Method for predicting water level and flow rate of plain river network based on hydro - hydrological coupling model

Abstract

The present invention discloses a method for predicting water level and flow rate of plain river networks based on a coupled hydrological and hydrodynamic model, including: S1. Obtain basin meteorological and hydrological data, basin characteristic data, hydrological model and hydrodynamic model parameter data, and basic data of plain river networks, and preprocess the above data to generate input files meeting the requirements of the coupled hydrological and hydrodynamic model; S2. Drive the hydrological model using meteorological and hydrological data, basin characteristic data, and hydrological model parameter data to obtain hydrological forecast results; S3. Set the boundaries of the hydrodynamic model according to different working conditions, and input the calculation results of the hydrological model into the hydrodynamic model to complete the coupling of the hydrological and hydrodynamic models; S4. Solve the coupled hydrological and hydrodynamic model to predict the water level and flow rate of plain river networks; The present invention has the advantages of high accuracy, strong reliability, and strong adaptability, and can be applied to flood forecasting and early warning, water resource utilization and management.

Description

Technical Field

[0001] The present invention relates to the technical field of hydrological forecasting, and particularly refers to a method for predicting the water level and flow rate of a plain river network based on a coupled hydrological-hydrodynamic model. Background Art

[0002] Plains in China account for 12% of the total national land area and are mainly distributed on both sides of rivers and in areas adjacent to the sea. The terrain of the plain area is flat and the river network is crisscrossed. Compared with the mountainous river network, the river network in the plain area is more complex. The mountainous area is mainly composed of dendritic river networks and linear river networks, while the plain is mainly composed of complex circular river networks. Obviously, the hydraulic calculation in the plain river network area is more complex. Coupled with the presence of numerous hydraulic structures (such as sluices, pumps, culverts, and weirs) in the plain river network area, it further increases the difficulty of hydraulic calculation in the plain river network area. The plain area has abundant rainfall and frequent flood disasters. Due to the flat terrain in the plain area, after a flood occurs, the water flow spreads over a wide area, the flood flow velocity is slow, and the inundation time is long. In addition, the plain area often has a large population density and relatively developed economy. Once a flood disaster occurs, it will cause immeasurable losses. To sum up, the research on the prediction of the water level and flow rate of the plain river network has very important theoretical and practical significance.

[0003] Flood forecasting is one of the important non-engineering measures for flood control and disaster reduction. High-precision flood forecasting will greatly reduce the losses caused by floods. Theory and practice have proved that the hydrodynamic model based on physical principles can accurately simulate the river runoff process, including common phenomena such as flood backwater, backwater, and overbank flow in the plain river network area. In addition, the hydrodynamic model can obtain an important hydraulic parameter, the water level, which the hydrological model cannot. In fact, in flood warning and navigation, the role of the water level is more important than the flow rate. However, an independent hydrodynamic model only has a simulation function and cannot perform forecasting. Practice has proved that coupling the hydrological model and the hydrodynamic model can make up for the deficiencies of each model and play a significant role in improving the accuracy of flood forecasting. The coupling of the hydrological model and the hydrodynamic model has shown important advantages in the fields of water resources management and hydrology. For example, the coupling of the hydrological model and the hydrodynamic model can provide more accurate hydrological information because the hydrological model is usually used to simulate surface water cycle processes such as rainfall and runoff, while the hydrodynamic model focuses more on the water flow and water level changes inside the river. The combination of the two can more comprehensively reflect the actual hydrological situation. Secondly, this coupling is very useful in flood prediction and management because it enables us to more accurately predict the occurrence and development trend of flood events, helps to take timely flood prevention and emergency response measures, and thus reduces the losses caused by floods. In addition, the coupling of the hydrological model and the hydrodynamic model can handle various complex working conditions in the prediction of the water level and flow rate of the plain river network.

