Dynamic water balance calculation method for river type reservoir

Abstract

The invention discloses a dynamic water balance calculation method for a river type reservoir. The dynamic water balance calculation method comprises the following steps: step 1, determining a river type reservoir control basin range and dividing water catchment units; 2, predicting the reservoir water amount of the river type reservoir based on the distributed hydrological model; 3, calculating the maximum possible water storage capacity of the riverway type reservoir; 4, calculating the water loss amount of the river type reservoir; 5, calculating the water storage capacity and the drainage capacity of the riverway type reservoir; and 6, correcting the water storage amount and the discharged water amount of the reservoir based on ecological flow control requirements. According to the method, the regulation, storage and discharge process of the river type reservoir can be dynamically adjusted and corrected, improvement of a downstream ecological system of the reservoir is promoted, important technical support is provided for water resource management, scheduling optimization and planning design of the river type reservoir, and overall improvement of the management efficiency of the river type reservoir is promoted.

Description

Technical Field

[0001] The present invention belongs to the technical field of hydrology and water resources management, and particularly relates to a method for calculating the dynamic water balance of a river-type reservoir. Background Art

[0002] River-type reservoirs are usually formed by building dams across rivers, which are important water conservancy project facilities. They have the dual characteristics of rivers and reservoirs, can regulate floods, and have multiple functions such as water supply, irrigation, power generation, and shipping. Since river-type reservoirs are built on the original river channels, they generally extend along the river channels and mostly show a long and narrow shape similar to the river channels, with a large aspect ratio of length to width. Due to the combined effects of basin inflow, reservoir power generation, and water intake and use in the reservoir area by human activities, the water level of river-type reservoirs varies greatly with seasons. During the flood season (high water season), the water level of river-type reservoirs rises rapidly, bringing greater flood control pressure. Usually, it is necessary to dynamically adjust the limit water level and empty the reservoir capacity in advance to cope with large floods; during the non-flood season (low water season) or peak water use period, the water level of river-type reservoirs drops significantly. Generally, the fluctuation of the reservoir water level directly affects the water storage volume of the reservoir and also affects the water discharge from the reservoir and ecological water use.

[0003] For a long time, the water balance of river-type reservoirs has been quantified through measured data and static water level-storage relationships to balance the relationship between inflow and outflow water volumes and water storage volumes. However, the following problems are faced, specifically including: 1) During the flood season, the existing methods cannot reflect the process of pre-discharging floods in different grades according to the inflow water volume, resulting in over-storage of the reservoir or insufficient flood control capacity and increasing the flood control pressure downstream; 2) During the non-flood season, the existing methods cannot reflect the control requirements for ecological flow discharge, which to a certain extent damages the ecological system downstream of the river-type reservoir.

[0004] Therefore, how to carry out dynamic calculation of water balance according to the characteristics of river-type reservoirs, comprehensively considering the requirements of reflecting pre-discharging floods in different grades and ecological flow control, has become an important technical problem urgently to be solved in this field. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for calculating the dynamic water balance of a river-type reservoir to solve the above technical problems.

[0006] To achieve the above purpose, the present invention provides the following technical solutions:

[0007] The present invention discloses a method for calculating the dynamic water balance of a river-type reservoir, and the method includes the following steps:

[0008] Step 1. Determine the control basin scope of the river-channel reservoir and divide the catchment units: Determine the control basin scope of the river-channel reservoir according to the determination rules of the control basin scope of the river-channel reservoir; comprehensively consider the similarities of terrain, soil, and vegetation characteristics within the basin, and divide the control basin scope of the river-channel reservoir into catchment units;

[0009] Step 2. Predict the inflow of the river-channel reservoir based on the distributed hydrological model: Take the river-channel reservoir as the control node, input the basic data, and establish a distributed hydrological model; establish the link between the rainfall forecast platform data or meteorological satellite and rain gauge radar data and the distributed hydrological model, and drive the hydrological model through real-time rainfall data to calculate the inflow of the river-channel reservoir, that is, the surface runoff volume and the net inflow of groundwater runoff collected within the control basin scope of the reservoir. The calculation formula is:

[0010] Qi t =Qa t +Qb t (1)

[0011] In the formula, Qi t is the inflow of the river-channel reservoir at the t-th time, in 10,000 m 3 ; Qa t is the surface runoff volume at the t-th time, in 10,000 m 3 ; Qb t is the net inflow of groundwater runoff at the t-th time, that is, the difference between the inflow and the outflow, in 10,000 m 3 ;

[0012] Step 3. Calculate the maximum possible water storage of the river-channel reservoir: First, determine the flood-season pre-discharge control water level of the river-channel reservoir: According to the characteristics of the river-channel reservoir, establish the function relationship between the inflow and the pre-discharge control water level based on the inflow prediction data, as shown in the following formula:

[0013] Ha t =fx(Qi t ) (2)

[0014] In the formula, Ha t is the flood-season pre-discharge control water level of the river-channel reservoir at the t-th time, in m; fx() is the function relationship between the flood-season inflow and the pre-discharge control water level;

[0015] Then, based on the determined flood-season pre-discharge control water level of the river-channel reservoir, determine the highest water level limit required for other comprehensive utilization functions of the river-channel reservoir, including navigation, water supply, power generation, and sediment discharge, so as to calculate the highest water level limit required for the comprehensive regulation of the river-channel reservoir. The calculation formula is:

[0016] Hm t =max (Ha t ,Hb t ,Hc t,Hd t ,He t ) (4)

[0017] In the formula, Hm t is the maximum water level limit required for the integrated operation of the river - type reservoir at the t - th time, m; Hb t is the maximum water level limit required for navigation of the river - type reservoir, m; Hc t is the maximum water level limit required for water supply of the river - type reservoir, m; Hd t is the maximum water level limit required for power generation of the river - type reservoir, m; He t is the maximum water level limit required for sediment discharge of the river - type reservoir, m; Hb t , Hc t , Hd t , He t are all determined by establishing corresponding functional relationships based on the inflow water volume;

[0018] Finally, based on the determined flood - season pre - discharge control water level of the river - type reservoir and the maximum water level limit required for integrated operation, and based on the water level - storage capacity functional relationship of the river - type reservoir, calculate the maximum possible water storage volume of the river - type reservoir. The calculation formula is:

[0019] Vm t = fz(Hm t ) (5)

[0020] In the formula, Vm t is the maximum possible water storage volume of the river - type reservoir at the t - th time, 10,000 m 3 ; fz() is the water level - storage capacity functional relationship of the river - type reservoir;

[0021] Step 4. Calculate the water loss of the river - type reservoir: First, segment the river - type reservoir according to the catchment unit: Based on the catchment units divided in Step 1, segment the river - type reservoir according to the connection points between the outlets of each catchment unit and the river - type reservoir (j = 1, 2, 3... J), where J is the total number of segments of the river - type reservoir;

[0022] Then, determine the reservoir evaporation water loss in segments: Obtain the water surface evaporation, rainfall, and water surface area of each segment of the river - type reservoir, and calculate the evaporation water loss of each segment of the river - type reservoir. The specific formula is:

[0023] Qe j,t = S j,t-1 ×(Ee j,t - Pe j,t )×10 -3 (6)

[0024] In the formula, Qe j,t is the evaporation water loss of the j - th segment of the river - type reservoir, 10,000 m 3 ; Eej,t is the water surface evaporation of the j-th section of the river-type reservoir at time t, in mm; Pe j,t is the rainfall of the j-th section of the river-type reservoir at time t, in mm; S j,t-1 is the water surface area of the j-th section of the river-type reservoir at time t-1, in 10,000 m 2 ;

[0025] Then, the seepage loss water volume of the reservoir is determined section by section: The seepage loss water volume of each section of the river-type reservoir includes two parts: the bottom seepage loss water volume and the bank slope seepage loss water volume. The calculation formula is:

[0026] Ql j,t = Qla j,t + Qlb j,t (7)

[0027] In the formula, Ql j,t is the seepage loss water volume of the j-th section of the river-type reservoir at time t, in 10,000 m 3 ; Qla j,t is the bottom seepage loss water volume of the j-th section of the river-type reservoir, in 10,000 m 3 ; Qlb j,t is the bank slope seepage loss water volume of the j-th section of the river-type reservoir, in 10,000 m 3 ;

