River flood flow monitoring method based on remote sensing image and hydrodynamic model fusion

Abstract

The invention relates to a river flood flow monitoring method based on remote sensing image and hydrodynamic model fusion, and belongs to the technical field of flood monitoring. The method comprises the following steps: dividing flood levels in a river drainage basin by combining historical rainfall and flood conditions, drawing flood hydrographs of different flood levels, determining 24-hour design rainstorm of each level of flood, establishing a river one-dimensional hydrodynamic model by utilizing section survey data, and constructing a water level-water surface width relationship of a section to be measured; solving the model to obtain a water level-flow relation curve of riverway water rising and water recession under each level of flood, determining the recurrence level of the flood, calculating the current water surface width of the to-be-measured riverway section, obtaining the corresponding water level, and calculating the water level of the to-be-measured riverway section. And selecting a corresponding water level-flow relation curve according to the flood level of the river channel and the stage of the flood flow process, and substituting into the curve to obtain the flood flow of the section to be measured in the current time period. According to the method, through water level inversion of different levels and different stages, the accuracy of inversion of the flood peak flow by the satellite remote sensing image is improved.

Description

Technical Field

[0001] The present invention relates to a method for monitoring river flood discharge based on the fusion of remote sensing images and hydrodynamic models, belonging to the technical field of flood monitoring. Background Art

[0002] Flood discharge monitoring is an important link in flood disaster forecasting. Quickly and accurately obtaining the flood peak during floods is the key to reducing flood disaster losses. The current monitoring of flood peak discharge depends on two methods: manual flow measurement and automated monitoring stations. The former requires wading operations using equipment such as current meters, which poses safety risks and low efficiency during flood periods. The latter, although equipped with advanced instruments such as ultrasonic flow meters, requires supporting power and communication facilities, which are difficult to implement in remote areas and face problems such as flood damage and high sensor maintenance costs. In addition, fixed monitoring stations need to regularly calibrate equipment and clean sediment, resulting in a heavy operation and maintenance burden.

[0003] For the monitoring blind areas of small and medium-sized rivers, satellite remote sensing technology can be used, combined with cross-section surveying data to construct a hydraulic model, and non-contact flow estimation can be achieved by inverting parameters such as water surface width and velocity distribution through remote sensing images. This space-air-ground collaborative monitoring mode has the advantages of rapid response and full-domain coverage.

[0004] Patent CN118794495A invented a calculation method for obtaining flood peak discharge by integrating hydrological calculations and remote sensing images. After obtaining the corresponding water level-discharge relationship mainly according to the Manning formula, the flood peak discharge is calculated by interpolating the obtained water level. However, since the Manning formula is an empirical formula under the condition of constant uniform flow, this method is only applicable to artificial channels with constant width and cross-section shape along the way, and is not applicable to most natural rivers with irregular and changing cross-section shapes along the way. Summary of the Invention

[0005] The purpose of the present invention is to overcome the above deficiencies and provide a method for monitoring river flood discharge based on the fusion of remote sensing images and hydrodynamic models, which improves the accuracy of inverting flood peak discharge from satellite remote sensing images through water level inversion at different levels and stages.

[0006] The technical solution adopted by the present invention is as follows: A method for monitoring river flood discharge based on the fusion of remote sensing images and hydrodynamic models, including the following steps: S1. Divide the flood levels within the river basin according to historical rainfall and flood conditions, draw the flood hydrographs of different flood levels of the cross-section of the river to be measured based on historical data as the typical flood discharge processes of each flood level; then determine the 24-hour design rainstorm for each flood level within the river basin according to the local hydrological manual, and use the comparison between the maximum 24-hour rainfall before the formation of this flood within the basin and the 24-hour design rainstorm to determine the recurrence period level of this flood; S2. Establish a one-dimensional hydrodynamic model of the river channel based on the Saint-Venant equations, construct the water level-water surface width relationship according to the river channel topographic survey data, calculate the parameters required for the hydrodynamic model calculation, namely hydraulic radius, cross-sectional area, and Chezy coefficient, based on the actual river channel topography and ground cover data, and calculate the water level-discharge relationship of the most downstream river channel according to the Chezy formula. Discretize the continuity equation and momentum equation in the Saint-Venant equations by the finite difference method, discretize the river channel into water level points and discharge points at appropriate time and space steps, and use the chasing method to solve the equation. Finally, obtain the water levels and discharges at various times and positions of the river channel during a flood process; S3. Extract the water levels and discharges at various times before the peak discharge of the cross-section to be measured, obtain the water level-discharge relationship during the rising stage of the river channel, and then extract the water levels and discharges at various times from the moment when the peak discharge is reached until the flood completely subsides for the cross-section to be measured, obtain the water level-discharge curve during the falling stage, so as to obtain the water level-discharge relationship curves of the rising and falling stages of the river channel under floods of various magnitudes; S4. Determine the recurrence level of this flood by comparing the maximum 24-hour rainfall before the formation of this flood with historical data, calculate the current water surface width of the cross-section of the river channel to be measured through satellite remote sensing image data, and then obtain the corresponding water level according to the relationship between the water level and water surface width of the river channel cross-section; S5. Select the corresponding water level-discharge relationship curve according to the determined flood level of the river channel and the stage of the flood discharge process, substitute the corresponding water level for linear interpolation, and calculate the flood discharge of the cross-section to be measured at the current time period.