[0004] Therefore, the hydrological model and the hydrodynamic model can be coupled, and the water level and flow rate of the plain river network can be predicted based on the coupled model. The advantages of the hydrological-hydrodynamic coupled model can be utilized to adapt to the complex working conditions of the plain river network, thereby improving the accuracy of the water level and flow rate prediction of the plain river network. Summary of the Invention

[0005] The purpose of the present invention is to overcome the above deficiencies and provide a method for predicting the water level and flow rate of a plain river network based on a hydrological-hydrodynamic coupled model, which can not only adapt to the complex working conditions of the plain river network, but also improve the prediction accuracy of the water level and flow rate of the plain river network, and can be widely applied to production practice with great application value.

[0006] The technical solution adopted by the present invention to solve the above technical problems is as follows:

[0007] A method for predicting the water level and flow rate of a plain river network based on a hydrological-hydrodynamic coupled model, which comprises the following steps:

[0008] S1. Obtain the basin meteorological and hydrological data, basin characteristic data, hydrological model and hydrodynamic model parameter data, and basic data of the plain river network, and preprocess the above data to generate an input file that meets the requirements of the hydrological-hydrodynamic coupled model;

[0009] S2. Use the meteorological and hydrological data, basin characteristic data, and hydrological model parameter data to drive the hydrological model to obtain the hydrological forecast results;

[0010] S3. Set the hydrodynamic model boundary according to different working conditions, and input the calculation results of the hydrological model into the hydrodynamic model to complete the coupling of the hydrological-hydrodynamic model;

[0011] S4. Solve the hydrological-hydrodynamic coupled model to predict the water level and flow rate of the plain river network.

[0012] Further, the step S1 includes the following steps:

[0013] S11. Obtain the basin meteorological and hydrological data, including measured and forecast rainfall data, measured flow data at stations, and measured water level data at stations;

[0014] S12. Obtain the basin characteristic data, including basin area, basin slope, sub-basin length, river length, and topographic index;

[0015] S13. Obtain the hydrological model and hydrodynamic model parameter data, including directly measurable physical parameters and non-physical parameters that can only be obtained through hydrological model parameter calibration;

[0016] S14. Obtain the basic data of the plain river network, including the river network geographic information layer, river network cross-section data, and elevation data of river network monitoring points;

[0017] S15. Preprocess the data in S11 to S14 according to the input requirements of the hydrological model and the hydrodynamic model.

[0018] Furthermore, the parameters of the hydrological model in step S2 are determined by calibration. The hydrological model adopts a conceptual hydrological model, and the hydrological forecast result is a set of flow time series values.

[0019] Furthermore, step S3 includes the following steps:

[0020] S31. Set the hydrodynamic model boundaries according to different working conditions. Specifically, for different working conditions encountered in the water level and flow prediction of the plain river network, set the hydrodynamic model boundaries respectively;

[0021] The four common working conditions in the water level and flow prediction of the plain river network and the setting methods of the hydrodynamic model boundaries for different working conditions are as follows:

[0022] Working condition 1: Concentrated inflow and outflow. Specifically, there is water inflow and outflow in a certain section of the plain river network. The setting method of the hydrodynamic model boundary for working condition 1 is as follows: The flow time series (t = 1, 2, 3, …, n) and (t = 1, 2, 3, …, n) can be obtained through manual setting or calculated by the hydrological model in S2, and a set of flow time series values is provided to the hydrodynamic model;

[0023] Working condition 2: The river channel is connected to a reservoir. Specifically, there is an area similar to a reservoir connected to a certain section of the river channel. The setting method of the hydrodynamic model boundary for working condition 2 is as follows: The flow time series (t = 1, 2, 3, …, n) can be obtained through manual setting or set according to certain control rules, and a set of flow time series values is provided to the hydrodynamic model;

[0024] Working condition 3: River channel weir gate control. Specifically, there are weir gates in the plain river network to control the water volume or water level of the river channel. The setting method of the hydrodynamic model boundary for working condition 3 is as follows: Set the opening degree e of the gate, the net width b of a single gate, the number of gate holes n of the weir gate, the vertical contraction coefficient of the gate; ε, the discharge coefficient γ of the free outflow of the gate hole, and the submergence coefficient σ of the gate s , the vertical contraction coefficient ε;