[0028] Among them, the calculation formula for the bottom seepage loss water volume Qla j,t is:

[0029] Qla j,t = Ka j,t × Aa j,t × La j,t × 10 -4 (8)

[0030] In the formula, Ka j is the bottom permeability coefficient of the j-th section of the river-type reservoir at time t, in m; Aa j,t is the seepage area of the bottom of the j-th section at time t, in m 2 ; La j,t is the hydraulic gradient of the bottom of the j-th section at time t, dimensionless;

[0031] The calculation formula for the bank slope seepage loss water volume Qlb j,t is:

[0032] Qlb j,t = Kb j,t × Ab j,t × Lb j,t × S j,t × 10 -4 (9)

[0033] In the formula, Kbj is the permeability coefficient of the bank slope at the j-th section and the t-th time of the river-channel reservoir, m; Ab j,t is the seepage area of the bank slope at the j-th section of the river-channel reservoir at the t-th time, m 2 ; Lb j,t is the hydraulic gradient of the bank slope at the j-th section of the river-channel reservoir at the t-th time, dimensionless; S j,t is the angle between the inclined plane of the bank slope at the j-th section of the river-channel reservoir and the horizontal plane;

[0034] Then, determine the water consumption of human economic and social activities section by section: The water consumption of human economic and social activities includes the water consumption brought by the water intake, water use, and drainage activities of various users of human economy and society from each section along the river-channel reservoir. Its sectional calculation formula is:

[0035]

[0036] In the formula, Qu j,t is the water consumption of human economic and social activities at the j-th section of the river-channel reservoir, 10,000 m 3 ; U j,t,k is the water intake of the k-th type of user at the j-th section of the river-channel reservoir at the t-th time, 10,000 m 3 ; Hr j,t,k is the water consumption coefficient of the k-th type of user at the j-th section of the river-channel reservoir at the t-th time, dimensionless; K is the total number of economic and social user types, units;

[0037] Finally, determine the water loss of the river-channel reservoir: The water loss of the river-channel reservoir is equal to the sum of the reservoir evaporation loss water volume, seepage loss water volume, and the water consumption of human economic and social activities. The calculation formula is:

[0038]

[0039] Qs t = Qe t + Ql t + Qu t (14)

[0040] In the formula, Qs t is the water loss of the river-channel reservoir at the t-th time, 10,000 m 3 ; Qe t , Ql t and Qu t are respectively the evaporation loss water volume, seepage loss water volume, and the water consumption of human economic and social activities of the river-channel reservoir at the t-th time, 10,000 m 3 ;

[0041] Step 5. Calculate the water storage volume and the discharge water volume of the river-channel reservoir: Considering comprehensively the inflow water volume, water loss, water storage volume, and discharge water volume of the river-channel reservoir, establish the water balance equation of the river-channel reservoir as:

[0042] Qi t = Vc t + Qs t + Qo t (15)

[0043] In the formula, Vc t is the water storage variable of the river - type reservoir at time t, that is, the difference between the water storage at time t and the water storage at time t - 1, in 10,000 m 3 ; Qo t is the discharge of the river - type reservoir at time t, in 10,000 m 3 ;

[0044] Determine the initial water storage V0 of the river - type reservoir, that is, the water storage at the initial time t = 1; then, according to the water balance of the river - type reservoir, combined with the calculation results of Step 2, Step 3 and Step 4, give the water storage variable of the river - type reservoir, and further calculate the water storage and discharge. The specific calculation formulas are as follows:

[0045] Vc t = min(Qi t - Qs t , Vm t - V t-1 ) (16)

[0046] V t = V t-1 + Vc t (17)

[0047]

[0048] In the formula, V t is the water storage of the river - type reservoir at time t, in 10,000 m 3 ; V t-1 is the water storage of the river - type reservoir at time t - 1, in 10,000 m 3 , which is obtained by recursive derivation from the initial water storage V0;

[0049] Step 6: Modify the water storage and discharge of the reservoir based on the requirements of ecological flow control: Determine the requirements of the ecological flow control index of the river - type reservoir. If the calculated discharge of the river - type reservoir is greater than or equal to the control index requirement, the ecological flow control index requirement is met, and the water balance calculation is terminated. Then, the water storage and discharge of the reservoir obtained above do not need to be modified;

[0050] If the calculated discharge of the river - type reservoir is less than the requirement of the control index, the correction calculations for the reservoir storage volume and discharge are carried out: First, calculate the available discharge of the river - type reservoir, that is, the inflow minus the loss water volume plus the storage volume at a certain time. If the value is less than or equal to the requirement of the ecological flow control index, all of it needs to be discharged; if it is greater than the requirement of the ecological flow control index, the discharge is carried out according to the requirement of the ecological flow control index. The specific calculation formula is as follows:

[0051] Qiz t = Qi t - Qs t + V t-1 (19)

[0052]

[0053] Vc′ t = min(Qi t - Qs t - Qo′ t ) (21)

[0054] V′ t = V t-1 + Vc′ t (22)

[0055] In the formula, Qiz t is the available discharge of the river - type reservoir at the t - th time, in 10,000 m 3 ; Qd t is the requirement of the ecological flow control index of the river - type reservoir at the t - th time, in 10,000 m 3 ; Qo′ t is the corrected discharge of the river - type reservoir at the t - th time, in 10,000 m 3 ; Vc′ t and V′ t are the corrected storage variable and storage volume of the river - type reservoir at the t - th time, respectively, in 10,000 m 3 .

[0056] Furthermore, the rule for determining the control basin scope of the river - type reservoir in step 1 is: The control basin scope of the river - type reservoir is the basin scope with the reservoir dam site as the outlet section, and all the upstream areas that can generate runoff and converge to this dam site section.

[0057] Furthermore, the specific process of dividing the catchment units for the control catchment area of the river-type reservoir in Step 1 is as follows: First, generate sub-basins: Divide based on the digital elevation model with the aid of GIS tools, specifically including steps of depression filling, calculation of flow direction and flow accumulation, setting of flow threshold, and automatically generating sub-basins based on the threshold of flow accumulation or river network nodes. On this basis, the watershed boundary can be manually adjusted and corrected in combination with on-site investigations; Then, determine the catchment units: On the basis of generating sub-basins, merge the sub-basins involved in the tributaries entering the river-type reservoir. The land area covered by each tributary entering the reservoir is used as an independent catchment unit, and all sub-basins involved in the tributaries entering the river-type reservoir are merged into this catchment unit. Merge the land sub-basins directly flowing into the river-type reservoir as a separate catchment unit.

[0058] Furthermore, the basic data described in Step 2 includes meteorological data, hydrological data, topographic and geomorphic data, land use data, soil type distribution data, social water use data, and water conservancy project data; the meteorological data includes daily data of precipitation, temperature, sunshine, wind speed, and humidity; the hydrological data includes daily measured runoff data of hydrological stations; the topographic and geomorphic data includes DEM data, river system data, and channel parameters; the social water use data includes water consumption of agriculture, industry, and domestic use, surface and underground water supply volume, water conveyance loss coefficients of industry and domestic use, irrigation water distribution coefficient, and water conveyance loss coefficient of irrigation canals; the water conservancy project data includes the distribution of large, medium, and small reservoirs and their characteristic parameters.

