Method for dynamic monitoring and flood prevention early warning of silt dam based on remote sensing image

Abstract

The invention provides a dynamic monitoring and flood prevention early warning method for a silt dam based on remote sensing images, and belongs to the technical field of hydraulic engineering safety monitoring. The method comprises the following steps: acquiring a satellite remote sensing image of which the resolution is less than 3m, preprocessing by ENVI software and marking a boundary; measuring the azimuth angle of the dam axis, and calculating the size of the dam body through pixels and a trigonometric function; the water depth is calculated by combining dam body parameters and pixel spacing, and the water area is calculated by using an NDWI index; then calculating the water storage capacity by using an integral method, and fitting to generate a storage capacity-water level curve; and finally, according to the reservoir capacity-water level dynamic curve, determining residual reservoir capacity and dividing risk levels, and setting a flood detention safety water depth line to implement flood prevention early warning. The advantages of large range and high timeliness of remote sensing images are utilized, dynamic monitoring of the water level and the water storage capacity of the silt dam is achieved, the reservoir capacity-water level curve is constructed, data support and decision basis are provided for flood control safety, the remaining reservoir capacity can be evaluated in real time, the flood control key time period can be determined, and operation management of the silt dam is facilitated.

Description

Technical Field

[0001] This invention relates to the field of water conservancy project safety monitoring technology, and in particular to a method for dynamic monitoring and flood early warning of silt-retaining dams based on remote sensing images. Background Technology

[0002] Silt-retention dams are core projects for soil and water conservation and ecological environment construction on the Loess Plateau, playing a vital role in sediment reduction, siltation, and flood control. However, water level monitoring of small and medium-sized silt-retention dams has long relied on manual inspections or simple instrument measurements, leading to problems such as large subjective errors, difficult equipment maintenance, and lack of monitoring in remote areas, resulting in insufficient prediction of flood retention capacity. Traditional reservoir capacity calculation methods, such as topographic contour lines and cross-section methods, all rely on on-site surveys, which are time-consuming, labor-intensive, and have low accuracy. While emerging technologies such as drones, GIS, and sonar have promoted research progress, their widespread application is limited by meteorological conditions and terrain. For example, drones have poor flight stability in high winds, unmanned vessels cannot obtain complete shorelines, and data acquisition is difficult.

[0003] Satellite remote sensing technology, with its advantages of wide coverage, high timeliness, and sub-meter resolution, provides a new approach for monitoring silt-retention dams. However, as planar data, remote sensing imagery cannot be directly used for reservoir capacity calculation. Existing technologies, such as combining GPS with echo sounders and TIN model fitting, have improved calculation accuracy, but still suffer from operational complexity or data dependency issues.

[0004] Therefore, there is an urgent need for a non-contact, high-precision flood control safety analysis method for silt-retaining dams based on remote sensing images, in order to break through the bottlenecks of traditional technologies and achieve dynamic monitoring and risk early warning. Summary of the Invention

[0005] To overcome the shortcomings of existing technologies, the purpose of this invention is to provide a method for dynamic monitoring and flood early warning of silt-retaining dams based on remote sensing images. By utilizing the advantages of remote sensing images, such as their wide coverage and high timeliness, the method enables dynamic monitoring of water levels and storage capacity of silt-retaining dams, constructs reservoir capacity-water level curves, provides data support and decision-making basis for flood control safety, and can assess the remaining reservoir capacity in real time, determine key flood control periods, and contribute to the operation and management of silt-retaining dams.

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

[0007] A method for dynamic monitoring and flood early warning of silt-retaining dams based on remote sensing imagery includes the following steps:

[0008] S1. Acquire remote sensing image data of silt-retention dams, select satellite data with a resolution of less than 3 meters, and preprocess the data using ENVI software to crop the study area and mark its boundary features.

[0009] S2. Based on the labeled research area, measure the azimuth angle between the dam axis and the due north direction, and convert the pixel coordinates of the dam crest and dam slope boundary into actual physical dimensions by using the number of pixels and trigonometric functions, and calculate the dam crest length, width and dam height;

[0010] S3. Based on the obtained dam height and upstream-downstream slope ratio parameters, combined with the pixel spacing between the dam crest and the water level line, calculate the water depth in front of the dam, extract the water area using the NDWI index, count the number of pixels, and calculate the water area.

[0011] S4. Combine the obtained water area data with the water depth of multiple periods, use the integral method to calculate the water storage capacity, and fit to generate a dynamic curve of reservoir capacity-water level.

[0012] S5. Based on the reservoir capacity-water level dynamic curve and the theoretical reservoir capacity, combined with the silt retention capacity and flood detention capacity, calculate the remaining reservoir capacity and classify the risk levels. Based on the reservoir capacity-water level dynamic curve, set the flood detention safety water depth line and implement flood prevention early warning.

