A method for calculating dynamic water balance of river type reservoir

Abstract

The application discloses a kind of river type reservoir dynamic water balance calculation method, comprising the following steps: step 1, determine the river type reservoir control basin range and divide catchment unit;Step 2, predict the river type reservoir's water inflow based on distributed hydrological model;Step 3, calculate the maximum possible storage of river type reservoir;Step 4, calculate the loss of river type reservoir water quantity;Step 5, calculate the storage of river type reservoir and discharge water quantity;Step 6, based on the ecological flow control requirements, the storage of reservoir and discharge water quantity are corrected.The method can realize dynamic adjustment and correction to the regulation and discharge process of river type reservoir, improve the downstream ecosystem of reservoir, provide important technical support for water resources management, scheduling optimization and planning design of river type reservoir, and promote the overall improvement of river type reservoir management efficiency.

Description

Technical Field

[0001] This invention belongs to the field of hydrology and water resources management technology, and in particular relates to a method for calculating the dynamic water balance of river-type reservoirs. Background Technology

[0002] River-type reservoirs are typically formed by constructing dams across rivers to block their flow. They are important water conservancy projects, possessing the dual characteristics of both rivers and reservoirs. They can regulate floodwaters and provide multiple functions including water supply, irrigation, power generation, and navigation. Because they are built on existing river channels, river-type reservoirs generally extend along the river's course, often exhibiting a long and narrow shape similar to the river channel, with a large length-to-width ratio. Due to the combined influence of factors such as water inflow, power generation, and water intake by human activities, the water level of river-type reservoirs fluctuates significantly with the seasons. During the flood season (high water season), the water level of river-type reservoirs rises rapidly, bringing significant flood control pressure. Dynamic adjustments to the water level limit are usually necessary to create storage capacity in advance to cope with major floods. During the non-flood season (dry season) or peak water consumption periods, the water level of river-type reservoirs decreases significantly. Overall, fluctuations in reservoir water levels directly affect the reservoir's storage capacity and also impact the amount of water discharged and ecological water use.

[0003] For a long time, the water balance of river-type reservoirs has been quantified by measured data and static water level-storage capacity relationship to determine the balance between inflow and storage. However, this method faces the following problems: 1) During the flood season, the existing method cannot reflect the flood grading and pre-discharge process based on the inflow, which leads to over-storage or insufficient flood control capacity of the reservoir, increasing downstream flood control pressure; 2) During the non-flood season, the existing method cannot reflect the control requirements of ecological flow release, which to some extent damages the downstream ecosystem of river-type reservoirs.

[0004] Therefore, how to conduct dynamic calculations of water balance based on the characteristics of river-type reservoirs and comprehensively consider the requirements of flood grading and pre-discharge and ecological flow control has become an important technical problem that urgently needs to be solved in this field. Summary of the Invention

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

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] This invention discloses a method for calculating the dynamic water balance of a river-type reservoir, the method comprising the following steps:

[0008] Step 1: Determine the catchment area of ​​the river-type reservoir and divide it into water catchment units: Determine the catchment area of ​​the river-type reservoir according to the rules for determining the catchment area of ​​the river-type reservoir; Taking into account the similarity of topography, soil and vegetation characteristics within the catchment area, divide the catchment area of ​​the river-type reservoir into water catchment units;

[0009] Step 2: Predict the inflow of river-type reservoirs based on a distributed hydrological model: Using the river-type reservoir as the control node, input basic data and establish a distributed hydrological model; establish a link between rainfall forecast platform data or meteorological satellite and rainfall radar data and the distributed hydrological model, drive the hydrological model with real-time rainfall data, and calculate the inflow of the river-type reservoir, that is, the net inflow of surface runoff and groundwater runoff collected within the watershed controlled by the reservoir. The calculation formula is:

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

[0011] In the formula, Qi t Let t be the inflow volume of the river-type reservoir at time t, in ten thousand m³. 3 Qa t Let be the surface runoff at time t, in ten thousand m³. 3 ;Qb t Let be the net inflow of groundwater at time t, i.e., the difference between the inflow and outflow, expressed in ten thousand m³. 3 ;

[0012] Step 3: Calculate the maximum possible storage capacity of the river-type reservoir: First, determine the pre-release control water level for the river-type reservoir during the flood season: Based on the characteristics of river-type reservoirs, establish a functional relationship between the inflow volume and the pre-release control water level based on the predicted inflow data, as shown in the following formula:

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

[0014] In the formula, Ha t Let f(t) be the pre-discharge control water level of the river-type reservoir at time t during the flood season, in meters; f(x) represents the functional relationship between the inflow of water during the flood season and the pre-discharge control water level.

[0015] Then, based on the determined flood season pre-release control water level of the river-type reservoir, the maximum water level limit required for the river-type reservoir to achieve other comprehensive utilization functions is determined, including navigation, water supply, power generation, and sediment discharge. The maximum water level limit required for the comprehensive operation of the river-type reservoir is then calculated using the following formula:

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

[0017] In the formula, Hm t The maximum water level limit required for the comprehensive operation of river-type reservoirs at time t, in meters (m); Hb t The maximum water level limit for navigation in river-type reservoirs, in meters (m); Hc t The maximum water level limit required for water supply to river-type reservoirs, in meters (m); Hd t The maximum water level limit required for hydroelectric power generation in river-type reservoirs, in meters (m); He t The maximum water level limit for sediment discharge from river-type reservoirs, in meters (m); Hb t Hc t Hd t He t All are determined by establishing corresponding functional relationships based on the inflow of water into the reservoir;

[0018] Finally, based on the determined flood season pre-release control water level of the river-type reservoir and the maximum water level limit required for comprehensive scheduling, the maximum possible water storage capacity of the river-type reservoir is calculated based on the water level-storage capacity function relationship. The calculation formula is as follows:

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

[0020] In the formula, Vm t Let m be the maximum possible water storage capacity of a river-type reservoir at time t, in ten thousand m³. 3 fz() represents the water level-storage capacity function relationship of a river-type reservoir.