[0059] Furthermore, the specific establishment of the functional relationship between the incoming water volume and the pre-discharge control water level based on the predicted incoming water volume data in Step 3 is as follows: Classify according to the incoming water volume of the river-type reservoir, and formulate the pre-discharge control water level for different levels of water volume. When the river-type reservoir is scheduled according to the three-level classified water volume, the calculation formula for the pre-discharge control water level is:

[0060]

[0061] In the formula, Qi1 t 、Qi2 t and Qi3 t are respectively the first-level, second-level, and third-level classification thresholds of the incoming water volume, in 10,000 m 3 ; the water volume thresholds are in ascending order: Qi1 t <Qi2 t <Qi3 t ; Ha3 t is the maximum pre-discharge water level limit of the reservoir at the t-th time when the incoming water volume is greater than or equal to the third-level classification threshold of the incoming water volume, in m; Ha2 tThe maximum pre-discharge water level limit of the reservoir at time t when the incoming water volume is greater than or equal to the second-level classification threshold of the incoming water volume and less than the third-level classification threshold, m; Ha1 t The maximum pre-discharge water level limit of the reservoir at time t when the incoming water volume is greater than or equal to the first-level classification threshold of the incoming water volume and less than the second-level classification threshold, m; The water levels of the river-type reservoir from low to high are: Ha3 t <Ha2 t <Ha1 t ; Hf is the flood control limited water level of the reservoir, m.

[0062] Furthermore, the water level-storage capacity function relationship of the river-type reservoir described in step 3 is obtained by comprehensively collecting reservoir topographic data, mathematical modeling, and curve fitting methods.

[0063] Furthermore, the water surface evaporation and rainfall of each section of the river-type reservoir described in step 4 are from actual observation data or calculated based on meteorological data; if there is no meteorological observation data for each section, the meteorological data for each section are estimated by numerical models, spatial interpolation methods, and remote sensing inversion methods; the water surface area of each section of the river-type reservoir is obtained through remote sensing images, topographic maps, or water level-area empirical fitting curves.

[0064] Furthermore, the total number of economic and social user types K = 4 in step 4, and k = 1, 2, 3, and 4 represent agricultural users, industrial users, domestic users, and ecological users respectively.

[0065] Furthermore, the determination of the initial water storage volume V0 of the river-type reservoir in step 5 is specifically as follows: The initial water storage volume of the river-type reservoir is determined according to the measured data, design parameters, or operating characteristics of the reservoir. The initial water storage volume is not lower than the dead storage volume and meets the comprehensive functional requirements of water supply, power generation, and ecology.

[0066] Furthermore, the determination of the ecological flow control index requirements of the river-type reservoir in step 6 is specifically as follows: The ecological flow control index requirements of the river-type reservoir are determined according to the demand characteristics of the ecological protection objects downstream of the reservoir, specifically including the survival and reproduction of aquatic organisms, the stability of wetland and riparian vegetation ecosystems, and other special ecological function requirements, and are reasonably determined by hydrological methods, hydraulic methods, biological habitat methods, and overall simulation methods; if the policy documents issued by the water administrative department have clearly specified the ecological flow index requirements for the reservoir, the requirements of the documents need to be followed.

[0067] The beneficial effects of the present invention are as follows: the method of the present invention constructs a distributed water cycle model, conducts water inflow forecasting, combines flood classification pre-discharge and other comprehensive scheduling rules, dynamically adjusts the maximum possible water storage capacity and sets ecological flow control index constraints, and realizes the dynamic calculation of the dynamic water balance of the river-type reservoir. The method of the present invention can dynamically adjust and correct the storage and discharge process of the river-type reservoir, and promote the improvement of the downstream ecosystem of the reservoir. The method of the present invention is systematic, scientific and operational, and can realize the dynamic quantitative analysis of the balance mechanism of all factors such as water inflow, discharge, loss and water storage of the river-type reservoir, providing important technical support for water resource management, scheduling optimization and planning and design of river-type reservoirs, and promoting the overall improvement of the management efficiency of river-type reservoirs.

[0068] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific implementation methods. BRIEF DESCRIPTION OF THE DRAWINGS

[0069] Figure 1 It is a schematic diagram of the process of the method of the present invention;

[0070] Figure 2 This is a schematic diagram of the division of the water catchment area of the river-type reservoir in Example 1;

[0071] Figure 3 It is a schematic diagram of the daily water inflow process of the water collection unit of the upstream water conservancy hub in Example 1;

[0072] Figure 4 It is a schematic diagram of the water level-storage capacity curve of the river-type reservoir in Example 1;

[0073] Figure 5 A schematic diagram of the daily water storage process and the maximum possible water storage capacity of the river-type reservoir in Example 1;

[0074] Figure 6 It is a schematic diagram of the sections of the river-type reservoir in the first embodiment;

[0075] Figure 7 It is a schematic diagram of the daily process of water loss of the river-type reservoir in Example 1;

[0076] Figure 8 Schematic diagram of daily discharge volume and ecological flow control requirements of a river-type reservoir in Example 1;

[0077] Figure 9 Schematic diagram of the daily water balance process of the river-type reservoir in Example 1. DETAILED DESCRIPTION

[0078] The present invention discloses a method for calculating the dynamic water balance of a river-type reservoir. Figure 1 As shown, the method comprises the following steps:

[0079] Step 1: Determine the control watershed scope of the river-type reservoir and divide the catchment units.

[0080] First, determine the control watershed scope of the river-type reservoir: The control watershed scope of the river-type reservoir is the watershed scope with the reservoir dam site as the outlet section, and all the upstream areas that can generate runoff and converge to this dam site section.

[0081] Then, divide the catchment units: Considering the similarity of characteristics such as terrain, soil, and vegetation in the watershed comprehensively, with terrain as the leading factor and sub-watersheds as the basis, divide the catchment units of the control watershed scope of the river-type reservoir:

[0082] 1) Generate sub-watersheds: It can be divided with the help of GIS tools based on the digital elevation model (DEM), specifically including steps such as depression filling, calculation of water flow direction and flow accumulation, setting of flow thresholds, etc., and sub-watersheds can be automatically generated based on the threshold of flow accumulation or river network nodes (such as tributary confluence points, reservoir inlets). On this basis, the watershed boundaries (such as interfering terrains like artificial channels, tunnels, etc.) can be manually adjusted and corrected in combination with on-site investigations.

[0083] 2) Determine the catchment units: On the basis of generating sub-watersheds, to improve the calculation efficiency, the sub-watersheds involved in the tributaries entering the river-type reservoir can be merged, and the land area covered by each tributary entering the reservoir is used as an independent catchment unit. It should be noted that all the sub-watersheds involved in the tributaries entering the river-type reservoir should be merged into this catchment unit. Similarly, the land sub-watersheds directly flowing into the river-type reservoir can be merged as a separate catchment unit.

[0084] Step 2: Predict the inflow water volume of the river-type reservoir based on the distributed hydrological model.

[0085] Taking the river-type reservoir as the control node, input the basic data to establish a distributed hydrological model. The basic data includes meteorological data (including daily data such as precipitation, temperature, sunshine, wind speed, humidity, etc.), hydrological data (including daily measured runoff data at hydrological stations, etc.), topographic and geomorphic data (including DEM data, river system data, channel parameters, etc.), land use data, soil type distribution data, social water use data (including water consumption for agriculture, industry, and domestic use, surface and underground water supply, water conveyance loss coefficients for industry and domestic use, irrigation water distribution coefficients, irrigation canal system water conveyance loss coefficients, etc.), and water conservancy project data (including the distribution and characteristic parameters of large, medium, and small reservoirs, etc.). Then, based on the measured runoff data at existing hydrological stations, carry out parameter calibration and model verification of the model.

[0086] Establish a link between the data of the rainfall forecasting platform (such as Alibaba Cloud) or meteorological satellites and rain gauging radars and the distributed hydrological model. Drive the hydrological model with real-time rainfall data to calculate the inflow of the river-type reservoir, that is, the surface runoff and the net inflow of groundwater runoff converged within the watershed controlled by the reservoir. The calculation formula is as follows:

[0087] Qi t =Qa t +Qb t (1)

[0088] In the formula, Qi t is the inflow of the river-type reservoir at time t, in 10,000 m 3 ; Qa t is the surface runoff at time t, in 10,000 m 3 ; Qb t is the net inflow of groundwater runoff at time t, that is, the difference between the inflow and the outflow, in 10,000 m 3 .

[0089] Step 3: Calculate the maximum possible water storage of the river-type reservoir.

[0090] (1) Determine the pre-discharge control water level of the river-type reservoir during the flood season.