[0013] Preferably, in S1, the satellite data includes GF-2 and WorldView-3, and during preprocessing, the radiometric calibration, atmospheric correction, orthorectification of the multispectral data, as well as the fusion of panchromatic data and multispectral data, are completed using ENVI5.6 software.

[0014] Preferably, in S1, the marked boundary features include manually visually interpreting and marking the dam crest, dam slope, water level line, dam body boundary, and water area boundary, and using the pixel statistics function of auxiliary software for identification; the auxiliary software is one of Photoshop, Arcmap, and ENVI.

[0015] Preferably, in S2, the azimuth angle between the dam axis and true north is measured, and the pixel coordinates of the dam crest and dam slope boundaries are converted into actual physical dimensions using the number of pixels and trigonometric functions. Specifically:

[0016] When the azimuth angle between the dam axis and due north is θ n When the dam crest length is reached, the formula for calculating it is:

[0017] L = n a ×R×cscθ n ;

[0018] The formula for calculating the width of the dam crest is:

[0019] B = n b ×R×cosθ n ;

[0020] In the formula, L is the length of the silt-retention dam crest, in meters; B is the width of the silt-retention dam crest, in meters; n a n represents the number of pixels between the dam axes;b θ represents the number of pixels between the widths of the dam crest; n R represents the azimuth angle of the silt-retaining dam; R is the side length of the pixel, in meters.

[0021] Preferably, in S2, the steps for calculating the dam height are as follows:

[0022] The formula for calculating the horizontal projection length of the downstream dam slope is:

[0023] L d =n s ×R×sinθ n ;

[0024] The dam height was then derived using the following formula:

[0025] H = L d ×tanθ d ;

[0026] In the formula, H represents the height of the silt-retaining dam, in meters; n S L represents the number of pixels between the top of the dam and the bottom of the dam downstream, pointing due north; d θ represents the horizontal projection length of the downstream dam slope, in meters. d The slope angle downstream of the silt-retaining dam.

[0027] Preferably, in S3, the process of calculating the water depth in front of the dam is as follows:

[0028] The formula for calculating the horizontal projected distance between the dam crest and the water level is:

[0029] L u =R×n u ×sinθ n ;

[0030] Then calculate the water depth using the formula:

[0031] H w =HL u ×sinθ u ;

[0032] In the formula, L u H is the straight-line distance between the dam crest and the water level line, in meters. w The depth of the silt-retaining dam is expressed in meters; n u θ represents the number of pixels between the dam crest and the water level line in the due north direction; u The slope angle upstream of the silt-retaining dam;

[0033] The formula for extracting the water area using the NDWI index is:

[0034]

[0035] In the formula, Green and NIR are the brightness values ​​of the green band and near-infrared band, respectively.

[0036] Preferably, in S3, the process of calculating the water area is as follows: the water area of ​​the silt-retaining dam is extracted using software, the number of pixels covered by the water area is counted, and the water area is calculated based on the image spatial resolution parameters, using the following formula:

[0037] S = n w ×R 2 ;

[0038] In the formula, S represents the water area of ​​the silt-retaining dam, in square meters; n w The number of pixels covered by the water area of ​​the silt-retaining dam.

[0039] Preferably, in S4, the process of calculating the water storage capacity using the integral method and fitting the dynamic curve of reservoir capacity-water level is as follows:

[0040] The water storage capacity is calculated using the following formula, which relates the water depth to the corresponding water area for multiple periods:

[0041]

[0042] In the formula, V w S represents water storage capacity, measured in cubic meters. i For water depth h i The corresponding water area, in square meters; h i Water depth, measured in meters;

[0043] When the actual water depth h i When the dam height is approximately equal to the design dam height, V w The theoretical reservoir capacity of the silt-retention dam was determined, and then the reservoir capacity value for periods without remote sensing imagery was extrapolated using function fitting. This was done when the measured water depth h... i When the designed dam height is not reached, the water storage capacity at the corresponding water level is estimated based on the curve, and a dynamic curve of reservoir capacity-water level is generated.

[0044] Preferably, in S5, the silt-retaining dam capacity V includes the sediment-trapping capacity Vs. L and flood detention capacity V z Two parts, combined with the silt retention capacity V L and flood detention capacity V Z By calculating the remaining storage capacity V rem With flood retention capacity V Z The risk level is classified according to the proportional relationship, and the safe water depth for flood detention is determined based on the reservoir capacity-water level dynamic curve, so as to realize the quantitative early warning of flood control safety of silt-retention dams. The specific standards are as follows:

[0045] Remaining storage capacity V rem =Theoretical reservoir capacity - Actual measured water storage;

[0046] When V rem ≥1.5V Z When it is low risk; when it is 1.3V Z ≤V rem <1.5V Z The risk level is medium; when V rem <1.3V Z It is a high-risk situation.

