrological method, and \(Q_{\text{final}}\) is the final ecological flow value.

[0022] S4: Based on the measured daily average flow and the ecological flow thresholds calculated by various hydrological methods, the frequency method is used to calculate the monthly ecological flow guarantee rate and set the ecological flow level threshold. Specifically, the calculation formula for the ecological flow guarantee rate is as follows:

[0023] P = N_{N_{N_text{Number of days to meet the target}}} N_{N_text{Total number of days}}} times 100%

[0024] Where P is the ecological assurance rate, N is the number of days during the evaluation period when the average daily flow exceeds the ecological flow threshold, and N is the total number of days during the evaluation period. Furthermore, based on the optimal ecological flow values, five levels of ecological flow thresholds were established, with clear flow ranges and corresponding color codes for each level to intuitively reflect the ecological flow status.

[0025] S5: Design a flexible discharge plan based on reservoir characteristics. When the monthly ecological flow guarantee rate is lower than 60%, additional ecological flow discharge facilities will be installed. Specific design principles include:

[0026] First, the water intake flow rate must meet the minimum operating water level requirements of the reservoir. For example, for Reservoir A, when the water level reaches 185.0 meters, the water intake flow rate should be no less than the minimum ecological flow rate of 2.09 cubic meters per second; for Reservoir B, when the water level reaches 176.04 meters, the water intake flow rate should be no less than 2.28 cubic meters per second; and for Reservoir C, when the water level reaches 398.04 meters, the water intake flow rate should be no less than 0.44 cubic meters per second.

[0027] Second, the water intake is arranged close to the center hole of the dam body to reduce the impact of siltation while meeting the structural and water flow requirements.

[0028] Third, construction is scheduled to take place during the dry season and be completed before the flood season to ensure the safety of the dam.

[0029] Furthermore, the present invention achieves the following beneficial effects through the above technical solution:

[0030] First, the present invention combines multiple hydrological methods with the entropy weight method, assigns reasonable weights, reduces the dispersion of the calculation results of a single method, improves the accuracy and consistency of ecological flow calculation, and provides accurate data support for ecological protection and water resources management.

[0031] Second, by analyzing the inter-annual and intra-annual changes in the ecological flow guarantee rate, a five-level ecological flow grade is set, enabling the reservoir to flexibly adjust its discharge strategy according to the real-time runoff grade, taking into account water demand while ensuring ecological needs.

[0032] Third, the emission plan formulated by the present invention comprehensively considers factors such as reservoir characteristics and climate change, has strong flexibility and dynamic adjustment capabilities, provides a scientific and feasible model for reservoir management, effectively responds to complex environments, improves the scientificity and effectiveness of management, and maintains the hydrological and ecological integrity of the basin.

[0033] In summary, the technical solution of the present invention is highly innovative and practical, and provides an effective solution to problems such as inaccurate ecological flow calculation in traditional methods, difficulty in balancing ecological protection and water demand, and insufficient ability of reservoir operation and management to cope with complex environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a specific flow diagram of the present invention;

[0035] Figure 2 This is a schematic diagram of the Tennant method used in this example to divide the reservoir's high water period and dry water period;

[0036] Figure 3 This is a schematic diagram of the entropy weight method calculation process in this example;

[0037] Figure 4 Schematic diagram of the entropy weight distribution of each hydrological method in this example;

[0038] Figure 5 This is a schematic diagram of the changing trend of the ecological flow guarantee rate of the reservoir in this example;

[0039] Figure 6 This is a schematic diagram of the reservoir ecological flow level classification and color identification in this example.