[0091] During the flood season, the river-type reservoir implements pre-discharge according to the inflow to make the downstream discharge as uniform as possible, thereby reducing the disturbance to the downstream water resources development and utilization and the ecosystem. The pre-discharge control water level establishes a functional relationship based on the inflow prediction data according to the characteristics of the river-type reservoir, as shown in the following formula:

[0092] Ha t =fx(Qi t ) (2)

[0093] In the formula, Ha t is the pre-discharge control water level of the river-type reservoir at time t, in m; fx() is the functional relationship between the inflow during the flood season and the pre-discharge control water level.

[0094] If the functional relationship between the inflow during the flood season and the pre-discharge control water level is too complex, it is not conducive to the efficient management of the river-type reservoir. In practice, the river-type reservoir can be classified according to the inflow, and the pre-discharge control water levels for different levels of water volume can be formulated. Generally, the higher the classification level, the larger the inflow, and the lower the pre-discharge control water level. For example, when the river-type reservoir is scheduled according to the three-level classified water volume, the calculation formula for the pre-discharge control water level is as follows:

[0095]

[0096] In the formula, Qi1 t , Qi2 t and Qi3t They are the first - level, second - level, and third - level classification thresholds of the water inflow into the reservoir, in 10,000 m³ 3 ; Usually, the water volume thresholds are in ascending order: Qi1 t <Qi2 t <Qi3 t ; Ha3 t is the maximum pre - discharge water level limit of the reservoir at time t when the water inflow into the reservoir is greater than or equal to the third - level classification threshold of the water inflow into the reservoir, in m; Ha2 t is the maximum pre - discharge water level limit of the reservoir at time t when the water inflow into the reservoir is greater than or equal to the second - level classification threshold of the water inflow into the reservoir and less than the third - level classification threshold, in m; Ha1 t is the maximum pre - discharge water level limit of the reservoir at time t when the water inflow into the reservoir is greater than or equal to the first - level classification threshold of the water inflow into the reservoir and less than the second - level classification threshold, in m; Usually, the water levels of river - type reservoirs are in ascending order: Ha3 t <Ha2 t <Ha1 t ; Hf is the flood - limit water level of the reservoir, in m.

[0097] The flood - limit water level, also known as the flood - control limit water level or the flood - season control water level, refers to the upper limit water level allowed for water storage in a river - type reservoir during the flood season. The determination and management of the flood - limit water level are conducive to coordinating the flood - control and water - utilization relationships of the river - type reservoir and ensuring that the reservoir plays its flood - control function. Usually, comprehensive requirements such as flood characteristics, reservoir characteristics, and flood - control needs need to be considered, and the flood - limit water level of the river - type reservoir is determined through quantitative calculation and dynamic adjustment techniques. Further, if the water administrative department has determined the flood - limit water level of the river - type reservoir through management measures, it can be directly adopted.

[0098] (2) Calculate the highest water level limit required for the comprehensive operation of the river - type reservoir.

[0099] Based on the above - determined flood - season pre - discharge control water level of the river - type reservoir, further determine the highest water level limit required for the river - type reservoir to achieve other comprehensive utilization functions (including navigation, water supply, power generation, and sediment discharge, etc.), so as to calculate the highest water level limit required for the comprehensive operation of the river - type reservoir. The calculation formula is as follows:

[0100] Hm t =max (Ha t ,Hb t ,Hc t ,Hd t ,He t ) (4)

[0101] In the formula, Hm t is the highest water level limit required for the comprehensive operation of the river - type reservoir at time t, in m; Hb t is the highest water level limit required for the navigation of the river - type reservoir, in m; Hct The maximum water level limit for the water supply requirement of the river - type reservoir, m; Hd t The maximum water level limit for the power generation requirement of the river - type reservoir, m; He t The maximum water level limit for the sediment discharge requirement of the river - type reservoir, m.

[0102] Similarly, Hb t 、Hc t 、Hd t 、He t are all determined by establishing corresponding functional relationships based on the inflow water volume.

[0103] (3) Calculate the maximum possible water storage capacity of the river - type reservoir.

[0104] The maximum possible water storage capacity of the river - type reservoir is affected by both its own design parameters and external water inflow conditions. Based on the flood - season pre - discharge control water level of the river - type reservoir determined above and the maximum water level limit required for comprehensive operation, and based on the water - level - storage - capacity functional relationship of the river - type reservoir, calculate the maximum possible water storage capacity of the river - type reservoir. The calculation formula is as follows:

[0105] Vm t =fz(Hm t ) (5)

[0106] In the formula, Vm t is the maximum possible water storage capacity of the river - type reservoir at time t, in 10,000 m 3 ; fz() is the water - level - storage - capacity functional relationship of the river - type reservoir. Among them, the water - level - storage - capacity functional relationship describes the water storage capacity of the river - type reservoir at different water levels, that is, the curve relationship between the storage capacity and the water level, which can be comprehensively obtained through methods such as reservoir topographic data collection, mathematical modeling, and curve fitting.

[0107] Step 4: Calculate the water loss of the river - type reservoir.

[0108] (1) Segment the river - type reservoir according to the catchment unit.

[0109] Affected by the characteristics of the original river, channel-type reservoirs usually extend along the original river course. During the operation of reservoir regulation, the water level change in the reservoir area will affect the upstream river course, forming a backwater area, which shows reservoir characteristics during reservoir impoundment and returns to natural river course characteristics after the water level drops. Along the channel-type reservoir from upstream to downstream, its riverbed morphology, geological parameters, and water intake activities on both banks will change dynamically with seasons, and the water loss of the channel-type reservoir should be calculated section by section. Based on the catchment units divided in Step 1, the channel-type reservoir is first segmented according to the connection points between the outlets of each catchment unit and the channel-type reservoir (j = 1, 2, 3…J), where J is the total number of segments of the channel-type reservoir. If J = 3, the channel-type reservoir can be divided into the tail section of the reservoir, the middle section of the reservoir, and the section near the dam. In subsequent calculations, the segmentation can be merged and refined according to factors such as the geological structure of the channel-type reservoir, the slope of the reservoir bank, or the thickness of the overburden layer, as well as the intensive characteristics of human water intake activities. Segmenting the channel-type reservoir can significantly improve the calculation accuracy of the water loss of the channel-type reservoir.

[0110] (2) Determine the reservoir evaporation loss water volume section by section.

[0111] Evaporation loss water volume is a component of the water loss of the channel-type reservoir, especially in arid regions or seasons with higher temperatures, and its impact is more significant. Evaporation loss water volume is usually affected by various factors such as meteorological conditions and reservoir area, and can be determined by methods such as the empirical formula method, remote sensing monitoring method, and on-site observation method according to the characteristics of the channel-type reservoir.

[0112] Obtain the water surface evaporation, rainfall, and water surface area of each section of the channel-type reservoir. Based on the obtained data, the evaporation loss water volume of each section of the channel-type reservoir is calculated as shown in the following formula:

[0113] Qe j,t =S k,t-1 ×(Ee j,t -Pe j,t )×10 -3 (6)

[0114] In the formula, Qe j,t is the evaporation loss water volume of the j-th section of the channel-type reservoir, in 10,000 m 3 , Ee j,t is the water surface evaporation of the j-th section of the channel-type reservoir at the t-th time, in mm; Pe j,t is the rainfall of the j-th section of the channel-type reservoir at the t-th time, in mm; S j,t-1 is the water surface area of the j-th section of the channel-type reservoir at the (t - 1)-th time, in 10,000 m 2 .

[0115] The water surface evaporation and rainfall of each section of a river - type reservoir are sourced from actual observed data or calculated based on meteorological data; if there is no segmented meteorological observation data, methods such as numerical models (e.g., WRF), spatial interpolation methods (e.g., Kriging method, etc.), and remote sensing inversion methods are required to estimate the meteorological data of each section. The water surface area of each section of a river - type reservoir can be obtained through remote sensing images, topographic maps, or water level - area empirical fitting curves.

[0116] (3) Determine the leakage loss water volume of the reservoir by section.