[0047] Preferably, the formula for calculating the flood detention safety water depth line is:

[0048] Flood retention safety depth line = H L +H Z +ΔH;

[0049] In the formula, H L For mud dam height; H Z The height of the flood detention dam is ΔH; ΔH is the safety freeboard ΔH, both in meters.

[0050] According to specific embodiments provided by the present invention, the present invention discloses the following technical effects:

[0051] This invention leverages the advantages of remote sensing imagery—wide coverage, high timeliness, and dynamic monitoring—to effectively solve the problems of low accuracy, difficult maintenance, and inability to provide long-term stable monitoring in silt-retention dam water level monitoring using traditional manual inspections and instrument measurements. Simultaneously, by interpreting the actual dimensions corresponding to pixels in remote sensing images, the water level and reservoir capacity in front of the dam are calculated, and a dynamic characteristic curve of reservoir capacity-water level is constructed. This allows for accurate acquisition of the water storage capacity and remaining reservoir capacity of the silt-retention dam, enabling a quantitative assessment of the flood control safety of the silt-retention dam. Furthermore, the method provided by this invention eliminates the need for on-site surveys, reducing manpower and material resources. It can quickly and reliably determine the dynamic changes in water level and storage capacity, providing data support and decision-making basis for the operation and management of silt-retention dams. It can also identify key flood control periods by analyzing historical data, serving as an effective means of emergency assessment of the safety status of silt-retention dams in flood control management. Attached Figure Description

[0052] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0053] Figure 1 This is a flowchart of a method for dynamic monitoring and flood early warning of silt-retaining dams based on remote sensing images according to the present invention;

[0054] Figure 2 This is a simplified schematic diagram of a silt-retaining dam provided by the present invention;

[0055] Figure 3 A schematic diagram of the calculation formula for silt-retaining dams provided by this invention;

[0056] Figure 4 The longitudinal section of the silt-retaining dam channel provided for this invention;

[0057] Figure 5 Cross-sectional view of the silt-retaining dam channel provided by the present invention;

[0058] Figure 6 This is a boundary segmentation diagram of a reservoir silt-retention dam provided in Embodiment 1 of the present invention;

[0059] Figure 7 This is a schematic diagram of the interpreted shape of a reservoir silt-retaining dam provided in Embodiment 1 of the present invention;

[0060] Figure 8 This is a reservoir capacity curve diagram of a silt-retaining dam provided in Embodiment 1 of the present invention;

[0061] Figure 9 This is a statistical chart of the water storage capacity of a reservoir silt-retaining dam from 2015 to 2023, provided in Embodiment 1 of the present invention.

[0062] Figure 10 This is a statistical chart of water level at a reservoir silt-retaining dam from 2015 to 2023, provided in Embodiment 1 of the present invention.

[0063] Figure 11 The remaining reservoir capacity of a silt-retention dam in a reservoir from 2015 to 2023 is provided in Embodiment 1 of the present invention. Detailed Implementation

[0064] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0065] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0066] like Figure 1 As shown, this invention provides a method for dynamic monitoring and flood early warning of silt-retaining dams based on remote sensing imagery, comprising the following steps:

[0067] S1. Acquire remote sensing image data of silt-retention dams, select satellite data with a resolution of less than 3 meters, and preprocess the data using ENVI software to crop the study area and mark its boundary features.

[0068] S2. Based on the labeled research area, measure the azimuth angle between the dam axis and the due north direction, and convert the pixel coordinates of the dam crest and dam slope boundary into actual physical dimensions by using the number of pixels and trigonometric functions, and calculate the dam crest length, width and dam height;

[0069] S3. Based on the obtained dam height and upstream-downstream slope ratio parameters, combined with the pixel spacing between the dam crest and the water level line, calculate the water depth in front of the dam, extract the water area using the NDWI index, count the number of pixels, and calculate the water area.

[0070] S4. Combine the obtained water area data with the water depth of multiple periods, use the integral method to calculate the water storage capacity, and fit to generate a dynamic curve of reservoir capacity-water level.

[0071] S5. Based on the reservoir capacity-water level dynamic curve and the theoretical reservoir capacity, combined with the silt retention capacity and flood detention capacity, calculate the remaining reservoir capacity and classify the risk levels. Based on the reservoir capacity-water level dynamic curve, set the flood detention safety water depth line and implement flood prevention early warning.

[0072] In S1, the satellite data includes GF-2 and WorldView-3. During preprocessing, the radiometric calibration, atmospheric correction, orthorectification of the multispectral data are completed using ENVI5.6 software, as well as the fusion of panchromatic and multispectral data. Generally, the dam outline can be identified and the dam can be distinguished from the surrounding terrain when the resolution of the remote sensing image data is less than 3 meters.

