CN114169047B - Method for calculating reservoir backwater range - Google Patents
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Abstract
The invention discloses a method for calculating a reservoir backwater range, which comprises the steps of collecting corresponding data of a reservoir, and developing a one-dimensional flood evolutionary model applicable to a current river network structure according to the principle of a san-Vinan equation set; according to the actual pre-dam application water level condition in the field flood, reducing each water level value by a fixed value in the water level process, and calculating a group of virtual water level line change processes for the reservoir by using the flood evolution model; according to the field flood process data, selecting the highest water surface line of a reservoir area and the corresponding moment, comparing the highest water surface line with a virtual water surface line at the same moment, wherein the difference value of the water surface line and the virtual water surface line is smaller than a given value, and the interval from a dam address to the tail end of backwater is the backwater influence range; the invention can reduce the dependence on the hydrologic data of the natural river channel before the construction of the warehouse; the applicability under the condition of large flood is good, and the coverage of the traditional method can be expanded; compared with the traditional method, the calculation accuracy is higher, and technical support can be provided for flood control and prosperous dispatching decisions of large reservoirs or step reservoirs.
Description
Technical Field
The invention belongs to the field of reservoir operation control, and particularly relates to a method for calculating a reservoir backwater range.
Background
The reservoir backwater is that after the dam is built, water flow reaches the dam and then is blocked to flow back, so that the water level of the area upstream of the dam is increased, and the interval from the tail end of backwater to the dam is called backwater range. Because the water conditions of the reservoirs are changed at all times, especially in the flood season, the position of the backwater tail end is dynamic in one field flood, and the calculation of the backwater tail end of the reservoirs plays an important role in judging the influence range of the field flood and deciding the dispatching scheme of the reservoirs.
Calculating the backwater end of the field flood, wherein the traditional method generally uses a location with a difference value smaller than a specified value between a reservoir backwater curve of the flood and a natural water surface line as the backwater end according to the definition of the backwater end, and searches for a location with the difference value smaller than the specified value as the backwater end by comparing the current field flood with the water surface line of the similar flood in the natural state before dam construction. This approach has a number of limitations:
(1) In general, the hydrologic data of the reservoir in a natural state before dam construction is less, the number of hydrologic (position) stations is limited, the accuracy of the hydrologic line is not high, and the demand of calculating the backwater tail end is difficult to support, so that the obtained result is generally rough;
(2) The reservoir backwater range is calculated mainly to cope with the situation of large field floods, the frequency of occurrence of large floods in history is relatively rare, and the situation very similar to the current field floods is difficult to find in the history data before the reservoir is dam built, especially for the very rare large floods.
For the above reasons, finding the backwater end of reservoirs, especially large reservoirs, has been a technical difficulty in the industry. The total length of the reservoir area of the three gorges reservoir in the Yangtze river basin in China is about 757km from the dam site to the cinTuo, the reservoir area backwater range has obvious influence on flood control, power generation, shipping and water resource scheduling, but the determination of the extra-large flood backwater range still adopts the traditional method, the result is usually inaccurate, and the actual application requirements cannot be completely met. Therefore, aiming at the technical problem of calculating the reservoir backwater range, no effective solution is proposed at present.
Disclosure of Invention
The invention aims to overcome the defects, and provides a method for calculating the backwater range of a reservoir, so as to solve the technical problems that the traditional method is influenced by the lack of historical data and similar flood cases, the applicable flood types are limited, the calculation accuracy is low, and the reasons for the defects are difficult to overcome.