[0007] In the above method, in step S1, the flood is divided into 5-year recurrence interval, 20-year recurrence interval, 50-year recurrence interval, 100-year recurrence interval according to the rainfall within 24 hours before the flood. Rainfall less than 5-year recurrence interval is of small flood magnitude, medium flood when it is 5 - 20-year recurrence interval, large flood when it is 20 - 50-year recurrence interval, and extremely large flood when it is over 50 years.

[0008] The one-dimensional Saint-Venant equation described in step S2 is as follows: , , where: Q is the discharge, m 3 / s; q is the lateral inflow, m 3 / s; A is the cross-sectional area, m 3 / s; h is the water level, m; R is the hydraulic radius, m; C is the Chezy coefficient; α is the momentum correction coefficient; g represents the acceleration due to gravity; t is time; x is the coordinate along the river channel, with the direction towards the water flow being positive; First, based on the actual terrain and surface cover data of the river channel, representative cross-sections are selected at intervals of 100 - 200 m along the river channel, and the hydraulic radius, wetted perimeter, cross-sectional area of flow, and Chezy coefficient at each water level of each cross-section are calculated to determine the input parameters required for model calculation. Subsequently, the Saint-Venant continuity equation and momentum equation are discretized using the four-point implicit equal-difference format, the river channel cross-section points are set as water level variable points, and flow variable points are set between adjacent water level points. For the uppermost calculation point, the flood hydrograph is introduced as the input boundary condition. For the lowermost boundary, the water level-discharge relationship curve of this cross-section is calculated using the Chezy formula, and the water level-discharge relationship is transformed into a linear constraint equation and embedded in the system as the downstream boundary condition. Finally, the equations of all water level points and flow points are integrated to construct a linear equation system, and the chase method is used for solution to directly obtain the water level-discharge relationship curves at each cross-section of the entire river channel under various working conditions.

[0009] The beneficial effects of the present invention are: (1) By combining remote sensing image inversion of water surface width and measured cross-section terrain data, it is not necessary to wade manually or rely on fixed monitoring stations, solving the problems of few monitoring stations and narrow coverage range of traditional hydrological stations; (2) Different water level inversion formulas for floods of different magnitudes and stages are adopted, avoiding the lag of traditional single-curve interpolation in the dynamic process of floods and improving the accuracy of satellite remote sensing image inversion of flood peak flow. Description of the Drawings

[0010] Figure 1 is the method flow chart of the present invention; Figure 2 is the typical flood flow process diagram of floods at all levels in the embodiment of the present invention; Figure 3 is the water level-discharge relationship diagram of the lowermost cross-section of the river channel calculated according to the Chezy formula in the embodiment of the present invention; Figure 4 is the water level-discharge relationship diagram during the rising and falling processes of floods at all levels in the embodiment of the present invention; (a) is a catastrophic flood, (b) is a major flood, (c) is a medium flood, and (d) is a minor flood; Figure 5 is the water level-water surface width relationship curve diagram of the cross-section to be measured in the embodiment of the present invention. Detailed Embodiments

[0011] The present invention will be further described below in conjunction with specific embodiments.

[0012] Embodiment 1 A method for monitoring river flood flow based on the fusion of remote sensing images and hydrodynamic models, including the steps (asFigure 1 ) as follows: S1. Divide the flood levels within the river basin according to historical rainfall and flood conditions. Calculate the flow processes of typical floods at all levels using the rainfall-runoff correlation diagram and instantaneous unit hydrograph method in the local hydrological manual. The 5-, 20-, 50-, and 100-year return period design flood process lines at the cross-section to be measured are used as the typical flood flow processes for small floods, medium floods, large floods, and extremely large floods respectively. The results are as Figure 2 .