[0073] The method involves manually visually interpreting and marking the dam crest, slope, water level, dam body boundary, and water area boundary, followed by pixel statistics using auxiliary software. The auxiliary software is one of Photoshop, Arcmap, or ENVI, enabling accurate identification of the dam crest boundary and water level. Furthermore, this method relies on the interpreter's professional knowledge of silt-retaining dams to minimize the identification bias of automated algorithms under complex boundary conditions, thus laying a reliable data foundation for subsequent reservoir capacity calculations and flood control analysis.

[0074] Reference Figure 2 This invention generalizes the design of silt-retaining dams into a quadrangular truncated pyramid, which facilitates the analysis of the dam's shape. Its characteristic parameters include the dam height H, dam crest length L, dam crest width B, upstream dam slope ratio m1, and downstream dam slope ratio m2.

[0075] Furthermore, this invention measures the azimuth angle between the dam's main axis and the north baseline based on remote sensing image data. Then, it identifies the boundary morphology of the silt-retaining dam and extracts positional information such as the dam crest, water level, and downstream dam base. After extracting the positional information, the measurement phase begins. When the angle between the dam axis and the north direction is close to 90°, i.e., when the dam boundary is approximately perpendicular to the pixel row and column direction of the remote sensing image, feature points are randomly selected on the dam axis, and the number of pixels between these points along the north direction and the downstream dam base is counted using software. The length and width of the pixels represent the actual dimensions. For the geometric features of the dam crest, the number of pixels between the dam axis in the west direction and the number of pixels between the dam crest width in the north direction are counted. Based on the number and size of the pixels, the basic geometric parameters of the dam crest are calculated, and the results are as follows. Figure 3 As shown.

[0076] When the angle between the dam's main axis and due north deviates by 90°, points are randomly selected along the dam axis, and the number of pixels between these points and the downstream dam base in the due west direction is counted. Similarly, for the dam crest geometry, points are randomly selected along the dam axis and crest width, and the number of pixels between the dam axis and the dam crest width in the due west direction is counted. After measurement, the obtained pixel counts are converted into actual physical distances based on the spatial resolution of the remote sensing image data. Key parameters such as the dam crest width, dam crest length, and the horizontal projection length of the downstream dam slope are derived using trigonometric relationships.

[0077] Specifically, in S2, the azimuth angle between the dam axis and true north is measured. The pixel coordinates of the dam crest and slope boundaries are then converted into actual physical dimensions using pixel count and trigonometric functions. Specifically:

[0078] When the azimuth angle between the dam axis and due north is θ n When the dam crest length is reached, the formula for calculating it is:

[0079] L = n a ×R×cscθ n ;

[0080] The formula for calculating the width of the dam crest is:

[0081] B = n b ×R×cosθ n ;

[0082] In the formula, L is the length of the silt-retention dam crest, in meters; B is the width of the silt-retention dam crest, in meters; n a n represents the number of pixels between the dam axes; b θ represents the number of pixels between the widths of the dam crest; n R represents the azimuth angle of the silt-retaining dam; R is the side length of the pixel, in meters.

[0083] The steps for calculating the dam height are as follows:

[0084] The formula for calculating the horizontal projection length of the downstream dam slope is:

[0085] L d =n s ×R×sinθ n ;

[0086] The dam height was then derived using the following formula:

[0087] H = L d ×tanθ d ;

[0088] In the formula, H represents the height of the silt-retaining dam, in meters; n S L represents the number of pixels between the top of the dam and the bottom of the dam downstream, pointing due north; d θ represents the horizontal projection length of the downstream dam slope, in meters. d The slope angle downstream of the silt-retaining dam.

[0089] In S3, the process of calculating the water depth in front of the dam is as follows:

[0090] The formula for calculating the horizontal projected distance between the dam crest and the water level is:

[0091] L u =R×n u ×sinθ n ;

[0092] Then calculate the water depth using the formula:

[0093] H w =HL u ×sinθ u ;

[0094] In the formula, L u H is the straight-line distance between the dam crest and the water level line, in meters. w The depth of the silt-retaining dam is expressed in meters; n u θ represents the number of pixels between the dam crest and the water level line in the due north direction; u The slope angle upstream of the silt-retaining dam;

[0095] The formula for extracting the water area using the NDWI index is:

[0096]

[0097] In the formula, Green and NIR are the brightness values ​​of the green band and near-infrared band, respectively.