[0117] The leakage loss water volume of a river - type reservoir mainly includes bank leakage loss, dam body, dam foundation, and around - dam leakage loss, etc., and is usually affected by different regional geological conditions (such as rock and soil properties, fault distribution, etc.), bank characteristics (such as slope, vegetation cover, etc.), anti - seepage measures, and control water level and other factors. The leakage loss water volume of each section of a river - type reservoir can be combined with the reservoir operation and regulation characteristics, and based on the data of geological and groundwater exploration and water level monitoring, determine parameters such as water head, seepage path, and permeability coefficient for quantitative calculation. The leakage loss water volume of each section of a river - type reservoir includes two parts: the bottom leakage loss water volume and the bank slope leakage loss water volume, which need to be calculated separately and then superimposed. The calculation formula is:

[0118] Ql j,t =Qla j,t +Qlb j,t (7)

[0119] In the formula, Ql j,t is the leakage loss water volume of the j - th section of the river - type reservoir at the t - th time, in 10,000 m 3 ; Qla j,t is the bottom leakage loss water volume of the j - th section of the river - type reservoir, in 10,000 m 3 ; Qlb j,t is the bank slope leakage loss water volume of the j - th section of the river - type reservoir, in 10,000 m 3 .

[0120] Since the bottom of a river - type reservoir is usually composed of porous media (such as sandy soil, clay, etc.), the seepage process is mostly laminar flow, and the water head difference is usually small, the one - dimensional vertical seepage formula of Darcy's law can be used for calculation, as shown in formula (8). It should be noted that Darcy's law is applicable to linear seepage. When the seepage velocity of each section of a river - type reservoir is high or the medium is heterogeneous, other more complex seepage and leakage formulas need to be used for calculation.

[0121] Qla j,t =Ka j,t ×Aa j,t ×La j,t ×10 -4 (8)

[0122] In the formula, Ka jis the bottom seepage coefficient of the j-th section of the river-type reservoir at time t, which reflects the water permeability of the bottom medium (such as soil or rock) and can be obtained through laboratory measurement or on-site pumping tests, m; Aa j,t is the seepage area of the j-th section of the reservoir bottom at time t, that is, the area perpendicular to the seepage direction at the reservoir bottom, which can be determined according to the reservoir bottom topography and geological conditions, m 2 ; La j,t is the hydraulic gradient of the reservoir bottom at the j-th section and time t, which represents the ratio of the water head difference at the reservoir bottom to the seepage path length and is calculated by measuring the water head difference and seepage path length between the upstream and downstream of the reservoir bottom, dimensionless.

[0123] During the bank slope seepage process of the river-type reservoir, it usually occurs in saturated soil and is mostly in laminar flow state. The Darcy's law inclined plane seepage formula can be used for calculation, as shown in Equation (9). Similar to the previous situation, it should be noted that Darcy's law is applicable to linear seepage. When the seepage velocity is high or the medium is heterogeneous, other more complex seepage and leakage formulas should be used for calculation.

[0124] Qlb j,t =Kb j,t ×Ab j,t ×Lb j,t ×S j,t ×10 -4 (9)

[0125] In the formula, Kb j is the bank slope seepage coefficient of the j-th section of the river-type reservoir at time t, which reflects the water permeability of the bank slope medium (such as soil or rock) and can be obtained through laboratory measurement or on-site pumping tests, m; Ab j,t is the seepage area of the j-th section of the river-type reservoir bank slope at time t, that is, the area perpendicular to the seepage direction of the bank slope inclined plane, which can be determined according to the bank slope topography and geological conditions, m 2 ; Lb j,t is the hydraulic gradient of the j-th section of the river-type reservoir bank slope at time t, which represents the ratio of the water head difference of the bank slope to the seepage path length and is calculated by measuring the water head difference and seepage path length between the upstream and downstream of the bank slope, dimensionless; S j,t is the angle between the inclined plane of the j-th section of the river-type reservoir bank slope and the horizontal plane, which is obtained through topographic measurement.

[0126] (4) Determine the water consumption of human economic and social activities by section.

[0127] The water consumption of human economic and social activities includes the water consumption brought about by the water intake, water use, and drainage activities of various users in human economic and social sectors (including agricultural users, industrial users, domestic users, and ecological users) from each section along the river-type reservoir. Since the user distribution and water intake and use characteristics of each section of the river-type reservoir are different, and this further affects the water surface area and water volume process of the next section of the river-type reservoir, it is necessary to calculate by section. The specific formula is as follows:

[0128]

[0129] In the formula, Qu j,t is the water consumption of human economic and social activities in the j-th section of the river-type reservoir, in 10,000 m 3 ; U j,t,k is the water intake of the k-th type of user at the j-th section of the river-type reservoir at the t-th time, in 10,000 m 3 ; Hr j,t,K is the water consumption coefficient of the k-th type of user at the j-th section of the river-type reservoir at the t-th time, dimensionless; K is the total number of economic and social user types, in number; here K = 4, and k = 1, 2, 3, and 4 represent four typical user types: agriculture, industry, domestic, and ecology respectively.

[0130] (5) Determine the water loss of the river-type reservoir.

[0131] The water loss of the river-type reservoir is equal to the sum of the evaporation loss water volume, seepage loss water volume, and water consumption of human economic and social activities, as shown in the following formula:

[0132]

[0133] Qs t = Qe t + Ql t + Qu t (14)

[0134] In the formula, Qs t is the water loss of the river-type reservoir at the t-th time, in 10,000 m 3 ; Qe t , Ql t and Qu t are the evaporation loss water volume, seepage loss water volume, and water consumption of human economic and social activities of the river-type reservoir at the t-th time respectively, in 10,000 m 3 .

[0135] Step 5: Calculate the water storage volume and the downstream discharge volume of the river-type reservoir.

[0136] (1) Determine the water balance relationship of the river-type reservoir.

[0137] Comprehensively considering the inflow water volume, water loss, water storage volume, and downstream discharge volume of the river-type reservoir, establish the water balance equation of the river-type reservoir as:

[0138] Qi t = Vc t + Qs t + Qo t (15)

[0139] Wherein, Vc t is the water storage variable of the river - type reservoir at time t (i.e., the difference between the water storage at time t and the water storage at time t - 1), in 10,000 m 3 ; Usually, an increase in the water storage of the river - type reservoir is positive, and a decrease is negative; Qo t is the discharge of the river - type reservoir at time t, in 10,000 m 3 .

[0140] (2) Determine the initial water storage of the river - type reservoir.

[0141] Determine the water storage at the initial time (t = 1) of the river - type reservoir, i.e., the initial water storage V0. The determination of the initial water storage is an important link to ensure the safe operation of the reservoir and the efficient utilization of water resources, and it can be determined according to the measured data, design parameters or operation characteristics of the reservoir. Usually, the initial water storage is not lower than the dead storage capacity and meets the comprehensive functional requirements such as water supply, power generation, and ecology.

[0142] (3) Determine the water storage and discharge of the river - type reservoir.

[0143] According to the water balance of the river - type reservoir, combined with the calculation results of steps 2, 3 and 4, give the water storage variable of the river - type reservoir, and further calculate the water storage and discharge. The specific calculation formulas are as follows:

[0144] Vc t = min(Qi t - Qs t , Vm t - V t-1 ) (16)

[0145] V t = V t-1 + Vc t (17)

[0146]

[0147] Wherein, V t is the water storage of the river - type reservoir at time t, in 10,000 m 3 ; V t-1 is the water storage of the river - type reservoir at time t - 1, in 10,000 m 3 , which can be obtained by recursive derivation from the initial water storage V0.

[0148] Step 6. Modify the reservoir storage volume and the discharged water volume based on the requirements of ecological flow control.

[0149] The discharged water volume of a river-channel reservoir is an important measure to ensure the ecological flow of the river and protect the biodiversity of aquatic organisms. The requirements for the ecological flow control index of a river-channel reservoir should be determined according to the demand characteristics of the ecological protection objects downstream of the reservoir, specifically including the survival and reproduction of aquatic organisms, the stability of wetland and riparian vegetation ecosystems, and other special ecological function requirements, etc. It can be reasonably determined by using methods such as the hydrological method, the hydraulic method, the biological habitat method, and the overall simulation method. If the relevant policy documents issued by the water administrative department have clearly specified the ecological flow index requirements for the reservoir, the managers of the river-channel reservoir need to follow these regulations to discharge the ecological flow. If the time step of the water balance calculation of the river-channel reservoir (such as minutes, hours) and the ecological flow control index is on a daily scale, then a time-scale conversion calculation is required. If the calculated discharged water volume of the river-channel reservoir is greater than or equal to the requirements of this control index, the ecological flow index requirements are met, and the water balance calculation terminates, and the above-obtained storage volume and discharged water volume do not need to be modified.