[0013] Then, determine the 5-year, 20-year, 50-year, and 100-year return period 24-hour design rainfalls within the river basin according to the local hydrological manual, and use the maximum 24-hour rainfall before the formation of this flood within the basin and the design rainfall to determine the return period level of this flood. When the rainfall of this time is less than the 5-year return period design rainfall, this flood is at the small flood level; when it is between 5 and 20 years return period, it is a medium flood; when it is between 20 and 50 years return period, it is a large flood; and when it is over 50 years return period, it is an extremely large flood. For example, the 24-hour design rainfall for a 5-year return period flood in a certain river is 134.3 mm, 191.9 mm for a 20-year return period, 228.3 mm for a 50-year return period, and 255.5 mm for a 100-year return period.

[0014] S2. Establish a one-dimensional hydrodynamic model of the river according to the one-dimensional Saint-Venant equations , , In the formula: Q is the flow rate, m 3 / s; q is the lateral inflow, m 3 / s. In this method, lateral inflow is not considered, q = 0; A is the cross-sectional area, m 3 / s; h is the water level, m; R is the hydraulic radius, m; C is the Chezy coefficient; α is the momentum correction coefficient; g represents the acceleration due to gravity; t is the time; x is the coordinate along the river, with the direction of the water flow as positive; The purpose of establishing this model is to obtain the accurate water level - discharge relationship curve of the river section to be measured under various working conditions, providing a basis for subsequent flow inversion. The implementation method is as follows: First, based on the actual terrain and surface cover data of the river, representative sections are selected along the river at intervals of 100 - 200 m, and the hydraulic radius, wetted perimeter, cross - sectional area, and Chezy coefficient at each water level of each section are calculated to determine the input parameters required for model calculation; Subsequently, the Saint - Venant continuity equation and momentum equation are discretized using the four - point implicit equal - difference format. The river section points are set as water level variable points (Z), and flow variable points (Q) are set between adjacent water level points; For the most upstream calculation point, the flood hydrograph is introduced as the input boundary condition; For the most downstream boundary, the water level - discharge relationship curve of this section is calculated using the Chezy formula (such as Figure 3 ), and the water level - discharge relationship is transformed into a linear constraint equation and embedded into the system as the downstream boundary condition. Finally, the equations of all water level points (Z) and flow points (Q) are integrated to construct a linear equation system, and the chasing method is used for solution, so as to directly obtain the water level - discharge relationship curves of each section of the entire river under various working conditions. (Reference: [1] Wang Deyuan. Computational Hydraulics Theory and Applications [M]. Science Press, 2011.). According to the river terrain survey data, the water level - water surface width relationship is constructed (such as Figure 5 ).

[0015] S3. Extract the water levels and discharges at each time before the flood peak flow of the section to be measured, and obtain the water level - discharge relationship during the rising stage of the river. Then extract the water levels and discharges at each time from the moment when the flood peak flow is reached until the flood completely subsides to obtain the water level - discharge curve during the falling stage. Repeat this process for floods of each recurrence period to obtain the water level - discharge curves during the rising and falling stages of floods of each magnitude (such as Figure 4 ).

[0016] S4. Determine the recurrence level of this flood by comparing the maximum 24 - hour rainfall before the formation of this flood with historical data. Calculate the current water surface width of the river section to be measured through satellite remote sensing image data, and then obtain the corresponding water level according to the relationship between the river section water level and the water surface width. The rainfall data for 24 hours before the flood is collected as 171 mm, so this flood belongs to a medium - sized flood. Subsequently, through remote sensing image interpretation, it is obtained that the river width during the rising stage of a certain flood at this section is 80 m, and by querying the corresponding section water level - water surface width curve, the water level at this time is 199.95 m.

[0017] S5. Select the corresponding water level - discharge relationship curve according to the determined flood level of the river and the stage of the flood flow process, substitute the corresponding water level for linear interpolation, and calculate the flood discharge of the section to be measured in the current period: Select the water level-discharge relationship curve during the medium flood rising process, and obtain the flood discharge at this location as 203 m³ / s based on the water level.

[0018] The above is a detailed description of the present invention in combination with specific embodiments, and the protection scope of the present invention is not limited thereto.