[0098] In S3, based on the geometric correction of remote sensing images, the water depth and area of ​​the silt-retaining dam are calculated. First, the spatial relationship between the dam crest and the water level is identified. When the angle between the dam's main axis and due north is close to 90°, feature points are randomly selected along the long side of the dam crest, and the pixel distance from this point to the water level is calculated vertically. If the angle between the dam's main axis and due north deviates from 90°, the measurement direction is adjusted, and feature points are reselected along the dam axis, calculating the pixel distance from this point to the water level (or its extension) horizontally. Based on the downstream dam slope parameters, the horizontal projection length is converted to the actual vertical height of the dam using trigonometric functions. Finally, the difference between this vertical height and the measured dam height is calculated to obtain the water depth of the silt-retaining dam. The water area of ​​the silt-retaining dam is extracted using software. The number of pixels covered by the water area is counted. The water area of ​​the silt-retaining dam is obtained based on the image spatial resolution parameters. Therefore, the process of calculating the water area is as follows: the water area of ​​the silt-retaining dam is extracted using software, the number of pixels covered by the water area is counted, and the water area is calculated based on the image spatial resolution parameters using the following formula:

[0099] S = n w ×R 2 ;

[0100] In the formula, S represents the water area of ​​the silt-retaining dam, in square meters; n w The number of pixels covered by the water area of ​​the silt-retaining dam.

[0101] This invention utilizes high-resolution remote sensing imagery data of silt-retention dams acquired via satellite, capturing data from low to high water levels. The remote sensing imagery data is analyzed and calculated according to the steps outlined above to obtain the water level and water area. An integral calculation method is used to determine the dam's storage capacity at high water levels. The maximum storage capacity corresponding to the measured water depth approaching the designed dam height is the theoretical reservoir capacity of the silt-retention dam. The bottom area of ​​the silt-retention dam is equivalently represented as the water area at the known lowest water level. In calculating the reservoir capacity of silt-retention dams, this invention equates the bottom area of ​​silt-retention dams under complex terrain conditions to the water area at the known lowest water level, facilitating reservoir capacity calculation.

[0102] Specifically, in S4, the process of calculating water storage using the integral method and fitting the dynamic curve of reservoir capacity-water level is as follows:

[0103] The water storage capacity is calculated using the following formula, which relates the water depth to the corresponding water area for multiple periods:

[0104]

[0105] In the formula, V w S represents water storage capacity, measured in cubic meters. i For water depth h i The corresponding water area, in square meters; h i Water depth, measured in meters;

[0106] When the actual water depth h i When the dam height is approximately equal to the design dam height, V w The theoretical reservoir capacity of the silt-retention dam was determined, and then the reservoir capacity value for periods without remote sensing imagery was extrapolated using function fitting. This was done when the measured water depth h... i When the designed dam height is not reached, the water storage capacity at the corresponding water level is estimated based on the curve, and a dynamic curve of reservoir capacity-water level is generated.

[0107] Reference Figure 4 and Figure 5 The silt-retaining dam capacity V includes the sediment retention capacity V. L and flood detention capacity V Z Two parts. The silt-trapping capacity V can be obtained by consulting the construction data of a certain silt-retaining dam. L Or, according to the silt retention capacity V in the "Technical Specification for Silt-Retaining Dams" (SL / T 804-2020) L The calculation formula is used to determine the height H of the silt-retaining dam. L Flood detention dam height H Z The silt-trapping dam consists of three parts: height H, safety height ΔH, and other components. L Flood detention dam height H Z The corresponding reservoir capacity is determined by referring to the water level-capacity curve according to regulations. The safe freeboard ΔH is obtained from the table in the "Technical Specification for Silt-Resisting Dams" (SL / T 804-2020). The remaining reservoir capacity V is calculated. rem With flood retention capacity V Z The risk level is classified according to the proportional relationship, and the safe water depth for flood detention is determined based on the reservoir capacity-water level dynamic curve, so as to realize the quantitative early warning of flood control safety of silt-retention dams. The specific standards are as follows:

[0108] Remaining storage capacity V rem =Theoretical reservoir capacity - Actual measured water storage;

[0109] When V rem ≥1.5V Z When it is low risk; when it is 1.3V Z ≤V rem <1.5V Z The risk level is medium; when V rem <1.3V Z It is a high-risk situation.

[0110] The formula for calculating the safe water depth line for flood detention is:

[0111] Flood retention safety depth line = H L +H Z +ΔH;

[0112] In the formula, H L For mud dam height; H Z The height of the flood detention dam is ΔH; ΔH is the safety freeboard ΔH, both in meters.

[0113] This invention analyzes flood control safety by measuring the remaining reservoir capacity ratio. After measuring water storage using remote sensing image data, when the remaining reservoir capacity is greater than 1.5 times the flood detention capacity, it indicates that siltation in the reservoir area has not yet reached the design siltation elevation, the flood detention capacity is still intact, and the dam's flood detention function meets design standards. When the remaining reservoir capacity is less than 1.5 times the flood detention capacity but greater than 1.3 times the remaining reservoir capacity, it indicates that the actual water level has entered the flood detention regulation zone, requiring water storage restrictions. When the remaining reservoir capacity is less than 1.3 times the flood detention capacity but greater than 1.1 times the remaining reservoir capacity, the flood detention capacity is insufficient. Different countermeasures can be taken based on the size of the remaining flood detention capacity to effectively avoid the risk of dam failure caused by insufficient capacity. This method enables a quantitative assessment of flood detention safety status, providing data support for the operation and management of silt-retention dams.