[0150] If the discharged water volume of the river-channel reservoir is less than the requirements of the ecological flow control index, the correction calculation of the reservoir storage volume and the discharged water volume should be carried out. The available discharged water volume of the river-channel reservoir should be calculated, that is, the inflow water volume minus the loss water volume plus the storage volume at a certain time. If its value is less than or equal to the requirements of the ecological flow control index, then all of it needs to be discharged to maximize the maintenance of the ecological system service function; if it is greater than the requirements of the ecological flow control index, then it is discharged according to the requirements of the ecological flow control index. The specific calculation formula is as follows:

[0151] Qiz t =Qi t - Qs t +V t-1 (19)

[0152]

[0153] Vc′ t =min(Qi t -Qs t - Qo′ t ) (21)

[0154] V′ t =V t-1 +Vc′ t (22)

[0155] In the formula, Qiz t is the available discharged water volume of the river-channel reservoir at the t-th time, in 10,000 m 3 ; Qd tEcological flow control index requirements for river-type reservoirs at time t, 10,000 m 3 ; Qo′ t is the corrected discharge volume of the river-type reservoir at time t, 10,000 m 3 ; Vc′ t and V′ t are the water storage variable and water storage capacity of the river-type reservoir at time t after correction, 10,000 m 3 .

[0156] Embodiment 1

[0157] This embodiment is an application example of the above method.

[0158] This example takes a river-type reservoir in the upper reaches of the Han River in my country as the research object. The river-type reservoir is a cascade development power station in the upper reaches of the Han River mainstream, located at dam site A. The basin area above the dam site is 42,400 km 2 , there are four main tributaries of the Han River entering the river-type reservoir. Using GIS tools, sub-basins were identified based on the digital elevation model DEM (spatial resolution is 30m*30m). Based on the identified sub-basins, the tributaries of the Han River entering the river-type reservoir were merged into independent catchment units, and the sub-basins directly entering the river-type reservoir were merged into the central urban catchment unit and the central urban foreign catchment unit. The spatial distribution of the catchment units is as follows: Figure 2 shown.

[0159] Based on the distributed hydrological model (WEP model), a normal water year (taking 2020 as an example) is selected to carry out daily scale calculations, and the water inflow forecast for the river-type reservoir is shown in Table 1. Since the river-type reservoir is located in a water-rich area, the inflow and outflow of groundwater runoff in this case are negligible. Among them, the daily water inflow process of the upstream water conservancy hub water catchment unit is as follows Figure 3 shown.

[0160] Table 1 Prediction of water inflow into river-type reservoirs based on distributed hydrological model

[0161] Number Catchment unit <![CDATA[Annual water inflow (100 million m 3 )]]> 1 Catchment unit of upstream water control project 153.17 2 Catchment unit of central urban area 0.30 3 Catchment unit outside central urban area 6.23 4 Catchment unit of tributary 1 (Yuehe River) 7.96 5 Catchment unit of tributary 2 (Jihe River) 2.67 6 Catchment unit of tributary 3 (Huangyanghe River) 2.85 7 Catchment unit of tributary 4 (Bahe River) 4.48 Total 177.67

[0162] Using the survey and design data, the water level-storage capacity curve of the river-type reservoir is given as follows: Figure 4 As shown in Figure 2, the normal water level of this river-type reservoir is 241 m, which corresponds to a storage capacity of 260 million m 3 The flood limit water level of 273m corresponds to a reservoir capacity of 175 million m 3 .

[0163] The floods in the basin above the dam site of the river-type reservoir are mainly caused by rainstorms, and the corresponding flood limit water level is 237 m. Generally, the flood season begins in late April and the peach flood occurs until the end of May; the main flood season is from July to October, and rainstorm floods mainly occur during this period. Among them, July in summer and September in autumn have the most floods. Summer floods are generally formed by rainstorms with high intensity, short duration and small rain area; autumn floods are generally formed by rainstorms that are stable and persistent with a large rain area, and the flood duration is long and the flood volume is large. According to the reservoir operation rules, the flood prevention pre-discharge rules for the river-type reservoir are shown in Table 1. According to the reservoir operation rules, based on the predicted value of the inflow, the pre-discharge control values of the reservoir water level for the river-type reservoir are shown in Table 2. That is, when the inflow is greater than or equal to 1900 m 3 / s and less than 2300 m 3 / s, the reservoir pre-discharges in advance and the reservoir water level drops to 237 m (the first level); when the predicted inflow is greater than or equal to 2300 m 3 / s and less than 3500 m 3 / s, the reservoir water level drops to 235 m (the second level); when the predicted inflow is greater than or equal to 3500 m 3 / s, the reservoir water level drops to 233 m (the third level).

[0164] Table 2 Flood prevention pre-discharge operation rules for river-type reservoirs

[0165] Number Inflow Reservoir control level Pre-discharge level 1 <![CDATA[≥1900 m 3 / s and < 2300 m 3 / s]]> Drop to 237m First level 2 <![CDATA[≥2300m 3 / s and < 3500m 3 / s]]> Drop to 235m Second level 3 <![CDATA[≥3500m 3 / s]]> Drop to 233m Third level

[0166] The maximum possible water storage calculated according to the above method is as Figure 5 shown. Affected by flood prevention pre-discharge and the flood limit water level, the maximum possible water storage significantly decreases during the peach flood period from late April to the end of May and from July to October. At some times, such as July 22, August 18 and August 19, due to the large predicted inflow floods and pre-discharge operation, the maximum possible water storage further decreases.

[0167] Considering that there are few human water intake activities around this river-type reservoir, it is mainly divided into two sections according to the geological conditions of the reservoir, namely the tail section of the reservoir and the dam site section, as Figure 6 shown. Among them, the tail section of the reservoir is located upstream of the confluence of tributary 3, and the dam site section is located downstream of the confluence to the dam site. According to the bottom characteristics of different sections of this river-type reservoir and the relevant parameters of the bank slopes provided by the design unit, combined with the characteristics of the reservoir water storage process, the annual water loss of this river-type reservoir is calculated to be 30.06 million m 3 , among which, the tail section of the reservoir is mainly composed of bedrock with small leakage, accounting for 19.6%, and the dam site section has a relatively large leakage due to its sandy soil structure, and its daily process is as Figure 7 shown.

[0168] The actual water storage capacity of river-type reservoirs is affected by the initial water storage capacity, inflow and water loss. The water storage capacity of the reservoir gradually increases at the beginning of the year and gradually approaches the maximum possible water storage capacity.

[0169] In order to alleviate the impact on the ecological environment of the downstream river section and protect the fish resources in the river section below the dam, according to the relevant planning and design institute, project acceptance opinions and water intake permit requirements, the river-type reservoir should have a daily minimum ecological flow of no less than 120m 3 / s. The discharge flow of the river-type reservoir calculated by the method of the present invention and the minimum ecological flow control requirements are as follows: Figure 8 As shown in the figure, due to the low minimum ecological flow control index, the reservoir discharge in this normal water year (2020) basically meets the control and assessment requirements of the minimum ecological flow. Furthermore, in special drought years, when the water inflow is small, the degree of guarantee of the minimum ecological flow needs to be verified.

[0170] The daily water balance process of the river-type reservoir is as follows Figure 9 As shown in the figure, it specifically includes the amount of water entering the reservoir, the amount of water lost, the amount of water discharged, and the amount of water stored. Due to the large amount of water entering the reservoir, the small storage capacity, and the small amount of water loss, most of the water entering the reservoir is discharged. The calculation results show that the annual water inflow of the river-type reservoir is 17.77 billion m 3 , of which the reservoir discharge accounted for 98.4%, and the loss of water accounted for only 0.16%. The maximum daily water storage increment of the reservoir was 31.93 million m 3 (November 6), the average daily water storage capacity is 210 million m 3 The water level reached normal level for 201 days, accounting for 54.9% of the total days in the year.