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

[0022] Then, the evaporation loss of the reservoir is determined segment by segment: The evaporation rate, rainfall, and surface area of ​​each segment of the river-type reservoir are obtained, and the evaporation loss of each segment is calculated using the following formula:

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

[0024] In the formula, Qe j,t The evaporation loss of the j-th section of the river-type reservoir is expressed in tens of thousands of m³. 3 ;Eej,t Pe represents the surface evaporation rate of a river-type reservoir at time t in segment j, in mm. j,t S represents the rainfall at time t in the j-th segment of a river-type reservoir, in mm; j,t-1 The water surface area of ​​the river-type reservoir at time t-1 in segment j is expressed in ten thousand m². 2 ;

[0025] Then, the water loss due to seepage in the reservoir is determined segment by segment: The water loss due to seepage in each segment of a river-type reservoir includes two parts: water loss due to seepage at the bottom of the reservoir and water loss due to seepage on the bank slope. The calculation formula is as follows:

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

[0027] In the formula, Ql j,t The leakage loss of water in the j-th segment of the river-type reservoir at time t is expressed in ten thousand m³. 3 Qla j,t The water loss due to seepage at the bottom of the j-th section of the river-type reservoir is 10,000 m³. 3 Qlb j,t The seepage loss of the bank slope of the j-th section of the river-type reservoir is 10,000 m³. 3 ;

[0028] Among them, the water loss due to seepage from the bottom of the reservoir is Qla j,t The calculation formula is:

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

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

[0031] Bank slope seepage loss Qlb j,t The calculation formula 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 Let Ab be the slope permeability coefficient of the j-th segment of a river-type reservoir at time t, in meters. j,t Let m be the seepage area of ​​the j-th section of the riverbank slope at time t in a river-type reservoir. 2 ;Lb j,t S is the hydraulic gradient of the j-th segment of the riverbank slope at time t in a river-type reservoir; it is dimensionless. j,t The angle between the slope of the j-th section of the river channel reservoir and the horizontal plane;

[0034] Then, the water consumption of human economic and social activities is determined in segments: the water consumption of human economic and social activities includes the water consumption caused by various human economic and social users' water intake, use, and drainage activities along the river-type reservoir in each segment. The calculation formula for each segment is as follows:

[0035]

[0036] In the formula, Qu j,t The water consumption for human economic and social activities in the j-th section of the river-type reservoir is 10,000 m³. 3 U j,t,k Let m be the water withdrawal volume of user k in segment j of a river-type reservoir at time t. 3 ;Hr j,t,k The water consumption coefficient of user type k at time t in segment j of a river-type reservoir is dimensionless; K is the total number of economic and social user types.

[0037] Finally, the water loss of a river-type reservoir is determined as follows: The water loss of a river-type reservoir is equal to the sum of water loss due to evaporation, water loss due to seepage, and water consumption due to human economic and social activities. The calculation formula is as follows:

[0038]

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

[0040] In the formula, Qs t Let t be the water loss of a river-type reservoir at time t, in ten thousand m³. 3 ;Qe t Ql t and Qu t These represent the water loss due to evaporation, water loss due to seepage, and water consumption due to human economic and social activities at time t, in ten thousand m³. 3 ;

[0041] Step 5: Calculate the storage and discharge of the river-type reservoir: Taking into account the inflow, outflow, storage, and discharge of the river-type reservoir, the water balance equation for the river-type reservoir is established as follows:

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

[0043] In the formula, Vc t Let be 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, expressed in ten thousand m³. 3 Qo t Let be the discharge volume of the river-type reservoir at time t, in ten thousand m³. 3 ;

[0044] Determine the initial water storage capacity V0 of the river-type reservoir, i.e., the water storage capacity at the initial time t=1; then, based on the water balance of the river-type reservoir and 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 capacity and outflow volume. The specific calculation formula is 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 Let t be the water storage capacity of the river-type reservoir at time t, in ten thousand m³. 3 V t-1 Let m be the water storage capacity of the river-type reservoir at time t-1, in ten thousand m³. 3 It is obtained recursively from the initial water storage volume V0;

[0049] Step 6: Correct the reservoir storage and discharge volume based on ecological flow control requirements: Determine the ecological flow control index requirements for river-type reservoirs. If the calculated discharge volume of the river-type reservoir is greater than or equal to the control index requirements, then the ecological flow control index requirements are met, the water balance calculation is terminated, and the reservoir storage and discharge volume obtained above do not need to be corrected.

[0050] If the calculated discharge volume of the river-type reservoir is less than the control target, a correction calculation for the reservoir's storage and discharge volume is performed: First, calculate the discharge capacity of the river-type reservoir, which is the inflow minus the loss plus the storage capacity at a certain time. If this value is less than or equal to the ecological flow control target, then all of it needs to be discharged; if it is greater than the ecological flow control target, then the discharge is carried out according to the ecological flow control target. 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 ) (twenty one)

[0054] V′ t =V t-1 +Vc′ t (twenty two)

[0055] In the formula, Qiz t Let t be the discharge capacity of a river-type reservoir at time t, in ten thousand m³. 3 ;Qd t The ecological flow control indicators for river-type reservoirs at time t, in 10,000 m³ 3 ;Qo′ t This is the corrected discharge volume of the river-type reservoir at time t, in ten thousand m³. 3 ;Vc′ t and V′ t These represent the corrected water storage variable and water storage capacity of the river-type reservoir at time t, in ten thousand m³. 3 .

[0056] Furthermore, the rule for determining the control basin of a river-type reservoir in step 1 is as follows: the control basin of a river-type reservoir is the basin area upstream of the reservoir dam site that can generate runoff and converge at the dam site section, with the dam site as the outlet section.

[0057] Furthermore, the specific process of dividing the control basin of the river-type reservoir into catchment units as described in step 1 is as follows: First, sub-basins are generated: using GIS tools and based on digital elevation models, the sub-basins are divided, specifically including depression filling, water flow direction and flow accumulation calculation, and flow threshold setting steps. Sub-basins are automatically generated based on the cumulative runoff threshold or river network nodes. On this basis, the watershed boundary can be manually adjusted and corrected in conjunction with field surveys. Then, the catchment units are determined: based on the generation of sub-basins, the sub-basins involved by the tributaries entering the river-type reservoir are merged. The land area covered by each tributary entering the reservoir is taken as an independent catchment unit, and all sub-basins involved by the tributaries entering the river-type reservoir are merged into this catchment unit. The land sub-basins that directly flow into the river-type reservoir are merged as separate catchment units.

[0058] Furthermore, the basic data mentioned in step 2 includes meteorological data, hydrological data, topographic data, land use data, soil type distribution data, social water use data, and water conservancy project data; the meteorological data includes daily data on precipitation, temperature, sunshine, wind speed, and humidity; the hydrological data includes daily measured runoff data from hydrological stations; the topographic data includes DEM data, river system data, and channel parameters; the social water use data includes water consumption for agriculture, industry, and domestic use, as well as surface and groundwater supply, industrial and domestic water conveyance loss coefficients, irrigation water allocation coefficients, and irrigation canal water conveyance loss coefficients; the water conservancy project data includes the distribution of large, medium, and small reservoirs and their characteristic parameters.