[0114] The invention will be further illustrated below using a silt-retention dam in a reservoir as a specific implementation method.

[0115] The dam of a certain reservoir is oriented roughly northwest to southeast, with an angle of 32° between the dam body and true north. It is a homogeneous roller-compacted earth dam, controlling a drainage area of ​​11.2 km². 2 The design flood recurrence period is 20 years. A reservoir's silt-retaining dam is 20m high, with a crest elevation of 974m, a crest width of 3m, and a crest length of 106m. The upstream slope ratio is 1:2 and 1:2.5, and the downstream slope ratio is 1:1.5 and 1:2. A 1.5m wide ramp is provided upstream and downstream at a dam height of 12m. The total reservoir capacity is 526,600 m³. 3 .

[0116] Ninety-six high-resolution remote sensing images of a reservoir's silt-retention dam, spanning from 2015 to 2023, were obtained through the National Remote Sensing Data and Application Service Platform. To provide an accurate data foundation for subsequent calculations of the dam's water level and capacity, the remote sensing image data was preprocessed using The Environment for Visualizing Images (ENVI) 5.6. This preprocessing included radiometric calibration, atmospheric correction, and orthorectification of the multispectral data, as well as orthorectification of the panchromatic data. The high-resolution panchromatic data was then fused with the low-resolution multispectral data to obtain high-resolution multispectral data. The desired study area was then cropped.

[0117] First, remote sensing image data of a reservoir's silt-retention dam dated February 22, 2020, was selected for shape interpretation. The spatial resolution of this image data is 2 meters (i.e., the length and width of a single pixel are 2 meters). Furthermore, due to the spring / winter season, there is sparse vegetation around the dam, reducing vegetation shading of the dam boundary. Additionally, there is no significant shadow interference around the dam and the surrounding water area. Then, based on a visual interpretation method, the shape and boundary features of the reservoir's silt-retention dam were identified and labeled on the remote sensing image data. The results are as follows: Figure 6 As shown.

[0118] like Figure 7 As shown, through software analysis of remote sensing image data, it was found that the dam crest occupies 3 pixels in the due west direction, the downstream dam slope occupies 20 pixels in the due west direction, and the horizontal pixel spacing between the dam crest and dam base is 24 pixels. Based on the remote sensing image resolution parameters, the number of pixels was converted into actual physical distances. Then, using trigonometric functions with an azimuth angle of 32°, parameters such as the dam crest width, dam crest length, and the horizontal projected length of the downstream dam slope were accurately calculated. The upstream and downstream slope ratio parameters were selected according to the "Technical Specification for Silt-Resisting Dams" (SL / T804-2020). The horizontal projected length of the downstream dam slope was converted into the dam height using the slope ratio.

[0119] The spatial relationship between the dam crest and the water level was identified using visual interpretation. The number of pixels between the dam crest and the water level in the due north direction was measured. The water depth of the silt-retaining dam was obtained using the calculation method and formula. Based on visual interpretation, the distance between the water level and the dam crest in the due west direction was 16 pixels, which means the horizontal distance between the water level and the dam crest in the due west direction is 32 meters. The angle between the silt-retaining dam and the vertical direction is known to be 32°. The horizontal projected straight-line distance between the water level and the dam crest was found to be 27.14 meters. The vertical height in the spatial direction was obtained as 12 meters using the slope ratio, which means the water level height is 8 meters. The water area of ​​the silt-retaining dam of a certain reservoir on February 22, 2020 was extracted using the Normalized Difference Water Index (NDWI).

[0120]

[0121] Green and NIR represent the brightness values ​​for the green and near-infrared bands, respectively. Water areas are white (value 1), and non-water areas are black (value 0), thus extracting the water area of ​​the silt-retaining dam. The number of pixels covered by the water area was counted, revealing that on February 22, 2020, the water area of ​​a certain reservoir's silt-retaining dam covered 2659 pixels, with a water area of ​​10636 square meters.

[0122] For a certain reservoir silt-retention dam, 95 remote sensing images from 2015 to 2023 were analyzed image by image to calculate the water level and water area. The analyzed remote sensing image data were processed by multiplying the water depth data by the corresponding water area, followed by integration and summation. This yielded the water storage capacity of the silt-retention dam during the period from 2015 to 2023 when the water depth was at its maximum. The results are shown in Table 1.

[0123] Table 1. Water depth and corresponding water storage capacity of some silt-retaining dam sections.

[0124]

[0125] Table 1 shows that the maximum water depth of a certain reservoir's silt-retention dam was 12.2 meters from 2015 to 2023. The results obtained by fitting the curve using software are as follows: Figure 8 As shown.