[0171] Finally, it should be noted that the above is only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred arrangement scheme, a person skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the spirit and scope of the technical solution of the present invention.

Claims

1. A method for calculating the dynamic water volume balance of a river-type reservoir, characterized in that, The method includes the following steps: Step 1: Determine the control watershed scope of the river-channel reservoir and divide the catchment units: Determine the control watershed scope of the river-channel reservoir according to the determination rules of the control watershed scope of the river-channel reservoir; comprehensively consider the similarities of terrain, soil, and vegetation characteristics within the watershed, and divide the control watershed scope of the river-channel reservoir into catchment units. Step 2: Predict the inflow of the river-channel reservoir based on the distributed hydrological model: Take the river-channel reservoir as the control node, input the basic data, and establish a distributed hydrological model; establish the link between the rainfall forecast platform data or meteorological satellite and rain gauge radar data and the distributed hydrological model, and drive the hydrological model through real-time rainfall data to calculate the inflow of the river-channel reservoir, that is, the surface runoff volume and the net inflow volume of groundwater runoff converged within the control watershed scope of the reservoir. The calculation formula is: Qi t = Qa t + Qb t (1) Where Qi t is the inflow of the river - type reservoir at time t, in 10,000 m 3 ; Qa t is the surface runoff at time t, in 10,000 m 3 ; Qb t is the net inflow of groundwater runoff at time t, that is, the difference between the inflow and the outflow, in 10,000 m 3 ; Step 3: Calculate the maximum possible water storage of the river-channel reservoir: First, determine the flood-season pre-discharge control water level of the river-channel reservoir: According to the characteristics of the river-channel reservoir, establish the functional relationship between the inflow and the pre-discharge control water level based on the predicted inflow data, as shown in the following formula: Ha t = fx(Qi t ) (2) where Ha t is the pre-discharge control water level of the river-type reservoir during the flood season at the t-th time, in m; fx() is the functional relationship between the inflow during the flood season and the pre-discharge control water level; Then, based on the determined flood-season pre-discharge control water level of the river-channel reservoir, determine the highest water level limit required for other comprehensive utilization functions of the river-channel reservoir, including navigation, water supply, power generation, and sediment discharge, so as to calculate the highest water level limit required for the comprehensive operation of the river-channel reservoir. The calculation formula is: Hm t = max(Ha t , Hb t , Hc t , Hd t , He t ) (4) where, Hm t is the maximum water level limit required for the integrated operation of the river-type reservoir at the t-th time, m; Hb t is the maximum water level limit required for navigation of the river-type reservoir, m; Hc t is the maximum water level limit required for water supply of the river-type reservoir, m; Hd t is the maximum water level limit required for power generation of the river-type reservoir, m; He t is the maximum water level limit required for sediment discharge of the river-type reservoir, m; Hb t , Hc t , Hd t , He t are all determined by establishing corresponding functional relationships based on the inflow water volume; Finally, according to the determined flood-season pre-discharge control water level of the river-channel reservoir and the highest water level limit required for comprehensive operation, based on the water level-storage function relationship of the river-channel reservoir, calculate the maximum possible water storage of the river-channel reservoir. The calculation formula is: Vm t = fz(Hm t ) (5) Where, Vm t is the maximum possible water storage capacity of the river - type reservoir at the t - th time, in 10,000 m 3 ; fz() is the water level - storage capacity functional relationship of the river - type reservoir; Step 4: Calculate the water loss of the river-channel reservoir: First, segment the river-channel reservoir according to the catchment units: Based on the catchment units divided in Step 1, segment the river-channel reservoir according to the connection points between the outlets of each catchment unit and the river-channel reservoir (j = 1, 2, 3…J), where J is the total number of segments of the river-channel reservoir. Then, determine the reservoir evaporation loss water volume segment by segment: Obtain the water surface evaporation volume, rainfall, and water surface area of each segment of the river-channel reservoir, and calculate the evaporation loss water volume of each segment of the river-channel reservoir. The specific formula is: Qe j,t = S j,t-1 × (Ee j,t - Pe j,t ) × 10 -3 (6) Where, Qe j,t is the evaporation loss water volume of the j-th section of the river-type reservoir, in 10,000 m 3 ; Ee j,t is the water surface evaporation of the j-th section of the river-type reservoir at the t-th time, in mm; Pe j,t is the rainfall of the j-th section of the river-type reservoir at the t-th time, in mm; S j,t-1 is the water surface area of the j-th section of the river-type reservoir at the (t - 1)-th time, in 10,000 m 2 ; Then, determine the reservoir leakage loss water volume segment by segment: The leakage loss water volume of each segment of the river-channel reservoir includes two parts: the bottom leakage loss water volume and the bank slope leakage loss water volume. The calculation formula is: Ql j,t = Qla j,t + Qlb j,t (7) Where Ql j,t is the seepage loss water volume of the j-th section of the river-type reservoir at the t-th time, in 10,000 m 3 ; Qla j,t is the bottom seepage loss water volume of the j-th section of the river-type reservoir, in 10,000 m 3 ; Qlb j,t is the bank slope seepage loss water volume of the j-th section of the river-type reservoir, in 10,000 m 3 ; Among them, the water leakage loss volume Qla at the bottom of the reservoir j,t is calculated by the following formula: Qla j,t = Ka j,t × Aa j,t × La j,t × 10 -4 (8) Where, Ka j is the bottom permeability coefficient of the j-th section of the river-type reservoir at the t-th time, m; Aa j,t is the seepage area of the j-th section of the reservoir bottom at the t-th time, m 2 ; La j,t is the hydraulic gradient of the reservoir bottom of the j-th section at the t-th time, dimensionless; The seepage loss water volume Qlb of the bank slope j,t The calculation formula is as follows: Qlb j,t = Kb j,t × Ab j,t × Lb j,t × S j,t × 10 -4 (9) Where, Kb j is the seepage coefficient of the bank slope at the j-th section and the t-th time of the river-channel reservoir, m; Ab j,t is the seepage area of the bank slope at the j-th section of the river-channel reservoir at the t-th time, m 2 ; Lb j,t is the hydraulic gradient of the bank slope at the j-th section of the river-channel reservoir at the t-th time, dimensionless; S j,t is the angle between the inclined plane of the bank slope at the j-th section of the river-channel reservoir and the horizontal plane; Then, determine the water consumption of human economic and social activities segment by segment: The water consumption of human economic and social activities includes the water consumption brought by the water intake, water use, and drainage activities of various users of human economy and society from each segment along the river-channel reservoir. The segment calculation formula is: Where Qu j,t is the water consumption of human economic and social activities in the j-th section of the river-type reservoir, in 10,000 m 3 ; U j,t,k is the water intake of the k-th type of user at the j-th section of the river-type reservoir at the t-th time, in 10,000 m 3 ; Hr j,t,k is the water consumption coefficient of the k-th type of user at the j-th section of the river-type reservoir at the t-th time, dimensionless; K is the total number of types of economic and social users, in number; Finally, determine the water loss of the river-channel reservoir: The water loss of the river-channel reservoir is equal to the sum of the reservoir evaporation loss water volume, leakage loss water volume, and water consumption of human economic and social activities. The calculation formula is: Qs t = Qe t + Ql t + Qu t (14) In the formula, Qs t is the water loss of the river-type reservoir at time t, in 10,000 m 3 ; Qe t , Ql t and Qu t are the evaporation loss water volume, seepage loss water volume and water consumption of human economic and social activities of the river-type reservoir at time t, respectively, in 10,000 m 3 ; Step 5: Calculate the water storage and discharge of the river-channel reservoir: Comprehensively consider the inflow, water loss, water storage, and discharge of the river-channel reservoir, and establish the water balance equation of the river-channel reservoir as: Qi t = Vc t + Qs t + Qo t (15) Where, Vc t is the water storage variable of the river-type reservoir at time t, that is, the difference between the water storage at time t and the water storage at time t - 1, in 10,000 m 3 ; Qo t is the discharge of the river-type reservoir at time t, in 10,000 m 3 ; Determine the initial water storage volume V0 of the river-channel reservoir, i.e., the water storage volume at the initial time t = 1; then, based on the water balance of the river-channel reservoir and combining the calculation results of Step 2, Step 3, and Step 4, give the water storage variable of the river-channel reservoir, and further calculate the water storage volume and the discharge water volume. The specific calculation formulas are as follows: Vc t = min(Qi t - Qs t , Vm t - V t-1 ) (16) V t = V t-1 + Vc t (17) Where, V t is the water storage volume of the river-type reservoir at the t-th time, in 10,000 m 3 ; V t-1 is the water storage volume of the river-type reservoir at the (t - 1)-th time, in 10,000 m 3 , which is recursively obtained from the initial water storage volume V0; Step 6. Correct the water storage volume and the discharge water volume of the reservoir based on the ecological flow control requirements: Determine the ecological flow control index requirements of the river-channel reservoir. If the calculated discharge water volume of the river-channel reservoir is greater than or equal to the control index requirements, the ecological flow control index requirements are met, and the water balance calculation terminates. Then, the water storage volume and the discharge water volume of the reservoir obtained above do not need to be corrected; If the calculated discharge water volume of the river-channel reservoir is less than the control index requirements, perform the correction calculation of the water storage volume and the discharge water volume of the reservoir: First, calculate the available discharge water volume of the river-channel reservoir, that is, the inflow water volume minus the loss water volume plus the water storage volume at a previous time. If its value is less than or equal to the ecological flow control index requirements, all of it needs to be discharged; if it is greater than the ecological flow control index requirements, discharge it according to the ecological flow control index requirements. The specific calculation formulas are as follows: Qiz t = Qi t - Qs t +V t-1 (19) Vc′ t = min(Qi t - Qs t - Qo′ t ) (21) V′ t = V t-1 + Vc′ t (22) Where, Qiz t is the available discharge of the river-type reservoir at time t, in 10,000 m 3 ; Qd t is the ecological flow control index requirement of the river-type reservoir at time t, in 10,000 m 3 ; Qo′ t is the corrected discharge of the river-type reservoir at time t, in 10,000 m 3 ; Vc′ t and V′ t are respectively the storage variable and storage volume of the corrected river-type reservoir at time t, in 10,000 m 3 .