The invention aims to solve the technical problems, and adopts the technical scheme that: a method for calculating the backwater range of a reservoir comprises the following steps,
step 1: the method comprises the steps of collecting the structure of a river network where a reservoir is located, section topography data of dry tributaries in the river network, upstream flow inlet positions, inlet positions from tributaries to dry flows, upstream inlet flow processes of the dry tributaries in field floods and water level process before the reservoir dam;
step 2: according to the principle of the san-Vinan equation set, a one-dimensional flood evolution model applicable to the current river network structure is developed by applying a Prosmann four-point differential format discrete equation;
step 3: according to the actual water level condition before the dam in the field flood, reducing each water level value by a fixed value in the water level process, keeping the flow of each inlet in the river network unchanged, and calculating a group of virtual water level line change processes for the reservoir by using the flood evolution model;
step 4: according to the field flood process data, the highest water surface line of the reservoir area and the corresponding moment are selected, the highest water surface line and the corresponding moment are compared with the virtual water surface line at the same moment, the water level difference value of the highest water surface line and the virtual water surface line is smaller than a given xi (xi >0, the specific value is different according to different reservoirs), namely the backwater tail end of the field flood, and the interval from the dam address to the backwater tail end is the backwater influence range.
Preferably, the step 2 further includes:
step 2.1: according to the Prosoman four-point differential format, the differential in the Save Vietnam equation set is replaced by a differential quotient to form a discrete nonlinear equation set, and a Taylor formula is adopted to develop the nonlinear term so as to linearize the nonlinear term;
step 2.2: and constructing a coefficient matrix of the linear equation set according to the river network structure, storing by using a compression format, and selecting an LU direct method solver for the equation set.
Preferably, the step 3 further includes:
step 3.1: the water level process comprises water level series measured values within a period of time, each water level value in the water level process is uniformly subtracted by 5m, the inlet flow values of main flows and tributaries in a river network are kept unchanged, virtual reservoir operation conditions are formed, and data preparation is carried out for calculating virtual water surface lines;
step 3.2: based on the flood evolution model developed in the step 2, taking the main flow and the tributary inlet flow in the river network as upper boundary conditions, taking the virtual water level in front of the dam as lower boundary conditions, and substituting the virtual water level into the model to calculate the virtual water level line in the time period of the field flood process.
Preferably, the step 4 further includes:
step 4.1: drawing a change process of the water surface line of a reservoir area in the field flood process, selecting the highest water surface line and recording the occurrence time of the highest water surface line;
step 4.2: in the calculated virtual water surface line, the water surface line at the same moment is selected to be compared with the actual water surface line, the water level elevation difference of the actual water surface line and the virtual water surface line at the same position is gradually reduced along the direction from the dam site to the reservoir tail, and the water level elevation difference is smaller than a given xi value to be used as the backwater tail end of the flood of the field, namely, the position where the influence of backwater of the reservoir disappears.
Preferably, in step 1, the structure of the river network where the reservoir is located, the section topography data of the dry tributary in the river network, the upstream flow inlet position, and the inlet position of the tributary to the dry flow need to collect the latest measurement data, and the data collection density in the upstream inlet flow process of the dry tributary in the field flood and the water level process before the reservoir dam is at least in the order of hours, and must belong to the same time period.
Preferably, in step 2, the selected LU direct solver needs a compressed storage format that can accommodate the coefficient matrix of the linear equation set.
Preferably, in step 3, when constructing the virtual water level, the value subtracted on the basis of the actual water level should not be too small, and sufficient space should be left for the difference ζ to be represented at the tail of the reservoir.
Preferably, in the step 4, the value range of xi is more than or equal to 0 and less than or equal to 0.3.
Compared with the prior art, the invention has the beneficial effects that:
(1) The backwater range of the field flood which does not appear in the history can be calculated without using and depending on the historical hydrologic data before dam construction. The water surface line for comparison is provided by a numerical simulation technology and is not limited by historical hydrologic data before dam construction, so that the backwater tail end of large-scale flood which does not occur before dam construction can be calculated, and the processable task boundary is widened;
(2) The calculation result has higher accuracy. After the numerical simulation method is adopted, the water coming condition in the current field flood can be used as a simulated boundary condition, the simulated condition is completely consistent with the actual condition, and the traditional method is to search similar flood in historical data, wherein the water coming size and composition of the similar flood have certain difference with the current field flood, and the conditions of the water coming from the similar flood are inconsistent with the current field flood, so that the method can obviously improve the calculation accuracy.