[0025] Working condition 4: The river channel suddenly widens. Specifically, the cross-section of the river channel in the plain river network suddenly widens. This working condition does not require manual setting, and the hydrological and hydrodynamic coupling model will automatically identify and process this working condition when solving;

[0026] S32. Input the calculation results of the hydrological model into the hydrodynamic model. Specifically, use the flow time series calculated by the hydrological model as the known condition for solving the hydrodynamic model equation. The hydrodynamic model equation is as follows:

[0027]

[0028] In the formula, Q is the flow rate (unit: m 3 / s), Z is the water level (unit: m), A is the cross-sectional area (unit: m 2 ), h is the water depth (unit: m), S0 is the bottom slope of the river, S f is the friction slope, and μ is the average cross-sectional velocity (unit: m / s);

[0029] The finite difference method is used to solve the hydrodynamic model equation. Specifically, the hydrodynamic model equation is discretized using the Preissmann implicit format, and the hydrodynamic model equation originally in the form of a partial differential equation is transformed into a system of linear equations with constant coefficients for solution. The formula for the system of linear equations regarding the water level Z and flow rate Q at time t + 1 at section j and section j + 1 after transformation is:

[0030]

[0031] In the formula, are the equation coefficients at section j at time t, and each coefficient is calculated through the following formulas:

[0032]

[0033]

[0034]

[0035]

[0036]

[0037]

[0038] In the formula, is the flow rate at section j at time t; is the water level at section j at time t; is the average water surface width of reach j at time t; Δx j is the reach length of reach j; θ is the weight coefficient; is the average flow rate of reach j; α is the momentum correction coefficient; c is the Chezy coefficient. The water level and flow rate values at each section at t = 0 are known, so the equation coefficients at time t can be obtained through formulas (3) to (8). S33. Complete the coupling of the hydrological and hydrodynamic models. Specifically, the water level and flow equations for the plain river network at time t+1 are as follows:

[0039]

[0040] The equation shown in formula (9) contains 12 unknowns but only 10 equations, so this equation cannot be solved. After adding the following two equations, the system of equations can meet the solution requirements:

[0041]

[0042]

[0043] In the formula, represents the flow at section 1 at time t+1, represents the water level at section 6 at time t+1; in order to solve the system of equations shown in formula (9), various working conditions also need to be considered;

[0044] The plain river network also includes several working conditions such as concentrated inflow, concentrated outflow, river channel connecting to a reservoir, and sudden widening of the river channel. The calculation formulas for each working condition are as follows:

[0045] Concentrated outflow:

[0046]

[0047] River channel connecting to a reservoir:

[0048]

[0049] Flow through a weir gate:

[0050]

[0051] In the formula, e is the opening height of the gate; b is the net width of a single gate; n is the number of gate openings; H0 is the head before the gate; ε is the vertical contraction coefficient; γ is the discharge coefficient of free outflow through the gate opening; σ s is the submergence coefficient;

[0052] Sudden widening of the river channel:

[0053]

[0054] Concentrated inflow:

[0055]

[0056] Adding formulas (12)-(16) to formula (9) gives the system of equations of the coupled model of the hydrological model and the hydrodynamic model.

[0057] Further, in step S4, to solve the hydrological-hydrodynamic coupling model for predicting the water levels and discharges in the plain river network, specifically: through steps S1 to S3, the input preparation of the hydrological-hydrodynamic coupling model is completed, and at the same time, the coupling of the hydrological model and the hydrodynamic model is completed. By solving the coupled model equations of the hydrological model and the hydrodynamic model, the water level and discharge processes of each cross-section in the plain river network can be obtained.

[0058] Advantages of the present invention:

[0059] Based on the hydrological-hydrodynamic coupling model, the present invention predicts the water levels and discharges in the plain river network. Compared with the traditional prediction models for water levels and discharges in the plain river network, it can adapt to the working conditions that occur most frequently in the plain river network, such as lateral inflow, lateral outflow, river channels connecting to reservoirs, sudden enlargement of river channel cross-sections, and flow through weirs and gates. It has the advantages of high accuracy, strong reliability, and strong adaptability, and can be applied to flood forecasting and early warning, water resource utilization and management. Description of the drawings

[0060] Figure 1 It is a method flow chart of a method for predicting water levels and discharges in a plain river network based on a hydrological-hydrodynamic coupling model.