[0059] Furthermore, the establishment of the functional relationship between inflow volume and pre-release control water level based on the predicted inflow volume in step 3 specifically involves: classifying the inflow volume of river-type reservoirs into different levels, and formulating pre-release control water levels for different levels of inflow volume. When river-type reservoirs are scheduled according to the three-level water volume classification, the calculation formula for the pre-release control water level is as follows:

[0060]

[0061] In the formula, Qi1 t Qi2 t and Qi3 t These are the threshold values ​​for the first, second, and third levels of inflow water volume, in 10,000 m³. 3 The water volume thresholds, in ascending order, are: Qi1 t <Qi2 t <Qi3 t ;Ha3 t Ha2 is the maximum pre-release water level limit of the reservoir at time t when the inflow is greater than or equal to the third-level threshold of the inflow; tLet Ha1 be the maximum pre-release water level limit of the reservoir at time t when the inflow is greater than or equal to the second-level threshold and less than the third-level threshold; t Let H be the maximum pre-release water level limit of the reservoir at time t when the inflow is greater than or equal to the first-level threshold and less than the second-level threshold, in meters; the water levels of river-type reservoirs from low to high are: Ha3 t <Ha2 t <Ha1 t Hf is the flood control limit water level of the reservoir, in meters (m).

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

[0063] Furthermore, the water surface evaporation and rainfall of each section of the river-type reservoir mentioned 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 is 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 empirical fitting curves of water level-area.

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

[0065] Furthermore, the determination of the initial water storage capacity V0 of the river-type reservoir in step 5 is as follows: the initial water storage capacity of the river-type reservoir is determined based on the measured data, design parameters or operating characteristics of the reservoir. The initial water storage capacity is not less than the dead storage capacity and meets the requirements of water supply, power generation and ecological comprehensive functions.

[0066] Furthermore, the ecological flow control indicators for river-type reservoirs, as described in step 6, are specifically determined as follows: the ecological flow control indicators for river-type reservoirs are determined based on the needs and 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. These indicators are reasonably determined using hydrological methods, hydraulic methods, biological habitat methods, and overall simulation methods. If the water administration department has already clearly specified the requirements for ecological flow indicators for reservoirs in its policy documents, then those documents must be followed.

[0067] The beneficial effects of this invention are as follows: The method described in this invention constructs a distributed water cycle model, predicts inflow, and combines flood-level pre-release with other comprehensive scheduling rules. By dynamically adjusting the maximum possible storage capacity and setting ecological flow control indicators, it achieves dynamic calculation of the dynamic water balance of river-type reservoirs. This method can dynamically adjust and correct the regulation and discharge processes of river-type reservoirs, promoting the improvement of the downstream ecosystem. The method described in this invention is systematic, scientific, and operable, enabling dynamic quantitative analysis of the balance mechanism of all elements in river-type reservoirs, including inflow, discharge, loss, and storage. It provides important technical support for water resource management, scheduling optimization, and planning design of river-type reservoirs, promoting the overall improvement of river-type reservoir management efficiency.

[0068] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments. Attached Figure Description

[0069] Figure 1 This is a schematic diagram of the method flow described in this invention;

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

[0071] Figure 3 This is a schematic diagram of the daily water inflow process of the upstream water conservancy hub's catchment unit in Example 1;

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

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

[0074] Figure 6 This is a schematic diagram of the segmented river-type reservoir in Example 1;

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

[0076] Figure 8 This is a schematic diagram illustrating the daily discharge volume and ecological flow control requirements of a river-type reservoir in Example 1.

[0077] Figure 9 This is a schematic diagram of the daily water balance process of a river-type reservoir in Example 1. Detailed Implementation

[0078] This invention discloses a method for calculating the dynamic water balance of a river-type reservoir, such as... Figure 1 As shown, the method includes the following steps:

[0079] Step 1: Determine the control area of ​​the river-type reservoir and divide it into catchment units.

[0080] First, determine the controlled watershed area of ​​a river-type reservoir: The controlled watershed area of ​​a river-type reservoir is the area of ​​all upstream watersheds that can generate runoff and converge at the dam site, with the dam site as the outlet section.

[0081] Then, the catchment area is divided into catchment units: taking into account the similarity of topography, soil, and vegetation characteristics within the watershed, and based on topography and sub-watersheds, the catchment area of ​​the river-type reservoir is divided into catchment units.

[0082] 1) Sub-basin generation: This can be achieved using GIS tools and based on a digital elevation model (DEM). The process includes filling depressions, calculating flow direction and cumulative discharge, and setting discharge thresholds. Sub-basins can be automatically generated based on confluence accumulation thresholds or river network nodes (such as tributary confluences or reservoir inlets). Furthermore, watershed boundaries (such as those caused by artificial channels or tunnels) can be manually adjusted and corrected based on field surveys.

[0083] 2) Determining Catchment Units: Based on the generation of sub-basins, to improve computational efficiency, sub-basins involved in tributaries flowing into channel-type reservoirs can be merged, with the land area covered by each tributary serving as an independent catchment unit. It is important to note that all sub-basins involved in tributaries flowing into channel-type reservoirs should be merged into this catchment unit. Similarly, land sub-basins directly flowing into channel-type reservoirs can be merged as separate catchment units.

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

[0085] Using river-type reservoirs as control nodes, a distributed hydrological model is established by inputting basic data. The basic data includes meteorological data (daily data on precipitation, temperature, sunshine, wind speed, and humidity), hydrological data (daily measured runoff data from hydrological stations), topographic data (DEM data, river system data, channel parameters, etc.), land use data, soil type distribution data, social water use data (agricultural, industrial, and domestic water consumption, surface and groundwater supply, industrial and domestic water conveyance loss coefficients, irrigation water allocation coefficients, irrigation canal water conveyance loss coefficients, etc.), and water conservancy project data (distribution of large, medium, and small reservoirs and their characteristic parameters, etc.). Then, based on the measured runoff data from existing hydrological stations, parameter calibration and model validation are conducted.

[0086] Establish a link between rainfall forecasting platform data (such as Alibaba Cloud) or meteorological satellite and rainfall radar data and a distributed hydrological model. Drive the hydrological model with real-time rainfall data to calculate the inflow of water into a river-type reservoir, that is, the net inflow of surface runoff and groundwater collected 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 Let t be the inflow volume of the river-type reservoir at time t, in ten thousand m³. 3 Qa t Let be the surface runoff at time t, in ten thousand m³. 3 ;Qb t Let be the net inflow of groundwater at time t, i.e., the difference between the inflow and outflow, expressed in ten thousand m³. 3 .

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

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

[0091] During the flood season, river-type reservoirs implement pre-discharge based on the inflow volume to ensure a more uniform discharge and minimize disturbance to downstream water resource development and the ecosystem. The pre-discharge control water level is determined based on the characteristics of river-type reservoirs and is established using a function derived from predicted inflow data, as shown in the following formula:

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

[0093] In the formula, Ha t Let f(t) be the pre-discharge control water level of the river-type reservoir at time t during the flood season, in meters; f(x) represents the functional relationship between the inflow of water during the flood season and the pre-discharge control water level.