Drawings
FIG. 1 is a schematic illustration of a proof fit of a corollary in the embodiment;
FIG. 2 is a flow chart of the method of the present invention;
FIG. 3 is a diagram showing the inflow of the branch ports of the river in the embodiment;
FIG. 4 is an explanatory diagram of the Primann four-point differential format of the embodiment;
FIG. 5 is a schematic diagram of the calculation of the end of return water during 2014 flood of the three gorges reservoir of an embodiment;
fig. 6 is a schematic diagram of the calculation of the end of return water during the 2020 year flood of the three gorges reservoir of the example.
Detailed Description
The invention is described in further detail below with reference to the drawings and the specific examples.
A method for calculating the backwater range of a reservoir comprises the following steps,
step 1: the method comprises the steps of collecting the structure of a river network where a reservoir is located, section topography data of dry tributaries in the river network, upstream flow inlet positions, inlet positions from tributaries to dry flows, upstream inlet flow processes of the dry tributaries in field floods and water level process before the reservoir dam;
step 2: according to the principle of the san-Vinan equation set, a one-dimensional flood evolution model applicable to the current river network structure is developed by applying a Prosmann four-point differential format discrete equation;
step 3: according to the actual water level condition before the dam in the field flood, reducing each water level value by a fixed value in the water level process, keeping the flow of each inlet in the river network unchanged, and calculating a group of virtual water level line change processes for the reservoir by using the flood evolution model;
step 4: according to the field flood process data, the highest water surface line of the reservoir area and the corresponding moment are selected, the highest water surface line and the corresponding moment are compared with the virtual water surface line at the same moment, the water level difference value of the highest water surface line and the virtual water surface line is smaller than a given xi (xi >0, the specific value is different according to different reservoirs), namely the backwater tail end of the field flood, and the interval from the dam address to the backwater tail end is the backwater influence range.
The step 2 further includes: step 2.1: according to the Prosoman four-point differential format, the differential in the Save Vietnam equation set is replaced by a differential quotient to form a discrete nonlinear equation set, and a Taylor formula is adopted to develop the nonlinear term so as to linearize the nonlinear term; step 2.2: and constructing a coefficient matrix of the linear equation set according to the river network structure, storing by using a compression format, and selecting an LU direct method solver for the equation set.
The step 3 further includes: step 3.1: the water level process comprises water level series measured values within a period of time, each water level value in the water level process is uniformly subtracted by 5m, the inlet flow values of main flows and tributaries in a river network are kept unchanged, virtual reservoir operation conditions are formed, and data preparation is carried out for calculating virtual water surface lines; step 3.2: based on the flood evolution model developed in the step 2, taking the main flow and the tributary inlet flow in the river network as upper boundary conditions, taking the virtual water level in front of the dam as lower boundary conditions, and substituting the virtual water level into the model to calculate the virtual water level line in the time period of the field flood process.
The step 4 further includes: step 4.1: drawing a change process of the water surface line of a reservoir area in the field flood process, selecting the highest water surface line and recording the occurrence time of the highest water surface line; step 4.2: in the calculated virtual water surface line, the water surface line at the same moment is selected to be compared with the actual water surface line, the water level elevation difference of the actual water surface line and the virtual water surface line at the same position is gradually reduced along the direction from the dam site to the reservoir tail, and the water level elevation difference is smaller than a given xi value to be used as the backwater tail end of the flood of the field, namely, the position where the influence of backwater of the reservoir disappears.
In step 1, the structure of the river network where the reservoir is located, the section topography data of the dry tributary in the river network, the upstream flow inlet position and the inlet position of the tributary to the dry flow need to collect the latest measurement data, and the data collection density in the upstream flow process of the dry tributary in the field flood and the water level application process in front of the reservoir dam is at least in the order of hours and must belong to the same time period.