[0061] Figure 2 It is a working condition diagram for predicting water levels and discharges in the plain river network of the present invention;

[0062] Figure 3 It is a schematic diagram of the plain river network of the present invention considering various working conditions;

[0063] Figure 4 It is a generalized diagram of the plain river network in the Xixi River Basin of Anhui Province in the specific embodiment of the present invention;

[0064] Figure 5 It is a comparison diagram of the prediction effects of dynamic calibration of hydrological model parameters in the specific embodiment of the present invention. Specific embodiments

[0065] The present invention will be further described in detail below with reference to the drawings and specific embodiments.

[0066] Embodiment 1: As Figure 1 shown, a method for predicting water levels and discharges in a plain river network based on a hydrological-hydrodynamic coupling model includes the steps of:

[0067] S1. Obtain the basin meteorological and hydrological data, basin characteristic data, hydrological model and hydrodynamic model parameter data, and plain river network basic data, and preprocess the above data to generate input files that meet the requirements of the hydrological-hydrodynamic coupling model;

[0068] S2. Drive the hydrological model using the meteorological and hydrological data, basin characteristic data, and hydrological model parameter data to obtain hydrological forecast results;

[0069] S3. Set the hydrodynamic model boundaries according to different working conditions, and input the calculation results of the hydrological model into the hydrodynamic model to complete the coupling of the hydrological and hydrodynamic models;

[0070] S4. Solve the coupled hydrological and hydrodynamic model to predict the water level and flow rate of the plain river network.

[0071] Preferably, the step S1 includes the following steps:

[0072] S11. Obtain the basin meteorological and hydrological data, including measured and forecast rainfall data, measured flow data at stations, and measured water level data at stations;

[0073] S12. Obtain the basin characteristic data, including basin area, basin slope, sub-basin length, river length, and topographic index;

[0074] S13. Obtain the hydrological model and hydrodynamic model parameter data, including directly measurable physical parameters and non-physical parameters that can only be obtained through hydrological model parameter calibration;

[0075] S14. Obtain the basic data of the plain river network, including the river network geographic information layer, river network cross-section data, and elevation data of river network monitoring points;

[0076] S15. Preprocess the data in S11 to S14 according to the input requirements of the hydrological model and the hydrodynamic model.

[0077] Preferably, the hydrological model parameters in the step S2 are obtained through hydrological model parameter calibration. The hydrological model adopts conceptual hydrological models, such as the Xin'anjiang model, NAM model, tank model, HBV model, etc. The hydrological forecast results are a set of flow time series values.

[0078] Preferably, the step S3 includes the following steps:

[0079] S31. Set the hydrodynamic model boundaries according to different working conditions, specifically: set the hydrodynamic model boundaries for different working conditions encountered in the water level and flow rate prediction of the plain river network respectively.

[0080] The four common working conditions in the water level and flow rate prediction of the plain river network and the setting methods of the hydrodynamic model boundaries for different working conditions are as follows:

[0081] Working condition 1: Concentrated inflow and outflow, specifically: There is water inflow and outflow in a certain reach of the plain river network (as shown in Figure 2 (a)). The setting method of the hydrodynamic model boundary for working condition 1 is specifically: The flow time series of inflow and outflow (t = 1, 2, 3,..., n) and (t = 1, 2, 3, …, n) can be obtained through manual setting or calculated by the hydrological model in S2. What is provided to the hydrodynamic model is a set of flow time series values.

[0082] Condition 2: The river channel is connected to a reservoir. Specifically, there is an area similar to a reservoir (such as lakes, flood storage and detention areas, ponds, polder areas, etc. commonly found in plain river networks) connected to a certain section of the river reach (as shown in Attachment Figure 2 (b)). The specific method for setting the boundary of the hydrodynamic model under Condition 2 is as follows: The flow time series (t = 1, 2, 3, …, n) can be obtained through manual setting or set according to certain control rules. What is provided to the hydrodynamic model is a set of flow time series values.