[0094] If the relationship between inflow volume and pre-release control water level during the flood season is too complex, it will hinder the efficient management of river-type reservoirs. In practice, river-type reservoirs can be categorized according to inflow volume, and different pre-release control water levels can be established for each level. Generally, the higher the categorization level, the larger the inflow volume, and the lower the pre-release control water level. For example, when a river-type reservoir is managed according to a three-level categorization of inflow volume, the formula for calculating the pre-release control water level is as follows:

[0095]

[0096] In the formula, Qi1 t Qi2 t and Qi3t These are the threshold values ​​for the first, second, and third levels of inflow water volume, in 10,000 m³. 3 The water volume thresholds are typically ordered from smallest to largest as follows: Qi1 t <Qi2 t <Qi3 t ;Ha3 t Ha2 is the maximum pre-release water level limit of the reservoir at time t when the inflow is greater than or equal to the third-level threshold of the inflow; t Let Ha1 be the maximum pre-release water level limit of the reservoir at time t when the inflow is greater than or equal to the second-level threshold and less than the third-level threshold; t Let Ht be the maximum pre-release water level limit of the reservoir at time t when the inflow is greater than or equal to the first-level threshold and less than the second-level threshold; Ht is the water level limit at time t when the inflow is greater than or equal to the first-level threshold and less than the second-level threshold. Typically, the water levels of river-type reservoirs, from lowest to highest, are: Ht = Ht. t <Ha2 t <Ha1 t Hf is the flood control limit water level of the reservoir, in meters (m).

[0097] The flood control limit level, also known as the flood limit water level or the flood season control water level, refers to the upper limit of water level at which a river-type reservoir is allowed to store water during the flood season. Determining and managing the flood control limit level is beneficial for balancing flood control and water use in river-type reservoirs, ensuring that the reservoir fulfills its flood control function. It typically requires considering comprehensive requirements such as flood characteristics, reservoir characteristics, and flood control needs, and is determined through quantitative calculations and dynamic adjustment techniques. Furthermore, if the water administrative department has already determined the flood control limit level for river-type reservoirs through management regulations, it can be directly adopted.

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

[0099] Based on the pre-release control water level for river-type reservoirs during the flood season determined above, the maximum water level limit required for river-type reservoirs to achieve other comprehensive utilization functions (including navigation, water supply, power generation, and sediment discharge) is further determined. The maximum water level limit required for the comprehensive operation of river-type reservoirs is then calculated using the following formula:

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

[0101] In the formula, Hm t The maximum water level limit required for the comprehensive operation of river-type reservoirs at time t, in meters (m); Hb t The maximum water level limit for navigation in river-type reservoirs, in meters (m); Hct The maximum water level limit required for water supply to river-type reservoirs, in meters (m); Hd t The maximum water level limit required for hydroelectric power generation in river-type reservoirs, in meters (m); He t The maximum water level limit for sediment discharge requirements of river-type reservoirs is given in meters (m).

[0102] Similarly, Hb t Hc t Hd t He t The corresponding functional relationships are determined based on the amount of water entering the reservoir.

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

[0104] The maximum possible storage capacity of a river-type reservoir is influenced by both its own design parameters and external water inflow conditions. Based on the aforementioned determined flood season pre-release control water level and the maximum water level limit required for comprehensive scheduling, the maximum possible storage capacity of the river-type reservoir is calculated using the water level-storage capacity function relationship. The calculation formula is as follows:

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

[0106] In the formula, Vm t Let m be the maximum possible water storage capacity of a river-type reservoir at time t, in ten thousand m³. 3 fz() represents the water level-storage capacity function relationship of a river-type reservoir. This function describes the reservoir's water storage capacity at different water levels, i.e., the curve relationship between reservoir capacity and water level. It can be derived 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) Divide river-type reservoirs into sections according to the catchment units.

[0109] Influenced by the original river characteristics, channel-type reservoirs typically extend along the existing river channel. During reservoir operation, water level changes in the reservoir area affect the upstream river channel, forming a backwater zone. This backwater zone exhibits reservoir characteristics during impoundment but reverts to natural river channel 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 dynamically change with the seasons. Therefore, the water loss of the channel-type reservoir should be calculated segment by segment. Based on the catchment units defined in step 1, the channel-type reservoir is first segmented according to the connection points between the outlet of each catchment unit and the channel-type reservoir (j = 1, 2, 3… J), where J is the total number of segments. For example, if J = 3, the channel-type reservoir can be divided into the tail section, the middle section, and the near-dam section. In subsequent calculations, the segmentation can be merged and refined based on factors such as the geological structure of the channel-type reservoir, the slope of the reservoir bank or the thickness of the overburden layer, and the intensity of human water intake activities. Dividing river-type reservoirs into sections can significantly improve the accuracy of calculating water loss in river-type reservoirs.

[0110] (2) Determine the amount of water lost due to evaporation in the reservoir in segments.

[0111] Evaporation loss constitutes a significant portion of water loss in river-type reservoirs, particularly in arid regions or during warmer seasons. Evaporation loss is typically influenced by various factors, including meteorological conditions and reservoir area, and can be determined using methods such as empirical formulas, remote sensing monitoring, and on-site observation, tailored to the characteristics of river-type reservoirs.

[0112] The evaporation rate, rainfall, and water surface area of ​​each section of the river-type reservoir were obtained. Based on the obtained data, the evaporation loss of each section of the river-type reservoir was calculated as follows:

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

[0114] In the formula, Qe j,t The evaporation loss of the j-th section of the river-type reservoir is expressed in tens of thousands of m³. 3 Ee j,t Pe represents the surface evaporation rate of a river-type reservoir at time t in segment j, in mm. j,t S represents the rainfall at time t in the j-th segment of a river-type reservoir, in mm; j,t-1 The water surface area of ​​the river-type reservoir at time t-1 in segment j is expressed in ten thousand m². 2 .

[0115] Evaporation and rainfall at different sections of a river-type reservoir are derived from actual observation data or calculated based on meteorological data. If segmented meteorological observation data is unavailable, meteorological data for each segment must be estimated using methods such as numerical models (e.g., WRF), spatial interpolation (e.g., Kriging method), or remote sensing inversion. The water surface area at different sections of a river-type reservoir can be obtained from remote sensing imagery, topographic maps, or empirical water level-area curves.

[0116] (3) Determine the amount of water lost due to seepage in the reservoir in sections.