Preferably, in step 2, the selected LU direct solver needs a compressed storage format that can accommodate the coefficient matrix of the linear equation set.
In step 3, when constructing the virtual water level, the value subtracted on the basis of the actual water level should not be too small, and sufficient space should be left to enable the difference ζ to be represented at the tail of the reservoir.
In the step 4, the value range of xi is more than or equal to 0 and less than or equal to 0.3.
According to the technical scheme, the actual operating water level (more than 2 m) in front of the dam is reduced by constructing the water supply condition which is completely consistent with the current field flood, and the virtual reservoir operating condition is obtained; taking the surface line as a boundary condition, and calculating a reservoir area water surface line under a virtual condition by using a numerical simulation technology for solving a one-dimensional Saint View south equation group; and finally, calculating the position of the backwater tail end by comparing the actual highest water surface line with the virtual water surface line at the same moment to obtain the backwater range of the field flood. The theoretical basis of the method is deduction on the definition of the backwater end, and the influence of the water level difference value xi is ignored for convenience of description.
Deducing: under certain conditions of reservoir flow and incoming water composition, such as the water level Z in front of the dam 2 >Z 1 The intersection point of the two corresponding water surface lines is Z 2 And the water returns to the tail end.
And (3) proving: as shown in figure 1 (see the attached drawing of the specification), the dam front water level Z 1 <Z 2 The corresponding water surface line is marked as C 1 、C 2 。C 0 Is a natural water surface line under the same warehouse-in flow and incoming water composition condition, and the corresponding dam site water level is Z 0 Obviously Z 0 <Z 1 <Z 2 . For the water surface line C 1 、C 2 They necessarily have backwater ends, i.e. with C 0 There are intersections, denoted as points A and B, respectively, due to Z 1 <Z 2 So the distance from the point A to the dam is smaller than that from the point B. Due to C 1 And C 0 Intersecting at point A, C after point A 1 And C 0 The sections are coincident in the curve AO. Thus, for natural water line C 0 Although the dotted line part of the figure is difficult to calculate, the AO segment is at C 1 Is present in the medium. Z is Z 2 The corresponding backwater end point B is C 2 And C 0 And is within the AO segment, so point B is also the intersection of the AO segment and C 2 The intersection point of (a), i.e. point B is C 1 And C 2 Is a cross point of (c). The syndrome is known.
The method for calculating the backwater range of the reservoir has important application in field flood prevention of large reservoirs. The three gorges reservoir is a diaphysis project of the Yangtze river basin of China, has remarkable benefits of flood control, power generation, shipping, water resource utilization and the like, and has remarkable influence on various operation management works due to backwater of the reservoir in the process of coping with the field flood, so that the embodiment selects and calculates the field flood backwater range of the three gorges reservoir.
The method for calculating the backwater range of the reservoir comprises the following steps,
step 1: the structure of the river network where the reservoir is located, the section topography data of the dry tributaries in the river network, the upstream flow inlet position, the inlet position of the tributaries to the dry tributaries, the upstream inlet flow process of the dry tributaries in the field flood and the water level process before the reservoir dam are collected.
The embodiment collecting three gorges reservoir river network structure comprises 14 larger first-order branches of Yangtze river main flow, jiang Ling river, yu Ling river, longxi river, wu Jiang river, cheng xi river, longxi river, xiaojiang river, shang Xihe, knife-sharpening xi, mei Xi river, daning river, along the ferry river, qing Kong river and Xiangxi river; the topography data comprises 417 sections of the main stream and 220 sections of the sub stream; the positions of the converging ports are marked by section positions; the field floods include the dry, upstream inlet flows of the tributaries and the operating water level before the dam at 2014, 9, 19 and 2020, 8, 18.
Step 2: according to the principle of the san-Vinan equation set, a one-dimensional flood evolution model applicable to the current river network structure is developed by applying a Prosmann four-point differential format discrete equation;
(1) Saint Vinan equation set
The water flow mathematical model mainly consists of a water flow continuous equation and a water flow motion equation, which are called a san-Vinan equation set.