[0083] Condition 3: The river channel is controlled by a weir gate. Specifically, in the plain river network, a weir gate controls the water volume or water level of the river channel (as shown in Attachment Figure 2 (c)). The specific method for setting the boundary of the hydrodynamic model under Condition 3 is as follows: Set the opening degree e of the gate, the net width b of a single gate, the number of gate openings n of the weir gate, the vertical contraction coefficient of the gate; ε, the discharge coefficient γ of the free outflow of the gate opening, and the submergence coefficient σ of the gate s , the vertical contraction coefficient ε.

[0084] Condition 4: The river channel suddenly widens. Specifically, the cross-section of the river channel in the plain river network suddenly widens (as shown in Attachment Figure 2 (d)). For this condition, no manual setting is required. When solving the coupled hydrological and hydrodynamic model, this condition will be automatically identified and processed.

[0085] S32. Input the calculation results of the hydrological model into the hydrodynamic model. Specifically, use the flow time series calculated by the hydrological model as the known conditions for solving the hydrodynamic model equation. Among them, the hydrodynamic model equation is as follows:

[0086]

[0087] In the formula, Q is the flow rate (unit, m 3 / s), Z is the water level (unit, m), A is the cross-sectional area (unit, m 2 ), h is the water depth (unit, m), S0 is the bottom slope of the river, S f is the friction slope, and μ is the average cross-sectional velocity (unit, m / s).

[0088] The hydrodynamic model equation is solved using the finite difference method. Specifically, the hydrodynamic model equation is discretized using the Preissmann implicit format, and the originally partial differential equation-based hydrodynamic model equation is transformed into a system of constant coefficient linear equations for solution. The formula for the linear equations of the water level Z and flow rate Q at the cross-section j and cross-section j + 1 at the time t + 1 after transformation is:

[0089]

[0090] In the formula, are the equation coefficients of river reach j at time t, and each coefficient is calculated through the following formulas:

[0091]

[0092]

[0093]

[0094]

[0095]

[0096]

[0097] In the formula, is the flow rate of cross-section j at time t; is the water level of cross-section j at time t; is the average river width of the water surface of river reach j at time t; Δx j is the length of river reach j; θ is the weight coefficient; is the average flow rate of river reach j; α is the momentum correction coefficient; c is the Chezy coefficient. The water level and flow rate values of each cross-section at t = 0 are known, so the equation coefficients at time t can be obtained through formulas (3) to (8)

[0098] S33. Complete the coupling of the hydrological and hydrodynamic models, specifically: As shown in the appendix Figure 3 is a schematic diagram of a plain river network considering different working conditions. The actual plain river network is more complex than this schematic diagram, but the coupling of the hydrological and hydrodynamic models of complex and simple plain river networks and the solution method of the coupling model are the same. Therefore, taking the appendix Figure 3 as an example to illustrate the coupling and solution methods of the hydrological and hydrodynamic models. The appendix Figure 3 The river network in it contains 6 cross-sections and 5 river reaches. There is a concentrated outflow in river reach 1, river reach 2 is connected to a reservoir, there is a weir gate on river reach 3, there is a working condition where the river channel suddenly widens in river reach 4, and there is a concentrated inflow in river reach 5. River reach 1 is connected to the basin S, and the hydrological model established for the basin S can provide a set of flow rate time series data (t = 1, 2, 3,..., n) as the boundary condition of the hydrodynamic model. There is a water level monitoring station in river reach 9, which can provide a set of water level time series (t = 1, 2, 3,..., n) as the boundary condition of the hydrodynamic model. Appendix Figure 3The water level and flow equations of the plain river network at time t+1 are as follows:

[0099]

[0100] The equation shown in formula (9) contains 12 unknowns but only 10 equations, so this equation cannot be solved. After adding the following two equations, the system of equations can meet the solution requirements:

[0101]

[0102]

[0103] In the formula, represents the flow rate at section 1 at time t+1, represents the water level at section 6 at time t+1. In order to solve the system of equations shown in formula (9), various working conditions shown in Appendix Figure 3 also need to be considered.