[0040] The accompanying drawings are marked as follows: 1. Data collection and organization; 2. Determination of training set and prediction set; 3. Network structure design; 4. Parameter setting; 5. Model construction and training; 6. Performance evaluation; 7. Result optimization; 8. Result output; 9. Monthly flow proportion; 10. Threshold dividing line; 11. Data preparation; 12. Standardization processing; 13. Information entropy calculation; 14. Comprehensive calculation; 15. Entropy weight distribution; 16. Changes in ecological guarantee rate; 17. Ecological flow level classification. DETAILED DESCRIPTION

[0041] This paper proposes a method for calculating reservoir ecological flow and determining discharge plans based on hydrological and entropy weight methods. The specific implementation process is described in detail, combined with the process and data processing steps in the accompanying drawings. The example uses the Jiaojiang River Basin in Zhejiang Province as the background and selects three typical reservoirs (Reservoir A, Reservoir B, and Reservoir C) as research objects. The effectiveness and practicality of the method are verified using actual data.

[0042] First, starting from S1, the historical runoff daily scale data of each hydrological station in the basin are collected and organized into monthly scale data. Figure 1 As shown, this step corresponds to figure mark 1, which indicates the process of data collection and collation. During the implementation process, the daily measured flow data of Reservoir A, Reservoir B and Reservoir C were obtained from 2005 to 2019. These data include daily average flow records, covering the basic characteristic parameters of the three reservoirs, such as catchment area, total storage capacity, normal storage capacity, multi-year average inflow and multi-year average runoff. For missing daily runoff data, linear interpolation is used to fill in to ensure data continuity and integrity. Subsequently, the daily runoff data are arithmetic averaged to generate monthly scale data to meet subsequent analysis needs. The core of this operation is to eliminate the impact of daily scale fluctuations on monthly scale calculations, while ensuring that the temporal resolution of the data is moderate.

[0043] Entering the S2 stage, based on daily or monthly runoff data, the ecological flow threshold is preliminarily calculated using five main hydrological methods. The specific implementation of this part can be referred to Figure 2Figure 9 shows a diagram of monthly flow ratios. The Tennant method, one of the most basic hydrological methods, divides the wet and dry seasons by calculating the ratio of each month's outflow to the multi-year average runoff. Using a 6% cutoff, the dry season is from November to February, and the wet season is from March to October. The Qp method divides flow data by month and performs frequency calculations, using the monthly average flow at a 90% guarantee rate as the ecological flow value. For example, the ecological flow calculated using the Qp method for Reservoir A is 2.67 cubic meters per second, for Reservoir B it is 3.16 cubic meters per second, and for Reservoir C it is 0.68 cubic meters per second. The Texas method, based on a 50% guarantee rate, uses 20% of the monthly average flow as the ecological flow, resulting in 1.46 cubic meters per second, 1.46 cubic meters per second, and 0.34 cubic meters per second for Reservoirs A, B, and C, respectively. The cumulative frequency curve method constructs a monthly hydrological frequency curve using long-term runoff data, calculating ecological flow at a 90% frequency. The results were 0.90 cubic meters per second, 0.79 cubic meters per second, and 0.001 cubic meters per second, respectively. The average runoff method, using the driest month, directly calculates ecological flow using a formula: 1.34 cubic meters per second, 1.17 cubic meters per second, and 0.24 cubic meters per second for Reservoirs A, B, and C, respectively. This combination of five methods was not randomly selected; rather, it was determined after in-depth analysis of the topography, climate characteristics, ecosystem types, and historical runoff data of the Jiaojiang River Basin in Zhejiang Province. The goal is to comprehensively cover ecological needs under different seasons and flow conditions.