2. The dynamic water volume balance calculation method for a river-channel reservoir according to claim 1, wherein The rule for determining the control basin scope of the river-channel reservoir described in Step 1 is: The control basin scope of the river-channel reservoir is the basin scope with the reservoir dam site as the outlet section, and all the upstream areas that can generate runoff and converge to this dam site section.

3. A method for calculating the dynamic water volume balance of a river-type reservoir according to claim 1, characterized in that, The specific process of dividing the catchment units for the control basin scope of the river-channel reservoir described in Step 1 is: First, generate sub-basins: Divide based on the digital elevation model with the aid of GIS tools, which specifically includes steps such as depression filling, calculation of water flow direction and flow accumulation, setting of flow threshold. Generate sub-basins automatically based on the threshold of flow accumulation or river network nodes. On this basis, the watershed boundary can be manually adjusted and corrected in combination with on-site investigations; then, determine the catchment units: On the basis of generating sub-basins, merge the sub-basins involved in the tributaries entering the river-channel reservoir. The land area covered by each incoming tributary is used as an independent catchment unit, and all the sub-basins involved in the incoming tributaries of the river-channel reservoir are merged into this catchment unit. Merge the land sub-basins directly flowing into the river-channel reservoir as a separate catchment unit.

4. A dynamic water volume balance calculation method for a river channel type reservoir according to claim 1, characterized in that, The basic data described in Step 2 includes meteorological data, hydrological data, topographic and geomorphic data, land use data, soil type distribution data, social water use data, and water conservancy project data; the meteorological data includes daily data of precipitation, temperature, sunshine, wind speed, and humidity; the hydrological data includes daily measured runoff data of hydrological stations; the topographic and geomorphic data includes DEM data, river system data, and channel parameters; the social water use data includes water consumption of agriculture, industry, and domestic use, surface and underground water supply volumes, water conveyance loss coefficients of industry and domestic use, irrigation water distribution coefficients, and water conveyance loss coefficients of irrigation canals; the water conservancy project data includes the distribution and characteristic parameters of large, medium, and small reservoirs.

5. A method for calculating the dynamic water volume balance of a river channel type reservoir according to claim 1, characterized in that, The specific method for establishing the functional relationship between the incoming reservoir water volume and the pre-discharge control water level described in Step 3 is as follows: The incoming water volume of the river-type reservoir is classified, and the pre-discharge control water levels for different levels of water volume are formulated. When the river-type reservoir is scheduled according to the three-level classified water volume, the calculation formula for the pre-discharge control water level is: Where, Qi1 t , Qi2 t and Qi3 t are the first-stage, second-stage, and third-stage classification thresholds of the water inflow into the reservoir, in 10,000 m 3 ; the water volume thresholds are in ascending order: Qi1 t < Qi2 t < Qi3 t ; Ha3 t is the maximum pre-discharge water level limit of the reservoir at time t when the water inflow into the reservoir is greater than or equal to the third-stage classification threshold of the water inflow into the reservoir, in m; Ha2 t is the maximum pre-discharge water level limit of the reservoir at time t when the water inflow into the reservoir is greater than or equal to the second-stage classification threshold of the water inflow into the reservoir and less than the third-stage classification threshold, in m; Ha1 t is the maximum pre-discharge water level limit of the reservoir at time t when the water inflow into the reservoir is greater than or equal to the first-stage classification threshold of the water inflow into the reservoir and less than the second-stage classification threshold, in m; the water levels of the river-type reservoir are in ascending order: Ha3 t < Ha2 t < Ha1 t ; Hf is the flood limit water level of the reservoir, in m.

6. The dynamic water volume balance calculation method for a river channel type reservoir according to claim 1, characterized in that The water level-storage capacity functional relationship of the river-type reservoir described in Step 3 is obtained through a comprehensive method of reservoir terrain data collection, mathematical modeling, and curve fitting.

7. A method for calculating the dynamic water volume balance of a river-channel reservoir according to claim 1, characterized in that, The water surface evaporation and rainfall of each section of the river-type reservoir described in Step 4 are derived from actual observation data or calculated based on meteorological data; if there is no meteorological observation data for each section, the meteorological data for each section are estimated through numerical models, spatial interpolation methods, and remote sensing inversion methods; the water surface area of each section of the river-type reservoir is obtained through remote sensing images, topographic maps, or water level-area empirical fitting curves.

8. A dynamic water volume balance calculation method for a river channel type reservoir according to claim 1, characterized in that, The total number of economic and social user types K = 4 in Step 4, and k = 1, 2, 3, and 4 represent agricultural users, industrial users, domestic users, and ecological users respectively.

9. A method for calculating the dynamic water volume balance of a river-type reservoir according to claim 1, characterized in that, The specific method for determining the initial water storage volume V0 of the river-type reservoir in Step 5 is as follows: The initial water storage volume of the river-type reservoir is determined based on the measured data, design parameters, or operating characteristics of the reservoir. The initial water storage volume is not lower than the dead storage capacity and meets the comprehensive functional requirements of water supply, power generation, and ecology.

10. A method for calculating the dynamic water volume balance of a river-type reservoir according to claim 1, characterized in that, The specific method for determining the ecological flow control index requirements of the river-type reservoir in Step 6 is as follows: The ecological flow control index requirements of the river-type reservoir are determined according to the demand characteristics of the ecological protection objects downstream of the reservoir, specifically including the survival and reproduction of aquatic organisms, the stability of wetland and riparian vegetation ecosystems, and other special ecological function requirements, and are reasonably determined by using hydrological methods, hydraulic methods, biological habitat methods, and overall simulation methods; if the policy documents issued by the water administrative department have clearly specified the ecological flow index requirements for the reservoir, the regulations in the documents need to be followed.

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