[0104] Appendix Figure 3 The plain river network shown also includes several working conditions such as concentrated inflow, concentrated outflow, river channel connecting to a reservoir, and sudden widening of the river channel. The calculation formulas for each working condition are as follows:

[0105] Concentrated outflow:

[0106]

[0107] River channel connecting to a reservoir:

[0108]

[0109] Weir gate flow:

[0110]

[0111] In the formula, e is the gate opening height; b is the net width of a single gate; n is the number of gate openings; H0 is the head before the gate; ε is the vertical contraction coefficient; γ is the flow coefficient of free outflow through the gate opening; σ s is the submergence coefficient.

[0112] Sudden widening of the river channel:

[0113]

[0114] Concentrated inflow:

[0115]

[0116] Adding formulas (12)-(16) to formula (9) gives the coupled model system of equations for the hydrological model and the hydrodynamic model.

[0117] Preferably, in step S4, the hydrological and hydrodynamic coupling model is solved to predict the water level and flow rate of the plain river network, specifically: through steps S1 to S3, the input preparation of the hydrological and hydrodynamic coupling model is completed, and the coupling of the hydrological model and the hydrodynamic model is also completed. By solving the coupled model equations of the hydrological model and the hydrodynamic model, the water level and flow rate processes of each section of the plain river network can be obtained.

[0118] Example 2: In this example, the Xixi River Basin in Anhui Province is taken as an example to illustrate the application of this method. The Xixi River Basin is mainly composed of plain river networks. As shown in the appendix Figure 4 shown, the basin contains 5 weir gates (Zhaohe Gate, Dongdawei Gate, Fenghuangjing Drainage and Irrigation Station, Fenghuangjing Gate, Huangluo Gate), 1 river is connected to a reservoir (River No. 5), 5 hydrological stations (Xixi River, Quekou, Liangjiaba, Wuwei, Kaichengqiao), 3 inter-basin inflows (at Quekou Hydrological Station, Liangjiaba Hydrological Station, Wuwei Hydrological Station), and 2 inter-basin outflows (River No. 13, River No. 14). The method and system for predicting the water level and flow rate of the plain river network based on the hydrological and hydrodynamic coupling model in this example can be implemented according to the following steps:

[0119] Step 1: Obtain the basin meteorological and hydrological data, basin characteristic data, hydrological model and hydrodynamic model parameter data, and plain river network basic data, and preprocess the above data to generate input files that meet the requirements of the hydrological and hydrodynamic coupling model;

[0120] The meteorological and hydrological data of the Xixi River Basin in Anhui Province from 2015 to 2017 were collected, with a time step of 1 hour. The basic data such as the river network geographic information layer, river network section data, and elevation data of river network monitoring points in the Xixi River Basin were obtained, as well as the basin characteristic data such as basin area, basin slope, sub-basin length, river length, and terrain index. In addition, the basin hydrological model parameters and hydrodynamic model parameter data were also obtained from the local hydrological bureau. Forecast processing was carried out on the obtained data to generate model input files that meet the hydrological and hydrodynamic coupling model.

[0121] Step 2: Use the meteorological and hydrological data, basin characteristic data, and hydrological model parameter data to drive the hydrological model to obtain hydrological forecast results;

[0122] Use the model input files generated in step 1 to drive the basin hydrological model, and the forecast flow rate processes of the Xixi River, Quekou, Liangjiaba, Wuwei, and Kaichengqiao hydrological stations are obtained through model calculations.