[0117] The seepage loss of river-type reservoirs mainly includes seepage loss from the reservoir bank, dam body, dam foundation, and around the dam. It is typically influenced by factors such as regional geological conditions (e.g., soil and rock properties, fault distribution), reservoir bank characteristics (e.g., slope, vegetation cover), seepage prevention measures, and water level control. The seepage loss of each section of a river-type reservoir can be quantitatively calculated by combining the reservoir's operational characteristics with data from geological and groundwater surveys and water level monitoring, determining parameters such as head, seepage path, and permeability coefficient. The seepage loss of each section of a river-type reservoir includes two parts: seepage loss from the reservoir bottom and seepage loss from the bank slopes. These need to be calculated separately and then summed. The calculation formula is as follows:

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

[0119] In the formula, Ql j,t The leakage loss of water in the j-th segment of the river-type reservoir at time t is expressed in ten thousand m³. 3 Qla j,t The water loss due to seepage at the bottom of the j-th section of the river-type reservoir is 10,000 m³. 3 Qlb j,t The seepage loss of the bank slope of the j-th section of the river-type reservoir is 10,000 m³. 3 .

[0120] Since the bottom of a river-type reservoir is usually composed of porous media (such as sand, clay, etc.), the seepage process is mostly laminar flow, and the head difference is usually small. Darcy's law vertical one-dimensional seepage formula can be used for calculation, as shown in equation (8). It should be noted that Darcy's law is applicable to linear seepage. When the seepage velocity in each section of the river-type reservoir is high or the medium is heterogeneous, other more complex seepage 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 jLet A be the reservoir bottom permeability coefficient at time t in segment j of a river-type reservoir. This coefficient reflects the permeability of the reservoir bottom medium (such as soil or rock) and can be obtained through laboratory testing or on-site pumping tests. (m) j,t Let be the seepage area at time t in segment j of the reservoir bottom, i.e., the area of ​​the reservoir bottom perpendicular to the seepage direction. This area can be determined based on the reservoir bottom topography and geological conditions, m. 2 ;La j,t Let be the hydraulic gradient of the reservoir bottom at time t in segment j, representing the ratio of the head difference at the reservoir bottom to the length of the seepage path. It is calculated by measuring the head difference between the upstream and downstream sides of the reservoir bottom and the length of the seepage path, and is dimensionless.

[0123] Since seepage on the bank slopes of river-type reservoirs usually occurs in saturated soil and is mostly in a laminar flow state, Darcy's law and the inclined plane seepage formula can be used for calculation, as shown in equation (9). Similar to the previous one, 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 Let be the slope permeability coefficient of the j-th segment of a river-type reservoir at time t, reflecting the permeability of the slope medium (such as soil or rock). It can be obtained through laboratory testing or on-site pumping tests, in m. j,t Let be the seepage area of ​​the j-th section of the riverbank slope at time t, i.e., the area of ​​the slope perpendicular to the seepage direction. This area can be determined based on the slope topography and geological conditions, in m. 2 ;Lb j,t Let S be the hydraulic gradient of the j-th section of the riverbank slope at time t, representing the ratio of the head difference on the slope to the seepage path length. It is calculated by measuring the head difference and seepage path length between the upstream and downstream sections of the slope and is dimensionless. j,t The angle between the slope of the j-th section of the river-type reservoir and the horizontal plane is obtained through topographic surveying.

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

[0127] Water consumption from human economic and social activities includes the water intake, use, and drainage activities of various users (including agricultural, industrial, residential, and ecological users) along the river-type reservoir. Because the distribution of users and water intake characteristics differ across sections of the river-type reservoir, thus affecting the water surface area and water volume of the next section, calculations need to be performed segment by segment. The specific formula is as follows:

[0128]

[0129] In the formula, Qu j,t The water consumption for human economic and social activities in the j-th section of the river-type reservoir is 10,000 m³. 3 U j,t,k Let m be the water withdrawal volume of user k in segment j of a river-type reservoir at time t. 3 ;Hr j,t,K The water consumption coefficient of user k in the j-th segment of a river-type reservoir at time t, dimensionless; K is the total number of economic and social user types; here K = 4, k = 1, 2, 3 and 4 represent the four typical user types of agriculture, industry, domestic and ecological, respectively.

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

[0131] The water loss of a river-type reservoir is equal to the sum of water loss due to evaporation, water loss due to seepage, and water consumption due to 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 Let t be the water loss of a river-type reservoir at time t, in ten thousand m³. 3 ;Qe t Ql t and Qu t These represent the water loss due to evaporation, water loss due to seepage, and water consumption due to human economic and social activities at time t, in ten thousand m³. 3 .

[0135] Step 5: Calculate the water storage capacity and outflow of the river-type reservoir.

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

[0137] Taking into account the inflow, outflow, storage, and discharge of a river-type reservoir, the water balance equation for a river-type reservoir is established as follows:

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

[0139] In the formula, Vc t Let be 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 ten thousand m³. 3 Generally, an increase in water storage in a river-type reservoir is considered positive, while a decrease is considered negative; Qo t Let be the discharge volume of the river-type reservoir at time t, in ten thousand m³. 3 .

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

[0141] Determining the initial water storage capacity (V0) of a river-type reservoir at the initial time (t=1) is crucial for ensuring the safe operation and efficient utilization of water resources. This initial water storage capacity can be determined based on measured data, design parameters, or operational characteristics of the reservoir. Typically, the initial water storage capacity should not be less than the dead storage capacity and should meet the comprehensive functional requirements for water supply, power generation, and ecological purposes.

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

[0143] Based on the water balance of the river-type reservoir, and combining the calculation results from steps 2, 3, and 4, the water storage variable of the river-type reservoir is given. Further calculations are then performed to obtain the water storage capacity and outflow volume. 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] In the formula, V t Let t be the water storage capacity of the river-type reservoir at time t, in ten thousand m³. 3 V t-1 Let m be the water storage capacity of the river-type reservoir at time t-1, in ten thousand m³. 3 It can be obtained recursively from the initial water storage volume V0.

[0148] Step 6: Adjust the reservoir storage and discharge volume based on ecological flow control requirements.

[0149] The discharge volume of river-type reservoirs is a crucial measure for ensuring ecological flow in rivers and protecting aquatic biodiversity. The ecological flow control indicators for river-type reservoirs should be determined based on the needs and characteristics of the ecological protection targets downstream of the reservoir. These include the survival and reproduction of aquatic organisms, the stability of wetland and riparian vegetation ecosystems, and other special ecological function requirements. These indicators can be reasonably determined using hydrological methods, hydraulic methods, biological habitat methods, and overall simulation methods. If relevant policy documents issued by the water administration department clearly specify the ecological flow indicators for reservoirs, river-type reservoir managers must comply with these regulations when discharging ecological flow. If the time step for the water balance calculation of the river-type reservoir is (e.g., minutes, hours), and the ecological flow control indicators are on a daily scale, then a time-scale conversion calculation is required. If the calculated discharge volume of the river-type reservoir is greater than or equal to the control indicator requirement, the ecological flow indicator requirement is met, the water balance calculation terminates, and the obtained storage and discharge volumes do not need to be corrected.