Claims

1. A method for monitoring river flood flow based on the fusion of remote sensing images and hydrodynamic models, characterized in that, The steps are as follows: S1. Divide the flood levels within the river channel basin in combination with historical rainfall and flood conditions. Based on historical data, draw the flood hydrographs at different flood levels for the cross-section of the river channel to be measured, serving as the typical flood flow processes for each flood level. Then, determine the 24-hour design rainfall for each flood level within the river channel basin according to the local hydrological manual, and use it to determine the recurrence period level of the current flood by comparing the maximum 24-hour rainfall before the formation of the current flood within the basin with the 24-hour design rainfall. S2. Establish a one-dimensional hydrodynamic model for the river channel based on the Saint-Venant equations. Construct the relationship between water level and water surface width for the river channel cross-section according to the river channel topographic survey data. Calculate the parameters required for the hydrodynamic model calculation, namely hydraulic radius, cross-sectional area, and Chezy coefficient, based on the actual river channel topography and ground cover data. And calculate the water level-discharge relationship for the most downstream river channel according to the Chezy formula. Discretize the continuity equation and momentum equation in the Saint-Venant equations by the finite difference method, discretize the river channel into water level points and discharge points at appropriate time and space steps, and use the chasing method to solve the equation. Finally, obtain the water levels and discharges at each time and each location during a flood process for the river channel. S3. Extract the water levels and discharges at each time before the peak discharge is reached at the cross-section to be measured to obtain the water level-discharge relationship during the rising stage of the river channel. Then, extract the water levels and discharges at each time from when the peak discharge is reached until the flood completely subsides at the cross-section to be measured to obtain the water level-discharge curve during the falling stage, thereby obtaining the water level-discharge relationship curves for the rising and falling stages of the river channel under floods of various magnitudes. S4. Determine the recurrence level of the current flood by comparing the maximum 24-hour rainfall before the formation of the current flood with historical data. Calculate the current water surface width of the cross-section of the river channel to be measured through satellite remote sensing image data, and then obtain the corresponding water level according to the relationship between the water level and water surface width of the river channel cross-section. S5. Select the corresponding water level-discharge relationship curve based on the determined flood level of the river channel and the stage of the flood flow process, substitute the corresponding water level for linear interpolation, and calculate the flood discharge for the current period at the cross-section to be measured.

2. The method for monitoring river flood flow based on the fusion of remote sensing images and hydrodynamic models according to claim 1, characterized in that, In step S1, the floods are divided into once-in-5-year, once-in-20-year, once-in-50-year, once-in-100-year floods according to the rainfall within 24 hours before the flood. Rainfall less than once-in-5-year is of small flood magnitude, medium flood when it is once-in-5-year to once-in-20-year, large flood when it is once-in-20-year to once-in-50-year, and extremely large flood when it is more than once-in-50-year.

3. The method for monitoring river flood flow based on the fusion of remote sensing images and hydrodynamic models according to claim 1, characterized in that, The one-dimensional Saint-Venant equations described in step S2 are as follows: ， ， In the formula: Q is the flow rate, m 3 / s; q is the lateral inflow, m 3 / s; A is the cross-sectional area of flow, m 3 / s; h is the water level, m; R is the hydraulic radius, m; C is the Chezy coefficient; α is the momentum correction coefficient; g represents the acceleration due to gravity; t is the time; x is the coordinate along the river channel, with the direction towards the water flow being positive.

4. The method for monitoring river flood flow based on the fusion of remote sensing images and hydrodynamic models according to claim 1, characterized in that, In step S2, first, based on the actual terrain and surface cover data of the river channel, representative cross-sections are selected along the river channel at intervals of 100 - 200 m, and the hydraulic radius, wetted perimeter, cross-sectional area of flow, and Chezy coefficient under each water level of each cross-section are calculated to determine the input parameters required for model calculation. Subsequently, the Saint-Venant continuity equation and momentum equation are discretized using the four-point implicit equal-difference format, the river channel cross-section points are set as water level variable points, and flow variable points are set between adjacent water level points. For the uppermost calculation point, the flood hydrograph is introduced as the input boundary condition. For the lowermost boundary, the water level-discharge relationship curve of this cross-section is calculated using the Chezy formula, and the water level-discharge relationship is transformed into a linear constraint equation and embedded in the system as the downstream boundary condition. Finally, the equations of all water level points and flow points are integrated to construct a linear equation system, and the chasing method is used for solution to directly obtain the water level-discharge relationship curves of each cross-section of the entire river channel under various working conditions.

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