[0123] Step 3: Set the hydrodynamic model boundaries according to different working conditions, and input the calculation results of the hydrological model into the hydrodynamic model to complete the coupling of the hydrological and hydrodynamic models;

[0124] In the embodiments, there are working conditions of inflow from the interval (at the gap hydrological station, Liangjiaba hydrological station, Wuwei hydrological station), outflow from the interval, river channel connecting to the reservoir (at the No. 5 river), sudden increase in cross-section (at the No. 1 river), and flow through weir gates (Zhaohe Weir, Dongdawei Weir, Fenghuangjing Drainage and Irrigation Station, Fenghuangjing Weir, Huangluo Weir). The method proposed by the present invention is used to handle each working condition, and a coupled hydrological and hydrodynamic model equation set is established. Among them, the flow process at the inflow from the interval comes from the predicted flow process calculated by the hydrological model in step two.

[0125] Step four: Solve the coupled hydrological and hydrodynamic model to predict the water level and flow in the plain river network;

[0126] By solving the coupled hydrological and hydrodynamic model equation set, the Figure 5 shown hydrological flow prediction process can be obtained. As can be seen from Figure 5 , the fitting degree between the predicted water level and flow values at the Liangjiaba Station and the measured values is very high, indicating that the method proposed by the present invention has a very high prediction accuracy.

[0127] The above embodiments are only the preferred technical solutions of the present invention and should not be regarded as limitations on the present invention. The embodiments in this application and the features in the embodiments can be arbitrarily combined with each other without conflict. The protection scope of the present invention should be the technical solutions recorded in the claims, including the equivalent replacement solutions of the technical features in the technical solutions recorded in the claims. That is, the equivalent replacement improvements within this scope are also within the protection scope of the present invention.

Claims

1. A method for predicting water level and flow rate in plain river networks based on a coupled hydrological and hydrodynamic model, characterized in that: It includes the following steps: S1. Obtain the basin meteorological and hydrological data, basin characteristic data, hydrological model and hydrodynamic model parameter data, and basic data of the plain river network, and preprocess the above data to generate input files meeting the requirements of the hydrological-hydrodynamic coupling model; S2. Use the meteorological and hydrological data, basin characteristic data, and hydrological model parameter data to drive the hydrological model to obtain hydrological forecast results; S3. Set the hydrodynamic model boundaries according to different working conditions, and input the calculation results of the hydrological model into the hydrodynamic model to complete the coupling of the hydrological-hydrodynamic model; S4. Solve the hydrological-hydrodynamic coupling model to predict the water level and flow in the plain river network; The step S3 includes the following steps: S31. Set the hydrodynamic model boundaries according to different working conditions, specifically: set the hydrodynamic model boundaries for different working conditions encountered in the process of predicting the water level and flow in the plain river network; The four common working conditions in the prediction of the water level and flow in the plain river network and the setting methods of the hydrodynamic model boundaries for different working conditions are as follows: Condition 1: Concentrated inflow and outflow, specifically: There is water inflow and outflow in a certain reach of the plain river network; The specific boundary setting method of the hydrodynamic model for Condition 1 is: the flow rate time series of inflow and outflow and can be obtained through manual setting or calculated by the hydrological model in S2, and a set of flow rate time series values are provided to the hydrodynamic model; Among them, ; Condition 2: The river channel is connected to the reservoir. Specifically, there is an area similar to a reservoir connected to a certain section of the river reach. The boundary setting method of the hydrodynamic model under Condition 2 is specifically as follows: the flow rate time series flowing into the reservoir is provided to the hydrodynamic model as a set of flow rate time series values through manual setting; among them, ; Condition 3: River weir and sluice control, specifically: there are weirs and sluices in the plain river network to control the water volume or water level of the river; the specific method for setting the hydrodynamic model boundary of Condition 3 is: set the opening degree of the gate , the net width of a single gate , the number of sluice openings of the weir and sluice , the vertical contraction coefficient of the gate , the discharge coefficient of free flow through the sluice opening , the submergence coefficient of the gate ; Working condition 4: The river channel suddenly widens, specifically: the cross-section of the river channel in the plain river network suddenly widens; this working condition does not require manual setting, and the hydrological-hydrodynamic coupling model will automatically identify and process this working condition when solving; S32. Input the calculation results of the hydrological model into the hydrodynamic model, specifically: use the flow time series calculated by the hydrological model as the known conditions for solving the hydrodynamic model equations; among them, the hydrodynamic model equations are as follows: Wherein, is the flow rate, is the water level, is the cross-sectional area, is the water depth, is the bottom slope of the river, is the friction slope, is the average cross-sectional velocity; The hydrodynamic model equations are solved using the finite difference method. Specifically, the hydrodynamic model equations are discretized using the Preissmann implicit scheme, and the hydrodynamic model equations originally in the form of partial differential equations are transformed into a system of constant coefficient linear equations for solution; after transformation, the cross-section and the cross-section At time, the linear equations for the water level and the flow rate are given by: In the formula, , , , , , are the equation coefficients of the river reach at moment, and each coefficient is calculated through the following formulas respectively: In the formula, is the cross-section at the flow rate at the moment; is the water level of the cross-section at the moment; is the average river width of the water surface of the river reach at the moment; is the length of the river reach of the river reach ; is the weight coefficient; is the average flow rate of the river reach ; is the momentum correction coefficient; is the Chezy coefficient; The water level and flow rate values of each cross-section at the moment are known, so the coefficients of each equation at the moment can be obtained through formulas (3) to (8) , , , , , ; S33. Complete the coupling of the hydrological and hydrodynamic models, specifically: The water level and flow equation formulas for the plain river network at are as follows: The equation shown in formula (9) contains 12 unknowns, but only 10 equations, so this equation cannot be solved. After adding the following two equations, the equation set can meet the solution requirements: In the formula, represents the flow rate of cross-section 1 at time represents the water level of cross-section 6 at time; In order to be able to solve the equation set shown in formula (9), various working conditions also need to be considered; There are also several working conditions in the plain river network, including concentrated inflow, concentrated outflow, river channel connected to a reservoir, and sudden widening of the river channel. The calculation formulas for each working condition are as follows: Concentrated outflow: River channel connected to a reservoir: Flow through a weir gate: If the weir gate is closed, then: （14） If the weir gate is open, then: Wherein, is the gate opening height; is the net width of a single gate; is the number of gate openings; is the water head in front of the gate; is the vertical contraction coefficient; is the discharge coefficient for free outflow of the gate opening; is the submergence coefficient; Sudden widening of the river channel: Concentrated inflow: Adding formulas (12)-(17) to formula (9) gives the coupling model equation set of the hydrological model and the hydrodynamic model.