[0150] If the outflow from a river-type reservoir is less than the ecological flow control target, a revised calculation of the reservoir's storage and outflow should be performed. The allowable outflow from the river-type reservoir should be calculated as: inflow minus losses plus the current storage capacity. If this value is less than or equal to the ecological flow control target, all outflow should be carried out to maximize the preservation of ecosystem service functions. If it exceeds the ecological flow control target, outflow should be carried out according to the ecological flow control target. 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 ) (twenty one)

[0154] V′ t =V t-1 +Vc′ t (twenty two)

[0155] In the formula, Qiz t Let t be the discharge capacity of a river-type reservoir at time t, in ten thousand m³. 3 ;Qd tThe ecological flow control indicators for river-type reservoirs at time t, in 10,000 m³ 3 ;Qo′ t This is the corrected discharge volume of the river-type reservoir at time t, in ten thousand m³. 3 ;Vc′ t and V′ t These represent the corrected water storage variable and water storage capacity of the river-type reservoir at time t, in ten thousand m³. 3 .

[0156] Example 1

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

[0158] This embodiment takes a channel-type reservoir on the upper reaches of the Han River in my country as the research object. This channel-type reservoir is a cascade hydropower station on the upper reaches of the Han River main stream, located at dam site A. The drainage area upstream of this dam site is 42,400 km². 2 Four major tributaries of the Han River flow into the river-type reservoir. Using GIS tools, sub-basins were identified based on a digital elevation model (DEM) with a spatial resolution of 30m*30m. Based on the identified sub-basins, the Han River tributaries flowing into the river-type reservoir were merged into independent catchment units. Sub-basins directly flowing into the river-type reservoir were merged into the central urban area catchment unit and the central urban area outflow catchment unit. The spatial distribution of the catchment units is as follows: Figure 2 As shown.

[0159] Based on the distributed hydrological model (WEP model), daily-scale calculations were performed using a normal water year (2020 as an example). The predicted inflow of water into 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 are negligible in this case study. The daily inflow process of the upstream water conservancy hub's catchment unit is shown below. Figure 3 As shown.

[0160] Table 1. Prediction of inflow to river-type reservoirs based on distributed hydrological models.

[0161] serial number water catchment unit <![CDATA[Annual water inflow (100 million m 3 )]]> 1 Upstream water conservancy hub catchment unit 153.17 2 Central urban watershed 0.30 3 Foreign exchange water unit in the central urban area 6.23 4 Tributary 1 catchment unit (Yuehe River) 7.96 5 Tributary 2 catchment unit (Jihe River) 2.67 6 Tributary 3 catchment unit (Huangyang River) 2.85 7 Tributary 4 catchment unit (Bahe River) 4.48 total 177.67

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

[0163] Floods in the basin above the dam site of river-type reservoirs are mainly caused by torrential rains, with a corresponding flood control limit level of 237m. The flood season typically begins in late April and ends in late May (the peak flood season); the main flood season is from July to October, during which torrential rains and floods primarily occur. The highest flood levels are in July (summer) and September (autumn). Summer floods are mostly formed by intense, short-duration torrential rains with a small affected area; autumn floods are generally formed by stable, prolonged torrential rains with a large affected area, resulting in longer durations and larger flood volumes. According to the reservoir operation regulations, the flood control pre-discharge rules for river-type reservoirs are shown in Table 1. Based on the predicted inflow, the pre-discharge control values ​​for the reservoir water level of river-type reservoirs are shown in Table 2. That is, the inflow is greater than or equal to 1900 m³ / h. 3 / s and less than 2300m 3 When the inflow rate is / s, the reservoir releases water in advance, lowering the water level to 237m (first stage); when the predicted inflow rate is greater than or equal to 2300m³ / s... 3 / s and less than 3500m 3 When the water level drops to 235m (second level) at a rate of / s; when the predicted inflow is greater than or equal to 3500m³ / s... 3 At a rate of / s, the reservoir water level drops to 233m (Level 3).

[0164] Table 2 Flood Control and Pre-discharge Scheduling Rules for River-type Reservoirs

[0165] serial number Inbound flow Reservoir control water level Pre-leakage level 1 <![CDATA[≥1900m 3 / s and <2300m 3 / s]]> Dropped to 237m Level 1 2 <![CDATA[≥2300m 3 / s and <3500m 3 / s]]> Reduced to 235m Level 2 3 <![CDATA[≥3500m 3 / s]]> Reduced to 233m Level 3

[0166] The maximum possible water storage capacity calculated using the above method is as follows: Figure 5 As shown, due to the influence of flood control pre-discharge and the flood control limit water level, the maximum possible water storage volume decreased significantly during the peach season from late April to the end of May and from July to October. At certain times, such as July 22, August 18, and August 19, the maximum possible water storage volume decreased further due to the predicted large inflow of floodwater and the pre-discharge scheduling.

[0167] Considering the limited human water use around this river-type reservoir, it is divided into two sections based primarily on its geological characteristics: the reservoir tail section and the dam site section. Figure 6 As shown in the diagram. The reservoir tail section is located upstream of the confluence of tributary 3, while the dam site section is located downstream of the confluence to the dam site. Based on the reservoir bottom characteristics and bank slope parameters of different sections of the river-type reservoir provided by the design unit, and combined with the reservoir impoundment process characteristics, the annual water loss of this river-type reservoir is calculated to be 30.06 million m³. 3 Among them, the tail section, mainly composed of bedrock, has low seepage, accounting for 19.6%, while the dam site section, with its sandy soil structure, has relatively high seepage. Its daily process is as follows: Figure 7 As shown.

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

[0169] To mitigate the ecological impact on the downstream river section and protect fish resources in the river downstream of the dam, in accordance with the relevant planning and design institutes, project acceptance opinions, and water intake permit requirements, the minimum daily ecological flow of this river-type reservoir should not be less than 120 m³ / h. 3 / s. The discharge flow and minimum ecological flow control requirements of river-type reservoirs calculated according to the method described in this invention are as follows: Figure 8 As shown, due to the relatively low minimum ecological flow control index, the reservoir discharge in this normal water year (2020) basically met the minimum ecological flow control assessment requirements. Furthermore, in exceptionally dry years with low inflow, the level of guarantee for the minimum ecological flow needs to be verified.

[0170] The daily water balance process of this river-type reservoir is as follows: Figure 9 As shown, the data specifically includes inflow, loss, discharge, and storage capacity. Due to its large inflow, relatively small capacity, and minimal loss, this river-type reservoir discharges most of its inflow. Calculations indicate that the annual inflow to this river-type reservoir is 17.77 billion m³. 3 Of this, 98.4% of the water was discharged from the reservoir, while only 0.16% was lost. The maximum daily average increase in reservoir storage was 31.93 million cubic meters. 3 (November 6th), the average daily water storage was 210 million cubic meters. 3 It took 201 days for the water to reach the normal storage level, accounting for 54.9% of the total number of days in the year.