[0044] The next step is the S3 stage, which uses the entropy weight method to assign weights to the calculation results of the five hydrological methods and comprehensively calculate the most suitable ecological flow threshold. The specific calculation process of this step can be referred to Figure 3and reference numerals 11 to 14. First, the monthly ecological flow guarantee rate results calculated by the five hydrological methods are sorted out and recorded as \(X_1,X_2,X_3,X_4,X_5\), where each \(X_i\) is a sequence containing multiple data points. Then, in order to eliminate the influence of different dimensions and orders of magnitude, the five sets of data are standardized using the range normalization method. The standardized value \(Z_{ij}\) is calculated by the formula \(\frac{X_{ij}-\min(X_j)}{\max(X_j)-\min(X_j)}\). After standardization, five sets of standardized data are obtained. Next, the information entropy of each indicator is calculated using the formula \(-k\sum_{i=1}^{n}p_{ij}\ln(p_{ij})\), where \(p_{ij}=\frac{Z_{ij}}{\sum_{i=1}^{n}Z_{ij}}\) is the weight of the \(i\)th data point under the \(j\)th hydrological method, \(k=\frac{1}{\ln(n)}\) is the coefficient, and \(n\) is the total number of data points. Based on the information entropy, the entropy weight of each hydrological method is calculated using the formula \(\frac{1-e_j}{\sum_{j=1}^{m}(1-e_j)}\), where \(e_j\) is the information entropy of the \(j\)th hydrological method and \(m\) is the number of hydrological methods. Finally, the ecological flow results calculated by each hydrological method are multiplied by their corresponding entropy weights, and the five weighted ecological flow results are summed to obtain the final ecological flow value. Through the above calculations, the final ecological flow of reservoirs A, B and C are 2.10 cubic meters per second, 2.28 cubic meters per second and 0.44 cubic meters per second respectively. This process is as follows Figure 4 As shown, reference numeral 15 represents the entropy weight distribution.

[0045] In the S4 stage, based on the measured daily average flow and the ecological flow thresholds calculated by various hydrological methods, the frequency method is used to calculate the monthly ecological flow guarantee rate and set the ecological flow level threshold. The specific implementation of this step can be referred to Figure 5and Figure 16. The formula for calculating the ecological flow guarantee rate is \(\frac{N_{\text{Number of days meeting the standard}}}{N_{\text{Number of days meeting the standard}}}\times 100\%\), where \(N_{\text{Number of days meeting the standard}}\) is the number of days during the evaluation period when the average daily flow exceeds the ecological flow threshold, and \(N_{\text{Number of days meeting the standard}}\) is the actual number of days during the evaluation period. For example, the interannual guarantee rate results for Reservoir A show that the ecological flow guarantee rates calculated by the Qp method and the Tennant method range from 40% to 50%. The guarantee rates calculated by the Texas method and the driest month average runoff method were 100% in 2006 and 2007 and 28% in 2018. The guarantee rate calculated by the cumulative frequency curve method exceeded 90% in all years except 2019, when it was 89%. Reservoir B's interannual guarantee rate exceeded 70% between 2005 and 2010, exceeded 60% between 2011 and 2016, and exceeded 50% between 2017 and 2019. Reservoir C's annual average guarantee rate was 56.94%. The ecological flow guarantee rates calculated using the five hydrological methods were similar and increased annually. Five ecological flow threshold levels were established based on the optimal ecological flow values, with clear flow ranges and corresponding color codes for each level to intuitively reflect ecological flow status. For example, Reservoir A's ecological flow demand was high from March to October, with the lowest threshold for good conditions reaching 4.27 cubic meters per second in June. Demand was lower from January to February and from November to December, averaging 0.96 cubic meters per second. Reservoir B's ecological flow demand was high from June to September, averaging 4.69 cubic meters per second, and averaging 2.62 cubic meters per second in March, April, May, and October. Reservoir C has a high ecological flow demand from June to October, with a maximum of 1.21 cubic meters per second in August. It has a low demand from November to February, with an average of 0.16 cubic meters per second. Figure 6 As shown, reference numeral 17 represents the ecological flow level classification.