2. The water level and flow prediction method for plain river networks based on the hydrological-hydrodynamic coupling model according to claim 1, characterized in that: The step S1 includes the following steps: S11. Obtain the basin meteorological and hydrological data, including measured and forecast rainfall data, measured flow data at stations, and measured water level data at stations; S12. Obtain the basin characteristic data, including basin area, basin slope, sub-basin length, river length, and topographic index; S13. Obtain the hydrological model and hydrodynamic model parameter data, including physical parameters that can be directly measured and non-physical parameters that can only be obtained through hydrological model parameter calibration; S14. Obtain the basic data of the plain river network, including the river network geographic information layer, river network cross-section data, and elevation data of river network monitoring points; S15. Preprocess the data in S11 to S14 according to the input requirements of the hydrological model and the hydrodynamic model.

3. The method for predicting water level and flow rate of plain river network based on hydrological-hydrodynamic coupling model according to claim 1, characterized in that: The hydrological model parameters in the step S2 are determined by the calibration method. The hydrological model adopts a conceptual hydrological model, and the hydrological forecast results are a set of flow time series values.

4. The method for predicting water level and flow rate of plain river network based on hydrological-hydrodynamic coupling model according to claim 1, characterized in that: In the step S4, the hydro - hydrological dynamic coupling model is solved to predict the water level and flow in the plain river network. Specifically, through steps S1 to S3, the input preparation of the hydro - hydrological dynamic coupling model is completed, and the coupling of the hydrological model and the hydrodynamic model is also completed. By solving the coupled model equations of the hydrological model and the hydrodynamic model, the water level and flow processes of each cross - section in the plain river network can be obtained.

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