[0171] Finally, it should be noted that the above description is only used to illustrate the technical solution of the present invention and not to limit it. Although the present invention has been described in detail with reference to the preferred arrangement, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solution of the present invention without departing from the spirit and scope of the technical solution of the present invention.

Claims

1. A method for calculating the dynamic water balance of a river-type reservoir, characterized in that, The method includes the following steps: Step 1: Determine the control basin area of ​​the river-type reservoir and divide it into catchment units: Determine the control basin area of ​​the river-type reservoir according to the rules for determining the control basin area; Taking into account the similarity of topography, soil and vegetation characteristics within the basin, divide the control basin area of ​​the river-type reservoir into catchment units; Step 2: Predict the inflow of river-type reservoirs based on a distributed hydrological model: Using the river-type reservoir as the control node, input basic data and establish a distributed hydrological model; establish a link between rainfall forecast platform data or meteorological satellite and rainfall radar data and the distributed hydrological model, drive the hydrological model with real-time rainfall data, and calculate the inflow of the river-type reservoir, that is, the net inflow of surface runoff and groundwater runoff collected within the watershed controlled by the reservoir. The calculation formula is: （1） In the formula, Let t be the inflow volume of the river-type reservoir at time t, in ten thousand m³. 3 ; Let be the surface runoff at time t, in ten thousand m³. 3 ; Let be the net inflow of groundwater at time t, i.e., the difference between the inflow and outflow, expressed in ten thousand m³. 3 ; Step 3: Calculate the maximum possible storage capacity of the river-type reservoir: First, determine the pre-release control water level for the river-type reservoir during the flood season: Based on the characteristics of river-type reservoirs, establish a functional relationship between the inflow volume and the pre-release control water level based on the predicted inflow data, as shown in the following formula: （2） In the formula, Let t be the pre-release control water level of the river-type reservoir during the flood season, in meters. The relationship between the inflow of water during the flood season and the pre-discharge control water level is shown in the function. Then, based on the determined flood season pre-release control water level of the river-type reservoir, the maximum water level limit required for the river-type reservoir to achieve other comprehensive utilization functions is determined, including navigation, water supply, power generation, and sediment discharge. The maximum water level limit required for the comprehensive operation of the river-type reservoir is then calculated using the following formula: （4） In the formula, Let m be the maximum water level limit required for the comprehensive operation of river-type reservoirs at time t. The maximum water level limit for navigation requirements of river-type reservoirs, in meters (m). The maximum water level limit for water supply requirements of river-type reservoirs, in meters; The maximum water level limit required for power generation in river-type reservoirs, in meters (m). The maximum water level limit for sediment discharge from a river-type reservoir, in meters (m). , , , All are determined by establishing corresponding functional relationships based on the inflow of water into the reservoir; Finally, based on the determined flood season pre-release control water level of the river-type reservoir and the maximum water level limit required for comprehensive scheduling, the maximum possible water storage capacity of the river-type reservoir is calculated based on the water level-storage capacity function relationship. The calculation formula is as follows: （5） In the formula, Let m be the maximum possible water storage capacity of a river-type reservoir at time t, in ten thousand m³. 3 ; The relationship between water level and reservoir capacity for river-type reservoirs; Step 4: Calculate the water loss of the river-type reservoir: First, divide the river-type reservoir into segments according to the catchment units: Based on the catchment units divided in Step 1, divide the river-type reservoir into segments according to the connection points between the outlet 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; Then, the evaporation loss of the reservoir is determined segment by segment: The evaporation rate, rainfall, and surface area of ​​each segment of the river-type reservoir are obtained, and the evaporation loss of each segment is calculated using the following formula: （6） In the formula, The evaporation loss of the j-th section of the river-type reservoir is expressed in tens of thousands of m³. 3 ; The water surface evaporation rate at time t in segment j of a river-type reservoir is expressed in mm. Let be the rainfall at time t in the j-th segment of the river-type reservoir, in mm; The water surface area of ​​the river-type reservoir at time t-1 in segment j is expressed in ten thousand m². 2 ; Then, the water loss due to seepage in the reservoir is determined segment by segment: The water loss due to seepage in each segment of a river-type reservoir includes two parts: water loss due to seepage at the bottom of the reservoir and water loss due to seepage on the bank slope. The calculation formula is as follows: （7） In the formula, The leakage loss of water in the j-th segment of the river-type reservoir at time t is expressed in ten thousand m³. 3 ; The water loss due to seepage at the bottom of the j-th section of the river-type reservoir is 10,000 m³. 3 ; The seepage loss of the bank slope of the j-th section of the river-type reservoir is 10,000 m³. 3 ; Among them, the water loss due to seepage at the bottom of the reservoir The calculation formula is: （8） In the formula, Let be the reservoir bottom permeability coefficient at time t in the j-th segment of a river-type reservoir, in meters. Let m be the seepage area at time t in the j-th segment of the reservoir bottom. 2 ; Let be the hydraulic gradient of the reservoir bottom at time t in segment j, which is dimensionless; bank slope seepage loss The calculation formula is: （9） In the formula, Let be the slope permeability coefficient of the j-th segment of the river-type reservoir at time t, in meters. Let m be the seepage area of ​​the j-th section of the riverbank slope at time t in a river-type reservoir. 2 ; Let be the hydraulic gradient of the j-th segment of the bank slope of a river-type reservoir at time t, which is dimensionless. The angle between the slope of the j-th section of the river channel reservoir and the horizontal plane; Then, the water consumption of human economic and social activities is determined in segments: the water consumption of human economic and social activities includes the water consumption caused by various human economic and social users' water intake, use, and drainage activities along the river-type reservoir in each segment. The calculation formula for each segment is as follows: （10） In the formula, The water consumption for human economic and social activities in the j-th section of the river-type reservoir is 10,000 m³. 3 ; Let m be the water withdrawal volume of user k in segment j of a river-type reservoir at time t. 3 ; The water consumption coefficient of user type k at time t in segment j of a river-type reservoir is dimensionless; K is the total number of economic and social user types. Finally, the water loss of a river-type reservoir is determined as follows: The water loss of a river-type reservoir is equal to the sum of water loss due to evaporation, water loss due to seepage, and water consumption due to human economic and social activities. The calculation formula is as follows: （11） （12） （13） （14） In the formula, Let t be the water loss of a river-type reservoir at time t, in ten thousand m³. 3 ; , and These represent the water loss due to evaporation, water loss due to seepage, and water consumption due to human economic and social activities at time t, in ten thousand m³. 3 ; Step 5: Calculate the storage and discharge of the river-type reservoir: Taking into account the inflow, outflow, storage, and discharge of the river-type reservoir, the water balance equation for the river-type reservoir is established as follows: （15） In the formula, Let be 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, expressed in ten thousand m³. 3 ; Let be the discharge volume of the river-type reservoir at time t, in ten thousand m³. 3 ; Determine the initial water storage capacity of river-type reservoirs This refers to the water storage volume at the initial time t=1. Then, based on the water balance of the river-type reservoir and the calculation results from steps 2, 3, and 4, the water storage variable of the river-type reservoir is given. Further calculations are then performed to obtain the water storage volume and the outflow volume. The specific calculation formulas are as follows: （16） （17） （18） In the formula, Let t be the water storage capacity of the river-type reservoir at time t, in ten thousand m³. 3 ; Let m be the water storage capacity of the river-type reservoir at time t-1, in ten thousand m³. 3 From the initial water storage It is obtained by recursion; Step 6: Correct the reservoir storage and discharge volume based on ecological flow control requirements: Determine the ecological flow control index requirements for river-type reservoirs. If the calculated discharge volume of the river-type reservoir is greater than or equal to the control index requirements, then the ecological flow control index requirements are met, the water balance calculation is terminated, and the reservoir storage and discharge volume obtained above do not need to be corrected. If the calculated discharge volume of the river-type reservoir is less than the control target, a correction calculation for the reservoir's storage and discharge volume is performed: First, calculate the discharge capacity of the river-type reservoir, which is the inflow minus the loss plus the storage capacity at a certain time. If this value is less than or equal to the ecological flow control target, then all of it needs to be discharged; if it is greater than the ecological flow control target, then the discharge is carried out according to the ecological flow control target. The specific calculation formula is as follows: （19） （20） （21） （22） In the formula, Let t be the discharge capacity of a river-type reservoir at time t, in ten thousand m³. 3 ; The ecological flow control indicators for river-type reservoirs at time t, in 10,000 m³ 3 ; This is the corrected discharge volume of the river-type reservoir at time t, in ten thousand m³. 3 ; and These represent the corrected water storage variable and water storage capacity of the river-type reservoir at time t, in ten thousand m³. 3 .