[0046] Finally, in the S5 phase, a flexible discharge plan will be designed based on reservoir characteristics. If the monthly ecological flow guarantee rate falls below 60%, additional ecological flow release facilities will be installed. Specific design principles include the following: First, the water intake flow must meet the reservoir's minimum operating water level. For example, for Reservoir A, when the water level reaches 185.0 meters, the water intake flow should be no less than the minimum ecological flow value of 2.09 cubic meters per second; for Reservoir B, when the water level reaches 176.04 meters, the water intake flow should be no less than 2.28 cubic meters per second; and for Reservoir C, when the water level reaches 398.04 meters, the water intake flow should be no less than 0.44 cubic meters per second. Second, the water intake should be located close to the dam's central hole to minimize the impact of siltation while meeting structural and flow pattern requirements. Third, construction should be scheduled during the dry season and completed before the flood season to ensure dam safety. For example, Reservoir A adopts an ecological siphon solution, Reservoir B renovates the water diversion system and adds drainage pipes, optimizes the tunnel design, and Reservoir C adopts a behind-the-dam ecological unit layout with the water intake close to the center hole of the dam body, and construction is scheduled during the dry season.

[0047] In summary, the present invention combines multiple hydrological methods with the entropy weight method and assigns reasonable weights, thereby reducing the dispersion of calculation results of a single method and improving the accuracy and consistency of ecological flow calculations. By analyzing the inter-annual and intra-annual changes in the ecological flow guarantee rate, a five-level ecological flow level is set, which enables the reservoir to flexibly adjust the discharge strategy according to the real-time runoff level, taking into account water demand while ensuring ecological needs. The formulated discharge plan comprehensively considers factors such as reservoir characteristics and climate change, has strong flexibility and dynamic adjustment capabilities, and provides a scientific and feasible model for reservoir management, effectively responds to complex environments, improves the scientificity and effectiveness of management, and maintains the hydrological and ecological integrity of the basin.

Claims

1. A method for calculating reservoir ecological flow and determining discharge scheme based on hydrology method and entropy weight method, characterized by The following steps are involved: Obtain daily historical runoff data from each hydrological station in the basin and organize it into monthly data; Five major hydrological methods were used to preliminarily calculate the ecological flow threshold. The entropy weight method was used to assign weights to the calculation results of the five hydrological methods and comprehensively calculate the most appropriate ecological flow threshold. Based on the measured daily average flow and the ecological flow threshold calculated by each hydrological method, the frequency method was used to calculate the monthly ecological flow guarantee rate and set the ecological flow level threshold. Design flexible discharge plans based on reservoir characteristics.

2. The method according to claim 1, wherein The missing parts of the historical runoff daily-scale data were filled by linear interpolation.

3. The method according to claim 2, wherein Monthly scale data are generated by taking the arithmetic mean of daily runoff data.

4. The method according to claim 1, wherein The five main hydrological methods include the Tennant method, the Qp method, the Texas method, the driest month mean flow method, and the cumulative frequency curve method.

5. The method according to claim 4, wherein Under extreme climatic conditions, the 7Q10 method or the intra-annual distribution method is used to supplement the calculation of ecological flow thresholds.

6. The method according to claim 1, wherein The entropy weight method includes the steps of normalization, information entropy calculation, entropy weight determination and weighted summation.

7. The method according to claim 6, wherein The standardization process uses the range standardization method, and the formula is \(Z_{ij}=\frac{X_{ij}-\min(X_j)}{\max(X_j)-\min(X_j)}\).

8. The method according to claim 1, wherein The calculation formula for the ecological flow guarantee rate is \(\frac{N_{\text{Number of days meeting the standard}}}{N_{\text{Total days}}}\times 100\%\).

9. The method according to claim 1, wherein The design principles of the discharge scheme include ensuring that the water intake flow meets the minimum operating water level requirements of the reservoir, arranging the water intake close to the center hole of the dam body, and arranging construction during the dry season and completing it before the flood season.

10. The method according to claim 9, wherein The minimum water intake flow rate is set according to the reservoir water level. For Reservoir A, when the water level reaches 185.0 meters, the water intake flow rate is not less than 2.09 cubic meters per second (1); for Reservoir B, when the water level reaches 176.04 meters, the water intake flow rate is not less than 2.28 cubic meters per second (2); for Reservoir C, when the water level reaches 398.04 meters, the water intake flow rate is not less than 0.44 cubic meters per second (3).

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