Water flow continuity equation:
equation of motion of water flow:
wherein t is more than or equal to 0, x is more than or equal to 0 and less than or equal to l, l represents river length, Z represents water level, Q represents flow, B represents river width, A represents water passing area, K represents flow modulus, g represents gravitational acceleration, Q represents linear flow, and v represents flow velocity. (1) Is the water flow continuity equation, and (2) is the water flow motion equation. For calculation of single river flow, the equation set also requires the following initial value conditions:
(1) initial conditions. At t=0, the water level and flow z| at each position of the river t＝0 ＝Z(x)，Q| t＝0 ＝Q(x)。
(2) Edge condition. The upstream inlet and downstream outlet of the river give the flow process line q=q (t) and the water level process line z=z (t) at any time t, respectively, or both boundary conditions are the relationship q=z (t) between flow and water level. In practice, because the upstream inlet flow and downstream outlet water level can be measured, it is common to apply the upstream flow process and downstream water level process as boundary conditions.
For river networks, the boundary conditions are different from those of single river channels. In general, the upstream inlet side condition of the river network is the inlet flow process of all river channels of the dry river and the tributary, and the downstream outlet side condition is the outlet water level process of the dry river. For tributaries, the boundary conditions lack the water level process at the sink, so that the boundary conditions need to be supplemented at the sink, also called internal boundary conditions, since the sink of tributaries to the main stream is inside the river network. The junction of the branch and the main flow in the three gorges reservoir area is only one branch, as shown in figure 3 (see the drawing of the specification), so that the flow conservation condition Q is increased at the junction 3 ＝Q 1 +Q 2 As an internal boundary condition.
(2) Discrete of equations
The one-dimensional san View equation set is a typical quasi-linear equation set, and is discretized by using the Prosman four-point eccentric hidden format, which has potential in dealing with the problem of non-constant water flow propagation in one-dimensional river channels. Firstly, intercepting a plurality of cross sections on a river to disperse the river length, and using i to represent a cross section number; and then dispersing the calculated time, wherein the time interval is marked as delta t, the j represents the time sequence number, and the theta represents the time weight factor. Fig. 4 shows the plassman four-point eccentric hidden format.
In this discrete format, the function value and each first partial derivative at point (x, t) can be calculated as follows:
wherein Deltax i Representing the distance from the i-th section to the i+1th section; Δt represents the time step, which uses a constant value and therefore is notSubscripts are noted. Substituting the function value and the partial derivative calculation formula in the formula (3) into the formulas (1) and (2) can obtain a discrete nonlinear equation set because the water flow motion equation contains nonlinear terms. In the numerical calculation method, the cost for solving the nonlinear equation set is high, and when river topography is complex, the iteration method is not easy to converge, so that the nonlinear term in the nonlinear equation set is linearized by adopting the linearization method and is converted into the linear equation set. Specifically, toAnd->Respectively represent the flow rate of the ith section from moment j to moment j+1 and the variation of the water level, so as to be +.>Representing the corresponding physical quantity of the ith section at time j, the following two linear equations can be listed on each river reach for the time interval Δt:
wherein each coefficient is as follows:
the calculation of the coefficients involvesAnd->The river width B and the flow modulus K are functions of the water level Z and can be calculated according to the topographic data of the section. Assuming that the river network contains the main stream and m 1 Strip tributary, river network sharing section m 2 The section divides the river network into m 2 -m 1 -1 river reach. The water flow evolution process of the river channel needs to be calculated to solve the water level and the flow of each section, so that the number of unknowns needing to be solved is 2m 2 And each. Equation 2 (m can be obtained according to equation (4) 2 -m 1 -1). m is m 1 The substream comprises m 1 Individual inlet flow boundary conditions and m 1 The internal boundary condition can be 2m 1 And equations. The main flow contains 1 inlet flow and 1 outlet water level boundary condition, 2 equations are available. Thus, the number of equations available for the entire river network is 2 (m 2 -m 1 -1)+2m 1 +2＝2m 2 Just as many unknowns, a closed system of linear equations may be constructed.