2. The method for calculating the dynamic water balance of a river-type reservoir according to claim 1, characterized in that, The rule for determining the controlled watershed of a river-type reservoir in step 1 is as follows: the controlled watershed of a river-type reservoir is the watershed area upstream of the reservoir dam site that can generate runoff and converge at the dam site cross section.

3. The method for calculating the dynamic water balance of a river-type reservoir according to claim 1, characterized in that, The specific process of dividing the control basin of a river-type reservoir into catchment units as described in step 1 is as follows: First, sub-basins are generated: using GIS tools and based on a digital elevation model, the sub-basins are divided, including filling depressions, calculating water flow direction and flow accumulation, and setting flow thresholds. Sub-basins are automatically generated based on the cumulative runoff threshold or river network nodes. Based on this, the watershed boundaries can be manually adjusted and corrected in conjunction with field surveys. Then, catchment units are determined: based on the generation of sub-basins, the sub-basins involved by tributaries flowing into the river-type reservoir are merged. The land area covered by each tributary flowing into the reservoir is taken as an independent catchment unit. All sub-basins involved by tributaries flowing into the river-type reservoir are merged into this catchment unit. The land sub-basins that flow directly into the river-type reservoir are merged as separate catchment units.

4. The method for calculating the dynamic water balance of a river-type reservoir according to claim 1, characterized in that, The basic data mentioned in step 2 includes meteorological data, hydrological data, topographic data, land use data, soil type distribution data, social water use data, and water conservancy project data. The meteorological data includes daily data on precipitation, temperature, sunshine, wind speed, and humidity. The hydrological data includes daily measured runoff data from hydrological stations. The topographic data includes DEM data, river system data, and channel parameters. The social water use data includes water consumption for agriculture, industry, and domestic use, as well as surface and groundwater supply, industrial and domestic water conveyance loss coefficients, irrigation water allocation coefficients, and irrigation canal water conveyance loss coefficients. The water conservancy project data includes the distribution of large, medium, and small reservoirs and their characteristic parameters.

5. The method for calculating the dynamic water balance of a river-type reservoir according to claim 1, characterized in that, Step 3, which establishes the functional relationship between inflow volume and pre-release control water level based on inflow volume prediction data, specifically involves: classifying the inflow volume of river-type reservoirs into different levels and formulating pre-release control water levels for each level. When river-type reservoirs are managed according to the three-level water volume classification, the calculation formula for the pre-release control water level is as follows: （3） In the formula, , and These are the threshold values ​​for the first, second, and third levels of inflow water volume, in 10,000 m³. 3 ; The water volume thresholds, in ascending order, are: ; The maximum pre-release water level limit of the reservoir at time t is the value in meters when the inflow is greater than or equal to the third-level threshold of the inflow. Let m be the maximum pre-release water level limit of the reservoir at time t when the inflow is greater than or equal to the second-level threshold and less than the third-level threshold; Let be the maximum pre-release water level limit of the reservoir at time t when the inflow is greater than or equal to the first-level threshold and less than the second-level threshold, in meters; the water levels of river-type reservoirs, from lowest to highest, are as follows: ; The water level is the flood control limit level of the reservoir, in meters (m).

6. The method for calculating the dynamic water balance of a river-type reservoir according to claim 1, characterized in that, The water level-storage capacity function relationship of the river-type reservoir mentioned in step 3 is obtained by combining reservoir topographic data collection, mathematical modeling, and curve fitting methods.

7. The method for calculating the dynamic water balance of a river-type reservoir according to claim 1, characterized in that, The water surface evaporation and rainfall of each section of the river-type reservoir mentioned 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 is estimated by numerical model, spatial interpolation method, or remote sensing inversion method; the water surface area of ​​each section of the river-type reservoir is obtained by remote sensing imagery, topographic map, or water level-area empirical fitting curve.

8. The method for calculating the dynamic water balance of a river-type reservoir according to claim 1, characterized in that, The total number of economic and social user types mentioned in step 4 is K=4, where k=1,2,3 and 4 represent agricultural users, industrial users, residential users and ecological users, respectively.

9. The method for calculating the dynamic water balance of a river-type reservoir according to claim 1, characterized in that, Step 5 describes determining the initial water storage capacity of the river-type reservoir. Specifically, the initial water storage capacity of a river-type reservoir is determined based on the reservoir's measured data, design parameters, or operational characteristics. The initial water storage capacity shall not be less than the dead storage capacity and shall meet the requirements for integrated functions of water supply, power generation, and ecology.

10. The method for calculating the dynamic water balance of a river-type reservoir according to claim 1, characterized in that, The specific requirements for determining the ecological flow control indicators for river-type reservoirs as described in step 6 are as follows: The ecological flow control indicators for river-type reservoirs are determined based on the needs and 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. They are reasonably determined using hydrological methods, hydraulic methods, biological habitat methods, and overall simulation methods. If the water administrative department has issued policy documents that clearly require ecological flow indicators for reservoirs, then the provisions of the documents must be followed.

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