[0126] In addition, 96 remote sensing images of a reservoir's silt-retaining dam from 2015 to 2023 were analyzed image by image. First, the water depth information of the silt-retaining dam was extracted from each image. Then, using an established reservoir capacity curve, the water storage capacity of the silt-retaining dam corresponding to each image was calculated. Finally, statistical analysis was performed on the data, and the final results are as follows: Figure 9 As shown. According to the preliminary design report of the reinforcement project of the main dam of a reservoir in a certain area, the flood detention capacity of the silt-retaining dam is 154,000 m³. 3 The silt retention capacity is 208,500 m³. 3 The total reservoir capacity is 362,500 m³. 3 Based on the reservoir capacity-water level curve, the silt-trapping dam is 14.25 meters high, the flood detention dam is 4.25 meters high, and the safety freeboard is 1.50 meters. Therefore, calculations show that 1.5 times the flood detention capacity is 231,000 m³. 3 1.3 times the flood retention capacity is 200,200 m³. 3 1.1 times the flood detention capacity is 169,400 m³. 3 Subsequently, the remaining storage capacity of 96 remote sensing image data from 2015 to 2023 was calculated as follows: Figure 11 As shown, a flood control analysis was conducted on the main dam of a reservoir. The results indicate that from 2015 to 2023, the remaining storage capacity of the silt-retention dam was mostly above 1.5 times the flood detention capacity, and in some months above 1.3 times the flood detention capacity. Furthermore, the water depth of the silt-retention dam calculated from remote sensing image data did not reach the safe flood detention depth line. Figure 10 As shown, this indicates that the silt-retaining dam of a certain reservoir is in a safe state.

[0127] Therefore, the aforementioned method for dynamic monitoring and flood early warning of silt-retaining dams based on remote sensing imagery effectively solves the problems of low accuracy, difficult maintenance, and inability to conduct long-term stable monitoring in silt-retaining dam water level monitoring by leveraging the advantages of remote sensing imagery's wide coverage, high timeliness, and dynamic monitoring capabilities. Simultaneously, by interpreting the actual dimensions corresponding to the pixels in the remote sensing imagery, the water level and reservoir capacity in front of the dam are calculated, and a dynamic characteristic curve of reservoir capacity-water level is constructed. This allows for accurate acquisition of the water storage capacity and remaining reservoir capacity of the silt-retaining dam, enabling a quantitative assessment of the flood control safety of the silt-retaining dam. Furthermore, the method provided by this invention eliminates the need for on-site surveys, reducing manpower and material resources. It can quickly and reliably determine the dynamic changes in water level and water storage capacity, providing data support and decision-making basis for the operation and management of silt-retaining dams. It can also identify key flood control periods by analyzing historical data, serving as an effective means of emergency assessment of the safety status of silt-retaining dams in flood control management.

[0128] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. Furthermore, those skilled in the art will recognize that, based on the ideas of the present invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A method for dynamic monitoring and flood early warning of silt-retention dams based on remote sensing imagery, characterized in that, Includes the following steps: S1. Acquire remote sensing image data of silt-retention dams, select satellite data with a resolution of less than 3 meters, and preprocess the data using ENVI software to crop the study area and mark its boundary features. S2. Based on the labeled research area, measure the azimuth angle between the dam axis and the due north direction, and convert the pixel coordinates of the dam crest and dam slope boundary into actual physical dimensions by using the number of pixels and trigonometric functions, and calculate the dam crest length, width and dam height; S3. Based on the obtained dam height and upstream-downstream slope ratio parameters, combined with the pixel spacing between the dam crest and the water level line, calculate the water depth in front of the dam, extract the water area using the NDWI index, count the number of pixels, and calculate the water area. S4. Combine the obtained water area data with the water depth of multiple periods, use the integral method to calculate the water storage capacity, and fit to generate a dynamic curve of reservoir capacity-water level. S5. Based on the reservoir capacity-water level dynamic curve and the theoretical reservoir capacity, combined with the silt retention capacity and flood detention capacity, calculate the remaining reservoir capacity and classify the risk levels. Based on the reservoir capacity-water level dynamic curve, set the flood detention safety water depth line and implement flood prevention early warning.

2. The method for dynamic monitoring and flood early warning of silt-retaining dams based on remote sensing imagery according to claim 1, characterized in that, In S1, the satellite data includes GF-2 and WorldView-3, and during preprocessing, the radiometric calibration, atmospheric correction, orthorectification, and fusion of panchromatic and multispectral data are completed using ENVI5.6 software.

3. The method for dynamic monitoring and flood early warning of silt-retaining dams based on remote sensing imagery according to claim 1, characterized in that, In S1, the marked boundary features include manually visually interpreting and marking the dam crest, dam slope, water level line, dam body boundary, and water area boundary, and using the pixel statistics function of auxiliary software for identification; the auxiliary software is one of Photoshop, Arcmap, and ENVI.