(3) Storage and solving of equation sets
After the Saint Vietnam equation set is discretized, the obtained sparse matrix needs to be stored in two stages.
The first stage is in the matrix generation process. In the process, the non-zero elements are gradually added into the coefficient matrix according to the river reach, if the conventional two-dimensional array storage is adopted, the non-zero elements can be quickly inserted, but the space occupied by the whole matrix is relatively large. Therefore, the matrix in the generation process is stored by adopting the cross linked list method, the matrix is stored by adopting the chain structure by adopting the cross linked list method, the non-zero element insertion operation can be completed in the O (1) time, only the non-zero element is needed to be stored, and the occupied storage space is small.
The second stage is in the solving of the system of equations. For most linear system of equations solvers, the most frequent operation is matrix multiplication, and therefore the computational efficiency of the solver depends primarily on the computational efficiency of the matrix multiplication. The cross linked list method is a chain type storage structure, and elements of the cross linked list method are stored in discontinuous storage units, so that the whole block of data reading is not facilitated. Therefore, when solving the system of equations, it is necessary to convert the chain storage structure into a continuous storage structure. The invention uses a compressed memory structure (CSR/CSC) according to rows (columns), and both structures can access the whole row or whole block of data with high efficiency, thereby being beneficial to improving the calculation efficiency of a solver.
Step 3: according to the actual pre-dam application water level condition in the field flood, reducing each water level value by 5m (at least more than 2 m) in the water level process, keeping the flow of each inlet in the river network unchanged, and calculating a group of virtual water level line change processes for the reservoir by using the flood evolution model;
step 3.1: the water level process comprises water level series measured values in a period of time, uniformly subtracting 5m, keeping the inlet flow values of main flows and branch flows in the river network unchanged, forming virtual reservoir operation conditions, and preparing data for calculating virtual water surface lines;
step 3.2: based on the flood evolution model developed in the step two, taking the main flow and the tributary inlet flow in the river network as upper boundary conditions, taking the virtual water level in front of the dam as lower boundary conditions, and substituting the virtual water level into the model to calculate the virtual water level line in the time period of the field flood process.
Step 4: according to the field flood process data, the highest water surface line of the reservoir area and the corresponding moment are selected, the highest water surface line and the corresponding moment are compared with the virtual water surface line at the same moment, the water level difference value of the highest water surface line and the virtual water surface line is smaller than a given xi (xi >0, the specific value is different according to different reservoirs), namely the backwater tail end of the field flood, and the interval from the dam address to the backwater tail end is the backwater influence range.
Step 4.1: drawing a change process of the water surface line of a reservoir area in the field flood process, selecting the highest water surface line and recording the occurrence time of the highest water surface line;
step 4.2: in the calculated virtual water surface line, the water surface line at the same moment is selected to be compared with the actual water surface line, the water level elevation difference of the actual water surface line and the virtual water surface line at the same position is gradually reduced along the direction from the dam site to the reservoir tail, and the water level elevation difference is smaller than a given xi value to be used as the backwater tail end of the flood of the field, namely, the position where the influence of backwater of the reservoir disappears. In this example, ζ is 0.3m.
Fig. 5 and 6 are calculated three gorges reservoir flood ends during 2014 and 2020 floods in this example. Wherein, the position of the backwater end of 9 th and 19 th of 2014 is about 656km (near the south China sea) from the dam site; the end position of the 18-day backwater in 8 months 2020 is about 633km (near neutron fall) from the dam site. Therefore, the invention provides a new method for accurately calculating the backwater end position of the reservoir in field floods.
The foregoing description of the preferred embodiments of the invention is not intended to be limiting, but rather is intended to cover all modifications, equivalents, alternatives, and improvements that fall within the spirit and scope of the invention.
Claims (6)
1. The method for calculating the backwater range of the reservoir is characterized by comprising the following steps of: it comprises the following steps of the method,
step 1: the method comprises the steps of collecting the structure of a river network where a reservoir is located, section topography data of dry tributaries in the river network, upstream flow inlet positions, inlet positions from tributaries to dry flows, upstream inlet flow processes of the dry tributaries in field floods and water level process before the reservoir dam;
step 2: according to the principle of the san-Vinan equation set, a one-dimensional flood evolution model applicable to the current river network structure is developed by applying a Prosmann four-point differential format discrete equation;
step 3: according to the actual water level condition before the dam in the field flood, reducing each water level value by a fixed value in the water level process, keeping the flow of each inlet in the river network unchanged, and calculating a group of virtual water level line change processes for the reservoir by using the flood evolution model;
step 4: according to the field flood process data, selecting the highest water surface line of a reservoir area and the corresponding moment, comparing the highest water surface line with a virtual water surface line at the same moment, wherein the position with the water level difference smaller than a given xi is the backwater end of the field flood, and the interval from a dam address to the backwater end is the backwater influence range;
the step 3 further includes:
step 3.1: the water level process comprises water level series measured values within a period of time, each water level value in the water level process is uniformly subtracted by 5m, the inlet flow values of main flows and tributaries in a river network are kept unchanged, virtual reservoir operation conditions are formed, and data preparation is carried out for calculating virtual water surface lines;
step 3.2: based on the flood evolution model developed in the step 2, taking the main flow and the tributary inlet flow in the river network as upper boundary conditions, taking the virtual water level in front of the dam as lower boundary conditions, and substituting the virtual water level into the model to calculate the virtual water level line in the time period of the scene flood process;
the step 4 further includes:
step 4.1: drawing a change process of the water surface line of a reservoir area in the field flood process, selecting the highest water surface line and recording the occurrence time of the highest water surface line;
step 4.2: in the calculated virtual water surface line, the water surface line at the same moment is selected to be compared with the actual water surface line, the water level elevation difference of the actual water surface line and the virtual water surface line at the same position is gradually reduced along the direction from the dam site to the reservoir tail, and the water level elevation difference is smaller than a given xi value to be used as the backwater tail end of the flood of the field, namely, the position where the influence of backwater of the reservoir disappears.
2. A method of calculating a reservoir return water range as claimed in claim 1, wherein: the step 2 further includes:
step 2.1: according to the Prosoman four-point differential format, the differential in the Save Vietnam equation set is replaced by a differential quotient to form a discrete nonlinear equation set, and a Taylor formula is adopted to develop the nonlinear term so as to linearize the nonlinear term;
step 2.2: and constructing a coefficient matrix of the linear equation set according to the river network structure, storing by using a compression format, and selecting an LU direct method solver for the equation set.
3. A method of calculating a reservoir return water range as claimed in claim 1, wherein: in step 1, the structure of the river network where the reservoir is located, the section topography data of the dry tributary in the river network, the upstream flow inlet position and the inlet position of the tributary to the dry flow need to collect the latest measurement data, and the data collection density in the upstream flow process of the dry tributary in the field flood and the water level application process in front of the reservoir dam is at least in the order of hours and must belong to the same time period.
4. A method of calculating a reservoir return water range as claimed in claim 1, wherein: in step 2, the selected LU direct solver needs a compressed storage format that can be adapted to the coefficient matrix of the linear equation set.
5. A method of calculating a reservoir return water range as claimed in claim 1, wherein: in step 3, when constructing the virtual water level, the value subtracted on the basis of the actual water level should not be too small, and sufficient space should be left to enable the difference ζ to be represented at the tail of the reservoir.
6. A method of calculating a reservoir return water range as claimed in claim 1, wherein: in the step 4, the value range of xi is more than or equal to 0 and less than or equal to 0.3.
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