4. The method for dynamic monitoring and flood early warning of silt-retaining dams based on remote sensing imagery according to claim 1, characterized in that, In S2, the azimuth angle between the dam axis and true north is measured. The pixel coordinates of the dam crest and slope boundaries are then converted into actual physical dimensions using pixel count and trigonometric functions. Specifically: When the azimuth angle between the dam axis and due north is θ n When the dam crest length is reached, the formula for calculating it is: L=n a ×R×cscθ n ; The formula for calculating the width of the dam crest is: B=n b ×R×cosθ n ; In the formula, L is the length of the silt-retention dam crest, in meters; B is the width of the silt-retention dam crest, in meters; n a n represents the number of pixels between the dam axes; b θ represents the number of pixels between the widths of the dam crest; n R represents the azimuth angle of the silt-retaining dam; R is the side length of the pixel, in meters.

5. The method for dynamic monitoring and flood early warning of silt-retaining dams based on remote sensing imagery according to claim 1, characterized in that, In S2, the steps for calculating the dam height are as follows: The formula for calculating the horizontal projection length of the downstream dam slope is: L d =n s ×r×sinθ n ; The dam height was then derived using the following formula: H=L d ×tanθ d ; In the formula, H represents the height of the silt-retaining dam, in meters; n S L represents the number of pixels between the top of the dam and the bottom of the dam downstream, pointing due north; d θ represents the horizontal projection length of the downstream dam slope, in meters. d The slope angle downstream of the silt-retaining dam.

6. The method for dynamic monitoring and flood early warning of silt-retaining dams based on remote sensing imagery according to claim 1, characterized in that, In S3, the process of calculating the water depth in front of the dam is as follows: The formula for calculating the horizontal projected distance between the dam crest and the water level is: L u =R×n u ×sinθ n ; Then calculate the water depth using the formula: H w =HL u ×sinθ u ; In the formula, L u H is the straight-line distance between the dam crest and the water level line, in meters. w The depth of the silt-retaining dam is expressed in meters; n u θ represents the number of pixels between the dam crest and the water level line in the due north direction; u The slope angle upstream of the silt-retaining dam; The formula for extracting the water area using the NDWI index is: In the formula, Green and NIR are the brightness values ​​of the green band and near-infrared band, respectively.

7. The method for dynamic monitoring and flood early warning of silt-retaining dams based on remote sensing imagery according to claim 1, characterized in that, In S3, the process of calculating the water area is as follows: The water area of ​​the silt-retaining dam is extracted using software, the number of pixels covering the water area is counted, and the water area is calculated based on the image spatial resolution parameters. The formula is: S=n w ×R 2 ; In the formula, S represents the water area of ​​the silt-retaining dam, in square meters; n w The number of pixels covered by the water area of ​​the silt-retaining dam.

8. A method for dynamic monitoring and flood early warning of silt-retaining dams based on remote sensing imagery according to claim 1, characterized in that, In S4, the process of calculating the water storage capacity using the integral method and fitting the dynamic curve of reservoir capacity-water level is as follows: The water storage capacity is calculated using the following formula, which relates the water depth to the corresponding water area for multiple periods: In the formula, V w S represents water storage capacity, measured in cubic meters. i For water depth h i The corresponding water area, in square meters; h i Water depth, measured in meters; When the actual water depth h i When the dam height is approximately equal to the design dam height, V w The theoretical reservoir capacity of the silt-retention dam was determined, and then the reservoir capacity value for periods without remote sensing imagery was extrapolated using function fitting. This was done when the measured water depth h... i When the designed dam height is not reached, the water storage capacity at the corresponding water level is estimated based on the curve, and a dynamic curve of reservoir capacity-water level is generated.

9. A method for dynamic monitoring and flood early warning of silt-retaining dams based on remote sensing imagery according to claim 1, characterized in that, In S5, the silt-retaining dam capacity V includes the sediment-trapping capacity V. L and flood detention capacity V z Two parts, combined with the silt retention capacity V L and flood detention capacity V Z By calculating the remaining storage capacity V rem With flood retention capacity V Z The risk level is classified according to the proportional relationship, and the safe water depth for flood detention is determined based on the reservoir capacity-water level dynamic curve, so as to realize the quantitative early warning of flood control safety of silt-retention dams. The specific standards are as follows: Remaining storage capacity V rem =Theoretical reservoir capacity - Actual measured water storage; When V rem ≥1.5V Z The risk level is currently low. When 1.3V Z ≤V rem <1.5V Z The risk level is medium; when V rem <1.3V Z It is a high-risk situation.

10. A method for dynamic monitoring and flood early warning of silt-retaining dams based on remote sensing imagery according to claim 1, characterized in that, The formula for calculating the safe water depth line for flood detention is: Flood retention safety depth line = H L +H Z +ΔH; In the formula, H L For mud dam height; H Z The height of the flood detention dam is ΔH; ΔH is the safety freeboard ΔH, both in meters.

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